Microdosimetry-based quality factors for ISO reference photon and beta sources: TOPAS Monte Carlo study

Abstract

In radiological protection, personnel dosimeters are calibrated in terms of operational quantities such as H p (10) and H p (0.07) against ISO reference photon and beta sources, respectively. H p (10) and H p (0.07) are defined at 1 cm and 0.07 μm depths in the ICRU-4 element tissue phantom. In present study, mean quality factor Q̅ is calculated at these depths using the TOPAS-based microdosimetric distributions at 1 μm site size and FLUKA-based Linear Energy Transfer (LET) dependent Q̅. The sources simulated are ISO reference narrow series X-rays, 137Cs and 147Pm, 85Kr, 90Sr/90Y and 106Ru/106Rh beta sources. Using the calculated microdosimetric distributions, Q̅ is calculated based on ICRP60 and ICRU40 recommendations, Keller-Hahn (KH) approximation, Microdosimetric Kinetic Model (MKM), Clonogenic Survival and Theory of Dual Radiation Action (TDRA). The study includes FLUKA-based Q̅ values calculated using Q(L) vs L relationship as per ICRP Report 60. The MKM, Clonogenic Survival-based RBE, ICRU40, TDRA and KH-based Q values of all the investigated sources are about unity. Depending on the source, microdosimetry-based Q̅ values using ICRP60 recommendations show significant difference from that calculated using other models. Q̅ values of 137Cs are unity, independent of the models.