Percentage depth dose evaluation in heterogeneous media using thermoluminescent dosimetry

Abstract

 The purpose of this study was to investigate the influence of lung heterogeneity on percentage depth dose (PDD) inside a soft tissue phantom. PDD curves were obtained experimentally through the use of LiF:Mg,Ti (TLD-100) thermoluminescent detectors and employing Eclipse treatment planning system algorithms Batho, Modified Batho, Equivalent TAR and anisotropic analytical algorithm (AAA) for a 15MV photon beam and field sizes of 1x1, 2x2, 5x5 and 10x10cm². Monte Carlo simulations were performed using the DOSRZnrc user code of EGSnrc. The experimental results agree to Monte Carlo simulations for all irradiation field sizes. Comparisons to Monte Carlo calculations show that the AAA can not accurately predict PDD values in lung for field sizes as 1 x 1 cm² and 2 x 2 cm². It was demonstrated that differences of 100% exist inside the lung region for the 1x1cm² field for the algorithms Batho, Modified Batho and Equivalent TAR .