空气压缩设备故障引起的螺旋断层放射治疗患者计划验证通过率偏低的案例分析

A case analysis of low pass rate of helical tomotherapy patient plan verification caused by air compression equipment failure

目的:分析影响螺旋断层放射治疗患者计划验证通过率的因素,解决通过率偏低的问题。方法:对以下因素逐一进行验证分析:①对ArcCHECK刻度文件重新校准,验证绝对剂量准确性;②对ArcCHECK矩阵校准文件重新校正,验证矩阵一致性;③利用第三方Matlab平台开源代码进行离线验证,测量计划系统剂量计算准确性;④通过每日输出点剂量测量和TomoDose测量,验证加速器输出量稳定性;⑤执行AAPM TG-148号报告第V.B.2.c项目和设计临床上常用的2.5 cm和5 cm铅门(Jaw)宽度的适形计划,验证Jaw到位精度;⑥设计临床中常用的2.5 cm和5 cm铅门宽度的适形计划和调强计划,验证多叶准直器(MLC)开关时间精度。结果:执行Arc CHECK刻度文件校准和矩阵重新校准之后,计划测试通过率无明显变化;Matlab离线验证脚本获取计划Gamma通过率,结果均在95%以上;晨检记录显示,加速器固定输出量偏差都小于2%,TomoDose结果表明加速器运行稳定;执行AAPM TG-148号报告第V.B.2.c项目检测Jaw到位精度的结果均在误差范围之内,2.5 cm与5 cm不同铅门宽度条件下适形计划,Gamma测试结果以及点剂量测量结果无明显差别;不同计划下点剂量验证误差随靶区形状不规则程度、计划复杂程度和Jaw增加而升高,证明MLC开关时间精度为主要故障因素。结论:排除多种影响因素后最终确定空气压缩设备故障引起的MLC开关时间精度问题才是导致验证通过率较差的主要原因。因此定期维护和保养空气压缩设备十分必要,同时在物理师执行质量保证项目时,应将空气压缩设备内容加入其中。

Objective Factors affecting the pass rate of helical tomotherapy(HT)patient plan verification were analyzed to solve the problem of low pass rate.Methods The following factors were verified and analyzed one by one:①The Arc CHECK scale files were recalibrated to verify the absolute dose accuracy;②The ArcCHECK matrix calibration files were recalibrated to verify the matrix consistency;③The dose calculation accuracy of the planning system was measured by off-line verification using opensource code of the third-party Matlab platform;④The stability of accelerator output was verified through daily output point dose measurement and Tomo Dose measurement;⑤The Jaw in-position accuracy was verified by performing the AAPM TG-148 report V.B.2.c Project and designing the conformal radiation(3 DCRT)plans with the field width of 2.5 cm and 5 cm commonly used in clinical practice;⑥The multi-leaf collimator(MLC)switching time accuracy was verified by designing 3 DCRT plans and intensity-modulation radiation therapy(IMRT)plans with the field width of 2.5 cm and 5 cm commonly used in clinical practice.Results There was no significant change in the plan test pass rate after the ArcCHECK scale files calibration and matrix recalibration;the Gamma pass rate of the plan obtained by off-line verification script of Matlab was above 95%;the morning inspection record showed that the fixed output deviation of the accelerator was less than 2%,and the TomoDose results showed that the accelerator operated stably;the results of Jaw in-position accuracy detected by implementing AAPM TG-148 report V.B.2.c project were within the error range,and Gamma test results and point dose measurement results showed no significant difference in the 3 DCRT plans under the conditions of different field width of 2.5 cm and 5 cm;the point dose verification error increased with the increase of target shape irregularity,plan complexity,and jaw under different plans,which proves that the accuracy of MLC switching time is the main fault factor.Conclusion After excluding a variety of influencing factors,MLC switching time accuracy caused by the failure of the air compression equipment is the main reason for the low verification pass rate after eliminating multiple contributing factors.Therefore,it is necessary to maintain the air compression equipment regularly.At the same time,the content of air compression equipment should be added in the quality assurance project performed by physicists.