Microdosimetric analysis of proton boron capture therapy using microdosimetric kinetic model

Abstract Objective . Proton boron capture therapy (PBCT) is a novel approach that utilizes alpha particles generated through the proton induced capture reaction with 11 B. Early studies reported substantial dose enhancements of 50%–96% near the Bragg peak, suggesting a promising therapeutic advantage. However, subsequent investigations have raised critical concerns regarding the practical feasibility of PBCT, primarily due to the relatively low reaction cross section in the Bragg peak region and the need for clinically unrealistic boron concentrations. The aim of this study is to evaluate Relative Biological Effectiveness (RBE) enhancement in PBCT using microdosimetric analysis across a wide range of boron concentrations. Approach . In the present work, we have employed Monte Carlo model using Particle and Heavy Ion Transport code System (PHITS) package combined with the Microdosimetric Kinetic Model to quantify both physical and biological dose enhancements at varying concentrations of 11 B. Main Results . Microdosimetric analysis revealed that the total dose is dominated by protons, although alpha particles dominate in regions of higher linear energy deposition. The resulting RBE enhancement factors were 1.0011, 1.0080, and 1.1275 (for Human Salivary Gland (HSG) cell type) for 100, 1000, and 10,000 ppm boron concentrations, respectively. While the enhancements at lower concentrations are negligible, a modest increase is observed at very high boron levels. Significance . Based on the resulting RBE enhancement factors, it can be concluded that although alpha particles generated via the p + 11 B → 3 α reaction contribute high-Linear Energy Transfer (LET) energy at the cellular level, the overall biological dose enhancement remains rather minimal. These results indicate that under clinically achievable boron concentrations, the therapeutic benefit of PBCT may be limited.