Comparative study of a microdosimetric biological weighting function for RBE10modeling in particle therapy with a solid state SOI microdosimeter.

Objective: The recently developed V79-RBE₁₀biological 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 RBE₁₀derived by this model (through the Particle and Heavy Ion Transport code System (PHITS) simulated d(y) spectra) is compared with values of RBE₁₀using experimentally derived d(y) spectra from a silicon-on-insulator (SOI) microdosimeter. Approach: Experimentally measured d(y) spectra are used to calculate an RBE₁₀value utilizing the V79-RBE₁₀BWF model as well as the modified microdosimetric kinetic model (MKM) to produce an RBE₁₀-vs-y_Dtrend 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 (HIMAC) biological beamline with¹²C ions. Main Results: The RBE₁₀-vs-y_Dtrend for¹H,⁴He,⁷Li,¹²C,¹⁴N,¹⁶O,²⁰Ne,²⁸Si,⁵⁶Fe, and¹²⁴Xe ions is examined with good agreement found between the SOI microdosimeter derived RBE₁₀values with the V79-RBE₁₀BWF model and MKM, as well as the PHITS simulations for¹H,⁴He,⁷Li,¹²C,¹⁶O and⁵⁶Fe ions while some discrepancies were seen for¹⁴N,²⁰Ne,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_Dvalues and an over estimation was observed for RBE₁₀values for the beamline specific simulation of the¹²C 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-RBE₁₀BWF model to derive RBE₁₀. The SOI microdosimeter is able to derive experimental values of y_Dand RBE₁₀for various ions in any irradiation condition utilizing other radiobiological models.