RapidArc Dynamic versus IMRT and VMAT for Endometrial Cancer SIB Radiotherapy

RapidArc Dynamic versus IMRT and VMAT for Endometrial Cancer SIB Radiotherapy | 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 RapidArc Dynamic versus IMRT and VMAT for Endometrial Cancer SIB Radiotherapy Yutong Zhao, Xinqiang Zhang, Xiaoshen Wang, Zejun Jiang, Xingmin Ma, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8666248/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 10 You are reading this latest preprint version Abstract Background Radiotherapy with simultaneous integrated boost (SIB) for endometrial cancer requires highly conformal dose distributions to reduce toxicity. RapidArc Dynamic (RAD), a novel technique combining dynamic arc delivery with strategic gantry pauses, may improve organ-at-risk (OAR) sparing and efficiency. Purpose By comparing RAD with conventional IMRT and VMAT for endometrial SIB radiotherapy, evaluating OAR sparing and treatment efficiency of RAD technique in endometrial cancer treatment. Methods and Materials : Thirty patients with high-intermediate risk endometrial cancer were retrospectively enrolled. Three plans (RAD, IMRT, VMAT) were generated per patient, prescribing 50.4 Gy to the planning target volume (PTV) and 61.6 Gy to the nodal clinical target volume (CTVn) in 28 fractions. Plans were evaluated for OAR dose constraints, conformity index (CI), inward-outward dose gradient ratio (IOR), monitor units (MU), and modulation complexity score (MCS). Results RAD plans demonstrated superior OAR sparing, with significantly fewer and less severe constraint violations for the bladder, rectum, small intestine, and bone marrow compared to IMRT and VMAT (Mann-Whitney U test, P < 0.05). RAD achieved a significantly higher CI than VMAT and a steeper inward dose gradient than both IMRT and VMAT. RAD also used significantly fewer MU than IMRT and exhibited higher MCS, indicating less complex delivery. Conclusions RAD provides superior OAR protection and steeper dose fall-offs compared to IMRT and VMAT, while maintaining high target dose conformity and improving delivery efficiency. It represents a highly promising technique for endometrial SIB radiotherapy, combining the advantages of IMRT and VMAT. Figures Figure 1 Figure 2 Figure 3 Introduction As an indispensable element of endometrial cancer management, radiotherapy includes techniques like simultaneous integrated boost (SIB), which delivers escalated doses to high-risk nodal regions [ 1 ]. A significant challenge with SIB, however, is the association between larger boost volumes or higher dose levels and an increased incidence of acute Grade ≥ 3 toxicities [ 2 ]. These adverse effects, which often involve non-gastrointestinal and urinary systems, result from the irradiation of healthy tissues adjacent to the target. Therefore, achieving highly conformal dose distributions is a critical requirement for optimizing SIB radiotherapy in endometrial cancer. Evolved from intensity-modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT) allows for the simultaneous dynamic modulation of gantry speed, multi-leaf collimator (MLC) shape, and dose rate, leading to reduced treatment delivery times and lower monitor units (MU) [ 3 – 5 ]. RapidArc Dynamic (RAD) solution is a recent innovation that integrates continuous VMAT arc delivery with static angle–modulated ports (STAMPs), allowing the gantry to pause at specific positions during dose delivery and incorporating a dynamically rotating collimator throughout the treatment arcs [ 6 , 7 ]. By comparing RAD against conventional VMAT, a multi-site planning study suggested that RAD can achieve equal or superior OAR sparing with generally reduced treatment delivery times. Specific benefits included a reduction of mean heart dose in breast cancer radiotherapy and improved bladder and rectum sparing in prostate radiotherapy [ 6 ]. However, the performance of RAD has not yet been evaluated specifically for endometrial cancer treatment or within the context of SIB radiotherapy. To address the identified knowledge gaps above, this study aims to investigate the feasibility of RAD treatment planning for SIB radiotherapy in endometrial cancer. The performance of the RAD technique will be quantitatively evaluated through a comparative planning study against conventional nine-fields IMRT and two-arcs VMAT. This study aims to examine whether the dynamic collimator rotation with strategic pauses of RAD could translate into dosimetric or efficiency benefits, and the potential for establishing RAD radiotherapy as a routine standard care for endometrial SIB treatments. Materials and Methods Data preparation A total of thirty patients with high-intermediate risk endometrial cancer (HIR-EC), who received SIB external beam radiotherapy (EBRT) at Shandong Cancer Hospital (Jinan city, Shandong province, China) between January 1, 2024, and January 1, 2025, were retrospectively enrolled in this single-centre study. The CT images for all eligible patients were subsequently collected and anonymized to ensure data privacy. Critical OARs, including the kidneys, small intestine, duodenum, spinal cord, bladder, rectum, femoral heads, and bone marrow, were initially delineated using a deep learning-based auto-segmentation software—AccuContour (version: 3.2, Manteia Technologies Co., Ltd.), which has demonstrated superior performance in contouring abdominal and pelvic OARs [ 8 – 10 ]. All auto-generated contours were subsequently reviewed and manually refined as necessary by an experienced radio-physicist (XQZ) and a radiology specialist (GZG) to ensure anatomical accuracy and adherence to institutional delineation protocols. Volume of interest definition This study adhered to established international guidelines from eviQ [ 11 ] and the National Comprehensive Cancer Network (NCCN) [ 12 ] for target volume delineation. For each patient, the gross tumour volume (GTV) was delineated on the planning CT to encompass the primary endometrial carcinoma, including any local spread. Involved lymph nodes were separately defined as the GTVn. The clinical target volume (CTV) was constructed as a Boolean union of the GTV and region of microscopic disease spread. These included the entire uterus, cervix, fallopian tubes, ovaries, the upper 50% of the vagina, along with the paravaginal soft tissues and parametrium. The duodenum and small intestine were explicitly cropped from the CTV. A separate CTV for the nodes (CTVn) was generated by applying a 5 mm isotropic expansion to the GTVn. Finally, the planning target volume (PTV) was created by adding an 8 mm isotropic margin to the CTV to account for setup uncertainties and internal anatomical motion. Treatment Planning For each enrolled patient, a comprehensive set of three distinct treatment plans was generated using the RAD, IMRT, and VMAT techniques. To ensure a consistent and clinically relevant dosimetric comparison, all planning adhered to the standardized dose constraints for OARs (listed in Table 1 ) and dose prescriptions as outlined by the eviQ guidelines [ 11 ]. The prescribed regimen delivered a total of 50.4 Gy in 28 fractions to the PTV. A SIB of 61.6 Gy was prescribed to the CTVn. For a plan to be considered acceptable, it was mandated that at least 95% of the PTV and the CTVn receive 100% of their respective prescribed doses. Table 1 List of OAR dose constraints. Organ Planning Aim Hard Constraint Spinal cord D max ≤ 40 Gy D max ≤ 45 Gy Small intestine V 45 ≤ 200 cc V 40 ≤ 70% V 40 ≤ 30%. V 45 ≤ 250 cc D max ≤ 55.5 Gy D 2cc ≤ 52 Gy D 2cc ≤ 51 Gy Duodenum V 55 ≤ 15 cc D 2cc ≤ 52 Gy D 2cc ≤ 51 Gy Rectum V 40 ≤ 50%. V 40 ≤ 60%. D max ≤ 55.5 Gy D 2cc ≤ 52.5 Gy D 2cc ≤ 50 Gy Bladder V 45 < 35%. V 45 ≤ 50%. D 2cc ≤ 52 Gy D 2cc ≤ 53.5 Gy Femoral heads V 30 ≤ 15% D max ≤ 55.5 Gy V 45 ≤ 50%. V 50 ≤ 10% Kidneys D mean ≤ 15 Gy V 12 ≤ 55% V 20 ≤ 32% V 23 ≤ 30% V 28 ≤ 20%. Bone marrow V 10 ≤ 80%. V 10 ≤ 90% V 40 ≤ 37%. D max , D mean : The maximum and average dose of the structure. D 2cc : The minimum dose delivered to the hottest 2 cubic centimeters of the structure. V X : The percentage volume that receives at least x Gy of radiation dose. To account for potential large inter- and intra-fraction motion of the bladder and rectum, and to further protect surrounding healthy tissues, two triangle-shaped regions of interest (Hot_Ant and Hot_Pos) were delineated, each positioned approximately 3.5 cm away from the PTV. In addition to adhering to standard OAR constraints, specific maximum dose suppression was applied to these ROIs. This supplementary optimization objective was implemented to minimize radiation exposure to adjacent normal tissues, while ensuring that it did not compromise the prescribed dose coverage for both the PTV and the CTVn. All treatment plans were optimized on a Eclipse treatment planning system (Varian Medical Systems, USA) with Photon Optimizer algorithm (version 18.1) for delivery on a Varian TrueBeam linear accelerator. All planning tasks were performed by a senior medical physicist (XQZ) with over five years of specialized experience. All plans were generated with beam energy of 6 MV. The dose rates were 1400 MU/min for RAD plans and 600 MU/min for non-RAD plans. Dose distribution were calculated using the Accuros XB algorithm with a dose grid size of \(\:2.5\:mm\times\:2.5\:mm\times\:3\:mm\) . The IMRT plans were designed using a standardized nine-field beam geometry with sliding window. These beams were statically positioned at approximately 40-degree intervals around the patient, creating a coplanar arrangement. For the VMAT technique, each plan consisted of two full 360-degree arcs. The first arc rotated clockwise from 181° to 179°, and the second arc rotated counterclockwise from 179° to 181°. To enhance modulation capabilities and reduce interleaf leakage, the collimator angles were fixed at 15° for the first arc and 345° for the second arc, providing complementary modulation patterns. For RAD treatment planning, Eclipse enables user-selected static angle modulated ports. A potential reduction in both optimization computation time and overall treatment delivery times was anticipated by this approach. The STAMPs provide adjustable control over the contribution of arc and static fields during plan optimization and delivery. This is governed by a weighting parameter with five distinct modes: “arc dominant” (-2), “arc” (-1), “balanced” (0), “static” (+ 1), and “static dominant” (+ 2). As mentioned above, the five modes correspond to having 2, 14, 26, 39, and 51 control points respectively at each paused gantry direction during the arc beam delivery. Selecting a higher static weighting, such as '+1', implies 39 control points in each specific static gantry direction within the RAD plan. This setting shows a greater inclination towards assigning a larger weight to STAMPs within the plan compared with weighting of “-1”. For this study, all RAD plans were generated using two full arcs, with STAMPs (gantry pauses) strategically set at 0° and 181°. Based on findings from prior investigations [ 6 ], the plans were optimized using a static field weighting of “+1” to enhance the benefits of the static ports while maintaining the efficiency of arc therapy. By maximizing the MLC modulation for target coverage, collimator rotation of all plans was optimized automatically in Eclipse. Plan evaluation To ensure a consistent comparison, all generated treatment plans were first normalized, such that 95% of the PTV received the prescription dose of 50.4 Gy. The performance of each technique was then evaluated and compared using standardized dose metrics defined in the planning protocol and dose-volume histograms (DVHs). To evaluate and compare the dose distribution conformity achieved by the three radiotherapy techniques, the conformity index (CI) was calculated for all generated plans. The index was defined as follows [ 13 – 15 ]: $$\:CI=\:\frac{{TV}_{PTV}^{2}}{TV\times\:PIV}$$ Where the \(\:{TV}_{PTV}\) stands for the target volume covered by the prescription isodose, TV and PIV represent the prescription isodose volume (total volume receiving at least the prescription dose) and volume of target, respectively. A CI value closer to 1 indicates a more ideal dose conformation. This study also innovated a novel method to quantitatively evaluate the directional gradient of the 3D radiation dose distribution at PTV surface, thereby identifying the radiotherapy technique that offers the steepest dose gradient toward the center of the PTV. First, for the surface voxels of the PTV, the dose gradient vector field is computed using the spatial derivatives of the dose distribution, normalized to the voxel size for correct physical units (Gy/mm). Subsequently, the surface normal vectors, pointing outward from the PTV, are estimated based on the geometry of the target volume. The interaction between the dose gradient and the surface geometry is analyzed by calculating the dot product between the gradient vector and the normal vector at each surface point. A negative dot product indicates the gradient points inward, while a positive value indicates an outward direction. Finally, the magnitudes of the inward and outward gradients are statistically aggregated to calculate the inward-outward ratio (IOR), providing a quantitative measure of dose fall-off sharpness and directionality. The modulation complexity score (MCS) was also calculated to evaluate the complexity of generated plans. By following the methodology developed by Masi et al. [ 16 ], the MCS was calculated by integrating leaf sequence variability (LSV) and aperture area variability (AAV) across control points, weighted by monitor units (MU).To evaluate the plan complexity more comprehensively, a multiplicative combination of leaf travel (LT) and MCSv (LTMSC) was also calculated: $$\:LTi=\frac{1000-LT}{1000}\:\:\:\:\:and\:\:\:\:\:LTMSC=\:LTi\bullet\:LTi$$ The higher complexity of a plan, a lower MSC and LTMSC would be calculated. All statistical tests in this research were performed by Mann-Whitney U test [ 17 , 18 ] with significance level of 0.05. Results A total of 90 radiotherapy plans (30 each for RAD, IMRT, and VMAT) were generated for 30 HIR-EC patients. All plans were normalized to ensure 95% of the PTV received 50.4 Gy, and all achieved 95% coverage of the CTVn by 61.6 Gy. Dose constraint assessments are summarized in Fig. 1 . RAD plans demonstrated the fewest and mildest instances of exceeding dose limits for the small intestine D 2cc < 52 Gy (RAD: 13 VS. IMRT: 23 VS. VMAT: 29), bladder V 45 < 50% (2 VS. 3 VS. 2), and bladder D 2cc < 53.5 Gy (3 VS. 9 VS. 13). While all plans violated the bone marrow constraint of V 10 < 90%, RAD plans showed significantly lower doses for most evaluated metrics - including rectum V 40 , D 2cc , D max , spinal cord D max , small Intestine D 2cc , left femur head V 30 , V 45 , and Marrow V 40 - compared to both IMRT and VMAT plans (P < 0.05). Additionally, RAD plans achieved significantly lower bladder V 45 than IMRT and lower small intestine D max and bladder D 2cc than VMAT (P < 0.05). RAD plans achieved an average CI of 0.833, comparable to IMRT (0.835) and significantly higher than two-arc VMAT plans (0.813) (P < 0.05). For CTV, the average IOR was highest for RAD plans (1.26), followed by IMRT (1.20) and VMAT (1.12), indicating steeper inward dose gradients with RAD. Statistical test demonstrated that the IOR of RAD plans was significantly higher than both IMRT and VMAT plans (P < 0.05). The dose gradient of a representative RAD plan is visualized in Fig. 2 , showing a rapid dose increase towards the CTV and a sharp fall-off towards surrounding organs at risk. Figure 3 displays the DVHs with 95% confidence intervals for the RAD, IMRT, and VMAT plans. The curves demonstrate that the RAD technique achieved lower dose exposures to the OARs across most dose intervals on average, including the high-dose region (> 50 Gy). The narrow band of 95% confidence intervals in the DVH of RAD plans indicated it enabled better OAR protection for the majority of patients. The average MU number for RAD, IMRT, and VMAT plans was 1314.7 (min ~ max: 946.6 ~ 1529.3, standard deviation: 99.4), 3334.0 (2124.4 ~ 3984.3, 364.0), and 527.8 (446.7 ~ 623.4, 38.2), respectively. For RAD, IMRT, and VMAT plans, the average MCS was 0.16 (0.13 ~ 0.19, 0.01), 0.03 (0.02 ~ 0.05, 0.01), and 0.26 (0.21 ~ 0.32, 0.03), while the LTMCS was 0.16 (0.13 ~ 0.18, 0.01), 0.03 (0.02 ~ 0.05, 0.01), and 0.25 (0.20 ~ 0.30, 0.02), respectively. RAD plans showed a significantly lower and higher (P < 0.05) MCS and LTMCS than VMAT and IMRT plans, respectively. Discussion The RAD solution demonstrates superior OAR sparing compared to IMRT and VMAT. As illustrated in Fig. 1 and Fig. 3 , RAD plans provided enhanced protection for OARs such as the bladder, rectum, small intestine, and bone marrow. This is clinically significant as studies have confirmed that strictly limiting parameters like the D 2cc for these OARs is key to reducing patient toxicity [ 19 , 20 ]. The observed reduction in OAR D 2cc with RAD planning directly explains its potential to yield lower toxicity and fewer side effects for patients. The RAD solution creates a steep dose gradient around the target volume. As the IOR and Fig. 2 illustrated, compared to nine-field IMRT and two-arc VMAT, RAD demonstrated the capability to carve the sharpest dose fall-off, thereby effectively extruding the dose inward toward the target and away from adjacent OARs. Furthermore, RAD plans achieved a significantly higher CI than VMAT and an equivalent CI to IMRT, indicating its ability to ensure sufficient target coverage by the prescribed isodose level. Compared to IMRT plans, a significantly lower MU number (P < 0.05) and a higher dose rate of RAD plans contribute to a shorter treatment time, which may reduce intra-fraction motion and consequently improve delivery accuracy. Moreover, RAD also demonstrated a significantly higher MCS and LTMCS than IMRT plans, indicating that RAD plans have simpler beam apertures and reduced leaf motion, which correlates with higher dosimetric accuracy, higher gamma passing rates in QA, and enhanced delivery reliability. However, it is important to note that the specific calculation methodology for MCS and LTMCS used in this study, which is subject to the maximum continuity constraints on the MLC operation sequence, could potentially lead to biased predictions of modulation complexity. Furthermore, this study employed PTV and clinical target volume of the nodes (CTVn) margins of 8 mm and 5 mm, respectively, which are potentially larger than those used in contemporary SIB protocols, to account for intra- and inter-fraction motion. The combination of the challenging multi-arc technique and these larger margins made it difficult to satisfy many OAR dose constraints, such as the V 10 Gy constraint of bone marrow. Future research should focus on comparing two-arc RAD, nine-field IMRT, and three-arc VMAT plans utilizing a reduced margin size to better balance target coverage and OAR sparing. Compared to RAD and nine-field IMRT plans, the two-arc VMAT plans demonstrated the highest number of violated dose constraints and the lowest CI, suggesting that a dual-arc VMAT approach may be insufficient for meeting the complex demands of modern SIB radiotherapy in endometrial cancer. Future research should focus on comparing RAD, nine-field IMRT, and three-arc VMAT plans. Based on our experience with treatment planning, RAD plans were generated with two gantry pauses (i.e. static fields) at 0° and 181° for each arc. However, further optimization in achieving an optimal balance between superior dose distribution and reduced plan complexity may be possible by strategically adjusting degrees and number of static fields or static field weighting employed within the RAD planning framework. Conclusions This study comprehensively evaluated the performance of RAD in comparison to conventional nine-field IMRT and two-arc VMAT for simultaneous integrated boost radiotherapy in endometrial cancer. The results demonstrate that RAD achieves superior OAR sparing, particularly for the bladder, rectum, small intestine, and bone marrow, with fewer and less severe violations of dose constraints. Additionally, RAD generates a steeper inward dose gradient, quantified by a higher IOR, and provides a CI comparable to IMRT and superior to VMAT, indicating excellent dose sculpting around the target volume. While RAD exhibits higher modulation complexity and significantly fewer monitor units than IMRT, contribution to potentially shorter treatment times and enhanced delivery efficiency. In conclusion, RAD represents a highly promising technique that combines the advantages of IMRT and VMAT techniques, warranting its consideration as a potential standard for endometrial SIB treatments. Abbreviations AAV: Aperture Area Variability CI: Conformity Index CTV: Clinical Target Volume DVH: Dose-Volume Histograms EBRT: External Beam Radiotherapy GTV: Gross Tumour Volume HIR-RC: High-intermediate Risk Endometrial Cancer IMRT: Intensity-modulated Radiation Therapy IOR: Inward-outward Dose Gradient Ratio MU: Monitor Units MCS: Modulation Complexity Score OAR: Organ-at-Risk PTV: Planning Target Volume RAD: RapidArc Dynamic SID: Simultaneous Integrated Boost STAMPs : Strategically Placed Key User-selected Static Angle Modulated Ports VMAT: Volumetric Modulated Arc Therapy LSV: Leaf Sequence Variability LTMSC: Leaf Travel (LT) and MCSv Declarations Conflict of interest statement: The authors declare that they have no competing interests. Human Ethics and Consent to Participate declarations The requirement for ethical approval and informed consent was waived by the Ethics Committee of Shandong Cancer Hospital and Institute (Shandong First Medical University and Shandong Academy of Medical Science) due to the retrospective nature of the study and the use of anonymized patient data. The authors confirm that all methods were performed in accordance with the relevant guidelines and regulations. This study was conducted in strict compliance with the Declaration of Helsinki. Funding statement: This study was supported by the Natural Science Foundation of Shandong (Grant ID: ZR2025QC1661), and the Key Research and Development Program of Xinjiang Uygur Autonomous Region of China (Grant ID: 2022B03019-5). Author Contribution YTZ performed investigation; Validation of results; Visualization of data; wrote the main manuscript textYTZ, XQZ, XSW, JL and HNXdesined methodology.YTZ, and XSW performed Formal analysis.YTZ, and XQZ responseded for Project administration.YTZ, XQZ, XSW, GZG and YY reviewed and edited the manscuript.XQZ, XSW, ZJJ, and XMM prepared resources for this research.XQZ, ZJJ, and XMM performed data curation.GZG and YY supervised this research. Acknowledgement The authors wish to express their sincere gratitude to Dr. Pejman Rowshanfarzad (The University of Western Australia) and Prof. Martin A. Ebert (Sir Charles Gairdner Hospital, The University of Western Australia) for their invaluable guidance and expertise, which were instrumental in the execution of this research and the preparation of the manuscript. Their insightful feedback greatly enhanced the quality of this work. Data Availability The data that support the findings of this study are available from Shandong Cancer Hospital, but restrictions apply to the availability of these data, which were used under license for the current study and so are not publicly available. The data are, however, available from the corresponding author upon reasonable request and with the permission of Shandong Cancer Hospital. References Hsieh K, et al. Risk-tailoring radiotherapy for endometrial cancer: a narrative review. Cancers. 2024;16(7):1346. Jensen GL, et al. Dose escalated simultaneous integrated boost of gross nodal disease in gynecologic cancers: a multi-institutional retrospective analysis and review of the literature. Radiation Oncol J. 2021;39(3):219. Fontenot J, et al. Single-arc volumetric-modulated arc therapy can provide dose distributions equivalent to fixed-beam intensity-modulated radiation therapy for prostatic irradiation with seminal vesicle and/or lymph node involvement. 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Outcome and toxicity of chemoradiation using volumetric modulated arc therapy followed by 3D image-guided brachytherapy for cervical cancer: Vietnam National Cancer Hospital experience. Rep Practical Oncol Radiotherapy. 2023;28(6):784–93. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 08 Apr, 2026 Reviews received at journal 16 Mar, 2026 Reviews received at journal 15 Mar, 2026 Reviewers agreed at journal 01 Mar, 2026 Reviewers agreed at journal 27 Feb, 2026 Reviewers agreed at journal 27 Feb, 2026 Reviewers invited by journal 27 Feb, 2026 Editor assigned by journal 04 Feb, 2026 Submission checks completed at journal 04 Feb, 2026 First submitted to journal 01 Feb, 2026 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. 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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-8666248","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":599247145,"identity":"b88dfdae-bd10-451f-9bf2-2134e6770c67","order_by":0,"name":"Yutong Zhao","email":"","orcid":"","institution":"Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Science","correspondingAuthor":false,"prefix":"","firstName":"Yutong","middleName":"","lastName":"Zhao","suffix":""},{"id":599247146,"identity":"0d6e348a-8f7f-4408-a486-5da41585edec","order_by":1,"name":"Xinqiang Zhang","email":"","orcid":"","institution":"Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Science","correspondingAuthor":false,"prefix":"","firstName":"Xinqiang","middleName":"","lastName":"Zhang","suffix":""},{"id":599247147,"identity":"19bef39f-3cf0-4f4c-a128-a79f292aa83c","order_by":2,"name":"Xiaoshen Wang","email":"","orcid":"","institution":"Varian Medical System, Clinical Application Department","correspondingAuthor":false,"prefix":"","firstName":"Xiaoshen","middleName":"","lastName":"Wang","suffix":""},{"id":599247148,"identity":"6d5635cc-930a-406b-bc27-0004782a82cf","order_by":3,"name":"Zejun Jiang","email":"","orcid":"","institution":"Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Science","correspondingAuthor":false,"prefix":"","firstName":"Zejun","middleName":"","lastName":"Jiang","suffix":""},{"id":599247149,"identity":"6a0a1e75-21ec-4494-9347-6833e42eea60","order_by":4,"name":"Xingmin Ma","email":"","orcid":"","institution":"Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Science","correspondingAuthor":false,"prefix":"","firstName":"Xingmin","middleName":"","lastName":"Ma","suffix":""},{"id":599247150,"identity":"956b4e68-4e98-4506-8ba5-205df07f9c92","order_by":5,"name":"Jing Liu","email":"","orcid":"","institution":"Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Science","correspondingAuthor":false,"prefix":"","firstName":"Jing","middleName":"","lastName":"Liu","suffix":""},{"id":599247151,"identity":"f28a3ce4-38d5-4dc3-a2d1-0404727fb73d","order_by":6,"name":"Haonan Xiao","email":"","orcid":"","institution":"Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Science","correspondingAuthor":false,"prefix":"","firstName":"Haonan","middleName":"","lastName":"Xiao","suffix":""},{"id":599247152,"identity":"ad48baba-630d-4247-9216-8467b7389568","order_by":7,"name":"Guanzhong Gong","email":"","orcid":"","institution":"Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Science","correspondingAuthor":false,"prefix":"","firstName":"Guanzhong","middleName":"","lastName":"Gong","suffix":""},{"id":599247153,"identity":"59837336-0f1e-4546-9426-aa6106ec6765","order_by":8,"name":"Yong Yin","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAxklEQVRIiWNgGAWjYDACZhjjeGPjgw+kaTlzuNlwBmnW3Uhvk+YgRqHBcd5jEh931Nrz3XzYIM3AYCen20BIy2G+NMmZZ44nzryd2GBcwJBsbHaAoBYeM2netmMJBkAtyTMYDiRuI1aLvcHNgw2HeUjQUsO44QZjYzNRWiQP8xhbzmw7kDjzTGIz4wwDIvzCd/6M4Y2PbXX2fMePP//xocJOjqAWhQMMLBIMDIdh7iSgHATkGxiYgcmkjgilo2AUjIJRMGIBAL7lSKLI1khdAAAAAElFTkSuQmCC","orcid":"","institution":"Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Science","correspondingAuthor":true,"prefix":"","firstName":"Yong","middleName":"","lastName":"Yin","suffix":""}],"badges":[],"createdAt":"2026-01-22 06:55:56","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8666248/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8666248/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104175765,"identity":"bd238b5c-8ac3-4a94-8ab6-67a8f7430c8a","added_by":"auto","created_at":"2026-03-08 16:32:34","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1140517,"visible":true,"origin":"","legend":"\u003cp\u003eAssessment of dose constraints for RAD, IMRT, and VMAT Plans in 30 Patients. The hard constraints were marked by red box. Symbols within cells denote the severity of over-doses based on thresholds: * for \u0026lt;5%, ** for \u0026lt;10%, *** for \u0026lt;20%, # for \u0026lt;50%, and ## for \u0026gt;50%. Symbol-free cells imply the dose limit was met.\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8666248/v1/8191637ae4e34c84aa9ab849.jpg"},{"id":104175764,"identity":"540baa4d-5b39-4310-ba99-b651c41a98ce","added_by":"auto","created_at":"2026-03-08 16:32:34","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":269126,"visible":true,"origin":"","legend":"\u003cp\u003eDose gradients of a RAD plan. The length and direction of arrow indicate gradient magnitude and gradient orientation (the direction where has the fastest speed of dose increasing).\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8666248/v1/9e8b6563a64c374569e33d53.jpg"},{"id":104175766,"identity":"5c84e2fe-931b-4f83-817f-8ba0f1899e15","added_by":"auto","created_at":"2026-03-08 16:32:35","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":898373,"visible":true,"origin":"","legend":"\u003cp\u003eMean DVH of RAD, IMRT, and VMAT plans with 95% confidence intervals for (A): Bladder; (B): Rectum, (C) Small intestine, (D) Marrow.\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8666248/v1/513da7188445c89e6333db9c.jpg"},{"id":104404548,"identity":"9647ed69-d3b0-4024-b17c-d9dab22e113a","added_by":"auto","created_at":"2026-03-11 12:20:30","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2901582,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8666248/v1/d772d596-379e-4099-bbf0-ba3cc1357ff3.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"RapidArc Dynamic versus IMRT and VMAT for Endometrial Cancer SIB Radiotherapy","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAs an indispensable element of endometrial cancer management, radiotherapy includes techniques like simultaneous integrated boost (SIB), which delivers escalated doses to high-risk nodal regions [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. A significant challenge with SIB, however, is the association between larger boost volumes or higher dose levels and an increased incidence of acute Grade\u0026thinsp;\u0026ge;\u0026thinsp;3 toxicities [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. These adverse effects, which often involve non-gastrointestinal and urinary systems, result from the irradiation of healthy tissues adjacent to the target. Therefore, achieving highly conformal dose distributions is a critical requirement for optimizing SIB radiotherapy in endometrial cancer.\u003c/p\u003e \u003cp\u003eEvolved from intensity-modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT) allows for the simultaneous dynamic modulation of gantry speed, multi-leaf collimator (MLC) shape, and dose rate, leading to reduced treatment delivery times and lower monitor units (MU) [\u003cspan additionalcitationids=\"CR4\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. RapidArc Dynamic (RAD) solution is a recent innovation that integrates continuous VMAT arc delivery with static angle\u0026ndash;modulated ports (STAMPs), allowing the gantry to pause at specific positions during dose delivery and incorporating a dynamically rotating collimator throughout the treatment arcs [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. By comparing RAD against conventional VMAT, a multi-site planning study suggested that RAD can achieve equal or superior OAR sparing with generally reduced treatment delivery times. Specific benefits included a reduction of mean heart dose in breast cancer radiotherapy and improved bladder and rectum sparing in prostate radiotherapy [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. However, the performance of RAD has not yet been evaluated specifically for endometrial cancer treatment or within the context of SIB radiotherapy.\u003c/p\u003e \u003cp\u003eTo address the identified knowledge gaps above, this study aims to investigate the feasibility of RAD treatment planning for SIB radiotherapy in endometrial cancer. The performance of the RAD technique will be quantitatively evaluated through a comparative planning study against conventional nine-fields IMRT and two-arcs VMAT. This study aims to examine whether the dynamic collimator rotation with strategic pauses of RAD could translate into dosimetric or efficiency benefits, and the potential for establishing RAD radiotherapy as a routine standard care for endometrial SIB treatments.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eData preparation\u003c/h2\u003e \u003cp\u003eA total of thirty patients with high-intermediate risk endometrial cancer (HIR-EC), who received SIB external beam radiotherapy (EBRT) at Shandong Cancer Hospital (Jinan city, Shandong province, China) between January 1, 2024, and January 1, 2025, were retrospectively enrolled in this single-centre study.\u003c/p\u003e \u003cp\u003eThe CT images for all eligible patients were subsequently collected and anonymized to ensure data privacy. Critical OARs, including the kidneys, small intestine, duodenum, spinal cord, bladder, rectum, femoral heads, and bone marrow, were initially delineated using a deep learning-based auto-segmentation software\u0026mdash;AccuContour (version: 3.2, Manteia Technologies Co., Ltd.), which has demonstrated superior performance in contouring abdominal and pelvic OARs [\u003cspan additionalcitationids=\"CR9\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. All auto-generated contours were subsequently reviewed and manually refined as necessary by an experienced radio-physicist (XQZ) and a radiology specialist (GZG) to ensure anatomical accuracy and adherence to institutional delineation protocols.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eVolume of interest definition\u003c/h3\u003e\n\u003cp\u003eThis study adhered to established international guidelines from eviQ [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] and the National Comprehensive Cancer Network (NCCN) [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] for target volume delineation. For each patient, the gross tumour volume (GTV) was delineated on the planning CT to encompass the primary endometrial carcinoma, including any local spread. Involved lymph nodes were separately defined as the GTVn. The clinical target volume (CTV) was constructed as a Boolean union of the GTV and region of microscopic disease spread. These included the entire uterus, cervix, fallopian tubes, ovaries, the upper 50% of the vagina, along with the paravaginal soft tissues and parametrium. The duodenum and small intestine were explicitly cropped from the CTV. A separate CTV for the nodes (CTVn) was generated by applying a 5 mm isotropic expansion to the GTVn. Finally, the planning target volume (PTV) was created by adding an 8 mm isotropic margin to the CTV to account for setup uncertainties and internal anatomical motion.\u003c/p\u003e\n\u003ch3\u003eTreatment Planning\u003c/h3\u003e\n\u003cp\u003eFor each enrolled patient, a comprehensive set of three distinct treatment plans was generated using the RAD, IMRT, and VMAT techniques. To ensure a consistent and clinically relevant dosimetric comparison, all planning adhered to the standardized dose constraints for OARs (listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and dose prescriptions as outlined by the eviQ guidelines [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The prescribed regimen delivered a total of 50.4 Gy in 28 fractions to the PTV. A SIB of 61.6 Gy was prescribed to the CTVn. For a plan to be considered acceptable, it was mandated that at least 95% of the PTV and the CTVn receive 100% of their respective prescribed doses.\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\u003eList of OAR dose constraints.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOrgan\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePlanning Aim\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHard Constraint\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpinal cord\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD\u003csub\u003emax\u003c/sub\u003e \u0026le; 40 Gy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eD\u003csub\u003emax\u003c/sub\u003e \u0026le; 45 Gy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSmall intestine\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003e45\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;200 cc\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eV\u003csub\u003e40\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;70%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003e40\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;30%.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eV\u003csub\u003e45\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;250 cc\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD\u003csub\u003emax\u003c/sub\u003e \u0026le; 55.5 Gy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eD\u003csub\u003e2cc\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;52 Gy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD\u003csub\u003e2cc\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;51 Gy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDuodenum\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003e55\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;15 cc\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eD\u003csub\u003e2cc\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;52 Gy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD\u003csub\u003e2cc\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;51 Gy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRectum\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003e40\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;50%.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eV\u003csub\u003e40\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;60%.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD\u003csub\u003emax\u003c/sub\u003e \u0026le; 55.5 Gy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eD\u003csub\u003e2cc\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;52.5 Gy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD\u003csub\u003e2cc\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;50 Gy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBladder\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003e45\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;35%.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eV\u003csub\u003e45\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;50%.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD\u003csub\u003e2cc\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;52 Gy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eD\u003csub\u003e2cc\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;53.5 Gy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFemoral heads\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003e30\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;15%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eD\u003csub\u003emax\u003c/sub\u003e \u0026le; 55.5 Gy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003e45\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;50%.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;10%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKidneys\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD\u003csub\u003emean\u003c/sub\u003e \u0026le; 15 Gy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003e12\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;55%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003e20\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;32%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003e23\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;30%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003e28\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;20%.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBone marrow\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003e10\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;80%.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eV\u003csub\u003e10\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;90%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003e40\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;37%.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eD\u003csub\u003emax\u003c/sub\u003e, D\u003csub\u003emean\u003c/sub\u003e: The maximum and average dose of the structure.\u003c/p\u003e \u003cp\u003eD\u003csub\u003e2cc\u003c/sub\u003e: The minimum dose delivered to the hottest 2 cubic centimeters of the structure.\u003c/p\u003e \u003cp\u003eV\u003csub\u003eX\u003c/sub\u003e: The percentage volume that receives at least x Gy of radiation dose.\u003c/p\u003e \u003cp\u003eTo account for potential large inter- and intra-fraction motion of the bladder and rectum, and to further protect surrounding healthy tissues, two triangle-shaped regions of interest (Hot_Ant and Hot_Pos) were delineated, each positioned approximately 3.5 cm away from the PTV. In addition to adhering to standard OAR constraints, specific maximum dose suppression was applied to these ROIs. This supplementary optimization objective was implemented to minimize radiation exposure to adjacent normal tissues, while ensuring that it did not compromise the prescribed dose coverage for both the PTV and the CTVn.\u003c/p\u003e \u003cp\u003eAll treatment plans were optimized on a Eclipse treatment planning system (Varian Medical Systems, USA) with Photon Optimizer algorithm (version 18.1) for delivery on a Varian TrueBeam linear accelerator. All planning tasks were performed by a senior medical physicist (XQZ) with over five years of specialized experience. All plans were generated with beam energy of 6 MV. The dose rates were 1400 MU/min for RAD plans and 600 MU/min for non-RAD plans. Dose distribution were calculated using the Accuros XB algorithm with a dose grid size of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:2.5\\:mm\\times\\:2.5\\:mm\\times\\:3\\:mm\\)\u003c/span\u003e\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eThe IMRT plans were designed using a standardized nine-field beam geometry with sliding window. These beams were statically positioned at approximately 40-degree intervals around the patient, creating a coplanar arrangement. For the VMAT technique, each plan consisted of two full 360-degree arcs. The first arc rotated clockwise from 181\u0026deg; to 179\u0026deg;, and the second arc rotated counterclockwise from 179\u0026deg; to 181\u0026deg;. To enhance modulation capabilities and reduce interleaf leakage, the collimator angles were fixed at 15\u0026deg; for the first arc and 345\u0026deg; for the second arc, providing complementary modulation patterns.\u003c/p\u003e \u003cp\u003eFor RAD treatment planning, Eclipse enables user-selected static angle modulated ports. A potential reduction in both optimization computation time and overall treatment delivery times was anticipated by this approach. The STAMPs provide adjustable control over the contribution of arc and static fields during plan optimization and delivery. This is governed by a weighting parameter with five distinct modes: \u0026ldquo;arc dominant\u0026rdquo; (-2), \u0026ldquo;arc\u0026rdquo; (-1), \u0026ldquo;balanced\u0026rdquo; (0), \u0026ldquo;static\u0026rdquo; (+\u0026thinsp;1), and \u0026ldquo;static dominant\u0026rdquo; (+\u0026thinsp;2). As mentioned above, the five modes correspond to having 2, 14, 26, 39, and 51 control points respectively at each paused gantry direction during the arc beam delivery. Selecting a higher static weighting, such as '+1', implies 39 control points in each specific static gantry direction within the RAD plan. This setting shows a greater inclination towards assigning a larger weight to STAMPs within the plan compared with weighting of \u0026ldquo;-1\u0026rdquo;. For this study, all RAD plans were generated using two full arcs, with STAMPs (gantry pauses) strategically set at 0\u0026deg; and 181\u0026deg;. Based on findings from prior investigations [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], the plans were optimized using a static field weighting of \u0026ldquo;+1\u0026rdquo; to enhance the benefits of the static ports while maintaining the efficiency of arc therapy. By maximizing the MLC modulation for target coverage, collimator rotation of all plans was optimized automatically in Eclipse.\u003c/p\u003e\n\u003ch3\u003ePlan evaluation\u003c/h3\u003e\n\u003cp\u003eTo ensure a consistent comparison, all generated treatment plans were first normalized, such that 95% of the PTV received the prescription dose of 50.4 Gy. The performance of each technique was then evaluated and compared using standardized dose metrics defined in the planning protocol and dose-volume histograms (DVHs).\u003c/p\u003e \u003cp\u003eTo evaluate and compare the dose distribution conformity achieved by the three radiotherapy techniques, the conformity index (CI) was calculated for all generated plans. The index was defined as follows [\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:CI=\\:\\frac{{TV}_{PTV}^{2}}{TV\\times\\:PIV}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere the \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{TV}_{PTV}\\)\u003c/span\u003e\u003c/span\u003e stands for the target volume covered by the prescription isodose, TV and PIV represent the prescription isodose volume (total volume receiving at least the prescription dose) and volume of target, respectively. A CI value closer to 1 indicates a more ideal dose conformation.\u003c/p\u003e \u003cp\u003eThis study also innovated a novel method to quantitatively evaluate the directional gradient of the 3D radiation dose distribution at PTV surface, thereby identifying the radiotherapy technique that offers the steepest dose gradient toward the center of the PTV. First, for the surface voxels of the PTV, the dose gradient vector field is computed using the spatial derivatives of the dose distribution, normalized to the voxel size for correct physical units (Gy/mm). Subsequently, the surface normal vectors, pointing outward from the PTV, are estimated based on the geometry of the target volume. The interaction between the dose gradient and the surface geometry is analyzed by calculating the dot product between the gradient vector and the normal vector at each surface point. A negative dot product indicates the gradient points inward, while a positive value indicates an outward direction. Finally, the magnitudes of the inward and outward gradients are statistically aggregated to calculate the inward-outward ratio (IOR), providing a quantitative measure of dose fall-off sharpness and directionality.\u003c/p\u003e \u003cp\u003eThe modulation complexity score (MCS) was also calculated to evaluate the complexity of generated plans. By following the methodology developed by Masi et al. [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], the MCS was calculated by integrating leaf sequence variability (LSV) and aperture area variability (AAV) across control points, weighted by monitor units (MU).To evaluate the plan complexity more comprehensively, a multiplicative combination of leaf travel (LT) and MCSv (LTMSC) was also calculated:\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:LTi=\\frac{1000-LT}{1000}\\:\\:\\:\\:\\:and\\:\\:\\:\\:\\:LTMSC=\\:LTi\\bullet\\:LTi$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe higher complexity of a plan, a lower MSC and LTMSC would be calculated. All statistical tests in this research were performed by Mann-Whitney U test [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] with significance level of 0.05.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eA total of 90 radiotherapy plans (30 each for RAD, IMRT, and VMAT) were generated for 30 HIR-EC patients. All plans were normalized to ensure 95% of the PTV received 50.4 Gy, and all achieved 95% coverage of the CTVn by 61.6 Gy. Dose constraint assessments are summarized in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. RAD plans demonstrated the fewest and mildest instances of exceeding dose limits for the small intestine D\u003csub\u003e2cc\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;52 Gy (RAD: 13 VS. IMRT: 23 VS. VMAT: 29), bladder V\u003csub\u003e45\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;50% (2 VS. 3 VS. 2), and bladder D\u003csub\u003e2cc\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;53.5 Gy (3 VS. 9 VS. 13). While all plans violated the bone marrow constraint of V\u003csub\u003e10\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;90%, RAD plans showed significantly lower doses for most evaluated metrics - including rectum V\u003csub\u003e40\u003c/sub\u003e, D\u003csub\u003e2cc\u003c/sub\u003e, D\u003csub\u003emax\u003c/sub\u003e, spinal cord D\u003csub\u003emax\u003c/sub\u003e, small Intestine D\u003csub\u003e2cc\u003c/sub\u003e, left femur head V\u003csub\u003e30\u003c/sub\u003e, V\u003csub\u003e45\u003c/sub\u003e, and Marrow V\u003csub\u003e40\u003c/sub\u003e - compared to both IMRT and VMAT plans (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Additionally, RAD plans achieved significantly lower bladder V\u003csub\u003e45\u003c/sub\u003e than IMRT and lower small intestine D\u003csub\u003emax\u003c/sub\u003e and bladder D\u003csub\u003e2cc\u003c/sub\u003e than VMAT (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eRAD plans achieved an average CI of 0.833, comparable to IMRT (0.835) and significantly higher than two-arc VMAT plans (0.813) (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). For CTV, the average IOR was highest for RAD plans (1.26), followed by IMRT (1.20) and VMAT (1.12), indicating steeper inward dose gradients with RAD. Statistical test demonstrated that the IOR of RAD plans was significantly higher than both IMRT and VMAT plans (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The dose gradient of a representative RAD plan is visualized in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, showing a rapid dose increase towards the CTV and a sharp fall-off towards surrounding organs at risk.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e displays the DVHs with 95% confidence intervals for the RAD, IMRT, and VMAT plans. The curves demonstrate that the RAD technique achieved lower dose exposures to the OARs across most dose intervals on average, including the high-dose region (\u0026gt;\u0026thinsp;50 Gy). The narrow band of 95% confidence intervals in the DVH of RAD plans indicated it enabled better OAR protection for the majority of patients.\u003c/p\u003e \u003cp\u003eThe average MU number for RAD, IMRT, and VMAT plans was 1314.7 (min\u0026thinsp;~\u0026thinsp;max: 946.6\u0026thinsp;~\u0026thinsp;1529.3, standard deviation: 99.4), 3334.0 (2124.4\u0026thinsp;~\u0026thinsp;3984.3, 364.0), and 527.8 (446.7\u0026thinsp;~\u0026thinsp;623.4, 38.2), respectively. For RAD, IMRT, and VMAT plans, the average MCS was 0.16 (0.13\u0026thinsp;~\u0026thinsp;0.19, 0.01), 0.03 (0.02\u0026thinsp;~\u0026thinsp;0.05, 0.01), and 0.26 (0.21\u0026thinsp;~\u0026thinsp;0.32, 0.03), while the LTMCS was 0.16 (0.13\u0026thinsp;~\u0026thinsp;0.18, 0.01), 0.03 (0.02\u0026thinsp;~\u0026thinsp;0.05, 0.01), and 0.25 (0.20\u0026thinsp;~\u0026thinsp;0.30, 0.02), respectively. RAD plans showed a significantly lower and higher (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05) MCS and LTMCS than VMAT and IMRT plans, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe RAD solution demonstrates superior OAR sparing compared to IMRT and VMAT. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, RAD plans provided enhanced protection for OARs such as the bladder, rectum, small intestine, and bone marrow. This is clinically significant as studies have confirmed that strictly limiting parameters like the D\u003csub\u003e2cc\u003c/sub\u003e for these OARs is key to reducing patient toxicity [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The observed reduction in OAR D\u003csub\u003e2cc\u003c/sub\u003e with RAD planning directly explains its potential to yield lower toxicity and fewer side effects for patients.\u003c/p\u003e \u003cp\u003eThe RAD solution creates a steep dose gradient around the target volume. As the IOR and Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e illustrated, compared to nine-field IMRT and two-arc VMAT, RAD demonstrated the capability to carve the sharpest dose fall-off, thereby effectively extruding the dose inward toward the target and away from adjacent OARs. Furthermore, RAD plans achieved a significantly higher CI than VMAT and an equivalent CI to IMRT, indicating its ability to ensure sufficient target coverage by the prescribed isodose level.\u003c/p\u003e \u003cp\u003eCompared to IMRT plans, a significantly lower MU number (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05) and a higher dose rate of RAD plans contribute to a shorter treatment time, which may reduce intra-fraction motion and consequently improve delivery accuracy. Moreover, RAD also demonstrated a significantly higher MCS and LTMCS than IMRT plans, indicating that RAD plans have simpler beam apertures and reduced leaf motion, which correlates with higher dosimetric accuracy, higher gamma passing rates in QA, and enhanced delivery reliability. However, it is important to note that the specific calculation methodology for MCS and LTMCS used in this study, which is subject to the maximum continuity constraints on the MLC operation sequence, could potentially lead to biased predictions of modulation complexity.\u003c/p\u003e \u003cp\u003eFurthermore, this study employed PTV and clinical target volume of the nodes (CTVn) margins of 8 mm and 5 mm, respectively, which are potentially larger than those used in contemporary SIB protocols, to account for intra- and inter-fraction motion. The combination of the challenging multi-arc technique and these larger margins made it difficult to satisfy many OAR dose constraints, such as the V\u003csub\u003e10 Gy\u003c/sub\u003e constraint of bone marrow. Future research should focus on comparing two-arc RAD, nine-field IMRT, and three-arc VMAT plans utilizing a reduced margin size to better balance target coverage and OAR sparing.\u003c/p\u003e \u003cp\u003eCompared to RAD and nine-field IMRT plans, the two-arc VMAT plans demonstrated the highest number of violated dose constraints and the lowest CI, suggesting that a dual-arc VMAT approach may be insufficient for meeting the complex demands of modern SIB radiotherapy in endometrial cancer. Future research should focus on comparing RAD, nine-field IMRT, and three-arc VMAT plans.\u003c/p\u003e \u003cp\u003eBased on our experience with treatment planning, RAD plans were generated with two gantry pauses (i.e. static fields) at 0\u0026deg; and 181\u0026deg; for each arc. However, further optimization in achieving an optimal balance between superior dose distribution and reduced plan complexity may be possible by strategically adjusting degrees and number of static fields or static field weighting employed within the RAD planning framework.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThis study comprehensively evaluated the performance of RAD in comparison to conventional nine-field IMRT and two-arc VMAT for simultaneous integrated boost radiotherapy in endometrial cancer. The results demonstrate that RAD achieves superior OAR sparing, particularly for the bladder, rectum, small intestine, and bone marrow, with fewer and less severe violations of dose constraints. Additionally, RAD generates a steeper inward dose gradient, quantified by a higher IOR, and provides a CI comparable to IMRT and superior to VMAT, indicating excellent dose sculpting around the target volume. While RAD exhibits higher modulation complexity and significantly fewer monitor units than IMRT, contribution to potentially shorter treatment times and enhanced delivery efficiency.\u003c/p\u003e \u003cp\u003eIn conclusion, RAD represents a highly promising technique that combines the advantages of IMRT and VMAT techniques, warranting its consideration as a potential standard for endometrial SIB treatments.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eAAV: Aperture Area Variability\u003c/p\u003e\n\u003cp\u003eCI: Conformity Index\u003c/p\u003e\n\u003cp\u003eCTV: Clinical Target Volume\u003c/p\u003e\n\u003cp\u003eDVH: Dose-Volume Histograms\u003c/p\u003e\n\u003cp\u003eEBRT: External Beam Radiotherapy\u003c/p\u003e\n\u003cp\u003eGTV: Gross Tumour Volume\u003c/p\u003e\n\u003cp\u003eHIR-RC: High-intermediate Risk Endometrial Cancer\u003c/p\u003e\n\u003cp\u003eIMRT: Intensity-modulated Radiation Therapy\u003c/p\u003e\n\u003cp\u003eIOR: Inward-outward Dose Gradient Ratio\u003c/p\u003e\n\u003cp\u003eMU: Monitor Units\u003c/p\u003e\n\u003cp\u003eMCS: Modulation Complexity Score\u003c/p\u003e\n\u003cp\u003eOAR: Organ-at-Risk\u003c/p\u003e\n\u003cp\u003ePTV: Planning Target Volume\u003c/p\u003e\n\u003cp\u003eRAD: RapidArc Dynamic\u003c/p\u003e\n\u003cp\u003eSID: Simultaneous Integrated Boost\u003c/p\u003e\n\u003cp\u003eSTAMPs : Strategically Placed Key User-selected Static Angle Modulated Ports\u003c/p\u003e\n\u003cp\u003eVMAT: Volumetric Modulated Arc Therapy\u003c/p\u003e\n\u003cp\u003eLSV: Leaf Sequence Variability\u003c/p\u003e\n\u003cp\u003eLTMSC: Leaf Travel (LT) and MCSv\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eConflict of interest statement:\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eHuman Ethics and Consent to Participate declarations\u003c/h2\u003e \u003cp\u003e The requirement for ethical approval and informed consent was waived by the Ethics Committee of Shandong Cancer Hospital and Institute (Shandong First Medical University and Shandong Academy of Medical Science) due to the retrospective nature of the study and the use of anonymized patient data. The authors confirm that all methods were performed in accordance with the relevant guidelines and regulations. This study was conducted in strict compliance with the Declaration of Helsinki.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding statement:\u003c/h2\u003e \u003cp\u003eThis study was supported by the Natural Science Foundation of Shandong (Grant ID: ZR2025QC1661), and the Key Research and Development Program of Xinjiang Uygur Autonomous Region of China (Grant ID: 2022B03019-5).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eYTZ performed investigation; Validation of results; Visualization of data; wrote the main manuscript textYTZ, XQZ, XSW, JL and HNXdesined methodology.YTZ, and XSW performed Formal analysis.YTZ, and XQZ responseded for Project administration.YTZ, XQZ, XSW, GZG and YY reviewed and edited the manscuript.XQZ, XSW, ZJJ, and XMM prepared resources for this research.XQZ, ZJJ, and XMM performed data curation.GZG and YY supervised this research.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors wish to express their sincere gratitude to Dr. Pejman Rowshanfarzad (The University of Western Australia) and Prof. Martin A. Ebert (Sir Charles Gairdner Hospital, The University of Western Australia) for their invaluable guidance and expertise, which were instrumental in the execution of this research and the preparation of the manuscript. Their insightful feedback greatly enhanced the quality of this work.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe data that support the findings of this study are available from Shandong Cancer Hospital, but restrictions apply to the availability of these data, which were used under license for the current study and so are not publicly available. The data are, however, available from the corresponding author upon reasonable request and with the permission of Shandong Cancer Hospital.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eHsieh K, et al. Risk-tailoring radiotherapy for endometrial cancer: a narrative review. Cancers. 2024;16(7):1346.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJensen GL, et al. Dose escalated simultaneous integrated boost of gross nodal disease in gynecologic cancers: a multi-institutional retrospective analysis and review of the literature. Radiation Oncol J. 2021;39(3):219.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFontenot J, et al. Single-arc volumetric-modulated arc therapy can provide dose distributions equivalent to fixed-beam intensity-modulated radiation therapy for prostatic irradiation with seminal vesicle and/or lymph node involvement. Br J Radiol. 2012;85(1011):231\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCambria R, et al. Planning study to compare dynamic and rapid arc techniques for postprostatectomy radiotherapy of prostate cancer. Strahlenther Onkol. 2014;190(6):569\u0026ndash;74.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOtto K. Volumetric modulated arc therapy: IMRT in a single gantry arc. Med Phys. 2008;35(1):310\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eClark R et al. Comparison of Advanced Dynamic Arc Therapy With Collimator Rotation and Fixed Integrated Gantry Positions to the Standard of Care Across Five Treatment Sites. Cureus, 2025. 17(6).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChung CV et al. \u003cem\u003eNovel volumetric modulated arc therapy approach for lattice radiation therapy for bulky liver tumors\u003c/em\u003e. Front Oncol. 2025;15:1680342. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3389/fonc.2025.1680342\u003c/span\u003e\u003cspan address=\"10.3389/fonc.2025.1680342\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. eCollection 2025.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYucheng L, et al. Development and validation of a deep reinforcement learning algorithm for auto-delineation of organs at risk in cervical cancer radiotherapy. Sci Rep. 2025;15(1):6800.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBowen Jones S, et al. Moving beyond mean heart dose: The importance of cardiac substructures in radiation therapy toxicity. J Med Imaging Radiat Oncol. 2024;68(8):974\u0026ndash;86.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDing M et al. Deep learning-based auto-contouring of organs/structures-at-risk for pediatric upper abdominal radiotherapy. Radiother Oncol, 2025: p. 110914.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e\u003cem\u003e3746-Gynaecological endometrium definitive EBRT with or without chemotherapy | eviQ\u003c/em\u003e. 2022 [cited 2025 11.17]; Available from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.eviq.org.au/radiation-oncology/gynaecological/3746-gynaecological-endometrium-definitive-ebrt-wi#dose-prescription\u003c/span\u003e\u003cspan address=\"https://www.eviq.org.au/radiation-oncology/gynaecological/3746-gynaecological-endometrium-definitive-ebrt-wi#dose-prescription\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAbu-Rustum N, et al. Uterine neoplasms, version 1.2023, NCCN clinical practice guidelines in oncology. J Natl Compr Canc Netw. 2023;21(2):181\u0026ndash;209.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGonultas L, Dirican B. The novel universal conformity index and unconformity index algorithms for radiotherapy treatment plans. Med Dosim. 2022;47(3):295\u0026ndash;300.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMenon SV, et al. Evaluation of plan quality metrics in stereotactic radiosurgery/radiotherapy in the treatment plans of arteriovenous malformations. J Med Phys. 2018;43(4):214\u0026ndash;20.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePaddick I. A simple scoring ratio to index the conformity of radiosurgical treatment plans. J Neurosurg. 2000;93(supplement3):219\u0026ndash;22.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMasi L, et al. Impact of plan parameters on the dosimetric accuracy of volumetric modulated arc therapy. Med Phys. 2013;40(7):071718.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWilcoxon F. Individual comparisons by ranking methods. Biometrics Bull. 1945;1(6):80\u0026ndash;3.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMann HB, Whitney DR. \u003cem\u003eOn a test of whether one of two random variables is stochastically larger than the other.\u003c/em\u003e The annals of mathematical statistics, 1947: pp. 50\u0026ndash;60.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eP\u0026ouml;tter R, et al. MRI-guided adaptive brachytherapy in locally advanced cervical cancer (EMBRACE-I): a multicentre prospective cohort study. Lancet Oncol. 2021;22(4):538\u0026ndash;47.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVan Anh DT, et al. Outcome and toxicity of chemoradiation using volumetric modulated arc therapy followed by 3D image-guided brachytherapy for cervical cancer: Vietnam National Cancer Hospital experience. Rep Practical Oncol Radiotherapy. 2023;28(6):784\u0026ndash;93.\u003c/span\u003e\u003c/li\u003e\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":"radiation-oncology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"raon","sideBox":"Learn more about [Radiation Oncology](http://ro-journal.biomedcentral.com/)","snPcode":"13014","submissionUrl":"https://submission.nature.com/new-submission/13014/3","title":"Radiation Oncology","twitterHandle":"@OncoBioMed","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-8666248/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8666248/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eRadiotherapy with simultaneous integrated boost (SIB) for endometrial cancer requires highly conformal dose distributions to reduce toxicity. RapidArc Dynamic (RAD), a novel technique combining dynamic arc delivery with strategic gantry pauses, may improve organ-at-risk (OAR) sparing and efficiency.\u003c/p\u003e\u003ch2\u003ePurpose\u003c/h2\u003e \u003cp\u003eBy comparing RAD with conventional IMRT and VMAT for endometrial SIB radiotherapy, evaluating OAR sparing and treatment efficiency of RAD technique in endometrial cancer treatment.\u003c/p\u003e\u003ch2\u003eMethods and Materials\u003c/h2\u003e \u003cp\u003e: Thirty patients with high-intermediate risk endometrial cancer were retrospectively enrolled. Three plans (RAD, IMRT, VMAT) were generated per patient, prescribing 50.4 Gy to the planning target volume (PTV) and 61.6 Gy to the nodal clinical target volume (CTVn) in 28 fractions. Plans were evaluated for OAR dose constraints, conformity index (CI), inward-outward dose gradient ratio (IOR), monitor units (MU), and modulation complexity score (MCS).\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eRAD plans demonstrated superior OAR sparing, with significantly fewer and less severe constraint violations for the bladder, rectum, small intestine, and bone marrow compared to IMRT and VMAT (Mann-Whitney U test, P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). RAD achieved a significantly higher CI than VMAT and a steeper inward dose gradient than both IMRT and VMAT. RAD also used significantly fewer MU than IMRT and exhibited higher MCS, indicating less complex delivery.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eRAD provides superior OAR protection and steeper dose fall-offs compared to IMRT and VMAT, while maintaining high target dose conformity and improving delivery efficiency. It represents a highly promising technique for endometrial SIB radiotherapy, combining the advantages of IMRT and VMAT.\u003c/p\u003e","manuscriptTitle":"RapidArc Dynamic versus IMRT and VMAT for Endometrial Cancer SIB Radiotherapy","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-08 16:32:30","doi":"10.21203/rs.3.rs-8666248/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-08T10:27:41+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-16T17:22:02+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-15T11:01:05+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"132908489884465160506799831936400999133","date":"2026-03-01T12:16:22+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"260909729791579715594458235946034272829","date":"2026-02-27T14:43:24+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"258243886835547317272244988899600708654","date":"2026-02-27T13:07:47+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-27T11:59:27+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-04T09:24:40+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-02-04T08:42:25+00:00","index":"","fulltext":""},{"type":"submitted","content":"Radiation Oncology","date":"2026-02-01T17:08:26+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"radiation-oncology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"raon","sideBox":"Learn more about [Radiation Oncology](http://ro-journal.biomedcentral.com/)","snPcode":"13014","submissionUrl":"https://submission.nature.com/new-submission/13014/3","title":"Radiation Oncology","twitterHandle":"@OncoBioMed","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"b2f59de8-a9e9-4b9c-a70c-5f8771e47c25","owner":[],"postedDate":"March 8th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-29T12:23:39+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-08 16:32:30","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8666248","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8666248","identity":"rs-8666248","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}