Sukumar Prabakar, Padmanaban Sriram, Rajasekaran Dhanabalan, Kannan Muniyappan, Nagarajan Vivekanandan
Medical Physics Department, Cancer Institute (WIA), India.
Anna University, India.
Rep Pract Oncol Radiother. 2012 Jul 15;17(6):324-31. doi: 10.1016/j.rpor.2012.06.003. eCollection 2012.
In measuring exit fluences, there are several sources of deviations which include the changes in the entrance fluence, changes in the detector response and patient orientation or geometry. The purpose of this work is to quantify these sources of errors.
The use of the volumetric modulated arc therapy treatment with the help of image guidance in radiotherapy results in high accuracy of delivering complex dose distributions while sparing critical organs. The transit dosimetry has the potential of Verifying dose delivery by the linac, Multileaf collimator positional accuracy and the calculation of dose to a patient or phantom.
The quantification of errors caused by a machine delivery is done by comparing static and arc picket fence test for 30 days. A RapidArc plan, created for the pelvis site was delivered without and with Rando phantom and exit portal images were acquired. The day to day dose variation were analysed by comparing the daily exit dose images during the course of treatment. The gamma criterion used for analysis is 3% dose difference and 3 mm distance to agreement with a threshold of 10% of maximum dose.
The maximum standard deviation for the static and arc picket fence test fields were 0.19 CU and 1.3 CU, respectively. The delivery of the RapidArc plans without a phantom shows the maximum standard deviation of 1.85 CU and the maximum gamma value of 0.59. The maximum gamma value for the RapidArc plan delivered with the phantom was found to be 1.2. The largest observed fluence deviation during the delivery to patient was 5.7% and the maximum standard deviation was 4.1 CU.
It is found from this study that the variation due to patient anatomy and interfraction organ motion is significant.
在测量出射注量时，存在多种偏差来源，包括入射注量的变化、探测器响应的变化以及患者的体位或几何形状变化。本研究的目的是对这些误差来源进行量化。
在放射治疗中借助图像引导使用容积调强弧形治疗可在保护关键器官的同时高精度地输送复杂的剂量分布。传输剂量测定法有潜力验证直线加速器的剂量输送、多叶准直器的位置精度以及患者或体模的剂量计算。
通过比较30天的静态和弧形栅栏测试来量化机器输送引起的误差。针对骨盆部位创建的快速弧形计划在不使用和使用朗多体模的情况下进行输送，并采集出射门静脉图像。通过比较治疗过程中的每日出射剂量图像来分析每日剂量变化。用于分析的伽马标准是3%的剂量差异和3毫米的距离一致性，阈值为最大剂量的10%。
静态和弧形栅栏测试野的最大标准偏差分别为0.19 CU和1.3 CU。不使用体模输送快速弧形计划时，最大标准偏差为1.85 CU，最大伽马值为0.59。使用体模输送快速弧形计划时，发现最大伽马值为1.2。在向患者输送过程中观察到的最大注量偏差为5.7%，最大标准偏差为4.1 CU。
本研究发现，由于患者解剖结构和分次间器官运动导致的变化是显著的。
