基于解剖结构的三维剂量验证系统物理模型测试及应用

Physical model test and application of three-dimensional dose verification system based on anatomical structure

目的:测试基于矩阵探测器测量引导,在患者解剖图像上对计划剂量进行扰动修正的三维剂量验证系统(3DVH)的准确性,评估其临床应用可行性。方法:分别设计一系列固体水模体测试计划,以指型电离室和慢感光胶片测量各测试计划的点剂量和平面剂量;利用3DVH系统得到重建剂量,将计划系统计算剂量和重建剂量分别与上述的测量剂量进行比较,以评估系统剂量重建准确性。分别选取头颈部肿瘤调强放疗(IMRT)计划和前列腺癌容积弧形调强(VMAT)计划各6例,比较计划系统计算剂量和3DVH系统重建剂量,分析系统验证结果的临床意义。结果:就点剂量而言,除6周期振荡窄缝野和模拟C形靶区的IMRT和VMAT计划外,其他测试例的计划系统计算剂量和指型电离室测量剂量的偏差、PDP重建剂量和电离室测量剂量的偏差均不超过3%;就面剂量而言,其他测试例计划系统计算剂量和PDP重建剂量分布的γ通过率(3%/3 mm)均高于98%。6例头颈部肿瘤IMRT计划靶区、PGTVnx、PGTVnd和6例前列腺癌VMAT计划靶区的D95和Dmean的重建偏差均小于3%,γ通过率均高于95%;两种计划的危及器官验证结果为,除IMRT计划左右晶体外,其他器官剂量-体积参数在总体上均有较好的符合率,γ通过率也均高于95%。结论:基于患者解剖结构的3DVH系统是调强剂量验证的一个理想工具,可以提供基于患者解剖信息的剂量验证评估。

Objective To measure the accuracy and evaluate the clinical application of three-dimensional dose verification sys- tem （3DVH） when the planning dose was perturbed and corrected on patients＇ anatomical images with the guidance of the matrix detector. Methods A series of solid water phantom test plans were designed and implemented. The point dose and plane dose were measured separately by the thimble ion-chamber and slow sensitive film. The planning dose was calculated from the planning system, while the reconstructed dose was obtained from 3DVH system. The calculated dose and the reconstructed dose were respectively compared with the measured dose to evaluate the accuracy of dose verification system. Six intensity modulated radiotherapy （IMRT） plans for head and neck neoplasms and six volumetric modulated arc therapy （VMAT） plans for prostate cancer were selected to compare with the dose calculated from the planning system and the reconstructed dose obtained from 3DVH system and to analyze the clinical significance of system verification results. Results Except the IMRT and VMAT plans of six periods oscillating sweeping gap field and mock C shape target, the deviation of the point dose calculated from planning system, and point dose measured by thimble ion-chamber, and that of planned dose perturbation （PDP） reconstructed point dose and measured point dose were not more than 3%. Comparing to the plane dose measured by slow sensitive film, the 7 passing rates （3%/3 mm） of plane dose calculated from planning systems and PDP reconstructed plane dose distribution were above 98%. The reconstructed deviations were all within 3% for the planning target volume （PTV）, PGTVnx, PGTVod of six IMRT plans for head and neck neoplasms, and D95 and Dmean of the PTV of six VMAT plans for prostate cancer, and their γ passing rates were all above 95%. Except the lens oflMRT plans, the dose-volume parameters of other organs at risk had a better coincidence rate and the γ passing rates were all higher than 95%. Conclusion The 3DVH based on patients＇ anatomical structure is a practical instrument for IMRT quality assurance, providing dose verification assessment based on anatomical structure.