Effect of inhomogeneity on accuracy of various IMRT dose calculation models / 中华放射医学与防护杂志

ABSTRACT

Objective To investigate the dosimetric performance of two algorithms for correcting the presence of tissue inhomogeneities,the finite site pencil beam (FSPB) and X-ray voxel Monte Carlo (XVMC) plans were implemented in the MONACO system,with the accuracy of application to clinic treatment of two algorithms were evaluated.Methods In a non-uniform artificial anthropomorphic phantom,regular open fields and intensity modulation radiated therapy (IMRT) plans of the MONACO were measured by using calibrated EBT2 films,and the dose accuracy of the two kinds of plans was analyzed by comparing the planned and measured plane dose.Results In an anthropomorphic phantom,the deviations between the calculated values by XVMC and the measured values by films were less than ± 2％.While the deviations of FSPB values between calculation and measurements was within ± 3％,except at the condition of 15 MV,10 cm ×2 cm field,the dose error in lung was up to 6.51％.The verification of individual IMRT beams based on films showed that the pass rates of calculation by XVMC and FSPB were larger than 90％ with γ criterion of 3％/3 mm and 4％/4 mm,respectively.At 3％/3 mm,the pass rates of FSPB were in the range of 80％-90％.At the same time,the pass rates of all individual fields were higher than 90％.Conclusions The accuracy of dose calculation of XVMC is better than that of FSPB when being in multi-segments and non-uniform media.The error of algorithm can be controlled within ±3％,for the calculation by XVMC.And the dose deficiency of PTV arising from algorithm can be avoided.