Supervisors info:
Εμφιετζόγλου Δημήτριος, Καθηγητής, Τμήμα Ιατρικής, Πανεπιστήμιο Ιωαννίνων
Αστρακάς Λουκάς, Αναπληρωματικός Καθηγητής, Τμήμα Ιατρικής, Πανεπιστήμιο Ιωαννίνων
Κυριακού Ιωάννα, Επίκουρη Καθηγήτρια, Τμήμα Ιατρικής, Πανεπιστήμιο Ιωαννίνων
Summary:
Background: Historically, the term “radiation quality” commonly refers to the type and energy of the radiation. Radiations of different quality often exhibit different relative biological effectiveness (RBE). To describe radiation-induced stochastic effects (like carcinogenesis) at low doses, the RBE is commonly replaced by the quality actor (Q). However, due to the high dispersion of experimental RBE values, it’s not yet possible to determine Q precisely. Thus, radiation protection organizations often use recommend different Q-values based on their methodologies. The aim of this work is to calculate the energy-dependence of Q for different hadron beams using various established analytic models.
Materials and Methods: Q-values over the energy range 1-1000 MeV/u were calculated for protons, helium, carbon, and oxygen ions using the standard Q(LET) expressions recommended by ICRP (Report 60), NASA’s z2/β2 track-structure model, the microdosimetric Theory of Dual Radiation Action, and Q(y) formulation suggested by ICRU (Report 40). For the microdosimetric-based methods, TDRA and ICRU, the stochastic distribution of microdosimetric lineal energy (y) was calculated through the Xapsos’s generalized analytic model using different energy-loss straggling distributions (Lognormal, Logistic and Erlang). All calculations refer to water medium.
Results: All models predict higher Q-values near the end of the ion track. For protons, Q becomes maximum at about 1 MeV/u while for the other hadrons Q is maximum in the range of 5-40 MeV/u depending on the ion type. For all ions, the ICRU methodology predicts the highest Q-values. Differences of proton Q-values among models become largest at low energies, whereas for heavier ions differences are largest for energies above 100 MeV/u.
Conclusions: The quality factor (Q) depends upon the type and energy of the ion but the exact dependence strongly varies with the adopted calculation methodology. Moreover, all models exhibit notable deviations from the LET-based recommendations of ICRP Report 60, especially the ICRU methodology that deviates on average ~100-200% depending on the ion type. The microdosimetric models (TDRA, ICRU) show similar trends and seem to predict the highest Q-values compared to both ICRP and NASA.
Keywords:
Quality factor, Q, Hadrons, Radiation protection
