Dynamic Distribution of Scattered Radiation in a CT Room, Utilizing a Semiconductor Survey Meter

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Consequently, there is no clear guidance on whether personnel involved in transporting infectious disease patients or radiological technologists who position patients should stay in the imaging room to prevent the spread of infection or evacuate to avoid radiation exposure. This study aimed to assess the temporal changes in the scattered radiation dose within the imaging room. In this study, a semiconductor survey meter was used to measure changes in the scattered radiation dose over time. The results allowed for the visualization of changes in scattered radiation dose over time as dynamic dose distributions (DDD). Unlike traditional dose assessments based on instantaneous measurements with a survey meter or cumulative doses with optically simulated luminescence (OSL) dosimeters, DDD elucidated the effects of tube current fluctuations and patient bed positioning on the scattered radiation intensity. These findings offer valuable for reviewing the behavior of medical staff who stay in the imaging room for infection control and provide important evidence for reducing radiation exposure. Radiation exposure Infection control CT Dose Distributions Scattered radiation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction The primary objective of diagnostic medical X-ray examinations is to ensure that the benefits to the patient outweigh any potential harm. Additionally, consideration must be given to the radiation exposure risks faced by the radiological staff and other individuals [ 1 ]. The radiological staff should adhere to the principles of justification and the optimization of protection as outlined in the radiological protection systems. In recent years, an increasing number of medical specialists have used fluoroscopy outside imaging departments. However, this practice has often been accompanied by inadequate attention to radiation protection and insufficient training. This trend may increase radiation risk to both staff and patients [ 2 ]. It is therefore becoming increasingly important to educate individuals about ethical values that support radiological protection systems [ 3 ]. Radiologists are exposed to radiation throughout their careers. Therefore, in all diagnostic medical X-ray examinations, not just fluoroscopy, occupational exposure should be reduced in the same manner as the medical exposure for patients [ 2 ]. Measures to reduce medical exposure to patients include the use of dose-reduction techniques for each X-ray equipment and the recommended use of diagnostic reference levels as a tool to optimize protection [ 4 ]. These actions that reduce the patient dose also reduce the occupational dose to radiological staff and the medical exposure to assisting personnel [ 2 ]. Additionally, using lead aprons, leaded glass eyewear, other types of shields, and radiation shielding screens can help reduce the radiation dose [ 2 , 5 , 6 , 7 ]. One measurement method used to assess the scattered radiation dose delivered by radiological staff and assisting personnel is scattered radiation distribution [ 6 , 8 , 9 , 10 ]. The scatter radiation distribution can be plotted by measuring the scatter radiation doses with an ionization chamber survey meter while moving sequentially through a grid or concentric circles of measurement points set up in an X-ray room [ 6 , 8 ]. Recently, a novel method for measuring the scattered radiation dose has been reported, which involves fixing optically simulated luminescence (OSL) dosimeters [ 11 , 12 ] to paper pipes arranged geometrically, similar to a jungle gym [ 9 , 10 ]. The measurement values from the survey meter represent the instantaneous dose rate, while the OSL dosimeters provide the accumulated dose, as shown in Fig. 1 (a, b). In examinations, such as fluoroscopy and CT, where X-rays are irradiated over time, it is not possible to evaluate the trend of scattered radiation dose over time. Recently, during the global outbreak of the novel coronavirus infection, medical workers involved in transporting infectious disease patients, as well as radiologic technologists positioning patients for CT scans, had to remain inside the CT room to prevent the spread of infection. This decision resulted in their exposure to radiation. There have been no reports justifying the need for personnel to remain in the CT room to prevent the spread of infection. If personnel are not needed for assisting a patient, their radiation exposure depends on their activities within the CT room, making it crucial to monitor the temporal changes in the scatter radiation dose. This study aimed to assess the temporal changes in the scattered radiation dose within the imaging room. In this study, a semiconductor survey meter was used to measure changes in the scattered radiation dose over time, as shown in Fig. 1 (c). The results allowed for the visualization of changes in the scattered radiation dose over time as dynamic dose distributions (DDD). The DDD provides insights into the protective actions of radiological staff and assisting personnel over time, based on the new dose index. Materials and Methods Semiconductor survey meter The RaySafe 452 radiation survey meter (FLUK Biomedical, Cleveland, Ohio) is a hybrid instrument that combines a semiconductor (silicon sensor) with a Geiger-Muller tube, complying with the International Electrotechnical Commission (IEC) 60846-1 [ 13 ]. This survey meter features a dose range of 0 µGy/h to 1.0 Gy/h, a rate resolution of 0.01 µGy/h, a dose resolution of 0.1 nGy, and an energy range of 30.0 keV to 7.0 MeV, with an energy response stabilizing to about 1.0 at 30.0 keV to 100.0 keV. These characteristics make it suitable for measuring scattered radiation doses in the room during diagnostic medical X-ray examination. It is necessary to pay attention to the angular response when measuring, as the detection unit’s sensitivity varies: 0.5 (90 ° and 270 ° at 33.0 keV) and 1.4 (90 ° and 270 ° at 65.0 keV) [ 14 , 15 ]. Characteristically, these algorithms are used to detect radiation changes with response times of 1 sec, averaged over four measurements per second [ 14 ]. In this study, Raysafe 452 was used to roughly measure the change in scattered radiation dose over time at a 1.0-second interval. Phantom and X-ray CT scanner An anthropomorphic RANDO man-model phantom (RAN110; Phantom Laboratory, Salem, NY, USA), representing a 175-cm tall, 73.5-kg human male with removable upper arms, was positioned lying on the patient bed in an X-ray CT scanner (Aquilion Prime; Cannon Medical Systems). The removable upper arms were then attached in the raised position, but the lower legs could not be attached because the connections were made of a metallic material. The RANDO phantom is constructed from a natural human skeleton and soft tissue-simulating material, consisting of a proprietary urethane formulation and lung-simulating material with the same effective atomic number as the soft tissue material but with a density that simulates the lungs in a median respiratory state. The RANDO phantom was considered a patient requiring assistance or with infectious diseases. The DDD was evaluated using CT scans from the chest to the pelvis, where changes in scattered radiation dose over time were anticipated. The CT scan was performed under the following scan conditions: tube voltage 120 kVp, scan rotation speed: 1.5 sec/rot, beam width: 0.5 mm×80 raw (40 mm), pitch factor: 65/80 (0.813), scan length: 760 mm, scan time: 37.6 sec, field-of-view: 320 mm, orbital synchronization system (+) of rotation start angle, and feet first. The tube current was set under two different conditions: a fixed 50 mA and automatic exposure controlled (AEC), with a maximum of 85 mA, averaging 57.5 mA equivalent (standard deviation of image noise: 7.0) (Fig. 2 ). The scan rotation speed was set to 1.0 sec/rot for the CT examination of patients. In this study, the scan rotation speed was slowed to 1.5 sec/rot to evaluate dose changes in detail. As a result of this setting, the X-ray tube rotation angle is shifted by 120 ° for each measurement interval of the survey meter. Dose measurement The scattered radiation dose in the CT room was measured at 50 cm intervals on one side of the patient bed (Fig. 3 A-G) with the bed as the center line (Fig. 3 G) and on the opposite side (Fig. 3 A’-F’). The measurement points were positioned at heights of 100 cm (57 points) and 150 cm (64 points) above the floor. Due to the presence of the patient bed, the points along the G row (-325 to 75) were measured only at 150 cm. The Raysafe 452 detector was positioned toward the isocenter using the laser beam of a laser rangefinder (GLM500; Bosch). A helical scan of the RANDO phantom was then conducted from the chest to the pelvis region for approximately 40 sec. During this scan, the scattered radiation dose inside the CT room was measured in terms of the accumulated air kerma (Gy) and air kerma rate (Gy/sec). The measurement values displayed on the Raysafe 452’s main unit screen were saved on a PC via Raysafe view software (FLUK Biomedical, Cleveland, Ohio). Each measurement value was divided by the pre-measured background value in the CT room (0.008 µGy/s) and multiplied by a calibration factor for traceability to national standards. The effective energy of the scattered radiation at each point was unknown. The primary beam of the Aquilion prime at 120kVp, previously evaluated using the Black Piranha semiconductor detector (RTI group AB, Mölndal, Sweden) of an X-ray analyzer along with a lead shield box (made of 3-mm-thick, 99.9% pure Pb; Acrobio Corp., Tokyo, Japan), was measured at 48.2 keV [ 16 ]. Based on this, we assumed an effective energy of 50 keV and adopted a calibration constant of 1.0 for the survey meter. Dose Distribution The dose distribution was plotted using graphing software (Surfer, Golden software) based on the measured scattered radiation doses accumulated over approximately 40 seconds (i.e., accumulated air kerma) during a chest-to-pelvis CT scan. The measurements were taken at both 100 cm and 150 cm above the floor with a fixed 50 mA, and at 100 cm and 150 cm with AEC set to 85 mA. Dose distributions were mapped from the measured scattered radiation doses data using the kriging method (geostatistical grid method) to facilitate visual comprehension. The scattered radiation doses were then visualized on a logarithmic scale. Subsequently, the maximum slope and slope direction were calculated from the measurements, and the direction vectors of the scattered radiation were plotted. Using the obtained dose distributions and vector plots, the effects of the X-ray output characteristics (fixed and AEC) and the direction of the scattered radiation spread were evaluated. Assistance was assumed to be performed at positions (x, y, z) = p(-50, -75, 100/150) and p(-50, 75, 100/150). The accumulated air kerma received by the assisting personnel per examination and the dose rate profile curves over time were also assessed. Moreover, the dose rate profile curves at characteristic measurement points, such as the head side of the patient bed p (0, -425, 100/150), the feet side of the patient bed p (0, 175, 100/150), and the lateral side of the gantry p (-150, -25/25, 100/150), were evaluated. Dynami Dose Distribution Dose distributions and vector plots were visualized based on measurements taken per unit time using a semiconductor survey meter. The data were edited to switch every second using video editing software (Wonder Filmora, Wondershare) and saved in MPEG-4 (.MP4) video file format. Such a change in dose distribution over time is termed DDD. We observed changes in the dose distributions and vector plots over time from the obtained DDD. The evaluation was performed by selecting the dose distributions and vector plots at 5-second intervals (5 sec: sternoclavicular joint, 10 sec: nipple, 15 sec: diaphragm, 20 sec: umbilicus, 25 sec: iliac crest, 30 sec: coccyx, and 35 sec: hipbone) for the visualized DDD. Results X-ray output difference between fixed 50 mA and AEC 85 mA CT examinations of the chest to pelvis region were conducted using a fixed tube current of 50 mA and with AEC set to a maximum of 85 mA (SD 7.0). The AEC of 85 mA was modulated from a minimum of 40 mA to a maximum of 85 mA depending on the imaging area, with an average of 56 mA. The tube current was adjusted to 67 mA (5 sec), 65 mA (10 sec), 44 mA (15 sec), 70 mA (20 sec), 82 mA (25 sec), 46 mA (30 sec), and 40 mA (35 sec). Therefore, the X-ray output with AEC was approximately 10% higher than that with fixed 50 mA (Fig. 2 ), which also affected the scattered radiation dose. Dose Distribution When the height from the floor remained consistent, the accumulated dose distribution of chest-to-pelvis CT scans demonstrated similar trends between the fixed 50 mA and AEC 85 mA, as depicted in Fig. 4 . In the case of the AEC, the air kerma of scatter radiation doses received by the assisting personnel during one examination were as follows: at position p(-50, -75): 139.7 µGy at 100 cm and 254.2 µGy at 150 cm; and at position p(-50, 75): 80.4 µGy at 100 cm and 83.7 µGy at 150 cm. The dose rate profile curves and their 3-period moving average were evaluated at the same positions, revealing differences in trends based on the positions and tube current mode (Fig. 5 ). The temporal modulation of air kerma suggests that changes in tube current affect the intensity of scatter radiation, as observed at position p(-50, 75) with AEC. Moreover, at a measurement height of 150 cm, there was a tendency for the air kerma to be higher at the start of measurements at p(-50, 75) and at the end of measurements at p(-50, -75). For p(-50, -75) with AEC, the air kerma was influenced by both these effects. Therefore, we hypothesized that the position of the patient bed influences the scattered radiation dose. To investigate this, the air kerma was evaluated by measuring the dose-rate profile curves at the foot side at position p(0,175) and head side at position p(0,-425) of the patient’s bed, with the x-ray tube current fixed at 50 mA. The RAND phantom, positioned on the patient’s bed in the feet first orientation, was scanned through the neck to the hipbone from 0 sec to 37.6 sec, resulting in the dose-rate profile curves shown in Fig. 6 . The air kerma showed high values during the scanning of the hip joint region (33 sec) at p(0, 175) and the chest region (10 sec) at p(0, -425). This suggests that the direction of the movement of the patient bed influences the scattered radiation dose. With the same AEC mode, the air kerma radiation dose received by the assisting personnel was lower on the gantry side at positions p(-150,-25) and p(-150,25) than that on the surroundings, measuring approximately 0.8 µGy at both measurement heights (Fig. 4 ). The dose rate profile curves on the gantry side showed a trend similar to that of the AEC modulation (Fig. 7 ). In this study, the spreading direction of the scattered radiation (i.e., maximum slope and slope direction) was visually indicated using vector plots of the air kerma. The vector plots extending from isocenter p(0, 0) to p(-300, -350) aligned with the direction of the scattered radiation dose distribution. On the gantry side, the direction of the vector plots was opposite to the X-ray output direction. A hotspot was detected near this area in the dose distribution (Fig. 4 ). DDD The DDDs and vector plots are shown in Fig. 8 . Even with a fixed tube current of 50 mA, the DDDs were not identical, but no significant drastic changes in the distribution were observed. Notably, regardless of the scan time, the air kerma at the assistance position p(-50, -75) by assisting personnel was higher, while the air kerma at the evacuation position on the gantry side p(-150,-25) and p(-150,25) was lower. Moreover, the differences in the dose distribution at arbitrary positions, as shown in Fig. 4 , were reflected in the DDD. For example, refer to the DDD at 25 sec (Fixed 50 mA vs. AEC 80 mA). The distortion in the vector plot on the gantry side, as shown in Fig. 6 , consistently became prominent at a height of 100 cm from the floor. Such distortions in the vector plots were sporadically identified at locations away from the isocenter. Notably, the DDDs at a height of 150 cm had a greater spread of scattered radiation than those at 100 cm. Furthermore, the temporal dose modulation of the air kerma at p(0, 175) and p(0, -425), as depicted in Fig. 6 , could also be visually confirmed by the spread of the distribution in the DDD. Discussion In this study, a new method called DDD was proposed to evaluate the temporal distribution of scattered air kerma within an X-ray CT room during X-ray CT examinations. This method is based on air kerma measurements using semiconductor detectors with a time resolution of 1.0 second, averaged over four measurements per second. The DDD provides a new perspective compared to conventional spatial dose distributions based on instantaneous or cumulative doses, indicating that modulations in the tube current and the position of the patient bed affect the scatter radiation. These results provide foundational evidence for reassessing actions aimed at reducing radiation exposure among medical staff who must remain in CT rooms. Scatter radiation is influenced by factors such as X-ray energy, thickness of the subject, field of irradiation, and material density. X-ray CT examinations are performed along the body axis with a constant tube voltage and slice thickness (i.e., field of irradiation). During this process, the proportion of scattered radiation is influenced by temporal changes in the thickness of the subject and material density of the organs and tissues included in the scan. To evaluate the relationship between the scan position on the human body and scattered radiation, measurements were taken with a fixed tube current of 50 mA under typical X-ray CT examination conditions, covering the chest to the pelvic region, as commonly practiced in clinical practice. Additionally, to evaluate changes in scattered radiation intensity, including those associated with X-ray output modulations, measurements were taken using the aforementioned scan conditions with clinical parameters set to AEC 85 mA (SD 7.0). The AEC 85 mA adjusts the tube current from a minimum of 40 mA to a maximum of 85 mA, depending on the scan position, with an average tube current of 56 mA. Therefore, the cumulative air kerma dose per examination was approximately 10% higher with AEC 85 mA than that with fixed 50 mA. In the dose distribution depicted in Fig. 4 , the dose values were evaluated logarithmically, which posed a challenge in discerning the detailed differences in dose between the fixed 50 mA and AEC 85 mA settings, particularly when measured at the same height from the floor. Differences in radiation exposure per examination for the assisting personnel were observed between positions p(-50, -75) and p(-50, 75), as depicted in Figs. 4 and 5 . The lead apron reduces the radiation dose to the trunk of the assisting personnel [ 17 – 20 ]. Therefore, the radiation exposure at a height of 150 cm from the floor (i.e., the lens level) increased when protective measures were not taken. To analyze the differences in dose trends at such positions, it is necessary to clearly delineate the temporal changes in the scattered radiation intensity. Therefore, the temporal dose profile curves were evaluated at the following characteristic measurement points: head side of the patient bed (0, -375), foot side of the patient bed (0, 125), and gantry side (-150, 25) (see Fig. 6 ). To evaluate the effect of the patient bed position on the scattered radiation intensity, temporal dose profile curves were assessed with the tube current fixed at 50 mA at positions (0, -375) and (0, 125). Despite the constant tube current, the air kerma varied with bed movement, suggesting that the direction of patient bed movement affects the scattered radiation. Upon X-ray exposure with AEC to a Rand phantom, periodic variations in the air kerma occur because of the modulation of the tube current in both the anterior-posterior and lateral directions. However, the tube current remained constant during evaluation. Periodic variations in air kerma were caused by a 120 °shift in the rotational position of the X-ray tube with each measurement, owing to the differing rotation speed of the X-ray tube (1.5 sec/rot) and the dosimeter’s temporal resolution (1.0 sec). Additionally, a moving average over three segments (360 °) was evaluated to smooth out fluctuations in the dose profile curves and discern trends. To simulate a typical CT examination, the scattered radiation dose received by the staff positioned at the gantry side positions (-150, -25) and (-150, 25) was evaluated with X-ray exposure at AEC 85 mA. As the air kerma obtained at each position showed similar results regardless of the position and height from the floor, trends were demonstrated using the mean and standard deviation (Fig. 7 ). Although the air kerma on the gantry side was in a very low dose range, it suggested a trend similar to the X-ray output variation caused by the AEC. Measures related to time, distance, and shielding are considered effective in reducing radiation exposure. When it is not possible to maintain distance within the X-ray CT room, retreating to the gantry side is highly effective. Disturbances in the dose field on the gantry side are indicated by the vector plot. The hotspot in the dose distribution was likely due to scattering from the wall. Investigating this scattering and implementing protective measures are essential for reducing dose exposure to staff who have retreated. The dose distribution based on the accumulated air kerma measured with the semiconductor detector (Fig. 4 ) exhibited a shape similar to previously reported distribution [ 6 , 8 , 9 ]. The results, when expanded to the dose distribution per unit time, are represented by the DDD (Fig. 8 ). After being saved in a video format file, the DDD was illustrated at 5-sec intervals. Evaluating the DDD clarified how changes in tube current and table position affect dose distribution. The DDD is expected to be useful for evaluating protective measures designed to reduce radiation dose for staff required to wait inside the room, as well as for assessing behavioral changes to further minimize their dose. The study focused on a single CT scanner model and a specific range of tube currents. Results might not be generalizable to other CT systems or different scanning protocols. Future studies should include various CT scanner models and different scanning protocols to assess the generalizability of the DDD method across different clinical settings. Conclusion In this study, a new method called DDD was proposed to evaluate the temporal scatter radiation distribution of air kerma in a CT room during CT examinations. These results are expected to be useful for evaluating protective measures aimed at dose reduction and considering behavioral changes among staff to further reduce their exposure. Statements and Declarations Availability of data and material The datasets collected and/or analyzed in the current study are available from the corresponding author upon reasonable request. Acknowledgments: We would like to thank Editage (www.editage.com) for English language editing. Funding This work was supported by JSPS KAKENHI (Grant Number: [JP23K07143]). Competing interests The authors have no relevant financial or non-financial interests to disclose. Author contributions JS and YN performed the scattered radiation measurements. TH and YM provided guidance for the interpretation of the results. YA and SK were major contributors to the writing of the manuscript. All authors read and approved the final manuscript. Ethics approval This is an observational study. No ethical approval is required. 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Federica Z, Jérémie D, Celine C, Nicolas A, Alicia DG, Jean PS, Michel H, Emmanuel R, Sonia S, Pierre EM (2021) Evaluation of a suspended radiation protection system to reduce operator exposure in cardiology interventional procedures . Catheter Cardiovasc Interv 98(5):E687-E694. https://doi.org/10.1002/ccd.29894. Helmut S, Maria Z, Heinrich E, Christoph H (2007) Shielding properties of lead-free protective clothing and their impact on radiation doses. Med Phys 34(11):4270-80. https://doi.org/10.1118/1.2786861. Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Major revisions 26 Mar, 2025 Reviewers agreed at journal 30 Dec, 2024 Reviewers invited by journal 28 Oct, 2024 Editor invited by journal 22 Sep, 2024 Editor assigned by journal 17 Sep, 2024 First submitted to journal 16 Sep, 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-5101243","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":371454068,"identity":"e07bd70f-0a57-4aae-ad13-f57d57027a8f","order_by":0,"name":"Masanao Kobayashi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABCUlEQVRIie2RsUoDQRCG51jYajDtBX0FYeRgTeDQVxkJxCbIgU1AIVaX5h7Ax0iVOnBw1wTSrpV3pLCxuHJBQfeMYJo9Uwru183Cx//PDoDH81dhirEnVkBsB9q9yW6lSsYn/ZStwgcqQdXkMRVtxI/i5nRe1g2TwKhASmpzAechB42BoxuXotaTKGSSqKxii41g+Miin4G8dSqrCVgFUT1nrSJmC81wbHe5enApm5etYQoxSr9SZkCaxVunolnZFELbrVXyVpHdKfpVDZgYw0ImxOMSaF2nw4w6dtlcb5/M+8dlLxXLMxPfAZWjXJtp4fyxfeT3SQJbaXemXxHV3nB/kOLxeDz/gk/vuFPcEGfrMQAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0003-0273-0755","institution":"Fujita Health University: Fujita Ika Daigaku","correspondingAuthor":true,"prefix":"","firstName":"Masanao","middleName":"","lastName":"Kobayashi","suffix":""},{"id":371454069,"identity":"d6b06ebd-ec0d-49c5-8890-deca335cb1ff","order_by":1,"name":"Juria Suzuki","email":"","orcid":"","institution":"Fujita Health University Hospital: Fujita Ika Daigaku Byoin","correspondingAuthor":false,"prefix":"","firstName":"Juria","middleName":"","lastName":"Suzuki","suffix":""},{"id":371454070,"identity":"68fb1a89-73d4-4e24-8024-57758db1ee87","order_by":2,"name":"Yusei Nishihara","email":"","orcid":"","institution":"Fujita Health University Banbuntane Hotokukai Hospital: Fujita Ika Daigaku Banbuntane Byoin","correspondingAuthor":false,"prefix":"","firstName":"Yusei","middleName":"","lastName":"Nishihara","suffix":""},{"id":371454071,"identity":"30865afb-95b3-406a-8487-ba81eeac46ba","order_by":3,"name":"Tomonobu Haba","email":"","orcid":"https://orcid.org/0000-0002-5257-6162","institution":"Fujita Health University: Fujita Ika Daigaku","correspondingAuthor":false,"prefix":"","firstName":"Tomonobu","middleName":"","lastName":"Haba","suffix":""},{"id":371454072,"identity":"242dda89-cf45-4de6-a8e0-a49c5f25d620","order_by":4,"name":"Matsunaga Yuta","email":"","orcid":"","institution":"Nagoya Kyoritsu Hospital: Nagoya Kyoritsu Byoin","correspondingAuthor":false,"prefix":"","firstName":"Matsunaga","middleName":"","lastName":"Yuta","suffix":""},{"id":371454073,"identity":"a568a4b2-cf50-4b2d-b007-de20af6bb885","order_by":5,"name":"Yasuki Asada","email":"","orcid":"","institution":"Fujita Health University: Fujita Ika Daigaku","correspondingAuthor":false,"prefix":"","firstName":"Yasuki","middleName":"","lastName":"Asada","suffix":""},{"id":371454074,"identity":"cc1767e6-0dcc-4a07-87d9-0f213c54e27d","order_by":6,"name":"Shigeki Kobayashi","email":"","orcid":"","institution":"Fujita Health University: Fujita Ika Daigaku","correspondingAuthor":false,"prefix":"","firstName":"Shigeki","middleName":"","lastName":"Kobayashi","suffix":""}],"badges":[],"createdAt":"2024-09-17 07:11:33","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5101243/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5101243/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":69356552,"identity":"bc582b81-85a7-4cef-987d-6ba8bc085cf3","added_by":"auto","created_at":"2024-11-19 13:51:44","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":151623,"visible":true,"origin":"","legend":"\u003cp\u003eOverview of dose measurement value based on different dosemeters (a) The ionization survey meter measures the instantaneous value of scatter radiation. (b) The OSL dosimeter measures the accumulated dose of scattered radiation during scanning. (c) The semiconductor survey meter measures the temporal variations of scatter radiation doses.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5101243/v1/f3018a2c6fc7afc06e4a6f0b.png"},{"id":69355708,"identity":"2ce1b805-a070-4acd-828a-bb6ecb5aced5","added_by":"auto","created_at":"2024-11-19 13:43:44","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":234620,"visible":true,"origin":"","legend":"\u003cp\u003eCT scan range from the chest to the pelvis and setting of tube currents\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5101243/v1/c9a21903775026dd035fb3ed.png"},{"id":69355703,"identity":"9ee62fe3-aa31-4d88-9ead-7e2777c31505","added_by":"auto","created_at":"2024-11-19 13:43:44","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":97969,"visible":true,"origin":"","legend":"\u003cp\u003eScatter radiation dose measurement point The heights measured from the floor were 100 cm and 150 cm.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5101243/v1/be1534ed4fc4a77e76fa7c9c.png"},{"id":69355705,"identity":"d79a4460-6bcf-45b2-9e2f-15bd15c24ee8","added_by":"auto","created_at":"2024-11-19 13:43:44","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":571146,"visible":true,"origin":"","legend":"\u003cp\u003eAccumulated scatter radiation dose distribution\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5101243/v1/ff8b76c129ae732419c17ede.png"},{"id":69356553,"identity":"7b34587f-a514-45b9-a0c3-496763b1161f","added_by":"auto","created_at":"2024-11-19 13:51:44","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":256993,"visible":true,"origin":"","legend":"\u003cp\u003eDose rate profile curves and its 3-period moving average at p(-50, -75) and p(-50, 75).\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5101243/v1/8037ffa2f711fb62b8f88599.png"},{"id":69355706,"identity":"9c904c59-21ee-4e57-94ec-8df9a6d8f383","added_by":"auto","created_at":"2024-11-19 13:43:44","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":116424,"visible":true,"origin":"","legend":"\u003cp\u003eDose rate profile curves and its 3-period moving average at p(0, 175) and p(0, -425).\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5101243/v1/37c13bc42913bfaa6f393a35.png"},{"id":69355701,"identity":"53feb382-bcae-4ed6-beb4-98eaf8cece7d","added_by":"auto","created_at":"2024-11-19 13:43:44","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":63118,"visible":true,"origin":"","legend":"\u003cp\u003eDose rate profile curves near the gantry side at p(-150,-25) and p(-150,25).\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5101243/v1/46acbdc6d4d5697f58654109.png"},{"id":69355704,"identity":"6cff2f66-567f-4c45-a3b9-6f9183443927","added_by":"auto","created_at":"2024-11-19 13:43:44","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":713692,"visible":true,"origin":"","legend":"\u003cp\u003eDDD with a 5-sec interval.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5101243/v1/daecaac649df4ebc618200bf.png"},{"id":69356554,"identity":"7c7c0982-dcbf-4793-9e40-27d03ff1364c","added_by":"auto","created_at":"2024-11-19 13:51:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2205718,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5101243/v1/eb7e2edc-7473-49b4-9c51-9040c0bb32b6.pdf"}],"financialInterests":"","formattedTitle":"Dynamic Distribution of Scattered Radiation in a CT Room, Utilizing a Semiconductor Survey Meter","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe primary objective of diagnostic medical X-ray examinations is to ensure that the benefits to the patient outweigh any potential harm. Additionally, consideration must be given to the radiation exposure risks faced by the radiological staff and other individuals [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. The radiological staff should adhere to the principles of justification and the optimization of protection as outlined in the radiological protection systems. In recent years, an increasing number of medical specialists have used fluoroscopy outside imaging departments. However, this practice has often been accompanied by inadequate attention to radiation protection and insufficient training. This trend may increase radiation risk to both staff and patients [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. It is therefore becoming increasingly important to educate individuals about ethical values that support radiological protection systems [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eRadiologists are exposed to radiation throughout their careers. Therefore, in all diagnostic medical X-ray examinations, not just fluoroscopy, occupational exposure should be reduced in the same manner as the medical exposure for patients [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Measures to reduce medical exposure to patients include the use of dose-reduction techniques for each X-ray equipment and the recommended use of diagnostic reference levels as a tool to optimize protection [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. These actions that reduce the patient dose also reduce the occupational dose to radiological staff and the medical exposure to assisting personnel [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Additionally, using lead aprons, leaded glass eyewear, other types of shields, and radiation shielding screens can help reduce the radiation dose [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOne measurement method used to assess the scattered radiation dose delivered by radiological staff and assisting personnel is scattered radiation distribution [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The scatter radiation distribution can be plotted by measuring the scatter radiation doses with an ionization chamber survey meter while moving sequentially through a grid or concentric circles of measurement points set up in an X-ray room [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Recently, a novel method for measuring the scattered radiation dose has been reported, which involves fixing optically simulated luminescence (OSL) dosimeters [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] to paper pipes arranged geometrically, similar to a jungle gym [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The measurement values from the survey meter represent the instantaneous dose rate, while the OSL dosimeters provide the accumulated dose, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (a, b). In examinations, such as fluoroscopy and CT, where X-rays are irradiated over time, it is not possible to evaluate the trend of scattered radiation dose over time.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eRecently, during the global outbreak of the novel coronavirus infection, medical workers involved in transporting infectious disease patients, as well as radiologic technologists positioning patients for CT scans, had to remain inside the CT room to prevent the spread of infection. This decision resulted in their exposure to radiation. There have been no reports justifying the need for personnel to remain in the CT room to prevent the spread of infection. If personnel are not needed for assisting a patient, their radiation exposure depends on their activities within the CT room, making it crucial to monitor the temporal changes in the scatter radiation dose.\u003c/p\u003e \u003cp\u003eThis study aimed to assess the temporal changes in the scattered radiation dose within the imaging room. In this study, a semiconductor survey meter was used to measure changes in the scattered radiation dose over time, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (c). The results allowed for the visualization of changes in the scattered radiation dose over time as dynamic dose distributions (DDD). The DDD provides insights into the protective actions of radiological staff and assisting personnel over time, based on the new dose index.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eSemiconductor survey meter\u003c/h2\u003e \u003cp\u003eThe RaySafe 452 radiation survey meter (FLUK Biomedical, Cleveland, Ohio) is a hybrid instrument that combines a semiconductor (silicon sensor) with a Geiger-Muller tube, complying with the International Electrotechnical Commission (IEC) 60846-1 [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. This survey meter features a dose range of 0 \u0026micro;Gy/h to 1.0 Gy/h, a rate resolution of 0.01 \u0026micro;Gy/h, a dose resolution of 0.1 nGy, and an energy range of 30.0 keV to 7.0 MeV, with an energy response stabilizing to about 1.0 at 30.0 keV to 100.0 keV. These characteristics make it suitable for measuring scattered radiation doses in the room during diagnostic medical X-ray examination. It is necessary to pay attention to the angular response when measuring, as the detection unit\u0026rsquo;s sensitivity varies: 0.5 (90 \u0026deg; and 270 \u0026deg; at 33.0 keV) and 1.4 (90 \u0026deg; and 270 \u0026deg; at 65.0 keV) [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Characteristically, these algorithms are used to detect radiation changes with response times of 1 sec, averaged over four measurements per second [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. In this study, Raysafe 452 was used to roughly measure the change in scattered radiation dose over time at a 1.0-second interval.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003ePhantom and X-ray CT scanner\u003c/h2\u003e \u003cp\u003eAn anthropomorphic RANDO man-model phantom (RAN110; Phantom Laboratory, Salem, NY, USA), representing a 175-cm tall, 73.5-kg human male with removable upper arms, was positioned lying on the patient bed in an X-ray CT scanner (Aquilion Prime; Cannon Medical Systems). The removable upper arms were then attached in the raised position, but the lower legs could not be attached because the connections were made of a metallic material. The RANDO phantom is constructed from a natural human skeleton and soft tissue-simulating material, consisting of a proprietary urethane formulation and lung-simulating material with the same effective atomic number as the soft tissue material but with a density that simulates the lungs in a median respiratory state. The RANDO phantom was considered a patient requiring assistance or with infectious diseases. The DDD was evaluated using CT scans from the chest to the pelvis, where changes in scattered radiation dose over time were anticipated. The CT scan was performed under the following scan conditions: tube voltage 120 kVp, scan rotation speed: 1.5 sec/rot, beam width: 0.5 mm\u0026times;80 raw (40 mm), pitch factor: 65/80 (0.813), scan length: 760 mm, scan time: 37.6 sec, field-of-view: 320 mm, orbital synchronization system (+) of rotation start angle, and feet first. The tube current was set under two different conditions: a fixed 50 mA and automatic exposure controlled (AEC), with a maximum of 85 mA, averaging 57.5 mA equivalent (standard deviation of image noise: 7.0) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The scan rotation speed was set to 1.0 sec/rot for the CT examination of patients. In this study, the scan rotation speed was slowed to 1.5 sec/rot to evaluate dose changes in detail. As a result of this setting, the X-ray tube rotation angle is shifted by 120 \u0026deg; for each measurement interval of the survey meter.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eDose measurement\u003c/h2\u003e \u003cp\u003eThe scattered radiation dose in the CT room was measured at 50 cm intervals on one side of the patient bed (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA-G) with the bed as the center line (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eG) and on the opposite side (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA\u0026rsquo;-F\u0026rsquo;). The measurement points were positioned at heights of 100 cm (57 points) and 150 cm (64 points) above the floor. Due to the presence of the patient bed, the points along the G row (-325 to 75) were measured only at 150 cm. The Raysafe 452 detector was positioned toward the isocenter using the laser beam of a laser rangefinder (GLM500; Bosch). A helical scan of the RANDO phantom was then conducted from the chest to the pelvis region for approximately 40 sec. During this scan, the scattered radiation dose inside the CT room was measured in terms of the accumulated air kerma (Gy) and air kerma rate (Gy/sec). The measurement values displayed on the Raysafe 452\u0026rsquo;s main unit screen were saved on a PC via Raysafe view software (FLUK Biomedical, Cleveland, Ohio). Each measurement value was divided by the pre-measured background value in the CT room (0.008 \u0026micro;Gy/s) and multiplied by a calibration factor for traceability to national standards. The effective energy of the scattered radiation at each point was unknown. The primary beam of the Aquilion prime at 120kVp, previously evaluated using the Black Piranha semiconductor detector (RTI group AB, M\u0026ouml;lndal, Sweden) of an X-ray analyzer along with a lead shield box (made of 3-mm-thick, 99.9% pure Pb; Acrobio Corp., Tokyo, Japan), was measured at 48.2 keV [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Based on this, we assumed an effective energy of 50 keV and adopted a calibration constant of 1.0 for the survey meter.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eDose Distribution\u003c/h2\u003e \u003cp\u003eThe dose distribution was plotted using graphing software (Surfer, Golden software) based on the measured scattered radiation doses accumulated over approximately 40 seconds (i.e., accumulated air kerma) during a chest-to-pelvis CT scan. The measurements were taken at both 100 cm and 150 cm above the floor with a fixed 50 mA, and at 100 cm and 150 cm with AEC set to 85 mA. Dose distributions were mapped from the measured scattered radiation doses data using the kriging method (geostatistical grid method) to facilitate visual comprehension. The scattered radiation doses were then visualized on a logarithmic scale. Subsequently, the maximum slope and slope direction were calculated from the measurements, and the direction vectors of the scattered radiation were plotted. Using the obtained dose distributions and vector plots, the effects of the X-ray output characteristics (fixed and AEC) and the direction of the scattered radiation spread were evaluated. Assistance was assumed to be performed at positions (x, y, z)\u0026thinsp;=\u0026thinsp;p(-50, -75, 100/150) and p(-50, 75, 100/150). The accumulated air kerma received by the assisting personnel per examination and the dose rate profile curves over time were also assessed. Moreover, the dose rate profile curves at characteristic measurement points, such as the head side of the patient bed p (0, -425, 100/150), the feet side of the patient bed p (0, 175, 100/150), and the lateral side of the gantry p (-150, -25/25, 100/150), were evaluated.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eDynami Dose Distribution\u003c/h2\u003e \u003cp\u003eDose distributions and vector plots were visualized based on measurements taken per unit time using a semiconductor survey meter. The data were edited to switch every second using video editing software (Wonder Filmora, Wondershare) and saved in MPEG-4 (.MP4) video file format. Such a change in dose distribution over time is termed DDD. We observed changes in the dose distributions and vector plots over time from the obtained DDD. The evaluation was performed by selecting the dose distributions and vector plots at 5-second intervals (5 sec: sternoclavicular joint, 10 sec: nipple, 15 sec: diaphragm, 20 sec: umbilicus, 25 sec: iliac crest, 30 sec: coccyx, and 35 sec: hipbone) for the visualized DDD.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eX-ray output difference between fixed 50 mA and AEC 85 mA\u003c/h2\u003e \u003cp\u003eCT examinations of the chest to pelvis region were conducted using a fixed tube current of 50 mA and with AEC set to a maximum of 85 mA (SD 7.0). The AEC of 85 mA was modulated from a minimum of 40 mA to a maximum of 85 mA depending on the imaging area, with an average of 56 mA. The tube current was adjusted to 67 mA (5 sec), 65 mA (10 sec), 44 mA (15 sec), 70 mA (20 sec), 82 mA (25 sec), 46 mA (30 sec), and 40 mA (35 sec). Therefore, the X-ray output with AEC was approximately 10% higher than that with fixed 50 mA (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), which also affected the scattered radiation dose.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eDose Distribution\u003c/h2\u003e \u003cp\u003eWhen the height from the floor remained consistent, the accumulated dose distribution of chest-to-pelvis CT scans demonstrated similar trends between the fixed 50 mA and AEC 85 mA, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. In the case of the AEC, the air kerma of scatter radiation doses received by the assisting personnel during one examination were as follows: at position p(-50, -75): 139.7 \u0026micro;Gy at 100 cm and 254.2 \u0026micro;Gy at 150 cm; and at position p(-50, 75): 80.4 \u0026micro;Gy at 100 cm and 83.7 \u0026micro;Gy at 150 cm. The dose rate profile curves and their 3-period moving average were evaluated at the same positions, revealing differences in trends based on the positions and tube current mode (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe temporal modulation of air kerma suggests that changes in tube current affect the intensity of scatter radiation, as observed at position p(-50, 75) with AEC. Moreover, at a measurement height of 150 cm, there was a tendency for the air kerma to be higher at the start of measurements at p(-50, 75) and at the end of measurements at p(-50, -75). For p(-50, -75) with AEC, the air kerma was influenced by both these effects. Therefore, we hypothesized that the position of the patient bed influences the scattered radiation dose. To investigate this, the air kerma was evaluated by measuring the dose-rate profile curves at the foot side at position p(0,175) and head side at position p(0,-425) of the patient\u0026rsquo;s bed, with the x-ray tube current fixed at 50 mA. The RAND phantom, positioned on the patient\u0026rsquo;s bed in the feet first orientation, was scanned through the neck to the hipbone from 0 sec to 37.6 sec, resulting in the dose-rate profile curves shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The air kerma showed high values during the scanning of the hip joint region (33 sec) at p(0, 175) and the chest region (10 sec) at p(0, -425). This suggests that the direction of the movement of the patient bed influences the scattered radiation dose. With the same AEC mode, the air kerma radiation dose received by the assisting personnel was lower on the gantry side at positions p(-150,-25) and p(-150,25) than that on the surroundings, measuring approximately 0.8 \u0026micro;Gy at both measurement heights (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The dose rate profile curves on the gantry side showed a trend similar to that of the AEC modulation (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). In this study, the spreading direction of the scattered radiation (i.e., maximum slope and slope direction) was visually indicated using vector plots of the air kerma. The vector plots extending from isocenter p(0, 0) to p(-300, -350) aligned with the direction of the scattered radiation dose distribution. On the gantry side, the direction of the vector plots was opposite to the X-ray output direction. A hotspot was detected near this area in the dose distribution (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eDDD\u003c/h2\u003e \u003cp\u003eThe DDDs and vector plots are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. Even with a fixed tube current of 50 mA, the DDDs were not identical, but no significant drastic changes in the distribution were observed. Notably, regardless of the scan time, the air kerma at the assistance position p(-50, -75) by assisting personnel was higher, while the air kerma at the evacuation position on the gantry side p(-150,-25) and p(-150,25) was lower. Moreover, the differences in the dose distribution at arbitrary positions, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, were reflected in the DDD. For example, refer to the DDD at 25 sec (Fixed 50 mA vs. AEC 80 mA). The distortion in the vector plot on the gantry side, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, consistently became prominent at a height of 100 cm from the floor. Such distortions in the vector plots were sporadically identified at locations away from the isocenter.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eNotably, the DDDs at a height of 150 cm had a greater spread of scattered radiation than those at 100 cm. Furthermore, the temporal dose modulation of the air kerma at p(0, 175) and p(0, -425), as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, could also be visually confirmed by the spread of the distribution in the DDD.\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this study, a new method called DDD was proposed to evaluate the temporal distribution of scattered air kerma within an X-ray CT room during X-ray CT examinations. This method is based on air kerma measurements using semiconductor detectors with a time resolution of 1.0 second, averaged over four measurements per second. The DDD provides a new perspective compared to conventional spatial dose distributions based on instantaneous or cumulative doses, indicating that modulations in the tube current and the position of the patient bed affect the scatter radiation. These results provide foundational evidence for reassessing actions aimed at reducing radiation exposure among medical staff who must remain in CT rooms.\u003c/p\u003e \u003cp\u003eScatter radiation is influenced by factors such as X-ray energy, thickness of the subject, field of irradiation, and material density. X-ray CT examinations are performed along the body axis with a constant tube voltage and slice thickness (i.e., field of irradiation). During this process, the proportion of scattered radiation is influenced by temporal changes in the thickness of the subject and material density of the organs and tissues included in the scan. To evaluate the relationship between the scan position on the human body and scattered radiation, measurements were taken with a fixed tube current of 50 mA under typical X-ray CT examination conditions, covering the chest to the pelvic region, as commonly practiced in clinical practice. Additionally, to evaluate changes in scattered radiation intensity, including those associated with X-ray output modulations, measurements were taken using the aforementioned scan conditions with clinical parameters set to AEC 85 mA (SD 7.0). The AEC 85 mA adjusts the tube current from a minimum of 40 mA to a maximum of 85 mA, depending on the scan position, with an average tube current of 56 mA. Therefore, the cumulative air kerma dose per examination was approximately 10% higher with AEC 85 mA than that with fixed 50 mA. In the dose distribution depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, the dose values were evaluated logarithmically, which posed a challenge in discerning the detailed differences in dose between the fixed 50 mA and AEC 85 mA settings, particularly when measured at the same height from the floor.\u003c/p\u003e \u003cp\u003eDifferences in radiation exposure per examination for the assisting personnel were observed between positions p(-50, -75) and p(-50, 75), as depicted in Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The lead apron reduces the radiation dose to the trunk of the assisting personnel [\u003cspan additionalcitationids=\"CR18 CR19\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Therefore, the radiation exposure at a height of 150 cm from the floor (i.e., the lens level) increased when protective measures were not taken. To analyze the differences in dose trends at such positions, it is necessary to clearly delineate the temporal changes in the scattered radiation intensity. Therefore, the temporal dose profile curves were evaluated at the following characteristic measurement points: head side of the patient bed (0, -375), foot side of the patient bed (0, 125), and gantry side (-150, 25) (see Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). To evaluate the effect of the patient bed position on the scattered radiation intensity, temporal dose profile curves were assessed with the tube current fixed at 50 mA at positions (0, -375) and (0, 125). Despite the constant tube current, the air kerma varied with bed movement, suggesting that the direction of patient bed movement affects the scattered radiation.\u003c/p\u003e \u003cp\u003eUpon X-ray exposure with AEC to a Rand phantom, periodic variations in the air kerma occur because of the modulation of the tube current in both the anterior-posterior and lateral directions. However, the tube current remained constant during evaluation. Periodic variations in air kerma were caused by a 120 \u0026deg;shift in the rotational position of the X-ray tube with each measurement, owing to the differing rotation speed of the X-ray tube (1.5 sec/rot) and the dosimeter\u0026rsquo;s temporal resolution (1.0 sec). Additionally, a moving average over three segments (360 \u0026deg;) was evaluated to smooth out fluctuations in the dose profile curves and discern trends.\u003c/p\u003e \u003cp\u003eTo simulate a typical CT examination, the scattered radiation dose received by the staff positioned at the gantry side positions (-150, -25) and (-150, 25) was evaluated with X-ray exposure at AEC 85 mA. As the air kerma obtained at each position showed similar results regardless of the position and height from the floor, trends were demonstrated using the mean and standard deviation (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). Although the air kerma on the gantry side was in a very low dose range, it suggested a trend similar to the X-ray output variation caused by the AEC.\u003c/p\u003e \u003cp\u003eMeasures related to time, distance, and shielding are considered effective in reducing radiation exposure. When it is not possible to maintain distance within the X-ray CT room, retreating to the gantry side is highly effective. Disturbances in the dose field on the gantry side are indicated by the vector plot. The hotspot in the dose distribution was likely due to scattering from the wall. Investigating this scattering and implementing protective measures are essential for reducing dose exposure to staff who have retreated. The dose distribution based on the accumulated air kerma measured with the semiconductor detector (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) exhibited a shape similar to previously reported distribution [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The results, when expanded to the dose distribution per unit time, are represented by the DDD (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). After being saved in a video format file, the DDD was illustrated at 5-sec intervals. Evaluating the DDD clarified how changes in tube current and table position affect dose distribution. The DDD is expected to be useful for evaluating protective measures designed to reduce radiation dose for staff required to wait inside the room, as well as for assessing behavioral changes to further minimize their dose. The study focused on a single CT scanner model and a specific range of tube currents. Results might not be generalizable to other CT systems or different scanning protocols. Future studies should include various CT scanner models and different scanning protocols to assess the generalizability of the DDD method across different clinical settings.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this study, a new method called DDD was proposed to evaluate the temporal scatter radiation distribution of air kerma in a CT room during CT examinations. These results are expected to be useful for evaluating protective measures aimed at dose reduction and considering behavioral changes among staff to further reduce their exposure.\u003c/p\u003e"},{"header":"Statements and Declarations","content":"\u003cp\u003e\u003cstrong\u003eAvailability of data and material\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets collected and/or analyzed in the current study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe would like to thank Editage (www.editage.com) for English language editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by JSPS KAKENHI (Grant Number: [JP23K07143]).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\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\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJS and YN performed the scattered radiation measurements.\u003csup\u003e\u0026nbsp;\u003c/sup\u003eTH and YM provided guidance for the interpretation of the results.\u003csup\u003e\u0026nbsp;\u003c/sup\u003eYA and SK were major contributors to\u0026nbsp;the writing of the manuscript. All authors read and approved the final manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis is an observational study. No ethical approval is required.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis is an observational study. No ethical approval is required.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to publish\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo ethical approval is required.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eInternational Commission on Radiological Protection (2007) ICRP Publication no. 103. The 2007 Recommendations of the International Commission on Radiological Protection. Ann. ICRP 37(2-4):1-32. https://doi.org/10.1016/j.icrp.2007.10.003\u003c/li\u003e\n\u003cli\u003eRehani MM, Ciraj-Bjelac O, Va\u0026ntilde;\u0026oacute; E, Miller DL, Walsh S, Giordano BD, Persliden J (2010) ICRP Publication 117. Radiological protection in fluoroscopically guided procedures performed outside the imaging department. Ann ICRP 40(6):1-102. https://doi.org/10.1016/j.icrp.2012.03.001.\u003c/li\u003e\n\u003cli\u003eCho KW, Cantone MC, Kurihara-Saio C, Le Guen B, Martinez N, Oughton D, Schneider T, Toohey R, Z\u0026ouml;Lzer F; Authors on behalf of ICRP (2018) ICRP Publication 138: Ethical Foundations of the System of Radiological Protection Ann ICRP 47(1):1-65. https://doi.org/10.1177/0146645317746010. \u003c/li\u003e\n\u003cli\u003eVa\u0026ntilde;\u0026oacute; E, Miller DL, Martin CJ, Rehani MM, Kang K, Rosenstein M, Ortiz-L\u0026oacute;pez P, Mattsson S, Padovani R, Rogers A; Authors on behalf of ICRP (2017) ICRP Publication 135: Diagnostic Reference Levels in Medical Imaging. Ann ICRP 46(1):1-144. https://doi.org/10.1177/0146645317717209. PMID: 29065694.\u003c/li\u003e\n\u003cli\u003eL\u0026oacute;pez PO, Dauer LT, Loose R, Martin CJ, Miller DL, Va\u0026ntilde;\u0026oacute; E, Doruff M, Padovani R, Massera G, Yoder C; Authors on Behalf of ICRP (2018) ICRP Publication 139: Occupational Radiological Protection in Interventional Procedures. Ann ICRP 47(2):1-118. https://doi.org/10.1177/0146645317750356.\u003c/li\u003e\n\u003cli\u003eKobayashi M, Koshida K, Suzuki S, Katada K (2011) Evaluation of geometric efficiency and radiation exposure in z-axis for volume scan. Radiat Prot Dosimetry 143(1):63-68. https://doi.org/10.1007/s00330-017-5177-1\u003c/li\u003e\n\u003cli\u003eInaba Y, Hitachi S, Watanuki M, Chida K (2021) Occupational Radiation Dose to Eye Lenses in CT-Guided Interventions Using MDCT-Fluoroscopy. Diagnostics (Basel) 11(4):646. https://doi.org/10.3390/diagnostics11040646.\u003c/li\u003e\n\u003cli\u003eVerdun FR, Aroua A, Baechler S, Schmidt S, Trueb PR, Bochud FO (2010) Criteria for establishing shielding of multi-detector computed tomography (MDCT) rooms. Radiat Prot Dosimetry 139(1-3):403-409. https://doi.org/10.1093/rpd/ncq100.\u003c/li\u003e\n\u003cli\u003eDaioku T, Kobayashi M, Oishi F (2021) Development of Visual Educational Materials for Radiation Protection in Computed Tomography. J Radiol Nurs 40(3):268-274. https://doi.org/10.1016/j.jradnu.2021.04.006\u003c/li\u003e\n\u003cli\u003eNakamura T, Shoichi S, Takei Y, Kobayashi M, Cruz V, Kobayashi I, Assegawa S, Kato K (2020). A more accurate and safer method for the measurement of scattered radiation in X-ray examination rooms. Radiol Phys Technol 13(1):69-75. https://doi.org/10.1007/s12194-019-00550-6\u003c/li\u003e\n\u003cli\u003eYukihara EG, McKeever SWS (2008) Optically stimulated luminescence (OSL) dosimetry in medicine. Phys Med Biol 53:R351\u0026ndash;R379. https://doi.org/10.1088/0031-9155/53/20/R01.\u003c/li\u003e\n\u003cli\u003eOkazaki T, Hayashi H, Takegami K, Okino H, Kimoto N, Maehata I, Kobayashi I (2016) Fundamental Study of nanoDot OSL Dosimeters for Entrance Skin Dose Measurement in Diagnostic X-ray Examinations. J Radiat Prot Res 41(3):229-236. https://doi.org/10.14407/jrpr.2016.41.3.229\u003c/li\u003e\n\u003cli\u003eInternational Electrotechnical Commission (2009) Radiation protection instrumentation - Ambient and/or directional dose equivalent (rate) meters and/or monitors for beta, X and gamma radiation - Part 1: Portable workplace and environmental meters and monitors. IEC 60846-1. (Geneva, Switzerland: IEC).\u003c/li\u003e\n\u003cli\u003eFLUKE Biomedical (2021) RAYSAFE 452 Radiation Survey Metrer. Useres Manual. PN 50000195-1.10\u003c/li\u003e\n\u003cli\u003eOmori Y, Ishizawa S, Kawaguchi W, Maki S, Yamada F, Murabayashi Y, Inaba Y, Chida K (2022) Fundamental Characteristics of a Hybrid Survey Meter -Measurement of Scattered Radiation-. Jpn J Radiat Saf Manag 21:2-9. http://dx.doi.org/https://doi.org/10.11269/jjrsm.21.2 \u003c/li\u003e\n\u003cli\u003eAkaishi H, Takeda H, Kanazawa Y, Yoshii Y, Asanuma O (2016) Development of a Lead-covered Case for a Wireless X-ray Output Analyzer to Perform CT Half-value Layer Measurements. Jpn J Radiol Technol 72(3): 244-250. https://doi.org/10.6009/jjrt.2016_JSRT_72.3.244\u003c/li\u003e\n\u003cli\u003eMori H, Koshida K, Ishigamori O, Matsubara K (2014) Evaluation of the effectiveness of X-ray protective aprons in experimental and practical fields. Radiol Phys Technol 7(1):158-166. https://doi.org/10.1007/s12194-013-0246-x.\u003c/li\u003e\n\u003cli\u003eChristelle H, J\u0026eacute;r\u0026eacute;mie D, Joanna DA, Alexandre H, Edilaine H, Pasquale L, Giulia T, Filip V (2023) Effectiveness of staff radiation protection devices for interventional cardiology procedures. Phys Med 107:102543. https://doi.org/10.1016/j.ejmp.2023.102543.\u003c/li\u003e\n\u003cli\u003eFederica Z, J\u0026eacute;r\u0026eacute;mie D, Celine C, Nicolas A, Alicia DG, Jean PS, Michel H, Emmanuel R, Sonia S, Pierre EM (2021) Evaluation of a suspended radiation protection system to reduce operator exposure in cardiology interventional procedures\u003cstrong\u003e. \u003c/strong\u003eCatheter Cardiovasc Interv 98(5):E687-E694. https://doi.org/10.1002/ccd.29894.\u003c/li\u003e\n\u003cli\u003eHelmut S, Maria Z, Heinrich E, Christoph H (2007) Shielding properties of lead-free protective clothing and their impact on radiation doses. Med Phys 34(11):4270-80. https://doi.org/10.1118/1.2786861.\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":true,"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":"Radiation exposure, Infection control, CT, Dose Distributions, Scattered radiation","lastPublishedDoi":"10.21203/rs.3.rs-5101243/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5101243/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe relationship between radiation exposure risk and infection control has not been adequately addressed. Consequently, there is no clear guidance on whether personnel involved in transporting infectious disease patients or radiological technologists who position patients should stay in the imaging room to prevent the spread of infection or evacuate to avoid radiation exposure. This study aimed to assess the temporal changes in the scattered radiation dose within the imaging room. In this study, a semiconductor survey meter was used to measure changes in the scattered radiation dose over time. The results allowed for the visualization of changes in scattered radiation dose over time as dynamic dose distributions (DDD). Unlike traditional dose assessments based on instantaneous measurements with a survey meter or cumulative doses with optically simulated luminescence (OSL) dosimeters, DDD elucidated the effects of tube current fluctuations and patient bed positioning on the scattered radiation intensity. These findings offer valuable for reviewing the behavior of medical staff who stay in the imaging room for infection control and provide important evidence for reducing radiation exposure.\u003c/p\u003e","manuscriptTitle":"Dynamic Distribution of Scattered Radiation in a CT Room, Utilizing a Semiconductor Survey Meter","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-19 13:43:39","doi":"10.21203/rs.3.rs-5101243/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revisions","date":"2025-03-27T01:01:50+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2024-12-30T10:16:30+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-10-28T22:06:01+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Physical and Engineering Sciences in Medicine","date":"2024-09-22T20:01:07+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-09-17T11:48:49+00:00","index":"","fulltext":""},{"type":"submitted","content":"Physical and Engineering Sciences in Medicine","date":"2024-09-17T03:10:30+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":"2efbef88-157c-477d-9b0d-7dcf56bfce89","owner":[],"postedDate":"November 19th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[],"tags":[],"updatedAt":"2025-12-28T22:31:55+00:00","versionOfRecord":[],"versionCreatedAt":"2024-11-19 13:43:39","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5101243","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5101243","identity":"rs-5101243","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}