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Proton RBE for early intestinal tolerance in mice after fractionated irradiation
J Gueulette1, J P Slabbert, L Böhm
1Université Catholique de Louvain, Cliniques Universitares St-Luc, 54 Avenue Hippocrate, 1200 Brussels, Belgium.
Summary
Proton relative biological effectiveness (RBE) for intestinal crypt regeneration in mice was independent of fractionation up to ten doses. This suggests proton RBE remains stable, supporting its clinical application in radiation therapy.
Area of Science:
- Radiation Biology
- Medical Physics
Background:
- Proton therapy is an advanced form of radiation oncology.
- Understanding the relative biological effectiveness (RBE) of protons is crucial for optimizing treatment plans.
- Fractionation, the division of radiation dose into smaller portions, can influence RBE.
Purpose of the Study:
- To investigate how the number of radiation fractions (or dose per fraction) affects the proton RBE.
- To compare proton RBE with that of cobalt-60 gamma rays.
Main Methods:
- Intestinal crypt regeneration in mice served as the biological endpoint.
- Relative biological effectiveness (RBE) was calculated relative to cobalt-60 gamma rays.
- Irradiations were performed in one, three, and ten fractions with a 3.5-hour interval.
- Proton irradiations utilized a 7-cm Spread Out Bragg Peak (SOBP).
Main Results:
- Proton RBE values were consistently around 1.14-1.15 across one, three, and ten fractions.
- Alpha/beta ratios were determined to be 7.6 Gy for gamma rays and 8.2 Gy for protons.
- Proton irradiations at the end of the SOBP showed 1.14 times greater effectiveness than at the middle.
Conclusions:
- Proton RBE for intestinal crypt regeneration is independent of fractionation up to ten fractions.
- The findings suggest proton RBE may remain stable for higher fraction numbers.
- Clinical applications should consider potential increased effectiveness at the end of the SOBP, and current clinical RBE values may underestimate proton RBE.