Monte Carlo simulation of secondary radiation exposure from high-energy photon therapy using an anthropomorphic phantom
Abstract
The development of intensity-modulated radiotherapy treatments delivering large amounts of monitor units (MUs) recently raised concern about higher risks for secondary malignancies. In this study, optimised combinations of several variance reduction techniques (VRTs) have been implemented in order to achieve a high precision in Monte Carlo (MC) radiation transport simulations and the calculation of in- and out-of-field photon and neutron dose-equivalent distributions in an anthropomorphic phantom using MCNPX, v.2.7. The computer model included a Varian Clinac 2100C treatment head and a high-resolution head phantom. By means of the applied VRTs, a relative uncertainty for the photon dose-equivalent distribution of <1 % in-field and 15 % in average over the rest of the phantom could be obtained. Neutron dose equivalent, caused by photonuclear reactions in the linear accelerator components at photon energies of approximately >8 MeV, has been calculated. Relative uncertainty, calculated for each voxel, could be kept below 5 % in average over all voxels of the phantom. Thus, a very detailed neutron dose distribution could be obtained. The achieved precision now allows a far better estimation of both photon and especially neutron doses out-of-field, where neutrons can become the predominant component of secondary radiation.
说的是调强放疗治疗安放了大量的探测单元，最近在引发恶性肿瘤的风险方面引起了高度的关注，使用的是MCNPX 2.7版本，用了一些列的方差减小技巧来使得MC辐射输运结果和人体体模中的场内场外光子和中子剂量分布达到较高的精度