Monte Carlo Calculation of Beam Quality and Phantom Scatter Corrections for Lithium Formate Electron Paramagnetic Resonance Dosimeter for High-energy Brachytherapy Dosimetry

PURPOSE To investigate beam quality correction, KQQ0 (r) and phantom scatter correction, Kphan (r) for lithium formate dosimeter as a function of distance r along the transverse axis of the high-energy brachytherapy sources 60Co, 137Cs, 192Ir and 169Yb using the Monte Carlo-based EGSnrc code system. MATERIALS AND METHODS The brachytherapy sources investigated in this study are BEBIG High Dose Rate (HDR) 60Co (model Co0.A86), 137Cs (model RTR), HDR 192Ir (model Microselectron) and HDR 169Yb (model 4140). The solid phantom materials investigated are PMMA, polystyrene, solid water, virtual water, plastic water, RW1, RW3, A150 and WE210. RESULT KQQ0 (r) is about unity and distance independent fo 60Co, 137Cs and 192Ir brachytherapy sources, whereas for the 169Yb source, KQQ0 (r) increases gradually to about 4 % larger than unity at a distance of 15 cm along the transverse axis of the source. For 60Co source, phantoms such as polystyrene, plastic water, solid water, virtual water, RW1, RW3 and WE210 are water-equivalent but PMMA and A150 phantoms show distance-dependent Kphan (r) values. For 137Cs and 192Ir sources, phantoms such as solid water, virtual water, RW1, RW3 and WE210 are water-equivalent. However, phantoms such as PMMA, plastic water, polystyrene and A150 showed distance-dependent Kphan (r) values, for these sources. For 169Yb source, all the investigated phantoms show distance-dependent Kphan (r) values. CONCLUSION KQQ0 (r) is about unity and distance independent for 60Co, 137Cs and 192Ir brachytherapy sources. Phantoms such as solid water, virtual water, RW1, RW3 and WE210 are water-equivalent for 60Co, 137Cs and 192Ir brachytherapy sources. For 169Yb source, all the investigated phantoms show distance-dependent Kphan (r) values.