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

<i>Objective:</i>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<i>d(y)</i>spectra) is compared with values of RBE₁₀using experimentally derived<i>d(y)</i>spectra from a silicon-on-insulator (SOI) microdosimeter.<i>Approach:</i>experimentally measured<i>d(y)</i>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-<i>y</i>_<i>D</i>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 with¹²C ions.<i>Main Results:</i>the RBE₁₀-vs-<i>y</i>_<i>D</i>trend 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, and²⁸Si ions. Deviations have been attributed to the difference in the derivation of the<i>d</i>(<i>y</i>) spectra based on the different methods utilized. Good agreement was found between<i>y</i>_<i>D</i>values and an over estimation was observed for RBE₁₀values for the beamline specific simulation of the¹²<i>C</i>ion beam.<i>Significance:</i>overall, this study shows that the SOI microdosimeter is a valuable tool that can be utilized for quick and accurate experimental derivation of the<i>d</i>(<i>y</i>) 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<i>y</i>_<i>D</i>and RBE₁₀for various ions in any irradiation condition utilizing other radiobiological models.