Comparative study of a microdosimetric biological weighting function for RBE10 modeling in particle therapy with a solid state SOI microdosimeter

Objective: the recently developed V79-RBE10 biological weighting function (BWF) model is a simple and robust tool for a fast relative biological effectiveness (RBE) assessment for comparing different exposure conditions in particle therapy. In this study, the RBE10 derived by this model (through the particle and heavy ion transport code system (PHITS) simulated d(y) spectra) is compared with values of RBE10 using experimentally derived d(y) spectra from a silicon-on-insulator (SOI) microdosimeter. Approach: experimentally measured d(y) spectra are used to calculate an RBE10 value utilizing the V79-RBE10 BWF model as well as the modified microdosimetric kinetic model (MKM) to produce an RBE10-vs-y D trend for a wide range of ions. In addition, a beamline specific PHITS simulation was conducted which replicated the exact experimental conditions that were used with the SOI microdosimeter at the heavy ion medical accelerator in Chiba biological beamline with 12C ions. Main Results: the RBE10-vs-y D trend for 1H, 4He, 7Li, 12C, 14N, 16O, 20Ne, 28Si, 56Fe, and 124Xe ions is examined with good agreement found between the SOI microdosimeter derived RBE10 values with the V79-RBE10 BWF model and MKM, as well as the PHITS simulations for 1H, 4He, 7Li, 12C, 16O, and 56Fe ions while some discrepancies were seen for 14N, 20Ne, and 28Si ions. Deviations have been attributed to the difference in the derivation of the d(y) spectra based on the different methods utilized. Good agreement was found between y D values and an over estimation was observed for RBE10 values for the beamline specific simulation of the 12 C ion beam. Significance: overall, this study shows that the SOI microdosimeter is a valuable tool that can be utilized for quick and accurate experimental derivation of the d(y) spectra, which can then be convoluted with the weighting function of the V79-RBE10 BWF model to derive RBE10. The SOI microdosimeter is able to derive experimental values of y D and RBE10 for various ions in any irradiation condition utilizing other radiobiological models.