Yamamoto Tokihiro, Teshima Teruki, Miyajima Satoshi, Matsumoto Masao, Shiomi Hiroya, Inoue Takehiro, Inoue Toshihiko, Hirayama Hideo
Department of Medical Engineering, Osaka University Graduate School of Medicine, Suita, Japan.
Radiat Med. 2002 Nov-Dec;20(6):305-10.
A Monte Carlo (MC) model of CyberKnife was developed as a quality assurance tool. The percentage depth dose (%dd) was verified by using this model.
An MC model was developed with Electron Gamma Shower version 4 (EGS4) in two steps: (1) a model of the CyberKnife treatment head and (2) a model of the collimator and phantom. The bremsstrahlung spectrum was calculated using the first model, and this spectrum was then used to calculate %dds with the second model. The calculated %dds for a large field (60 mm diameter) and three small fields (30, 15, and 5 mm diameter) were compared with those measured with a diamond detector.
The MC-calculated and measured %dd-curves for the 60 mm diameter field were in excellent agreement (<1.85%), thus confirming the validity of the model. Discrepancies between the calculated and measured %dd-curves increased with decreasing field size, with considerable discrepancy (11.62%) for the 5 mm diameter field due to lateral electron disequilibrium. Accurate dose can be determined with MC even in small fields.
The MC technique can provide reliable standard data for accurate dose delivery with high-technology radiotherapies using small beams.
开发一种射波刀的蒙特卡罗（MC）模型作为质量保证工具。使用该模型对百分深度剂量（%dd）进行验证。
使用电子伽马射线模拟程序第4版（EGS4）分两步开发MC模型：（1）射波刀治疗头模型和（2）准直器与体模模型。使用第一个模型计算轫致辐射谱，然后用该谱通过第二个模型计算%dd。将大野（直径60 mm）和三个小野（直径30、15和5 mm）计算得到的%dd与用金刚石探测器测量得到的结果进行比较。
直径60 mm射野的MC计算%dd曲线与测量曲线吻合良好（<1.85%），从而证实了模型的有效性。计算得到的%dd曲线与测量曲线之间的差异随射野尺寸减小而增大，由于横向电子不平衡，直径5 mm射野的差异相当大（11.62%）。即使在小野中，MC也能准确确定剂量。
MC技术可为使用小射束的高科技放射治疗准确输送剂量提供可靠的标准数据。
