Validation of patient-specific metal 3D shielding block usability with GafChromic EBT3 film

Validation of patient-specific metal 3D shielding block usability with GafChromic EBT3 film | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Validation of patient-specific metal 3D shielding block usability with GafChromic EBT3 film KYUNG-HWAN JUNG, KI-YOON LEE, HYUN-DONG KIM, JANG-OH KIM, JUN-BONG SHIN, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5537761/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 5 You are reading this latest preprint version Abstract Keloids are abnormal scars that result from excessive fibrous tissue proliferation during wound healing, with recurrence rates of 80–100% when treated with surgery alone. As a result, radiation therapy has become an essential adjunct treatment to reduce recurrence, with electron beam therapy demonstrating significant effectiveness. This study aims to optimize dose distribution in keloid radiotherapy using patient-specific shielding blocks and evaluate the radiation shielding performance of metal 3D shielding blocks fabricated through rapid prototyping as a potential alternative to conventional Cerrobend blocks. Monte Carlo simulations (GATE v8.0) and experimental validation using GafChromic EBT3 film were conducted for 6 MeV and 12 MeV electron beams to analyze the shielding efficiency of stainless steel 316L(SUS 316L), brass, and pure copper. The results confirmed that the fabricated metal 3D shielding blocks met the required transmission rate criteria (≤ 5%) and demonstrated strong agreement with Monte Carlo simulations. Pure copper exhibited excellent shielding performance with dosimetric characteristics comparable to Cerrobend, while brass showed superior mechanical strength, making it a promising material for long-term durability. Additionally, SUS 316L demonstrated excellent corrosion resistance and minimal deformation over repeated use, enhancing its clinical applicability. The difference between the off-axis and isodose curves of the cerrobend cutout and those of the metal prototypes was found to be minimal, indicating that the fabricated shielding blocks provided comparable dose distribution characteristics. The findings of this study suggest that metal 3D shielding blocks could serve as a viable alternative to conventional Cerrobend blocks, paving the way for personalized and precision radiation therapy. Further research is necessary to enhance mechanical durability, reduce radiation scattering, and develop lightweight shielding materials, ultimately improving the precision and efficiency of patient-specific electron beam therapy. Keloid Electron beam Shielding block Monte Carlo simulation GafChromic EBT3 Rapid prototyping Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction In radiation therapy, high-energy electron beams are effective in delivering a lethal dose to skin diseases and skin cancer while minimizing the dose to surrounding healthy tissues due to their buildup characteristics at a specific depth [1]. Keloids are raised, reddish scars that form on the skin when wounds fail to heal properly. When treated with surgery alone, the recurrence rate is reported to be 80–100%. Therefore, the standard treatment for keloids currently involves radiation therapy in combination with surgery.[2] A follow-up study on low-dose radiation therapy after surgical excision of refractory chest keloids reported that recurrence did not occur in approximately 90% of cases.[3] Such findings highlight the positive role of radiation therapy for keloids, and to achieve effective treatment, field shaping that considers the irregular size of scar tissue is essential [4]. Keloids are typically small lesions ranging from 1 to 3 cm, and while a 6 × 6 cm² field size is commonly used in treatment, smaller cutouts may sometimes be required. In the current clinical environment, cast shielding blocks, known as Cerrobend, are manufactured using a low-melting-point lead alloy(LMA) composed of lead, cadmium, bismuth, and tin (density = 9.4 g/cm³) to facilitate simpler field shaping.[5] However, the casting process generates toxic fumes and metal dust, posing occupational hazards and necessitating strict regulatory management and specialized expertise in hospitals. To address these issues while maintaining equivalent shielding performance, rapid prototyping methods such as CNC machining and 3D printing are being used. Rapid prototyping enables the fabrication of three-dimensional products from digital scan data and is widely utilized in engineering and manufacturing industries [6]. While 3D printing has been explored for its applicability in producing dense metal composite filaments for shielding purposes, it has been reported to have low density and inherent filament inconsistencies.[7–8] Additionally, for small field sizes, treatment planning systems (TPS) may struggle to accurately predict scatter radiation, leading to deviations. Incorporating high-density materials such as tungsten within filaments may further increase scatter, potentially reducing dose uniformity and precision.[9–10] A pure copper cutout fabricated via CNC machining has been reported to be dosimetrically equivalent to Cerrobend in small 6 × 6 cm² fields, with a ± 2% dose agreement or 99% pass rate based on a 2%/1 mm gamma index criterion. Furthermore, it has been observed that the use of pure copper can reduce out-of-field dose by decreasing bremsstrahlung radiation.[11] However, pure copper exhibits several mechanical disadvantages when reused over time. Due to its low hardness and high ductility, repeated use in applicators or mechanical impacts, such as drops, can lead to deformation. Additionally, exposure to air can cause surface oxidation and corrosion. To overcome these limitations, further research is needed on metallic shielding materials with densities similar to traditional lead alloys. However, studies specifically focusing on shielding materials for high-energy electron beams remain insufficient. Therefore, this study aims to quantitatively propose the required thickness to achieve shielding performance using metallic materials utilized in rapid prototyping through GATE (Geant4 application for tomographic emission) simulations, a medical computational modeling tool. Therefore, this study aims to quantitatively propose the required thickness to achieve effective shielding performance using metallic materials applied in rapid prototyping, through GATE (Geant4 application for tomographic emission) simulations, a medical computational modeling tool. Additionally, automated extraction software will be implemented to streamline the treatment process, facilitating the fabrication of metal 3D shielding blocks, which will be validated using GafChromic EBT film by comparing their performance with conventional Cerrobend cutouts. 2. Methods and Materials 1. Monte Carlo Simulation 1–1. Electron beam modeling To evaluate the source term for 6 MeV and 12 MeV electron beams, the TrueBeam model (Varian Medical Systems, Palo Alto, USA) was selected as the medical linear accelerator, and the Monte Carlo simulation tool GATE v8.0 was utilized[12]. The energy spectrum of the electron beam was derived using PRIMO software, which is based on the PENLOPE code and is capable of simulating the spectrum of Varian medical linear accelerators in Fig. 1 . The spectrum for 6 MeV and 12 MeV, commonly used in clinical practice, was calculated and set accordingly[13]. The spectrum provided by the software accounts for the source term, considering components from the primary collimator to the applicator. To validate the source term, the simulated percentage depth dose(PDD) and the PDD measured using the TrueBeam system were compared, focusing on the maximum dose depth(D max ). The reference depths in the water phantom for electron beam energies of 6 MeV and 12 MeV, measured using a Farmer-type chamber(FC65-G) following the TG-51 protocol, are 1.3 cm and 2.9 cm, respectively, within the TrueBeam system. The experimental setup included a water phantom (50 × 50 × 30 cm³) positioned at a source-to-surface distance (SSD) of 100 cm. The applicator field size was set to 10 cm × 10 cm for electron beam irradiation. The energy bin spacing within the simulation was set to 0.1 cm to calculate the PPD value. 1–2. Evaluation of shielding performance using metal 3D shielding specimens The shielding performance against high-energy electron beams is primarily determined by the density and atomic number of a material. For alloys, which cannot be defined by a single atomic number, the average atomic number was calculated by considering the atomic numbers of the major constituent elements and their proportions, using mass percentages as weighting factors. Additionally, the heat and X-rays generated from the interaction between electrons and matter may indirectly influence the shielding performance, necessitating the consideration of physicochemical properties. This study selected stainless steel 316L(SUS 316L), brass, and pure copper materials commonly employed in rapid prototyping with densities of 8 g/cm³ or higher for evaluation. Table. 1 summarizes the material properties. The physicochemical properties of each metal relevant to radiation transport modeling were validated using data provided by the Pacific Northwest National Laboratory.[14] Table 1 Physical properties of the selected metal materials for manufacturing shielding blocks Material Stainless steel 316L (SUS 316L) Brass Pure copper Density [g/cm 3 ] 8.00 8.07 8.92 Thermal Conductivity (W/m·K) 16.2 109–125 401 Electrical Conductivity (%IACS) 2.4 28–37 100 Mechanical Strength (MPa) 480–620 300–500 200–250 Composition Fe 67.37%, Cr 17.00%, Ni 12.00%, Mo 2.50%, Si 1.00%, P 0.05%, S 0.03%, C 0.03%, Mn 0.02% Cu 63%, Zn 37% Cu 100% Atomic number(Z) 26.2 29.4 29 According to the AAPM Task Group 25, high-energy electron beams require shielding that achieves a penetration rate of 5% or less, with a minimum lead thickness requirement of 2 mm per MeV in water or soft tissue. The rule of thumb for LMA incorporates an additional scaling factor of 1.2 times the required thickness for Pb due to density differences[15]. Therefore, density scaling was performed using the following Eq. ( 1 ) to determine the theoretical thickness required to meet the transmission criteria for the three selected materials.[16] $$\:{t}_{x}=\:\frac{{\rho\:}_{Pb}}{{\rho\:}_{x}}\:\times\:\:{t}_{pb}$$ 1 \(\:{t}_{x}\) the required thickness of the material 𝑋 \(\:{\rho\:}_{x}\) the required thickness of the material 𝑋 \(\:{\rho\:}_{Pb}\) the density of lead ( \(\:\rho\:\) =11.34 g/cm³) \(\:{t}_{pb}\) the required thickness of lead for shielding at a given electron beam energy Subsequently, the electron beam shielding performance for each material was evaluated using GATE v8.0 at 1 mm intervals. The thicknesses corresponding to a penetration rate within 5% were considered, and shielding specimens with an internal fill of 100% were fabricated through CNC machining in a manner similar to metal 3D printing, selecting practical thicknesses for each material to ensure ease of processing. The dimensions of the shielding specimens were set to 15 cm × 15 cm, while the electron beam field size from the linear accelerator was configured to 10 cm × 10 cm. An RW3 slab phantom was positioned at a SSD of 100 cm in Fig. 2 . To assess shielding performance, the metal shielding specimens were placed at the center of the phantom, and an ionization chamber was positioned beneath the phantom surface. The penetration rate was calculated as the relative dose ratio between measurements obtained with and without the shielding material. Measurements were taken three times, each based on 300 MU, and the average value was used as the final result. The simulation method replicated the same geometric conditions as the experimental setup. 2. Validate the usability of metal 3D shielding blocks created with automated subtraction software To enable automated extraction, software based on MATLAB (R2022b) was developed, as illustrated in Fig. 3 . The software utilizes shaping surfaces derived from DICOM data. It generates random points using elements connected to the selected nodes and creates a mesh through triangular division, connecting the edge parts to construct a shielding block model. The dimensions of the selected image can be freely configured. In this experiment, the surface of the shape was generated based on a patient case derived from the treatment planning system. Subsequently, a shielding block was fabricated using a subtraction technique to exclude the treatment area, and the size of the shielding block was set to 6 cm × 6 cm to form a small field. The height was determined as a thickness ensuring a penetration rate of less than 5% for 12 MeV, and the model was extracted as an STL file, a format commonly compatible with rapid prototyping. Following this, metal 3D shielding blocks were manufactured using CNC techniques from SUS 316L, brass, and pure copper. Additionally, to compare differences with metal 3D printing, an extra SUS 316L block was fabricated. To perform dosimetry of metal 3D shielding blocks manufactured with GafChromic EBT3 film, dose-pixel value calibration curves were performed from 0 MU to 800 MU irradiated for electron beams of 6 MeV and 12 MeV [17]. The film was inserted and positioned at 100 cm between the source and the solid water phantom surface, considering the D max for each electron beam from the phantom surface, as depicted in Fig. 4 . The irradiated films were scanned in standard mode with a resolution of 72 dpi at 48 bits using a flatbed film scanner, the EPSON Expression 12000XL (Seiko Epson Corporation, Japan), after approximately 48 hours for stabilization[18]. To minimize the influence of film orientation, the same orientation was applied to all scans. Unirradiated films were scanned and corrected using the analysis software DoseLab (Mobiys Medical Systems, Houston, TX) to account for the uniformity effects of the scanner light source. The dose distribution curves for each electron beam for different materials were then compared. 3. Results 1–1. Electron beam modeling To evaluate the high-energy electron beams of 6 MeV and 12 MeV used in this study, the PDD measured using GATE v8.0 and a Farmer-type chamber was compared, as shown in Fig. 5 . As a result, the D max for the 6 MeV electron beam was found to be 1.4 cm in GATE v8.0 and 1.35 cm in the experiment, as specified in Table. 2. A difference of 0.05 to 0.1 cm from the reference depth was observed. For the 12 MeV electron beam, the simulation produced the same reference depth as the experimental measurement. The beam quality index R 50 was determined using linear interpolation, and the difference between the simulation and experimental results for both energies was 0.01 cm, indicating strong agreement between the two methods. Furthermore, the results confirm that the penetration depth of the electron beam is proportional to its energy. However, differences between the PDD curves in the dose fall-off region were observed. Table 2 D max and R 50 Values for Electron Beams in Open Field Conditions Energy Method D max (cm) R 50 (cm) 6 Reference(Z ref ) 1.30 - Measurement 1.35 2.40 GATE v8.0 1.40 2.39 12 Reference(Z ref ) 2.90 - Measurement 2.99 5.04 GATE v8.0 2.90 5.05 1–2. Evaluation of shielding performance using metal 3D shielding specimens To achieve a penetration rate of 5% or less, the required theoretical thickness for each material was calculated using density scaling, and the shielding effectiveness was analyzed by comparing GATE v8.0 simulations with experimental measurements. The calculated theoretical thicknesses required for a 6 MeV electron beam were 3.8 mm for pure copper, 4.0 mm for brass, and 4.3 mm for SUS steel 316L. For a 12 MeV electron beam, the required thicknesses were 7.6 mm for pure copper, 8.4 mm for brass, and 8.5 mm for SUS 316L. The electron beam penetration rates measured for the fabricated metal shielding specimens are presented in Fig. 6 . For the 6 MeV electron beam, when using a 4 cm thick shielding specimen, the penetration rates were 1.3% for pure copper, 1.3% for brass, and 1.2% for SUS 316L. The discrepancies between simulation and experimental results were 1.14%, 1.33%, and 1.20%, respectively. For 12 MeV electron beams, the required thickness for 95% shielding, based on actual measurements, was 7.6 mm, 7.0 mm, and 6.6 mm for SUS 316L, brass, and pure copper, respectively, with penetration rates of 3.60%, 3.80%, and 3.80%, The discrepancies between the simulation and experimental results were 1.00%, 1.70%, and 1.61%, respectively. 2. Validation of the usability of metal 3D shielding blocks created with automated subtraction software The pure copper, brass, and SUS 316L shielding blocks were subjected to automated subtraction using MATLAB-based software. Subsequently, metal 3D shielding blocks were fabricated through rapid prototyping. The dimensions of the shielding blocks illustrated in Fig. 7 , which were manufactured by rapid prototyping, were 6 cm × 6 cm. To verify shape accuracy, the original image was printed on a transparent sheet, enabling visual quality assurance and an initial qualitative comparison of the fabricated shielding blocks. For calibration of the films required in subsequent experiments, electron beams of 6 MeV and 12 MeV were used to irradiate the films at 0, 50 MU, 100 MU, 150 MU, 200 MU, 300 MU, 500 MU, and 800 MU. The irradiated films were calibrated using DoseLab software to obtain the final dose-pixel curves, as shown in Fig. 8 . The films were converted into doses for each material using DoseLab and plotted against the center to represent the dose distribution within a two-dimensional volume. The off-axis ratio distribution within the planning target volume (PTV) are displayed in Fig. 9 . To analyze the penumbra characteristics of the 6 MeV electron beam, the off-axis ratio was measured at the D max of 1.3 cm for five different materials in Table. 3: Cerrobend, Pure Copper, Brass, SUS 316L, and SUS 316L(3D printing). The comparison was conducted with Cerrobend as the reference, and the dose distribution characteristics in the penumbra region were evaluated. Data were recorded at representative distances of 1.35, 2.18, 3.28, 5.56, and 6.29 cm, corresponding to off-axis ratio levels of 20, 80, and 100%. Similarly, the penumbra characteristics of a 12 MeV electron beam were analyzed for the same five materials in Table. 4. The off-axis ratio was measured at a D max of 2.9 cm, with Cerrobend as the reference for comparison. The dose distribution characteristics in the penumbra region were evaluated, and data were recorded at representative distances of 0.03, 1.00, 2.73, 4.25, and 5.46 cm, corresponding to off-axis ratio levels of 20, 80, and 100%. Cerrobend demonstrated superior performance in the outer penumbra region. At 1.35 cm and 20 percent off-axis ratio, the value for Cerrobend was 0.212, similar to those of Pure Copper at 0.210, Brass at 0.202, and SUS 316L(3D printing) at 0.198, while SUS 316L exhibited a relatively lower value of 0.137. At 2.18 cm and 80 percent off-axis ratio, Cerrobend increased to 0.806, whereas Pure Copper reached 0.771, Brass 0.780, and SUS 316L(3D printing) 0.725, while SUS 316L remained lower at 0.689. At 3.28 cm and 100 percent off-axis ratio, all materials except SUS 316L, which recorded 0.963, achieved a value of 1.0. In the outer penumbra region, at 5.56 cm and 80 percent off-axis ratio, Cerrobend was 0.794, similar to Pure Copper at 0.790, while Brass was slightly lower at 0.756, and SUS 316L recorded the highest value at 0.876. At 6.29 cm and 20 percent off-axis ratio, Cerrobend recorded 0.212, comparable to Pure Copper at 0.223 and SUS 316L(3D printing) at 0.216, while Brass had the lowest value at 0.190, and SUS 316L had the highest at 0.304. The penumbra analysis for the 12 MeV electron beam exhibited trends similar to those observed at 6 MeV. At 0.03 cm and 20 percent off-axis ratio, the value for Cerrobend was 0.269, higher than that of Pure Copper at 0.229 and SUS 316L at 0.181, but lower than those of Brass at 0.159 and SUS 316L(3D printing) at 0.134. At 1.00 cm and 80 percent off-axis ratio, the value for Cerrobend increased to 0.807, followed by Pure Copper at 0.748, SUS 316L at 0.648, and SUS 316L(3D printing) at 0.460, with Brass recording the lowest value at 0.597. At 2.73 cm and 100 percent off-axis ratio, both Cerrobend and SUS 316L(3D printing) achieved a value of 1.0, while Pure Copper was slightly lower at 0.995, SUS 316L at 0.991, and Brass had the lowest value at 0.973. In the outer penumbra region, at 4.25 cm and 80 percent off-axis ratio, the value for Cerrobend was 0.798, lower than those of Pure Copper at 0.833 and Brass at 0.894, but higher than those of SUS 316L at 0.866 and SUS 316L(3D printing) at 0.920. At 5.46 cm and 20 percent off-axis ratio, Cerrobend recorded 0.202, lower than Pure Copper at 0.248, Brass at 0.319, SUS 316L at 0.296, and SUS 316L(3D printing) at 0.442. Table 3 Off-axis ratio measurements for 6 MeV electron beam Distance (cm) Cerrobend Pure copper Brass SUS 316L SUS 316L (3D Printing) 1.35(20%) 0.212 0.210 0.202 0.137 0.198 2.18(80%) 0.806 0.771 0.780 0.689 0.725 3.28(100%) 1.000 1.000 1.000 0.963 1.000 5.56(80%) 0.794 0.790 0.756 0.876 0.766 6.29(20%) 0.212 0.223 0.190 0.304 0.216 Table 4 Off-axis ratio measurements for 6 MeV electron beam Distance (cm) Cerrobend Pure copper Brass SUS 316L SUS 316L (3D Printing) 0.03(20%) 0.269 0.229 0.159 0.181 0.134 1.00(80%) 0.807 0.748 0.597 0.648 0.460 2.73(100%) 1.000 0.995 0.973 0.991 1.000 4.25(80%) 0.798 0.833 0.894 0.866 0.920 5.46(20%) 0.202 0.248 0.319 0.296 0.442 Subsequently, the full width at half maximum(FWHM) was analyzed in Table. 5. This metric is defined as the distance between two points where the dose reaches 50% of the maximum, serving as an indicator of beam width and dose distribution spread. At 6 MeV, Cerrobend exhibited the narrowest full width at half maximum at 3.986 cm, indicating the most concentrated dose distribution, while Brass had the widest at 4.537 cm. SUS 316L and SUS 316L three-dimensional printing showed similar values of 4.502 and 4.506 cm, respectively. At 12 MeV, FWHM increased for all materials, with SUS 316L recording the widest value at 4.574 cm and Cerrobend maintaining the narrowest at 4.045 cm. The increase in full width at half maximum from 6 MeV to 12 MeV was smallest for Brass and SUS 316L(3D printing) at 0.029 cm and largest for SUS 316L at 0.072 cm. Cerrobend and Pure Copper exhibited increases of 0.059 and 0.053 cm, respectively. The average increase in FWHM was 0.0484 cm, corresponding to an approximate 1.1% variation with increasing energy. Table 5 The full width at half maximum measurements for 6 MeV, 12 MeV electron beam Material 6 MeV FWHM(cm) 12 MeV FWHM(cm) ΔFWHM (cm) Cerrobend 3.986 4.045 + 0.059 Pure copper 4.513 4.566 + 0.053 Brass 4.537 4.566 + 0.029 SUS 316L 4.502 4.574 + 0.072 SUS 316L (3D Printing) 4.506 4.535 + 0.029 In the isodose distribution curve, at 6 MeV, a low-melting lead alloy exhibited 160 cGy in the high-dose region, while SUS 316L, brass, and pure copper exhibited 160 cGy, 160 cGy, and 150 cGy, respectively. At 12 MeV, a low-melting lead alloy showed 220 cGy in the high dose region, while SUS 316L, brass, and pure copper demonstrated 210 cGy, 220 cGy, and 220 cGy, respectively. In the low-dose region, all materials exhibited similar dose distributions as before. This result confirms that the rapid prototyping-processed metal 3D shielding blocks perform as well as traditional shielding blocks in Fig. 10 . 4. Discussion In this study, modeling was conducted for the 6 MeV and 12 MeV electron beams used in keloid radiotherapy. Several limitations were identified. For the 6 MeV electron beam, a depth difference of 0.05 to 0.1 cm was observed. In contrast, the identical reference depth obtained from both simulation and experimental measurements for the 12 MeV electron beam can be attributed to the higher energy stability, greater beam linearity, and smaller scattering angle of the high energy electron beam. The differences between the PDD curves in the dose fall-off region may stem from a combination of factors, including variations in secondary electron transport modeling, contributions from bremsstrahlung X-rays, differences in water phantom density, discrepancies in electron beam energy spectrum modeling, and Monte Carlo simulation parameters such as energy cut-off values (E cut , P cut ). Additionally, the design of the linear accelerator head, including elements such as the scattering foil, collimators, and applicator, could contribute to these differences in the dose fall-off region. Inaccuracies in simulating the geometry or material properties of the head components may affect the accuracy of the dose distribution, particularly in regions of rapid dose attenuation where small changes in beam characteristics have a pronounced effect. To minimize these discrepancies, further optimization of simulation parameters is necessary, along with additional experimental validation to improve agreement between Monte Carlo simulations and measured data in the low energy region. To analyze the penetration performance of the electron beam subsequently, density scaling was used to calculate the theoretical thickness for each material, which was then validated through simulation and experimental measurements. For all materials, the electron beam shielding achieved a penetration rate within the target range of less than 5% at thicknesses lower than the theoretically required values. This indicates that the theoretical approach based on density scaling can serve as a reliable predictive tool for designing electron beam shields. However, for the 6 MeV electron beam at a 2 mm thickness, the difference between simulation and experimental results was minimal at 0.1% for pure copper, whereas the experimental values were higher for brass at 5.74% and for SUS 316L at 17.9%, with the latter showing the largest deviation. Figure 10 presents the analysis results of the transmitted electron beam through simulation, visually depicting the distribution of electrons passing through the shield specimen and the contribution of bremsstrahlung X-rays. Notably, the significant discrepancy between simulation and experimental results observed in SUS 316L was accompanied by a pronounced contribution from bremsstrahlung X-rays. Bremsstrahlung X-rays are generated during the interaction of high-energy electrons with the material, and it is possible that the crystalline structure characteristics and actual composition ratios of the alloy in SUS 316L and brass led to the generation of more radiation. This study evaluated the characteristics of the manufactured 3D metal shielding blocks in relation to the penumbra effect of a 12 MeV electron beam, with Cerrobend serving as the reference material. Pure Copper exhibited a pattern similar to Cerrobend, though it showed slightly higher residual doses at 4.25 cm with a value of 0.833 and at 5.46 cm with a value of 0.248, indicating intermediate performance. Brass recorded the lowest OAR at 2.73 cm with a value of 0.973, suggesting a slight reduction in field uniformity, but displayed a relatively high residual dose at 5.46 cm with a value of 0.319, indicating a slower dose fall-off in the outer regions. SUS 316L demonstrated elevated initial OAR values at 0.03 cm with a value of 0.181 and at 1.00 cm with a value of 0.648, as well as residual OAR values at 4.25 cm with a value of 0.866 and at 5.46 cm with a value of 0.296 throughout the penumbra region, reflecting an expanded dose distribution due to increased scattering. In contrast, SUS 316L produced with 3D printing technology benefited from this manufacturing process, resulting in a lower initial OAR at 0.03 cm with a value of 0.134, but exhibited the highest residual OAR values at 4.25 cm with a value of 0.920 and at 5.46 cm with a value of 0.442, indicating insufficient scattering control under high-energy conditions and suggesting the need for further optimization at higher energies. Future investigations into material-specific penumbra characteristics across various energies and field sizes are essential to expand clinical applicability. Regarding the analysis of electron beam full width at half maximum changes and material-specific properties, the increase in FWHM for all materials at 12 MeV compared to 6 MeV reflects the enhanced lateral scattering and wider penumbra associated with higher energy. This is attributed to the deeper penetration of 12 MeV electrons compared to 6 MeV, resulting in more scattering interactions. The average delta FWHM with a value of 0.0484 cm, representing a 1.1 percent change, indicates a relatively small change relative to the energy increase, suggesting that the scattering effect does not scale linearly with energy. SUS 316L exhibited the widest FWHM at 12 MeV with a value of 4.574 cm, with the largest delta FWHM at 0.072 cm, indicating that its alloy properties with iron, chromium, and nickel induced greater scattering at higher energies. Conversely, SUS 316L produced with 3D printing showed a smaller delta FWHM at 0.029 cm than SUS 316L, suggesting that 3D printing technology may improve microstructure and suppress scattering. Brass displayed the widest FWHM at 6 MeV with a value of 4.537 cm, but its minimal change in delta FWHM at 0.029 cm indicates low sensitivity to energy variations. Pure Copper maintained an intermediate FWHM at 6 MeV with a value of 4.513 cm and at 12 MeV with a value of 4.566 cm, demonstrating balanced performance between Cerrobend and SUS 316L. These findings underscore the significant influence of material-specific scattering properties and energy-dependent beam width variations on clinical applications. Future studies should include a detailed analysis of the correlation between scattering coefficients and penumbra width to quantitatively elucidate material-specific characteristics. In this study, as a preliminary investigation for the fabrication of a metal 3D shielding block, a 2D dose distribution analysis was conducted using Gafchromic EBT3 film. Previous studies have identified several limitations in dosimetry using EBT film. During the film readout process, variations in scanner sensitivity and positional dependence can introduce measurement discrepancies. In particular, optical density (OD) values may vary depending on the scanning orientation, necessitating a standardized methodology to ensure reliable comparisons. Additionally, dose discrepancies tend to increase in small-field measurements. To enhance reproducibility, further repeated experiments and the use of films of various sizes will be conducted. Moreover, various scanning techniques will be employed, and the measured dose distributions will be verified through comparisons with reference dosimetry methods such as ion chamber measurements and Monte Carlo simulations. 5. Conclusions This study validated the usability of patient-specific metal 3D shielding blocks fabricated through rapid prototyping by comparing their dosimetric performance with conventional Cerrobend blocks. Monte Carlo simulations and experimental measurements were conducted for 6 MeV and 12 MeV electron beams using GafChromic EBT3 film. The results confirmed that shielding blocks made of SUS 316L, brass, and pure copper achieved a penetration rate within 5%, meeting the required shielding criteria. The experimental values showed strong agreement with theoretical predictions, demonstrating the feasibility of using alternative metals for clinical shielding applications. Furthermore, analysis of the penumbra effect and dose distribution revealed that pure copper exhibited dose characteristics comparable to Cerrobend, whereas SUS 316L and brass showed minor variations due to increased scattering. The study also highlighted the influence of manufacturing techniques on dose uniformity, particularly in 3D printed SUS 316L, which exhibited increased residual dose levels in high-energy conditions. Overall, the findings indicate that metal 3D shielding blocks manufactured via rapid prototyping provide effective radiation shielding with dosimetric characteristics comparable to conventional materials. However, further optimization of material selection and processing methods is necessary to minimize scattering effects and enhance clinical applicability. Future studies should explore the long-term mechanical durability of these materials and investigate their performance across different field sizes and beam energies to establish standardized clinical implementation guidelines. Declarations Acknowledgments This research was supported by Kangwon National Univesity, funded by National University Developmet Project in 2024. Funding The authors have no relevant financial or non-financial interests to disclose. The authors have no competing interests to declare that are relevant to the content of this article. References van Hezewijk M, Creutzberg CL, Putter H, Chin A, Schneider I, Hoogeveen M, Willemze R, Marijnen CAM (2010) Efficacy of a hypofractionated schedule in electron beam radiotherapy for epithelial skin cancer: Analysis of 434 cases. 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Polymers 16:769. https://doi.org/10.3390/polym16060769 Jreije A, Mutyala SK, Urbonavičius BG, Šablinskaitė A, Keršienė N, Puišo J, Rutkūnienė Ž, Adlienė D (2023) Modification of 3D printable polymer filaments for radiation shielding applications. Polymers 15:1700. https://doi.org/10.3390/polym15071700 Schulz JB, Gibson C, Dubrowski P, Marquez CM, Million L, Qian Y, Skinner L, Yu AS (2023) Shaping success: clinical implementation of a 3D-printed electron cutout program in external beam radiation therapy. Front Oncol 13:1237037. https://doi.org/10.3389/fonc.2023.1237037 Michiels S, Mangelschots B, De Roover R, Devroye C, Depuydt T (2018) Production of patient-specific electron beam aperture cut-outs using a low-cost, multi-purpose 3D printer. J Appl Clin Med Phys 19(5):756–760. https://doi.org/10.1002/acm2.12421 Rusk BD, Carver RL, Gibbons JP, Hogstrom KR (2016) A dosimetric comparison of copper and Cerrobend electron inserts. J Appl Clin Med Phys 17(5):245–261. https://doi.org/10.1120/jacmp.v17i5.6282 Jan S, Santin G, Strul D, Staelens S, Assié K, Autret D, Avner S, Barbier R, Bardies M, Bloomfield PM, Brasse D, Breton V, Bruyndonckx P, Buvat I, Chatziioannou AF, Choi YH, Chung YH, Comtat C, Donnarieix D, Ferrer L, Glick SJ, Groiselle CJ, Guez D, Kerhoas-Cavata S, Kirov AS, Kohli V, Koole M, Krieguer M, van der Laan DJ, Lamare F, Largeron G, Lartizien C, Lazaro D, Maas MC, Maigne L, Mayet F, Melot F, Merheb C, Pennacchio E, Perez J, Pietrzyk U, Rannou FR, Rey M, Schaart DR, Schmidtlein CR, Simon L, Song TY, Vieira JM, Visvikis D, Van de Walle R, Wieërs E, Morel C (2004) GATE: A simulation toolkit for PET and SPECT. Phys Med Biol 49:4543–4561. Brualla L, Rodriguez M, Sempau J, Andreo P (2019) PENELOPE/PRIMO-calculated photon and electron spectra from clinical accelerators. Radiat Oncol 14:6. https://doi.org/10.1186/s13014-018-1186-8 Detwiler RJ, McConn RJ, Kamuda MM, Fite JR, Stokes AR (2021) Compendium of Material Composition Data for Radiation Transport Modeling . Pacific Northwest National Laboratory (PNNL), Rev. 2. https://compendium.cwmd.pnnl.gov/ Almond PR, Biggs PJ, Coursey BM, Hanson WF, Huq MS, Nath R, & Rogers DW (1999). AAPM's TG‐51 protocol for clinical reference dosimetry of high‐energy photon and electron beams Medical physics 26(9):1847-1870. https://doi.org/10.1118/1.598691 Rusk BD (2014) A dosimetric comparison of copper and Cerrobend electron insets. Louisiana State University. http://etd.lsu.edu/docs/available/etd-06162014-153414/ Lewis DF, Chan MF (2016) Technical note: On GAFChromic EBT-XD film and the lateral response artifact. Med Phys 43(2):643–649. https://doi.org/10.1118/1.4939226 Lewis DF, Chan MF (2015) Correcting lateral response artifacts from flatbed scanners for radiochromic film dosimetry. Med Phys 42(1):416–429. https://doi.org/10.1118/1.4903758 Ulya S, Wibowo WE, Nuruddin N, & Pawiro SA (2017) Dosimetric characteristics of gafchromic EBT3 film on small field electron beam. In Journal of Physics: Conference Series 851(1):012023. https://doi.org/10.1088/1742-6596/851/1/012023 Sipilä P, Ojala, J, Kaijaluoto S, Jokelainen I, & Kosunen A (2016) Gafchromic EBT3 film dosimetry in electron beams—energy dependence and improved film read‐out. Journal of applied clinical medical physics 17 (1): 360-373. https://doi.org/10.1120/jacmp.v17i1.5970 Cite Share Download PDF Status: Under Revision Version 1 posted Reviewers agreed at journal 31 Mar, 2025 Reviewers invited by journal 22 Mar, 2025 Editor invited by journal 22 Mar, 2025 First submitted to journal 21 Mar, 2025 Editorial decision: Major revisions 04 Dec, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5537761","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":432549735,"identity":"92d6968e-bc1d-460d-9ce9-412b071ee691","order_by":0,"name":"KYUNG-HWAN JUNG","email":"","orcid":"","institution":"Kangwon National University","correspondingAuthor":false,"prefix":"","firstName":"KYUNG-HWAN","middleName":"","lastName":"JUNG","suffix":""},{"id":432549736,"identity":"c8c20f3c-4b6a-4ee5-89c1-fd07c7679d24","order_by":1,"name":"KI-YOON LEE","email":"","orcid":"","institution":"Kangwon National 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10:05:02","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":102001,"visible":true,"origin":"","legend":"\u003cp\u003eNormalized electron spectrum for 6, 12 MeV using PRIMO software\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-5537761/v1/bb52a1a43271b2e4ee30ee84.png"},{"id":79177235,"identity":"2930c10c-9d51-48ca-968b-2e29dc8b5235","added_by":"auto","created_at":"2025-03-25 10:05:02","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":211808,"visible":true,"origin":"","legend":"\u003cp\u003eExperimental schematic for calculating thickness parameters of a shielding specimen\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-5537761/v1/46ecc03b3d31d897c4ceb5d1.png"},{"id":79179220,"identity":"691246e0-21a9-4b87-b817-c5b78278f46e","added_by":"auto","created_at":"2025-03-25 10:13:02","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":118494,"visible":true,"origin":"","legend":"\u003cp\u003eSoftware workflow for automated subtraction\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-5537761/v1/41038db8d390f36ff9a7e759.png"},{"id":79177253,"identity":"47456149-47da-41ef-9acb-c61c8f7afab1","added_by":"auto","created_at":"2025-03-25 10:05:03","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":313126,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of the metal 3D shielding block experiment with GafChromic EBT3 film\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-5537761/v1/e0fdf9afa577044efd182651.png"},{"id":79179955,"identity":"a9a7756d-c261-490d-a4d0-05468667f432","added_by":"auto","created_at":"2025-03-25 10:21:02","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":105992,"visible":true,"origin":"","legend":"\u003cp\u003ePercent depth dose profiles for each energy measured in the open field at (a) 6 MeV and (b) 12 MeV\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-5537761/v1/d9a51fbf1e0fd25f4b43702b.png"},{"id":79180941,"identity":"15f8f29f-731c-4514-a4c4-4444bcecefbd","added_by":"auto","created_at":"2025-03-25 10:29:02","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":112946,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of penetration rates for pure copper, brass, and SUS 316L at (a) 6 MeV and (b) 12 MeV, measured using GATE v8.0 simulation and experimental data across different thicknesses\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-5537761/v1/b50e86cc388a333177856db5.png"},{"id":79179225,"identity":"f4e8e9f3-4a4e-4af4-83be-34e80788f497","added_by":"auto","created_at":"2025-03-25 10:13:02","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":166487,"visible":true,"origin":"","legend":"\u003cp\u003eMetal 3D (a) Pure copper, (b) Brass, (c) SUS 316L, and (d) SUS 316L(3D Printing) shielding blocks made using rapid prototyping processes\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-5537761/v1/4cbd322e92c9c98fa3c0ade5.png"},{"id":79181388,"identity":"ac842d14-5bec-4c5e-837c-8a7e7ea958bd","added_by":"auto","created_at":"2025-03-25 10:37:03","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":160964,"visible":true,"origin":"","legend":"\u003cp\u003eDose-pixel calibration curves with GafChromic EBT3 film\u003c/p\u003e\n\u003cp\u003e(a) before irradiation, (b) after irradiation, and (c) calibration curve for electron beam 6 MeV and 12 MeV\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-5537761/v1/8c706d2484eef4c45358078b.png"},{"id":79179229,"identity":"019e9440-1735-4eb8-97da-94666f0c9db1","added_by":"auto","created_at":"2025-03-25 10:13:03","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":245683,"visible":true,"origin":"","legend":"\u003cp\u003eOff-axis ratio distribution of metal 3D shielding blocks for each energy (a) 6 MeV (b) 12 MeV\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-5537761/v1/e11436fad5af4969db9e548e.png"},{"id":79179962,"identity":"8dfc4f1b-7dd5-43e5-b385-1c151844ca49","added_by":"auto","created_at":"2025-03-25 10:21:03","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":509773,"visible":true,"origin":"","legend":"\u003cp\u003eThe isodose distribution of metal 3D shielding blocks for each energy (a) 6 MeV (b) 12 MeV\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-5537761/v1/ea111368685c3ada3dfb07c7.png"},{"id":79181389,"identity":"979ed9ff-626e-4087-94ea-fbafac496047","added_by":"auto","created_at":"2025-03-25 10:37:03","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":251185,"visible":true,"origin":"","legend":"\u003cp\u003eFig. 10 Normalized fractions of bremsstrahlung X-rays and transmitted electrons as a function of shielding thickness for a (a) 6 MeV (b) 12 MeV electron beam\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-5537761/v1/ebae2fb34ab28e0cbe6c60d9.png"},{"id":79181391,"identity":"a2756207-0e54-4ced-8ac1-78cd3fb57053","added_by":"auto","created_at":"2025-03-25 10:37:09","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3035551,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5537761/v1/52e0260c-1155-4984-83f7-514dd44e5cb7.pdf"}],"financialInterests":"","formattedTitle":"Validation of patient-specific metal 3D shielding block usability with GafChromic EBT3 film","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eIn radiation therapy, high-energy electron beams are effective in delivering a lethal dose to skin diseases and skin cancer while minimizing the dose to surrounding healthy tissues due to their buildup characteristics at a specific depth [1]. Keloids are raised, reddish scars that form on the skin when wounds fail to heal properly. When treated with surgery alone, the recurrence rate is reported to be 80\u0026ndash;100%. Therefore, the standard treatment for keloids currently involves radiation therapy in combination with surgery.[2] A follow-up study on low-dose radiation therapy after surgical excision of refractory chest keloids reported that recurrence did not occur in approximately 90% of cases.[3] Such findings highlight the positive role of radiation therapy for keloids, and to achieve effective treatment, field shaping that considers the irregular size of scar tissue is essential [4]. Keloids are typically small lesions ranging from 1 to 3 cm, and while a 6 \u0026times; 6 cm\u0026sup2; field size is commonly used in treatment, smaller cutouts may sometimes be required. In the current clinical environment, cast shielding blocks, known as Cerrobend, are manufactured using a low-melting-point lead alloy(LMA) composed of lead, cadmium, bismuth, and tin (density\u0026thinsp;=\u0026thinsp;9.4 g/cm\u0026sup3;) to facilitate simpler field shaping.[5] However, the casting process generates toxic fumes and metal dust, posing occupational hazards and necessitating strict regulatory management and specialized expertise in hospitals. To address these issues while maintaining equivalent shielding performance, rapid prototyping methods such as CNC machining and 3D printing are being used. Rapid prototyping enables the fabrication of three-dimensional products from digital scan data and is widely utilized in engineering and manufacturing industries [6]. While 3D printing has been explored for its applicability in producing dense metal composite filaments for shielding purposes, it has been reported to have low density and inherent filament inconsistencies.[7\u0026ndash;8] Additionally, for small field sizes, treatment planning systems (TPS) may struggle to accurately predict scatter radiation, leading to deviations. Incorporating high-density materials such as tungsten within filaments may further increase scatter, potentially reducing dose uniformity and precision.[9\u0026ndash;10] A pure copper cutout fabricated via CNC machining has been reported to be dosimetrically equivalent to Cerrobend in small 6 \u0026times; 6 cm\u0026sup2; fields, with a\u0026thinsp;\u0026plusmn;\u0026thinsp;2% dose agreement or 99% pass rate based on a 2%/1 mm gamma index criterion. Furthermore, it has been observed that the use of pure copper can reduce out-of-field dose by decreasing bremsstrahlung radiation.[11] However, pure copper exhibits several mechanical disadvantages when reused over time. Due to its low hardness and high ductility, repeated use in applicators or mechanical impacts, such as drops, can lead to deformation. Additionally, exposure to air can cause surface oxidation and corrosion. To overcome these limitations, further research is needed on metallic shielding materials with densities similar to traditional lead alloys. However, studies specifically focusing on shielding materials for high-energy electron beams remain insufficient. Therefore, this study aims to quantitatively propose the required thickness to achieve shielding performance using metallic materials utilized in rapid prototyping through GATE (Geant4 application for tomographic emission) simulations, a medical computational modeling tool. Therefore, this study aims to quantitatively propose the required thickness to achieve effective shielding performance using metallic materials applied in rapid prototyping, through GATE (Geant4 application for tomographic emission) simulations, a medical computational modeling tool. Additionally, automated extraction software will be implemented to streamline the treatment process, facilitating the fabrication of metal 3D shielding blocks, which will be validated using GafChromic EBT film by comparing their performance with conventional Cerrobend cutouts.\u003c/p\u003e"},{"header":"2. Methods and Materials","content":"\u003ch3\u003e1. Monte Carlo Simulation\u003c/h3\u003e\n\u003cp\u003e1\u0026ndash;1. Electron beam modeling\u003c/p\u003e \u003cp\u003eTo evaluate the source term for 6 MeV and 12 MeV electron beams, the TrueBeam model (Varian Medical Systems, Palo Alto, USA) was selected as the medical linear accelerator, and the Monte Carlo simulation tool GATE v8.0 was utilized[12]. The energy spectrum of the electron beam was derived using PRIMO software, which is based on the PENLOPE code and is capable of simulating the spectrum of Varian medical linear accelerators in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The spectrum for 6 MeV and 12 MeV, commonly used in clinical practice, was calculated and set accordingly[13]. The spectrum provided by the software accounts for the source term, considering components from the primary collimator to the applicator. To validate the source term, the simulated percentage depth dose(PDD) and the PDD measured using the TrueBeam system were compared, focusing on the maximum dose depth(D\u003csub\u003emax\u003c/sub\u003e). The reference depths in the water phantom for electron beam energies of 6 MeV and 12 MeV, measured using a Farmer-type chamber(FC65-G) following the TG-51 protocol, are 1.3 cm and 2.9 cm, respectively, within the TrueBeam system. The experimental setup included a water phantom (50 \u0026times; 50 \u0026times; 30 cm\u0026sup3;) positioned at a source-to-surface distance (SSD) of 100 cm. The applicator field size was set to 10 cm \u0026times; 10 cm for electron beam irradiation. The energy bin spacing within the simulation was set to 0.1 cm to calculate the PPD value.\u003c/p\u003e\n\u003ch3\u003e1–2. Evaluation of shielding performance using metal 3D shielding specimens\u003c/h3\u003e\n\u003cp\u003eThe shielding performance against high-energy electron beams is primarily determined by the density and atomic number of a material. For alloys, which cannot be defined by a single atomic number, the average atomic number was calculated by considering the atomic numbers of the major constituent elements and their proportions, using mass percentages as weighting factors. Additionally, the heat and X-rays generated from the interaction between electrons and matter may indirectly influence the shielding performance, necessitating the consideration of physicochemical properties. This study selected stainless steel 316L(SUS 316L), brass, and pure copper materials commonly employed in rapid prototyping with densities of 8 g/cm\u0026sup3; or higher for evaluation. Table. 1 summarizes the material properties. The physicochemical properties of each metal relevant to radiation transport modeling were validated using data provided by the Pacific Northwest National Laboratory.[14]\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePhysical properties of the selected metal materials for manufacturing shielding blocks\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStainless steel 316L\u003c/p\u003e \u003cp\u003e(SUS 316L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBrass\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePure copper\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDensity\u003c/p\u003e \u003cp\u003e[g/cm\u003csup\u003e3\u003c/sup\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8.92\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThermal Conductivity (W/m\u0026middot;K)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e16.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e109\u0026ndash;125\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e401\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElectrical Conductivity (%IACS)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e28\u0026ndash;37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMechanical Strength (MPa)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e480\u0026ndash;620\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e300\u0026ndash;500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e200\u0026ndash;250\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComposition\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFe 67.37%, Cr 17.00%,\u003c/p\u003e \u003cp\u003eNi 12.00%, Mo 2.50%,\u003c/p\u003e \u003cp\u003eSi 1.00%, P 0.05%,\u003c/p\u003e \u003cp\u003eS 0.03%, C 0.03%,\u003c/p\u003e \u003cp\u003eMn 0.02%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCu 63%, Zn 37%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCu 100%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAtomic number(Z)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e29.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e29\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAccording to the AAPM Task Group 25, high-energy electron beams require shielding that achieves a penetration rate of 5% or less, with a minimum lead thickness requirement of 2 mm per MeV in water or soft tissue. The rule of thumb for LMA incorporates an additional scaling factor of 1.2 times the required thickness for Pb due to density differences[15]. Therefore, density scaling was performed using the following Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) to determine the theoretical thickness required to meet the transmission criteria for the three selected materials.[16]\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:{t}_{x}=\\:\\frac{{\\rho\\:}_{Pb}}{{\\rho\\:}_{x}}\\:\\times\\:\\:{t}_{pb}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cstrong\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{t}_{x}\\)\u003c/span\u003e\u003c/span\u003e\u003c/strong\u003e \u003cp\u003e \u003cem\u003ethe required thickness of the material \u0026#119883;\u003c/em\u003e \u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\rho\\:}_{x}\\)\u003c/span\u003e\u003c/span\u003e\u003c/strong\u003e \u003cp\u003e \u003cem\u003ethe required thickness of the material \u0026#119883;\u003c/em\u003e \u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\rho\\:}_{Pb}\\)\u003c/span\u003e\u003c/span\u003e\u003c/strong\u003e \u003cp\u003e \u003cem\u003ethe density of lead (\u003c/em\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e \u003c/span\u003e \u003cem\u003e=11.34 g/cm\u0026sup3;)\u003c/em\u003e\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{t}_{pb}\\)\u003c/span\u003e\u003c/span\u003e\u003c/strong\u003e \u003cp\u003e \u003cem\u003ethe required thickness of lead for shielding at a given electron beam energy\u003c/em\u003e \u003c/p\u003e \u003c/p\u003e \u003cp\u003eSubsequently, the electron beam shielding performance for each material was evaluated using GATE v8.0 at 1 mm intervals. The thicknesses corresponding to a penetration rate within 5% were considered, and shielding specimens with an internal fill of 100% were fabricated through CNC machining in a manner similar to metal 3D printing, selecting practical thicknesses for each material to ensure ease of processing. The dimensions of the shielding specimens were set to 15 cm \u0026times; 15 cm, while the electron beam field size from the linear accelerator was configured to 10 cm \u0026times; 10 cm. An RW3 slab phantom was positioned at a SSD of 100 cm in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. To assess shielding performance, the metal shielding specimens were placed at the center of the phantom, and an ionization chamber was positioned beneath the phantom surface. The penetration rate was calculated as the relative dose ratio between measurements obtained with and without the shielding material. Measurements were taken three times, each based on 300 MU, and the average value was used as the final result. The simulation method replicated the same geometric conditions as the experimental setup.\u003c/p\u003e \n\u003ch3\u003e2. Validate the usability of metal 3D shielding blocks created with automated subtraction software\u003c/h3\u003e\n\u003cp\u003eTo enable automated extraction, software based on MATLAB (R2022b) was developed, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The software utilizes shaping surfaces derived from DICOM data. It generates random points using elements connected to the selected nodes and creates a mesh through triangular division, connecting the edge parts to construct a shielding block model. The dimensions of the selected image can be freely configured. In this experiment, the surface of the shape was generated based on a patient case derived from the treatment planning system. Subsequently, a shielding block was fabricated using a subtraction technique to exclude the treatment area, and the size of the shielding block was set to 6 cm \u0026times; 6 cm to form a small field. The height was determined as a thickness ensuring a penetration rate of less than 5% for 12 MeV, and the model was extracted as an STL file, a format commonly compatible with rapid prototyping. Following this, metal 3D shielding blocks were manufactured using CNC techniques from SUS 316L, brass, and pure copper. Additionally, to compare differences with metal 3D printing, an extra SUS 316L block was fabricated.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo perform dosimetry of metal 3D shielding blocks manufactured with GafChromic EBT3 film, dose-pixel value calibration curves were performed from 0 MU to 800 MU irradiated for electron beams of 6 MeV and 12 MeV [17]. The film was inserted and positioned at 100 cm between the source and the solid water phantom surface, considering the D\u003csub\u003emax\u003c/sub\u003e for each electron beam from the phantom surface, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The irradiated films were scanned in standard mode with a resolution of 72 dpi at 48 bits using a flatbed film scanner, the EPSON Expression 12000XL (Seiko Epson Corporation, Japan), after approximately 48 hours for stabilization[18]. To minimize the influence of film orientation, the same orientation was applied to all scans. Unirradiated films were scanned and corrected using the analysis software DoseLab (Mobiys Medical Systems, Houston, TX) to account for the uniformity effects of the scanner light source. The dose distribution curves for each electron beam for different materials were then compared.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"3. Results","content":"\u003ch3\u003e1–1. Electron beam modeling\u003c/h3\u003e\n\u003cp\u003eTo evaluate the high-energy electron beams of 6 MeV and 12 MeV used in this study, the PDD measured using GATE v8.0 and a Farmer-type chamber was compared, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. As a result, the D\u003csub\u003emax\u003c/sub\u003e for the 6 MeV electron beam was found to be 1.4 cm in GATE v8.0 and 1.35 cm in the experiment, as specified in Table. 2. A difference of 0.05 to 0.1 cm from the reference depth was observed. For the 12 MeV electron beam, the simulation produced the same reference depth as the experimental measurement. The beam quality index R\u003csub\u003e50\u003c/sub\u003e was determined using linear interpolation, and the difference between the simulation and experimental results for both energies was 0.01 cm, indicating strong agreement between the two methods. Furthermore, the results confirm that the penetration depth of the electron beam is proportional to its energy. However, differences between the PDD curves in the dose fall-off region were observed.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eD\u003csub\u003emax\u003c/sub\u003e and R\u003csub\u003e50\u003c/sub\u003e Values for Electron Beams in Open Field Conditions\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEnergy\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMethod\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eD\u003csub\u003emax\u003c/sub\u003e(cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eR\u003csub\u003e50\u003c/sub\u003e(cm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eReference(Z\u003csub\u003eref\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMeasurement\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.40\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGATE v8.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.39\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eReference(Z\u003csub\u003eref\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMeasurement\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.04\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGATE v8.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003e1–2. Evaluation of shielding performance using metal 3D shielding specimens\u003c/h3\u003e\n\u003cp\u003eTo achieve a penetration rate of 5% or less, the required theoretical thickness for each material was calculated using density scaling, and the shielding effectiveness was analyzed by comparing GATE v8.0 simulations with experimental measurements. The calculated theoretical thicknesses required for a 6 MeV electron beam were 3.8 mm for pure copper, 4.0 mm for brass, and 4.3 mm for SUS steel 316L. For a 12 MeV electron beam, the required thicknesses were 7.6 mm for pure copper, 8.4 mm for brass, and 8.5 mm for SUS 316L. The electron beam penetration rates measured for the fabricated metal shielding specimens are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. For the 6 MeV electron beam, when using a 4 cm thick shielding specimen, the penetration rates were 1.3% for pure copper, 1.3% for brass, and 1.2% for SUS 316L. The discrepancies between simulation and experimental results were 1.14%, 1.33%, and 1.20%, respectively. For 12 MeV electron beams, the required thickness for 95% shielding, based on actual measurements, was 7.6 mm, 7.0 mm, and 6.6 mm for SUS 316L, brass, and pure copper, respectively, with penetration rates of 3.60%, 3.80%, and 3.80%, The discrepancies between the simulation and experimental results were 1.00%, 1.70%, and 1.61%, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003e2. Validation of the usability of metal 3D shielding blocks created with automated subtraction software\u003c/h3\u003e\n\u003cp\u003eThe pure copper, brass, and SUS 316L shielding blocks were subjected to automated subtraction using MATLAB-based software. Subsequently, metal 3D shielding blocks were fabricated through rapid prototyping. The dimensions of the shielding blocks illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, which were manufactured by rapid prototyping, were 6 cm \u0026times; 6 cm. To verify shape accuracy, the original image was printed on a transparent sheet, enabling visual quality assurance and an initial qualitative comparison of the fabricated shielding blocks.\u003c/p\u003e\u003cp\u003eFor calibration of the films required in subsequent experiments, electron beams of 6 MeV and 12 MeV were used to irradiate the films at 0, 50 MU, 100 MU, 150 MU, 200 MU, 300 MU, 500 MU, and 800 MU. The irradiated films were calibrated using DoseLab software to obtain the final dose-pixel curves, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eThe films were converted into doses for each material using DoseLab and plotted against the center to represent the dose distribution within a two-dimensional volume. The off-axis ratio distribution within the planning target volume (PTV) are displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo analyze the penumbra characteristics of the 6 MeV electron beam, the off-axis ratio was measured at the D\u003csub\u003emax\u003c/sub\u003e of 1.3 cm for five different materials in Table. 3: Cerrobend, Pure Copper, Brass, SUS 316L, and SUS 316L(3D printing). The comparison was conducted with Cerrobend as the reference, and the dose distribution characteristics in the penumbra region were evaluated. Data were recorded at representative distances of 1.35, 2.18, 3.28, 5.56, and 6.29 cm, corresponding to off-axis ratio levels of 20, 80, and 100%. Similarly, the penumbra characteristics of a 12 MeV electron beam were analyzed for the same five materials in Table. 4. The off-axis ratio was measured at a D\u003csub\u003emax\u003c/sub\u003e of 2.9 cm, with Cerrobend as the reference for comparison. The dose distribution characteristics in the penumbra region were evaluated, and data were recorded at representative distances of 0.03, 1.00, 2.73, 4.25, and 5.46 cm, corresponding to off-axis ratio levels of 20, 80, and 100%. Cerrobend demonstrated superior performance in the outer penumbra region. At 1.35 cm and 20 percent off-axis ratio, the value for Cerrobend was 0.212, similar to those of Pure Copper at 0.210, Brass at 0.202, and SUS 316L(3D printing) at 0.198, while SUS 316L exhibited a relatively lower value of 0.137. At 2.18 cm and 80 percent off-axis ratio, Cerrobend increased to 0.806, whereas Pure Copper reached 0.771, Brass 0.780, and SUS 316L(3D printing) 0.725, while SUS 316L remained lower at 0.689. At 3.28 cm and 100 percent off-axis ratio, all materials except SUS 316L, which recorded 0.963, achieved a value of 1.0. In the outer penumbra region, at 5.56 cm and 80 percent off-axis ratio, Cerrobend was 0.794, similar to Pure Copper at 0.790, while Brass was slightly lower at 0.756, and SUS 316L recorded the highest value at 0.876. At 6.29 cm and 20 percent off-axis ratio, Cerrobend recorded 0.212, comparable to Pure Copper at 0.223 and SUS 316L(3D printing) at 0.216, while Brass had the lowest value at 0.190, and SUS 316L had the highest at 0.304. The penumbra analysis for the 12 MeV electron beam exhibited trends similar to those observed at 6 MeV. At 0.03 cm and 20 percent off-axis ratio, the value for Cerrobend was 0.269, higher than that of Pure Copper at 0.229 and SUS 316L at 0.181, but lower than those of Brass at 0.159 and SUS 316L(3D printing) at 0.134. At 1.00 cm and 80 percent off-axis ratio, the value for Cerrobend increased to 0.807, followed by Pure Copper at 0.748, SUS 316L at 0.648, and SUS 316L(3D printing) at 0.460, with Brass recording the lowest value at 0.597. At 2.73 cm and 100 percent off-axis ratio, both Cerrobend and SUS 316L(3D printing) achieved a value of 1.0, while Pure Copper was slightly lower at 0.995, SUS 316L at 0.991, and Brass had the lowest value at 0.973. In the outer penumbra region, at 4.25 cm and 80 percent off-axis ratio, the value for Cerrobend was 0.798, lower than those of Pure Copper at 0.833 and Brass at 0.894, but higher than those of SUS 316L at 0.866 and SUS 316L(3D printing) at 0.920. At 5.46 cm and 20 percent off-axis ratio, Cerrobend recorded 0.202, lower than Pure Copper at 0.248, Brass at 0.319, SUS 316L at 0.296, and SUS 316L(3D printing) at 0.442.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eOff-axis ratio measurements for 6 MeV electron beam\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDistance\u003c/p\u003e \u003cp\u003e(cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCerrobend\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePure copper\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eBrass\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSUS 316L\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSUS 316L\u003c/p\u003e \u003cp\u003e(3D Printing)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.35(20%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.212\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.210\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.202\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.137\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.198\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2.18(80%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.806\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.771\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.780\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.689\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.725\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3.28(100%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.963\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5.56(80%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.794\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.790\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.756\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.876\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.766\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6.29(20%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.212\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.223\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.190\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.304\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.216\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eOff-axis ratio measurements for 6 MeV electron beam\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDistance\u003c/p\u003e \u003cp\u003e(cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCerrobend\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePure copper\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eBrass\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSUS 316L\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSUS 316L\u003c/p\u003e \u003cp\u003e(3D Printing)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.03(20%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.269\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.229\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.159\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.181\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.134\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.00(80%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.807\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.748\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.597\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.648\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.460\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2.73(100%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.995\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.973\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.991\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4.25(80%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.798\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.833\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.894\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.866\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.920\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5.46(20%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.202\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.248\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.319\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.296\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.442\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eSubsequently, the full width at half maximum(FWHM) was analyzed in Table. 5. This metric is defined as the distance between two points where the dose reaches 50% of the maximum, serving as an indicator of beam width and dose distribution spread. At 6 MeV, Cerrobend exhibited the narrowest full width at half maximum at 3.986 cm, indicating the most concentrated dose distribution, while Brass had the widest at 4.537 cm. SUS 316L and SUS 316L three-dimensional printing showed similar values of 4.502 and 4.506 cm, respectively. At 12 MeV, FWHM increased for all materials, with SUS 316L recording the widest value at 4.574 cm and Cerrobend maintaining the narrowest at 4.045 cm. The increase in full width at half maximum from 6 MeV to 12 MeV was smallest for Brass and SUS 316L(3D printing) at 0.029 cm and largest for SUS 316L at 0.072 cm. Cerrobend and Pure Copper exhibited increases of 0.059 and 0.053 cm, respectively. The average increase in FWHM was 0.0484 cm, corresponding to an approximate 1.1% variation with increasing energy.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe full width at half maximum measurements for 6 MeV, 12 MeV electron beam\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6 MeV FWHM(cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12 MeV FWHM(cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eΔFWHM (cm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCerrobend\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.986\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.045\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e+\u0026thinsp;0.059\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePure copper\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.513\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.566\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e+\u0026thinsp;0.053\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBrass\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.537\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.566\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e+\u0026thinsp;0.029\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSUS 316L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.502\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.574\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e+\u0026thinsp;0.072\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSUS 316L\u003c/p\u003e \u003cp\u003e(3D Printing)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.506\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.535\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e+\u0026thinsp;0.029\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIn the isodose distribution curve, at 6 MeV, a low-melting lead alloy exhibited 160 cGy in the high-dose region, while SUS 316L, brass, and pure copper exhibited 160 cGy, 160 cGy, and 150 cGy, respectively. At 12 MeV, a low-melting lead alloy showed 220 cGy in the high dose region, while SUS 316L, brass, and pure copper demonstrated 210 cGy, 220 cGy, and 220 cGy, respectively. In the low-dose region, all materials exhibited similar dose distributions as before. This result confirms that the rapid prototyping-processed metal 3D shielding blocks perform as well as traditional shielding blocks in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e10\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eIn this study, modeling was conducted for the 6 MeV and 12 MeV electron beams used in keloid radiotherapy. Several limitations were identified. For the 6 MeV electron beam, a depth difference of 0.05 to 0.1 cm was observed. In contrast, the identical reference depth obtained from both simulation and experimental measurements for the 12 MeV electron beam can be attributed to the higher energy stability, greater beam linearity, and smaller scattering angle of the high energy electron beam. The differences between the PDD curves in the dose fall-off region may stem from a combination of factors, including variations in secondary electron transport modeling, contributions from bremsstrahlung X-rays, differences in water phantom density, discrepancies in electron beam energy spectrum modeling, and Monte Carlo simulation parameters such as energy cut-off values (E\u003csub\u003ecut\u003c/sub\u003e, P\u003csub\u003ecut\u003c/sub\u003e). Additionally, the design of the linear accelerator head, including elements such as the scattering foil, collimators, and applicator, could contribute to these differences in the dose fall-off region. Inaccuracies in simulating the geometry or material properties of the head components may affect the accuracy of the dose distribution, particularly in regions of rapid dose attenuation where small changes in beam characteristics have a pronounced effect. To minimize these discrepancies, further optimization of simulation parameters is necessary, along with additional experimental validation to improve agreement between Monte Carlo simulations and measured data in the low energy region. To analyze the penetration performance of the electron beam subsequently, density scaling was used to calculate the theoretical thickness for each material, which was then validated through simulation and experimental measurements. For all materials, the electron beam shielding achieved a penetration rate within the target range of less than 5% at thicknesses lower than the theoretically required values. This indicates that the theoretical approach based on density scaling can serve as a reliable predictive tool for designing electron beam shields. However, for the 6 MeV electron beam at a 2 mm thickness, the difference between simulation and experimental results was minimal at 0.1% for pure copper, whereas the experimental values were higher for brass at 5.74% and for SUS 316L at 17.9%, with the latter showing the largest deviation. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e10\u003c/span\u003e presents the analysis results of the transmitted electron beam through simulation, visually depicting the distribution of electrons passing through the shield specimen and the contribution of bremsstrahlung X-rays. Notably, the significant discrepancy between simulation and experimental results observed in SUS 316L was accompanied by a pronounced contribution from bremsstrahlung X-rays. Bremsstrahlung X-rays are generated during the interaction of high-energy electrons with the material, and it is possible that the crystalline structure characteristics and actual composition ratios of the alloy in SUS 316L and brass led to the generation of more radiation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThis study evaluated the characteristics of the manufactured 3D metal shielding blocks in relation to the penumbra effect of a 12 MeV electron beam, with Cerrobend serving as the reference material. Pure Copper exhibited a pattern similar to Cerrobend, though it showed slightly higher residual doses at 4.25 cm with a value of 0.833 and at 5.46 cm with a value of 0.248, indicating intermediate performance. Brass recorded the lowest OAR at 2.73 cm with a value of 0.973, suggesting a slight reduction in field uniformity, but displayed a relatively high residual dose at 5.46 cm with a value of 0.319, indicating a slower dose fall-off in the outer regions. SUS 316L demonstrated elevated initial OAR values at 0.03 cm with a value of 0.181 and at 1.00 cm with a value of 0.648, as well as residual OAR values at 4.25 cm with a value of 0.866 and at 5.46 cm with a value of 0.296 throughout the penumbra region, reflecting an expanded dose distribution due to increased scattering. In contrast, SUS 316L produced with 3D printing technology benefited from this manufacturing process, resulting in a lower initial OAR at 0.03 cm with a value of 0.134, but exhibited the highest residual OAR values at 4.25 cm with a value of 0.920 and at 5.46 cm with a value of 0.442, indicating insufficient scattering control under high-energy conditions and suggesting the need for further optimization at higher energies. Future investigations into material-specific penumbra characteristics across various energies and field sizes are essential to expand clinical applicability. Regarding the analysis of electron beam full width at half maximum changes and material-specific properties, the increase in FWHM for all materials at 12 MeV compared to 6 MeV reflects the enhanced lateral scattering and wider penumbra associated with higher energy. This is attributed to the deeper penetration of 12 MeV electrons compared to 6 MeV, resulting in more scattering interactions. The average delta FWHM with a value of 0.0484 cm, representing a 1.1 percent change, indicates a relatively small change relative to the energy increase, suggesting that the scattering effect does not scale linearly with energy. SUS 316L exhibited the widest FWHM at 12 MeV with a value of 4.574 cm, with the largest delta FWHM at 0.072 cm, indicating that its alloy properties with iron, chromium, and nickel induced greater scattering at higher energies. Conversely, SUS 316L produced with 3D printing showed a smaller delta FWHM at 0.029 cm than SUS 316L, suggesting that 3D printing technology may improve microstructure and suppress scattering. Brass displayed the widest FWHM at 6 MeV with a value of 4.537 cm, but its minimal change in delta FWHM at 0.029 cm indicates low sensitivity to energy variations. Pure Copper maintained an intermediate FWHM at 6 MeV with a value of 4.513 cm and at 12 MeV with a value of 4.566 cm, demonstrating balanced performance between Cerrobend and SUS 316L. These findings underscore the significant influence of material-specific scattering properties and energy-dependent beam width variations on clinical applications. Future studies should include a detailed analysis of the correlation between scattering coefficients and penumbra width to quantitatively elucidate material-specific characteristics. In this study, as a preliminary investigation for the fabrication of a metal 3D shielding block, a 2D dose distribution analysis was conducted using Gafchromic EBT3 film. Previous studies have identified several limitations in dosimetry using EBT film. During the film readout process, variations in scanner sensitivity and positional dependence can introduce measurement discrepancies. In particular, optical density (OD) values may vary depending on the scanning orientation, necessitating a standardized methodology to ensure reliable comparisons. Additionally, dose discrepancies tend to increase in small-field measurements. To enhance reproducibility, further repeated experiments and the use of films of various sizes will be conducted. Moreover, various scanning techniques will be employed, and the measured dose distributions will be verified through comparisons with reference dosimetry methods such as ion chamber measurements and Monte Carlo simulations.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eThis study validated the usability of patient-specific metal 3D shielding blocks fabricated through rapid prototyping by comparing their dosimetric performance with conventional Cerrobend blocks. Monte Carlo simulations and experimental measurements were conducted for 6 MeV and 12 MeV electron beams using GafChromic EBT3 film. The results confirmed that shielding blocks made of SUS 316L, brass, and pure copper achieved a penetration rate within 5%, meeting the required shielding criteria. The experimental values showed strong agreement with theoretical predictions, demonstrating the feasibility of using alternative metals for clinical shielding applications. Furthermore, analysis of the penumbra effect and dose distribution revealed that pure copper exhibited dose characteristics comparable to Cerrobend, whereas SUS 316L and brass showed minor variations due to increased scattering. The study also highlighted the influence of manufacturing techniques on dose uniformity, particularly in 3D printed SUS 316L, which exhibited increased residual dose levels in high-energy conditions. Overall, the findings indicate that metal 3D shielding blocks manufactured via rapid prototyping provide effective radiation shielding with dosimetric characteristics comparable to conventional materials. However, further optimization of material selection and processing methods is necessary to minimize scattering effects and enhance clinical applicability. Future studies should explore the long-term mechanical durability of these materials and investigate their performance across different field sizes and beam energies to establish standardized clinical implementation guidelines.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by Kangwon National Univesity, funded by National University Developmet Project in 2024.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003eThe authors have no competing interests to declare that are relevant to the content of this article.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003evan Hezewijk M, Creutzberg CL, Putter H, Chin A, Schneider I, Hoogeveen M, Willemze R, Marijnen CAM (2010) Efficacy of a hypofractionated schedule in electron beam radiotherapy for epithelial skin cancer: Analysis of 434 cases. \u003cem\u003eRadiother Oncol\u003c/em\u003e 95:245\u0026ndash;249. https://doi.org/10.1016/j.radonc.2010.02.024\u003c/li\u003e\n\u003cli\u003eMankowski P, Kanevsky J, Tomlinson J, Dyachenko A, Luc M (2017) Optimizing radiotherapy for keloids: a meta-analysis systematic review comparing recurrence rates between different radiation modalities. Annals of plastic surgery 78(4):403-411. https://doi.org/10.1097/SAP.0000000000000989\u003c/li\u003e\n\u003cli\u003eHa B, Kim SJ, Lee YJ, Im S \u0026amp; Park TH (2023) Early outcomes of complete excision followed by immediate postoperative single fractional 10 Gy for anterior chest keloids: a preliminary results. \u003cem\u003eInternational Wound Journal\u003c/em\u003e \u003cem\u003e20\u003c/em\u003e(5):1418-1425. https://doi.org/10.1111/iwj.13996\u003c/li\u003e\n\u003cli\u003eKawai Y, Tamura M, Amano M, Kosugi T, \u0026amp; Monzen H (2021) First clinical experience of tungsten rubber electron adaptive therapy with real-time variable-shape tungsten rubber \u003cem\u003eAnticancer Research\u003c/em\u003e \u003cem\u003e41\u003c/em\u003e(2): 919-925. https://doi.org/10.21873/anticanres.14845\u003c/li\u003e\n\u003cli\u003eKhan FM, Doppke KP, Hogstrom KR, Kutcher GJ, Nath R, Prasad SC, Purdy JA, Rozenfeld M, Werner BL (1991) Clinical electron-beam dosimetry: Report of AAPM Radiation Therapy Committee Task Group No. 25. \u003cem\u003eMed Phys\u003c/em\u003e 18(1):73\u0026ndash;107. https://doi.org/10.1118/1.596802\u003c/li\u003e\n\u003cli\u003eNegi S, Dhiman S, Sharma RK (2014) Basics and applications of rapid prototyping medical models. \u003cem\u003eRapid Prototyp J\u003c/em\u003e 20(3):256\u0026ndash;267. https://doi.org/10.1108/RPJ-07-2012-0065\u003c/li\u003e\n\u003cli\u003eVel\u0026aacute;squez J, Fuentealba M, Santib\u0026aacute;\u0026ntilde;ez M (2024) Characterization of radiation shielding capabilities of high concentration PLA-W composite for 3D printing of radiation therapy collimators. \u003cem\u003ePolymers\u003c/em\u003e 16:769. https://doi.org/10.3390/polym16060769\u003c/li\u003e\n\u003cli\u003eJreije A, Mutyala SK, Urbonavičius BG, \u0026Scaron;ablinskaitė A, Ker\u0026scaron;ienė N, Pui\u0026scaron;o J, Rutkūnienė Ž, Adlienė D (2023) Modification of 3D printable polymer filaments for radiation shielding applications. \u003cem\u003ePolymers\u003c/em\u003e 15:1700. https://doi.org/10.3390/polym15071700\u003c/li\u003e\n\u003cli\u003eSchulz JB, Gibson C, Dubrowski P, Marquez CM, Million L, Qian Y, Skinner L, Yu AS (2023) Shaping success: clinical implementation of a 3D-printed electron cutout program in external beam radiation therapy. \u003cem\u003eFront Oncol\u003c/em\u003e 13:1237037. https://doi.org/10.3389/fonc.2023.1237037\u003c/li\u003e\n\u003cli\u003eMichiels S, Mangelschots B, De Roover R, Devroye C, Depuydt T (2018) Production of patient-specific electron beam aperture cut-outs using a low-cost, multi-purpose 3D printer. \u003cem\u003eJ Appl Clin Med Phys\u003c/em\u003e 19(5):756\u0026ndash;760. https://doi.org/10.1002/acm2.12421\u003c/li\u003e\n\u003cli\u003eRusk BD, Carver RL, Gibbons JP, Hogstrom KR (2016) A dosimetric comparison of copper and Cerrobend electron inserts. \u003cem\u003eJ Appl Clin Med Phys\u003c/em\u003e 17(5):245\u0026ndash;261. https://doi.org/10.1120/jacmp.v17i5.6282\u003c/li\u003e\n\u003cli\u003eJan S, Santin G, Strul D, Staelens S, Assi\u0026eacute; K, Autret D, Avner S, Barbier R, Bardies M, Bloomfield PM, Brasse D, Breton V, Bruyndonckx P, Buvat I, Chatziioannou AF, Choi YH, Chung YH, Comtat C, Donnarieix D, Ferrer L, Glick SJ, Groiselle CJ, Guez D, Kerhoas-Cavata S, Kirov AS, Kohli V, Koole M, Krieguer M, van der Laan DJ, Lamare F, Largeron G, Lartizien C, Lazaro D, Maas MC, Maigne L, Mayet F, Melot F, Merheb C, Pennacchio E, Perez J, Pietrzyk U, Rannou FR, Rey M, Schaart DR, Schmidtlein CR, Simon L, Song TY, Vieira JM, Visvikis D, Van de Walle R, Wie\u0026euml;rs E, Morel C (2004) GATE: A simulation toolkit for PET and SPECT. \u003cem\u003ePhys Med Biol\u003c/em\u003e 49:4543\u0026ndash;4561.\u003c/li\u003e\n\u003cli\u003eBrualla L, Rodriguez M, Sempau J, Andreo P (2019) PENELOPE/PRIMO-calculated photon and electron spectra from clinical accelerators. \u003cem\u003eRadiat Oncol\u003c/em\u003e 14:6. https://doi.org/10.1186/s13014-018-1186-8\u003c/li\u003e\n\u003cli\u003eDetwiler RJ, McConn RJ, Kamuda MM, Fite JR, Stokes AR (2021) \u003cem\u003eCompendium of Material Composition Data for Radiation Transport Modeling\u003c/em\u003e. Pacific Northwest National Laboratory (PNNL), Rev. 2. https://compendium.cwmd.pnnl.gov/\u003c/li\u003e\n\u003cli\u003eAlmond PR, Biggs PJ, Coursey BM, Hanson WF, Huq MS, Nath R, \u0026amp; Rogers DW (1999). AAPM\u0026apos;s TG‐51 protocol for clinical reference dosimetry of high‐energy photon and electron beams Medical physics 26(9):1847-1870. https://doi.org/10.1118/1.598691\u003c/li\u003e\n\u003cli\u003eRusk BD (2014) A dosimetric comparison of copper and Cerrobend electron insets. Louisiana State University. http://etd.lsu.edu/docs/available/etd-06162014-153414/\u003c/li\u003e\n\u003cli\u003eLewis DF, Chan MF (2016) Technical note: On GAFChromic EBT-XD film and the lateral response artifact. \u003cem\u003eMed Phys\u003c/em\u003e 43(2):643\u0026ndash;649. https://doi.org/10.1118/1.4939226\u003c/li\u003e\n\u003cli\u003eLewis DF, Chan MF (2015) Correcting lateral response artifacts from flatbed scanners for radiochromic film dosimetry. \u003cem\u003eMed Phys\u003c/em\u003e 42(1):416\u0026ndash;429. https://doi.org/10.1118/1.4903758\u003c/li\u003e\n\u003cli\u003eUlya S, Wibowo WE, Nuruddin N, \u0026amp; Pawiro SA (2017) Dosimetric characteristics of gafchromic EBT3 film on small field electron beam. In \u003cem\u003eJournal of Physics: Conference Series\u003c/em\u003e 851(1):012023. https://doi.org/10.1088/1742-6596/851/1/012023\u003c/li\u003e\n\u003cli\u003eSipil\u0026auml; P, Ojala, J, Kaijaluoto S, Jokelainen I, \u0026amp; Kosunen A (2016) Gafchromic EBT3 film dosimetry in electron beams\u0026mdash;energy dependence and improved film read‐out. \u003cem\u003eJournal of applied clinical medical physics\u003c/em\u003e \u003cem\u003e17\u003c/em\u003e(1): 360-373. https://doi.org/10.1120/jacmp.v17i1.5970\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"physical-and-engineering-sciences-in-medicine","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"apes","sideBox":"Learn more about [Physical and Engineering Sciences in Medicine](http://link.springer.com/journal/13246)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/apes/default.aspx","title":"Physical and Engineering Sciences in Medicine","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Keloid, Electron beam, Shielding block, Monte Carlo simulation, GafChromic EBT3, Rapid prototyping","lastPublishedDoi":"10.21203/rs.3.rs-5537761/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5537761/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eKeloids are abnormal scars that result from excessive fibrous tissue proliferation during wound healing, with recurrence rates of 80\u0026ndash;100% when treated with surgery alone. As a result, radiation therapy has become an essential adjunct treatment to reduce recurrence, with electron beam therapy demonstrating significant effectiveness. This study aims to optimize dose distribution in keloid radiotherapy using patient-specific shielding blocks and evaluate the radiation shielding performance of metal 3D shielding blocks fabricated through rapid prototyping as a potential alternative to conventional Cerrobend blocks. Monte Carlo simulations (GATE v8.0) and experimental validation using GafChromic EBT3 film were conducted for 6 MeV and 12 MeV electron beams to analyze the shielding efficiency of stainless steel 316L(SUS 316L), brass, and pure copper. The results confirmed that the fabricated metal 3D shielding blocks met the required transmission rate criteria (\u0026le;\u0026thinsp;5%) and demonstrated strong agreement with Monte Carlo simulations. Pure copper exhibited excellent shielding performance with dosimetric characteristics comparable to Cerrobend, while brass showed superior mechanical strength, making it a promising material for long-term durability. Additionally, SUS 316L demonstrated excellent corrosion resistance and minimal deformation over repeated use, enhancing its clinical applicability. The difference between the off-axis and isodose curves of the cerrobend cutout and those of the metal prototypes was found to be minimal, indicating that the fabricated shielding blocks provided comparable dose distribution characteristics. The findings of this study suggest that metal 3D shielding blocks could serve as a viable alternative to conventional Cerrobend blocks, paving the way for personalized and precision radiation therapy. Further research is necessary to enhance mechanical durability, reduce radiation scattering, and develop lightweight shielding materials, ultimately improving the precision and efficiency of patient-specific electron beam therapy.\u003c/p\u003e","manuscriptTitle":"Validation of patient-specific metal 3D shielding block usability with GafChromic EBT3 film","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-03-25 10:04:57","doi":"10.21203/rs.3.rs-5537761/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-03-31T22:45:35+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-03-22T20:05:37+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Physical and Engineering Sciences in Medicine","date":"2025-03-22T08:49:35+00:00","index":"","fulltext":""},{"type":"submitted","content":"Physical and Engineering Sciences in Medicine","date":"2025-03-21T04:58:57+00:00","index":"","fulltext":""},{"type":"decision","content":"Major revisions","date":"2024-12-04T17:29:41+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"physical-and-engineering-sciences-in-medicine","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"apes","sideBox":"Learn more about [Physical and Engineering Sciences in Medicine](http://link.springer.com/journal/13246)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/apes/default.aspx","title":"Physical and Engineering Sciences in Medicine","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"d577350f-394f-416d-a79f-dc8ca5a45ff1","owner":[],"postedDate":"March 25th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[],"tags":[],"updatedAt":"2025-05-13T11:37:38+00:00","versionOfRecord":[],"versionCreatedAt":"2025-03-25 10:04:57","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5537761","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5537761","identity":"rs-5537761","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}