An assessment of dose enhancement factor for 170Tm and 125I brachytherapy sources in presence of activation elementsusing Monte Carlo method

Background and Photon activation therapy is a radiation technique in which the energy deposition within a tumor can be increased by provoking the emission of Auger electrons emitted through photoelectric effect, through the addition of high Z elements. In this process the DNA molecules are as targets for the Auger electrons which are emitted from high Z atoms. The aim of this study is to assess dose enhancement factor for 170Tm and 125I brachytherapy sources, in photon activation therapy in presence of various activation elements in tumor, using Monte Carlo method. In present study 125I source Iso Aid Advantage (model IA1-125A) and a hypothetical 170Tm source were simulated usingMonte Carlo code MCNPX. Calculating and verifying TG-43 parameters, dose enhancement factor on the transverse axis in presence of activation elements like Pt, Ag, gold and iodine inside tumor obtained with the concentration of 7, 18 and 30 mg/ml in photon activation therapy, individually. Dose rate constant and radial dose functions for the sources were in agreement with the previous studies. Maximum dose enhancement factor obtained 4.87 which belongs to 170Tm with the concentration of 30 mg/ml. DEF for 170Tm source was more than 125I in the presence of all activation elements. In DEF point of view, using gold inside tumor can be more beneficial in photon activation therapy. Also 170Tm brachytherapy source is recommended in photon activation therapy.