APPLICABILITY OF PURE PROPANE GAS FOR MICRODOSIMETRY AT BRACHYTHERAPY ENERGIES: A FLUKA STUDY

Applicability of pure propane gas for microdosimetric measurements at photon energies relevant in brachytherapy is studied using the Monte Carlo-based FLUKA code. Monoenergetic photons in the energy range of 20-1250 keV and brachytherapy sources such as 103Pd, 125I, 169Yb, 192Ir, 137Cs and 60Co are considered in the study. Using the calculated values of energy deposited in the sensitive region of LET-1/2 tissue-equivalent proportional counter filled with pure propane gas and tissue-equivalent propane gas, values of density scaling factor for the site sizes of 1 and 8 μm are obtained. The study shows that density of propane gas should be lowered by a factor of about 0.93 for 169Yb, 192Ir, 137Cs and 60Co sources for the site sizes of 1-8 μm. For 125I source, the density of propane gas requires a scaling of 0.93 for 1 μm site size, whereas for site sizes 2-8 μm, density need not be altered. 103Pd source does not require density scaling for site sizes 1-8 μm.