20-1000keV 能区光子束的 VMC++ 验证。

VMC++ validation for photon beams in the energy range of 20-1000 keV.

机构信息

Division of Medical Radiation Physics, Inselspital and University of Berne, CH-3010 Berne, Switzerland.

出版信息

Med Phys. 2010 Oct;37(10):5218-27. doi: 10.1118/1.3488892.

DOI:10.1118/1.3488892

PMID:21089755

Abstract

PURPOSE

In high energy teletherapy, VMC++ is known to be a very accurate and efficient Monte Carlo (MC) code. In principle, the MC method is also a powerful dose calculation tool in other areas in radiation oncology, e.g., brachytherapy or orthovoltage radiotherapy. However, VMC++ is not validated for the low-energy range of such applications. This work aims in the validation of the VMC++ MC code for photon beams in the energy range between 20 and 1000 keV.

METHODS

Dose calculations were performed in different 40 x 40 x 40 cm3 phantoms of different materials. Dose distributions of monoenergetic (ranging from 20 to 1000 keV) 10 x 10 and 2 x 2 cm2 parallel beams were calculated. Voxel sizes of 4 x 4 x 4 and 1 x 1 x 1 mm3 were used for the dose calculations. The resulting dose distributions were compared to those calculated using EGSnrc, which is used as a golden standard in this work.

RESULTS

At energies between 100 and 1000 keV, EGSnrc and VMC++ calculated dose distributions agree within the statistical uncertainty of about 1% (1sigma). At energies < or = 50 keV, dose differences of up to 1.6% (in % of D(max)) occur when VMC++ and EGSnrc are compared. Turning off Rayleigh scattering, binding effects for Compton scattering, and the atomic relaxation after photoelectric absorption in EGSnrc (all not implemented in VMC++) leads to an agreement between both MC codes within statistical uncertainty. Further, using the KERMA approximation feature implemented in VMC++ leads to very efficient simulations in the energy range between 20 and 1000 keV.

CONCLUSIONS

Further improvements for very low energies in accuracy of VMC++ could be achieved by implementing Rayleigh scattering, binding effects for Compton scattering, and the atomic relaxation after photoelectric absorption. Implementation into VMC++ of KERMA approximation has been validated.

摘要

目的

在高能远距离放射治疗中，VMC++是一种非常精确和高效的蒙特卡罗（MC）代码。原则上，MC 方法也是放射肿瘤学中其他领域（例如近距离放射治疗或正交千伏放射治疗）强大的剂量计算工具。然而，VMC++尚未针对此类应用的低能范围进行验证。本工作旨在验证 VMC++ MC 代码在 20keV 至 1000keV 光子束范围内的性能。

方法

在不同材料的 40x40x40cm3 体模中进行剂量计算。计算了单能（范围 20keV 至 1000keV）10x10 和 2x2cm2 平行束的剂量分布。使用 4x4x4 和 1x1x1mm3 的体素大小进行剂量计算。将计算得到的剂量分布与使用 EGSnrc 计算的结果进行比较，EGSnrc 在本工作中用作金标准。

结果

在 100keV 至 1000keV 能量范围内，EGSnrc 和 VMC++ 计算的剂量分布在约 1%（1sigma）的统计不确定性内一致。在能量≤50keV 时，当 VMC++ 和 EGSnrc 进行比较时，会出现高达 1.6%（D(max)的百分比）的剂量差异。在 EGSnrc 中关闭瑞利散射、康普顿散射的束缚效应以及光电吸收后的原子弛豫（均未在 VMC++ 中实现）会导致两个 MC 代码在统计不确定性内一致。此外，在 VMC++ 中使用 KERMA 近似功能可在 20keV 至 1000keV 的能量范围内实现非常高效的模拟。