RBE variation between fast neutron beams as a function of energy. Intercomparison involving 7 neutrontherapy...

Area of Science:

• Medical Physics
• Radiobiology
• Radiation Oncology

Background:

• The relative biological effectiveness (RBE) in fast neutron therapy is crucial for treatment efficacy.
• Neutron energy spectra, influenced by particle energy and production reactions, significantly impact RBE.
• Facility-specific factors like targets and collimation also affect neutron spectra and RBE, necessitating intercomparisons.

Purpose of the Study:

• To conduct radiobiological intercomparisons of fast neutron therapy beams across multiple international centers.
• To determine the RBE of different neutron therapy facilities using a standardized biological system.
• To investigate factors influencing RBE, including fractionation, dose rate, and phantom depth.

Main Methods:

• Utilized intestinal crypt regeneration in mice as the radiobiological assay for RBE determination.
• Performed intercomparisons at seven neutron therapy centers with varying proton and deuteron beams.
• Combined radiobiological assessments with dosimetric and microdosimetric investigations where feasible.

Main Results:

• Observed RBE values ranged from 1.50 ± 0.04 to 2.24 ± 0.11, indicating significant inter-center variability.
• RBE for intestinal crypt regeneration correlated with RBE for LD50 at 6 days in specific centers.
• Investigated additional factors like fractionation, dose rate, and phantom depth, providing further insights into RBE variations.

Conclusions:

• Direct radiobiological intercomparisons are essential for understanding and standardizing RBE in fast neutron therapy.
• Variations in RBE highlight the need for facility-specific characterization and quality assurance.
• The findings contribute to optimizing fast neutron therapy protocols and ensuring consistent clinical outcomes.