Biological intercomparison using gut crypt survivals for proton and carbon-ion beams

Area of Science:

• Medical physics
• Radiation oncology
• Radiobiology

Background:

• Charged particle therapy requires biological information for accurate dose prescription.
• Relative biological effectiveness (RBE) is crucial but varies with cell type, endpoint, dose, and fractionation.
• A reproducible biological model is needed for inter-facility comparisons.

Purpose of the Study:

• To compare the biological effectiveness of proton and carbon ion beams across different facilities.
• To assess the reproducibility of RBE measurements using mouse gut crypt survival as an endpoint.
• To evaluate inter-institutional variations in biological effectiveness for charged particle therapy.

Main Methods:

• Utilized mouse gut crypt survival as the biological endpoint to assess cell-killing efficiency.
• Compared proton beams from three Japanese facilities against reference Linac X-ray machines (4 and 6 MeV).
• Evaluated carbon ion beams from NIRS/HIMAC and GSI/SIS at multiple positions within a spread-out Bragg peak (SOBP).

Main Results:

• Proton RBE values relative to X-rays ranged from 0.96 to 1.11, with a coefficient of variance (CV) of 4.0–5.1%.
• Carbon ion beams exhibited smaller inter-institutional differences (around 1%) in biological effectiveness within the SOBP.
• CV for carbon ions was consistently low (< 1.7%) across proximal, middle, and distal SOBP regions.

Conclusions:

• Inter-institutional variation in biological effectiveness is significantly smaller for carbon ions compared to protons.
• Beam-spreading methods for carbon ions do not critically impact gut crypt survival.
• These findings support the potential for more standardized biological dose prescriptions in carbon ion therapy.