γ刀焦点计划剂量与实测剂量相对偏差的测量与分析

Measurement and analysis of the relative deviation between the planned dose and the measured dose of gamma knife

目的测量γ刀焦点计划剂量与实测剂量的相对偏差,分析产生偏差的原因,探讨提高放射治疗剂量准确性的方法。方法使用PTW公司UNIDOS型剂量仪、31010型0.125cc电离室、60019型半导体探测器及山东省医学科学院放射医学研究所研制的RTP-H1型放射治疗质量控制检测模体,按照《X、γ射线立体定向放射治疗系统质量控制检测规范》(WS 582—2017)中的测量方法对1台奥沃公司生产的头部γ刀焦点计划剂量与实测剂量的相对偏差进行测量。焦点计划剂量与实测剂量的相对偏差在±5.0%以内的评价为合格。结果该γ刀4个准直器焦点计划剂量与实测剂量的相对偏差为:-0.31%(18#准直器)、-1.58%(14#准直器)、-0.48%(8#准直器)和0.45%(4#准直器)。结论所检测的该γ刀4个准直器焦点计划剂量与实测剂量的相对偏差全部符合行业标准要求。根据国际原子能机构(IAEA)483号技术报告,使用电离室探测器测量吸收剂量时,电离室探测器有效收集体积的边界和被测照射野边界的距离应满足侧向带电粒子平衡的距离要求。

Objective To measuring the relative deviation between the planned dose and the measured dose ofγknife,analysis the causes of the deviation,in order to improve the accuracy of radiotherapy dose.Methods Using the PTW UNIDOS dosimeter,31010-type 0.125cc ionization chamber,60019-type semiconductor detector and RTP-H1 radiotherapy quality control testing phantom developed by Institute of Radiation Medicine,Shandong Academy of Medicine Sciences,and according to the methods in the Specifications for testing of quality control in X andγray stereotactic radiotherapy system(WS 582—2017),the relative deviation between the planned dose and the measured dose of a head gamma knife produced by Ovo Company was measured.A relative deviation within±5.0%was evaluated to be acceptable.Results The relative deviations between the planned dose and the measured dose of the four collimators were-0.31%(18#collimator),-1.58%(14#collimator),-0.48%(8#collimator)and 0.45%(4#collimator).Conclusion The relative deviations between the planned dose and the measured dose of the four collimators are all meet the requirements of the national standard.According to the International Atomic Energy Agency technical report(IAEA)483,when measuring the absorbed dose using an ionization chamber detector,the distance between the boundary of the effective volume of ionization chamber detector and the boundary of the measured irradiation field should meet the distance requirement for the balance of laterally charged particles.