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, () and phantom scatter correction, () for lithium formate dosimeter as a function of distance r along the transverse axis of the high-energy brachytherapy sources Co, Cs, Ir and Yb using the Monte Carlo-based EGSnrc code system.

Materials And Methods: The brachytherapy sources investigated in this study are BEBIG High Dose Rate (HDR) Co (model Co0.A86), Cs (model RTR), HDR Ir (model Microselectron) and HDR Yb (model 4140). The solid phantom materials investigated are PMMA, polystyrene, solid water, virtual water, plastic water, RW1, RW3, A150 and WE210.

Result: () is about unity and distance independent fo Co, Cs and Ir brachytherapy sources, whereas for the Yb source, () increases gradually to about 4 % larger than unity at a distance of 15 cm along the transverse axis of the source. For Co 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 () values. For Cs and Ir 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 () values, for these sources. For Yb source, all the investigated phantoms show distance-dependent () values.

Conclusion: () is about unity and distance independent for Co, Cs and Ir brachytherapy sources. Phantoms such as solid water, virtual water, RW1, RW3 and WE210 are water-equivalent for Co, Cs and Ir brachytherapy sources. For Yb source, all the investigated phantoms show distance-dependent () values.