基于电子射野影像装置的容积调强弧形治疗二维剂量验证研究

The study of two-dimensional dosimetric verifications of volumetric intensity-modulated arc therapy based on electronic portal imaging devices

目的基于电子射野影像装置（EPID）建立二维剂量精确重建模型并验证容积调强弧形治疗（VIMAT）剂量，与其他测量工具进行比较与分析。方法采用EPID进行VIMAT的二维剂量验证，基于卷积、反卷积以及修正函数建立二维剂量重建模型。通过电离室测量的离轴比剂量曲线并用最小二乘法确定计算模型参数。对12例不同部位肿瘤患者的VIMAT计划用电离室测量中心点剂量，采用其他平面剂量测量工具测量相应平面剂量分布。所有工具测量深度均设置为10cm，并采用γ分析法比较测量结果。结果对中心点绝对剂量，EPID与电离室测量结果偏差〈1．5％。对平面剂量，2％2mm标准下EPID与Seven29、Matrixx的平均叮通过率分别为98．9％、99．8％，3％3mm标准下EPID与治疗计划系统计算结果的平均γ通过率为99．9％。结论基于EPID建立的二维剂量重建模型能很好地用于调强放疗二维剂量验证工作，今后将考虑将该模型拓展到均匀模体的三维剂量验证中。

Objective To develop an accurate 2D dose reconstruction model using electronic portal imaging device （EPID）. 2D dosimetric verifications of volumetric intensity-modulated arc therapy （VIMAT） were done using the model. And the results were compared to other dosimeters. Methods The EPID-based dose reconstruction model was using convolve, deconvolve and correction function. The dose profiles which were obtained by the ion chamber were used to determine the model parameters. A total of 12 VIMAT plans for the treatment of anatomical sites of various complexities were chosen. The results obtained from EPID were compared to other dosimeters and treatment planning system （TPS）. The ion chamber was used to measure the central point absolute doses. Other dosimeters were used to measure the plane dose distributions. All dosimeters measured the dose at 10 cm depth. The results were analyzed using ~/- evaluation method. Results Regarding absolute central point doses, the ion chamber results were within 1.5% of the EPID results. For the comparison to Seven29 and Matrixx, the average γ pass rates with 2% and 2 mm criteria were 98.9% and 99. 8% respectively. For the dose distributions measured by EPID and calculated by TPS, the γ pass rates with 3% and 3 mm criteria were 99. 9%. Conclusions The presented results which were obtained from the comparison of measured and calculated doses show the reliability of our EPID-based dose reconstruction model. With the model, EPID can be a reliable and fast tool for IMRT plan dosimetric verification. The model expanded to the 3D dosimetric verification in the uniform phantom will be considered as the next work.