Equivalent Dose Calculation Using Simulated Rbe for Alpha Particles from an Alpha Dart Source (224Ra)
Abstract
Purpose
Calculation of the equivalent dose in Diffusing alpha-emitters Radiation Therapy (Alpha DaRT) depends strongly on the spatial dose distribution and the radiobiological impact of emitted alpha particles [1-3]. Current practice in clinical treatment planning systems is to use a constant RBE value of 5 for the alpha dose.
Methods
In this study, we used Geant4-DNA track-structure simulations to evaluate the radiobiological effectiveness (RBE) of DNA double-strand breaks (RBEDSB) and single-strand breaks (RBESSB) as functions of distance from the source. Co-60 was used as a standard reference beam We calculated the atomic fractions and associated alpha energy spectra at varying radial distances from an Alpha DaRT source.
Results
Our results indicate that RBEDSB values remain consistently high across all radial distances from the source (range: 4.84 - 5.34), converging to approximately 4.84 at distances beyond 3.60 mm from the source (< 1% statistical uncertainty). These findings are in good agreement with previously reported data by Ballisat et al. [3]. In contrast, RBESSB values ranged from 0.83 to 0.92 over distances of 0.35 to 4.00 mm from the source.
Conclusion
This study provides a quantitative framework for modeling the RBE of alpha particles in Alpha DaRT. Incorporating RBEDSB values as a function of distance into TG-43–based dosimetric formalism would significantly enhance the accuracy of equivalent dose calculations in clinical treatment planning.