A ternary model of proton therapy based on boron medium radiosensitization and enhancement paths: a Monte Carlo simulation.

Background: To overcome proton therapy limitations [low linear energy transfer (LET) radiation with a relative biological effectiveness (RBE) typically ranging from 1.1 to 1.2], radiosensitization techniques can be employed to increase the radiosensitivity of tumor cells and improve the effectiveness of radiation therapy. In this study, we suggest using a boron-based medium to overcome the biological limitations of proton therapy. By inducing the hydrogen-boron fusion reaction (p + B → 3α) of incident protons and capturing thermal neutrons [B + n → Li (0.84 MeV) + He (1.47 MeV) + γ (0.477 MeV)], high LET α particles can be released. We propose a "ternary" radiotherapy model to enhance the biological effect of proton therapy.

Methods: Using Monte Carlo simulation, the possibility of interacting low-energy proton beams with B and thermal neutrons with B to produce α particles with higher RBE to enhance the biological effect of proton radiotherapy were investigated. And the number and location of α particles and thermal neutrons produced by the interaction of protons with natural boron had also been studied.

Results: Under the basic principle of the "ternary" radiotherapy model, comparative analyses of neutrons and α particles produced by proton beams of different energies incident on the phantoms, which were composed of boron isotopes of different concentrations in proportion to the phantoms, have shown that the α particle yield decreased with decreasing boron doping concentration, whereas the neutron yield increased with decreasing boron doping concentration. The distribution of thermal neutrons and α particles in the longitudinal direction of the proton beam were also studied, and it was found that the number of α particles produced was high at high boron concentrations, and the locations of α and thermal neutrons were close to the treatment target.

Conclusions: The proton therapy ternary model is theoretically feasible from the perspective of mathematical analysis and Monte Carlo simulation experiments.