不同背向散射条件对晨检仪QABC+测量结果的影响-《中国医学物理学杂志》

文章信息/Info

Title:: Effects of different backscattering conditions on QABC+ measurements

作者:: 龙亮1; 徐中标1; 韩俊杰1; 吕凤泉1; 黄唯1; 梁瑜1; 高兴旺1; 2; 1.广东省人民医院/广东省医学科学院放疗科，广东广州 510080； 2.中国医学科学院肿瘤医院深圳医院设备物资部，广东深圳 518116

Author(s):: LONG Liang1; XU Zhongbiao1; HAN Junjie1; L?Fengquan1; HUANG Wei1; LIANG Yu1; GAO Xingwang1; 2; 1. Department of Radiotherapy, Guangdong Provincial Peoples Hospital/Guangdong Academy of Medical Sciences, Guangzhou 510080, China 2. Department of Medical Device Management, Shenzhen Center, Cancer Hospital, Chinese Academy of Medical Sciences, Shenzhen 518116, China

Keywords:: Keywords: QA beamchecker plus backscatter linear accelerator treatment couch quality control

摘要:: 目的：研究不同背向散射条件对晨检仪QABC+测量结果的影响。方法：将QABC+和参考电离室模块（由指型电离室和固体水构成）分别放在加速器治疗床的两个固定位置（头部A和网部B），源到上表面距离100 cm。以QABC+和参考电离室模块下方铺垫的固体水厚度作为变量（0~8 cm、10 cm、15 cm），测量对应背向散射因子[Bs]值。结果：固体水厚度超过5 cm之后，参考电离室测的[Bs]值趋于稳定，变化在1%内。QABC+测的[Bs]值偏大且在5~15 cm固体水之间仍有3.1%的增长；治疗床A位置等效为5 cm固体水。结论：QABC+测量结果受到背向散射的影响较常规电离室要大，且测得[Bs]值被放大，背向散射条件的轻微变化可能导致晨检仪误报。建议在晨检仪使用前应通过实验测量确定背向散射条件对其读数的影响，或者固定摆位条件以保证散射条件的稳定，使晨检设备高效、稳定、可靠地工作。【关键词】晨检仪；背向散射；直线加速器；治疗床；质量控制

Abstract:: Abstract: Objective To investigate the effects of different backscattering conditions on the measurement results of the QA beamchecker plus (QABC+). Methods QABC+ and a reference phantom composed of PTW thimble ionization chamber and solid water were placed at the fixed positions (positions A and B) on the treatment couch, with the source-to-surface distance of 100 cm. Taking the thickness (0-8 cm, 10 cm, and 15 cm) of solid water under the reference phantom and QABC+ as the variations, the corresponding backscatter factor (Bs) was measured. Results Once the solid water thickness exceeded 5 cm, the Bs measured by the reference ionization chamber tended to be stable and varied within 1%, while the Bs measured by QABC+ was larger and still increased by 3.1% for 5 to 15 cm of solid water. Position A on the couch was equivalent to 5 cm of solid water. Conclusion QABC+ measurements are more affected by backscatter than conventional ionization chambers, and the Bs are amplified. Slight differences in backscattering conditions may cause false alarms from QABC+. It is recommended that before the use of daily QA instrument, the effects of backscattering conditions on its reading should be determined through experimental measurement, and the positioning conditions should be fixed to ensure the stability of scattering conditions and make daily QA instrument work efficiently, stably and reliably.