Evaluation of Inhomogeneity Correction Performed by Radiotherapy Treatment Planning System

Abstract

Aim of this study is to evaluate the efficacy of inhomogeneity corrections calculated by radiotherapy treatment planning system (TPS) using various densities of materials. Gammex Computed tomography electron density inserts (EDI's; 14 no's) were used to generate the CT to ED curve with high speed GE CT scanner by noting down the respective HU values of each rod. Treatment plans were generated in XiO TPS with three inhomogeneous phantoms (comprising combination of water, lung and bone equivalent slabs) with different field sizes and for EDI (8 no's) inserted in slots of acrylic tray and validation was carried out using 2D array detector with 20cm×20cm field size for 200 MU. Point dose and fluence measurements were carried with inhomogeneous phantoms combinations and EDI's (placed on the locally fabricated box filled with water medium). The mean percentage deviations with standard deviation of calculated point doses against measured ones obtained with 2D array detector at iso-center plane for all three inhomogeneous phantom combinations were found to be -1.13%±0.13%, -3.51%±0.14% and -0.63%±0.27% respectively. On point doses measured under each individual EDI, over all percentage deviation with standard deviation observed is -2.04% ± 1.1%. The described method can be implemented in any newly established radiotherapy department as a routine quality measure of TPS to verify its efficacy in performing of inhomogeneity calculation.