School of Mathematical and Physical Sciences, The University of Newcastle, NSW 2308, Australia.
Med Phys. 2013 Aug;40(8):081715. doi: 10.1118/1.4816384.
Pretreatment verification of volumetric modulated arc therapy (VMAT) dose delivery with electronic portal imaging device (EPID) uses images integrated over the entire delivery or over large subarcs. This work aims to develop a new method for gantry-angle-resolved verification of VMAT dose delivery using EPID.
An EPID dose prediction model was used to calculate EPID images as a function of gantry angle for eight prostate patient deliveries. EPID image frames at 7.5 frames per second were acquired during delivery via a frame-grabber system. The gantry angle for each image was encoded in kV frames which were synchronized to the MV frames. Gamma analysis results as a function of gantry angle were assessed by integrating the frames over 2° subarcs with an angle-to-agreement tolerance of 0.5° about the measured image angle.
The model agreed with EPID images integrated over the entire delivery with average Gamma pass-rates at 2%, 2 mm of 99.7% (10% threshold). The accuracy of the kV derived gantry angle for each image was found to be 0.1° (1 SD) using a phantom test. For the gantry-resolved analysis all Gamma pass-rates were greater than 90% at 3%, 3 mm criteria (with only two exceptions), and more than 90% had a 95% pass-rate, with an average of 97.3%. The measured gantry angle lagged behind the predicted angle by a mean of 0.3°±0.3°, with a maximum lag of 1.3°.
The method provides a comprehensive and highly efficient pretreatment verification of VMAT delivery using EPID. Dose delivery accuracy is assessed as a function of gantry angle to ensure accurate treatment.
使用电子射野影像装置（EPID）对容积调强弧形治疗（VMAT）剂量传递进行预处理验证时，会综合整个传递过程或大的亚弧来使用图像。本研究旨在开发一种使用 EPID 进行机架角度分辨 VMAT 剂量传递验证的新方法。
使用 EPID 剂量预测模型来计算 8 例前列腺患者治疗的机架角度与 EPID 图像之间的关系。通过帧抓取系统在治疗过程中以每秒 7.5 帧的速度获取 EPID 图像帧。将每个图像的机架角度编码到千伏帧中，这些千伏帧与兆伏帧同步。通过在 2°的亚弧上对图像进行积分，并将测量图像角度的 0.5°角度容差作为角度一致性的容差，来评估作为机架角度函数的伽马分析结果。
该模型与整个治疗过程中综合的 EPID 图像吻合良好，2%、2mm 时的平均伽马通过率为 99.7%（10%的阈值）。通过对体模的测试发现，每张图像的千伏衍生机架角度的精度为 0.1°（1 个标准差）。对于机架分辨分析，所有伽马通过率在 3%、3mm 标准下均大于 90%（仅有两个例外），超过 90%的通过率达到 95%，平均通过率为 97.3%。测量的机架角度滞后于预测的角度，平均滞后 0.3°±0.3°，最大滞后 1.3°。
该方法提供了一种使用 EPID 对 VMAT 传递进行全面且高效的预处理验证的方法。通过评估剂量传递与机架角度的关系，确保了治疗的准确性。
