治疗床及固定装置对容积旋转调强放疗剂量衰减的影响及其校正方法的评估

Impact of treatment couch and immobilization device on VMAT radiotherapy dose and its correction method

目的:研究治疗床、固定装置对容积旋转调强放疗(VMAT)剂量衰减的影响,并对剂量校正方法进行评估。方法:分别将固体水置于治疗床的薄、中、厚3个部分,执行无治疗床的VMAT计划,测量固体水中心的剂量,然后修正治疗床,并实测剂量。在固体水上表面放置一块固定架,执行一个未将体位固定装置勾画进外轮廓的VMAT计划,然后修正体位固定装置。将固体水连同下方的固定架分别放置于治疗床的薄、中、厚3个部分上,执行未进行治疗床和体位固定装置剂量校正VMAT计划,然后修正治疗床和体位固定装置。结果:治疗床薄、中、厚3个部分的剂量衰减影响分别为1.63%、2.18%、3.17%,校正后剂量影响只有0.36%、0.20%和0.04%。固定装置导致的剂量偏差为2.61%,校正后的剂量影响只有-0.68%。薄、中、厚治疗床加固定装置整体的剂量影响分别为3.86%、4.66%、5.57%,校正后的剂量影响只有-0.24%、-0.33%、-0.57%。结论:治疗床和固定装置会导致VMAT计划剂量衰减,通过在CT图像中加入虚拟治疗床和将固定装置包含进外轮廓的校正方法是有效的。

Objective:To investigate the effect of treatment couch,immobilization devices on the radiation dose attenuation for volumetric modulation arc therapy(VMAT),and to evaluate the accuracy of the recommended dose correction method.Methods:The solid water phantom was placed on the thin,medium,and thick parts of the treatment couch,respectively.The VMAT plans with no treatment couch were performed,and these VMAT plans were corrected and measured.The carbon fiber was placed on the upper surface of the solid water;a VMAT plan excluding the outer contour of immobili-zation device was performed,corrected,and measured.The solid water was placed on the thin,medi-um,and thick parts of the treatment couch,respectively,with the carbon fiber below.The VMAT plans with uncorrected doses were performed.These VMAT plans were corrected and measured.Results:The dose attenuation of the thin,medium and thick parts of the treatment bed reached1.63%,2.18%and 3.17%,respectively,and the dose attenuation after calibration were only0.36%,0.20%and 0.04%,respectively.The dose attenuation of immobilization device was2.61%,and the corrected dose attenuation was only-0.68%.The overall dose attenuation of thin,medium and thick treatment bed was 3.86%,4.66%,and 5.57%,respectively.The corrected dose attenuation was only-0.24%,-0.33%,and-0.57%,respectively.Conclusion:The treatment couch and immobilization device have impact on dose attenuation in VMAT radiotherapy.It is recom-mended to insert a virtual treatment couch and include the external contour of the immobilization de-vice.