EVALUATION OF CHANGES IN DOSE DISTRIBUTIONS IN THE PRESENCE OF TISSUE INHOMOGENITY OF BRAKITHERAPY TREATMENT PLANNING SYSTEMS BY DOSIMETRIC METHODS
Project no. 90 · Status: Kapanmış · 2017
Summary
Aim: The aim of the study is to investigate the dose changes in target volume and surrounding organs at risk in the presence and absence of tissue inhomogeneities for brachytherapy treatment. Materials and Methods: For dose measurements; 30x30x30 cm3 water phantom, Gafchromic EBT3 film, MicroSelectron high dose rate (HDR) brachytherapy treatment device (Ir-192) and 4x4 cm2 field sizes with 0.5, 1, 1.5, 2 and 2.5 cm thickness materials for air, fungus for lung and teflon for bone inhomogeneity were used. Dose measurements were taken by placing films at 0.5, 1, 1.5 and 2 cm distances from the materials positioned next to the source in the phantom filled with water. Dose measurement values in inhomogeneity materials were normalized to dose measurement values in water and the effect of inhomogenities on dose was determined. Results: In the presence of air and lungs, for the thinnest inhomogeneity material thickness from the source to the determined furthest distance from the water, average is 1.22% and 0.78%, respectively, the dose increase by 9.00% and 6.69% for the thickest inhomogeneity material, and -1.53% and -6.38% dose reduction was determined for bone. The dose effect of inhomogeneous materials relative to water increases with thickness and generally with distance. Conclusions:For TPS systems that do not take into account the effect of inhomogenities of different intensity on dose distribution in treatment areas and surroundings and make dose calculation according to a homogeneous water environment, necessary dose correction factors should be applied and it is recommended to use TPS that takes into account the inhomogeneity effects.