| Wu Yiming,Du Xiaohong,Li Lin,et al.A methodological study on spot isocenter performance verification for pencil beam scanning proton radiotherapy systems[J].Chinese Journal of Radiological Medicine and Protection,2026,46(8):763-768 |
| A methodological study on spot isocenter performance verification for pencil beam scanning proton radiotherapy systems |
| Received:November 21, 2025 |
| DOI：10.3760/cma.j.cn112271-20251121-00407 |
| KeyWords:Proton therapy|Quality control|EBT4 radiochromic film|Phantom for isocentric spot analysis |
| FundProject:北京市自然科学基金(L2602050) |
| Author Name | Affiliation | E-mail | | Wu Yiming | Beijing Prevention and Treatment Hospital of Occupational Disease, Beijing 100093, China | | | Du Xiaohong | Beijing Prevention and Treatment Hospital of Occupational Disease, Beijing 100093, China | | | Li Lin | Beijing Prevention and Treatment Hospital of Occupational Disease, Beijing 100093, China | | | Yu Pei | Beijing Prevention and Treatment Hospital of Occupational Disease, Beijing 100093, China | | | Zhang Deqin | Beijing Prevention and Treatment Hospital of Occupational Disease, Beijing 100093, China | | | Pan Yi | Beijing Prevention and Treatment Hospital of Occupational Disease, Beijing 100093, China | | | Luo Jingwen | Beijing Prevention and Treatment Hospital of Occupational Disease, Beijing 100093, China | | | Fan Ziyan | Beijing Prevention and Treatment Hospital of Occupational Disease, Beijing 100093, China | | | Liu Lantao | Beijing Prevention and Treatment Hospital of Occupational Disease, Beijing 100093, China | lantao.liu@163.com |
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| Abstract:: |
| Objective To assess the feasibility of the combination of an self-designed phantom for isocentric spot analysis and EBT4 radiochromic films in measuring spot isocenter deviations at multiple gantry angles, and to establish a method for quality control (QC) of spot isocenter that is suitable for pencil beam scanning (PBS) proton radiotherapy systems. Methods To address the incompatibility between the designed phantom and existing two-dimensional array detectors at non-horizontal and non-vertical gantry angles, EBT4 radiochromic films were introduced to measure the deviations between the spot isocenter and the patient positioning laser isocenter in the radiotherapy room. The optimal color channel for film readout was determined using an ultraviolet-visible (UV-Vis) spectrophotometer, followed by the establishment of a standardized image analysis workflow and guidelines for parameter selection. Irradiation measurements were performed at varying gantry angles, and the spatial deviation between the spot isocenter and the positioning laser isocenter was analyzed. Results Experimental measurements at varying gantry angles indicated that the combination of the independently designed phantom and EBT4 radiochromic films can accurately identify the deviations between the spot isocenter and the positioning laser isocenter. The maximum deviation measured 0.88 mm, below the tolerance limit of 1 mm specified in the Standard for testing of quality control in medical proton/heavy ion radiotherapy equipment (WS 816-2023) Conclusions The proposed method meets the QC requirements for radiation-beam isocenter deviations specified in WS 816-2023. This method is particularly suitable for isocenter verification in PBS proton therapy systems under varying gantry angles, providing a method ological reference for proton therapy centers to establish standardized and reproducible QC workflows. |
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