Chow Vivian U Y, Kan Monica W K, Chan Anthony T C
Department of Clinical Oncology, Prince of Wales Hospital, Hong Kong SAR, China.
Department of Clinical Oncology, The Chinese University of Hong Kong, Hong Kong SAR, China.
J Appl Clin Med Phys. 2020 Nov;21(11):179-187. doi: 10.1002/acm2.13053. Epub 2020 Oct 19.
An in-house trajectory log analysis program (LOGQA) was developed to evaluate the delivery accuracy of volumetric-modulated arc therapy (VMAT) for stereotactic body radiation therapy (SBRT). Methods have been established in LOGQA to provide analysis on dose indices, gantry angles, and multi-leaf collimator (MLC) positions. Between March 2019 and May 2020, 120 VMAT SBRT plans of various treatment sites using flattening filter-free (FFF) mode were evaluated using both LOGQA and phantom measurements. Gantry angles, dose indices, and MLC positions were extracted from log and compared with each plan. Integrated transient fluence map (ITFM) was reconstructed from log to examine the deviation of delivered fluence against the planned one. Average correlation coefficient of dose index versus gantry angle and ITFM for all patients were 1.0000, indicating that the delivered beam parameters were in good agreement with planned values. Maximum deviation of gantry angles and monitor units (MU) of all patients were less than 0.2 degree and 0.03 % respectively. Regarding MLC positions, maximum and root-mean-square (RMS) deviations from planned values were less than 0.6 mm and 0.3 mm respectively, indicating that MLC positions during delivery followed planned values in precise manner. Results of LOGQA were consistent with measurement, where all gamma-index passing rates were larger than 95 %, with 2 %/2 mm criteria. Three types of intentional errors were introduced to patient plan for software validation. LOGQA was found to recognize the introduced errors of MLC positions, gantry angles, and dose indices with magnitudes of 1 mm, 1 degree, and 5 %, respectively, which were masked in phantom measurement. LOGQA was demonstrated to have the potential to reduce or even replace patient-specific QA measurements for SBRT plan delivery provided that the frequency and amount of measurement-based machine-specific QA can be increased to ensure the log files record real values of machine parameters.
开发了一个内部轨迹日志分析程序（LOGQA）来评估立体定向体部放射治疗（SBRT）中容积调强弧形治疗（VMAT）的照射准确性。LOGQA中已建立了相关方法，以对剂量指数、机架角度和多叶准直器（MLC）位置进行分析。在2019年3月至2020年5月期间，使用LOGQA和模体测量对120个采用无均整器（FFF）模式的不同治疗部位的VMAT SBRT计划进行了评估。从日志中提取机架角度、剂量指数和MLC位置，并与每个计划进行比较。从日志中重建积分瞬态注量图（ITFM），以检查实际注量与计划注量的偏差。所有患者剂量指数与机架角度以及ITFM的平均相关系数均为1.0000，表明实际射束参数与计划值高度吻合。所有患者的机架角度和监测单位（MU）的最大偏差分别小于0.2度和0.03%。关于MLC位置，与计划值的最大偏差和均方根（RMS）偏差分别小于0.6毫米和0.3毫米，表明照射过程中MLC位置精确地遵循计划值。LOGQA的结果与测量结果一致，其中所有伽马指数通过率均大于95%，标准为2%/2毫米。为了进行软件验证，在患者计划中引入了三种类型的故意误差。结果发现，LOGQA能够识别分别为1毫米、1度和5%量级的MLC位置、机架角度和剂量指数的引入误差，这些误差在模体测量中被掩盖了。结果表明，只要基于测量的特定机器质量保证的频率和数量能够增加，以确保日志文件记录机器参数的真实值，LOGQA就有可能减少甚至取代SBRT计划照射的患者特定质量保证测量。
