Murali V, Gopalakrishna Kurup P G, Bhuvaneswari N, Sudahar H, Muthukumaran M
Department of Radiotherapy, Apollo Speciality Hospitals, Chennai - 600 035, India.
J Radiosurg SBRT. 2013;2(2):85-98.
Multiplan treatment planning system, used with Cyberknife system, provides the option of using either the ray tracing algorithm or the Monte Carlo algorithm for the final dose calculation. In order to compare and validate the dose calculations of these algorithms, especially in a heterogeneous medium, a lung phantom study was carried out. Validation has been done with thermoluminiscent dosimetry (TLD) using lithium fluoride rods for the point doses and film dosimetry using EBT2 films for the dose distribution. In the point dose measurements, an agreement of 100.1+2.6 % (1 SD) is observed with the Monte Carlo dose calculation, whereas it is only 91.2+ 3.2% (1 SD) with the ray tracing calculation. On subjecting the dose distributions from irradiated EBT2 films for validation of Monte Carlo calculation MC , over 96% of the pixels pass the gamma criteria of 3mm and 3cGy.On analyzing the dose profiles from EBT2 films and the corresponding profiles from the plan calculated using the Monte Carlo algorithm, it is seen that the maximum distance-to-agreement values are within the 3mm criteria set, whereas the maximum values are as high as 8 mm when compared with plan calculated using ray tracing algorithm. The results of the actual measurements are more consistent with the dose calculation by the Monte Carlo algorithm.
与射波刀系统配合使用的多平面治疗计划系统，提供了在最终剂量计算中使用光线追踪算法或蒙特卡罗算法的选项。为了比较和验证这些算法的剂量计算，特别是在非均匀介质中的剂量计算，进行了一项肺部模体研究。使用氟化锂棒进行热释光剂量测定（TLD）来验证点剂量，使用EBT2薄膜进行胶片剂量测定来验证剂量分布。在点剂量测量中，与蒙特卡罗剂量计算的一致性为100.1±2.6%（1标准差），而与光线追踪计算的一致性仅为91.2±3.2%（1标准差）。对经照射的EBT2薄膜的剂量分布进行蒙特卡罗计算MC验证时，超过96%的像素通过了3mm和3cGy的伽马标准。分析EBT2薄膜的剂量剖面和使用蒙特卡罗算法计算的计划中的相应剖面，可以看出最大距离一致性值在设定的3mm标准范围内，而与使用光线追踪算法计算的计划相比，最大值高达8mm。实际测量结果与蒙特卡罗算法的剂量计算更为一致。
