THE ROLE OF PARTICLE SPECTRA IN MODELING THE RELATIVE BIOLOGICAL EFFECTIVENESS OF PROTON RADIOTHERAPY BEAMS

Area of Science:

• Medical Physics
• Radiation Oncology
• Nuclear Interactions in Biological Tissues

Background:

• Radiotherapy beams, including protons and heavier ions, produce secondary particles via nuclear interactions within patient tissues.
• Current radiobiological models often use dose-averaged linear energy transfer (LET), but the inclusion or exclusion of secondary particles affects these calculations.
• This variation in secondary particle consideration impacts the predicted relative biological effectiveness (RBE) of radiation therapy beams.

Purpose of the Study:

• To quantitatively assess the influence of secondary radiation spectra on averaged LET values.
• To determine the impact of secondary particles on the prediction of relative biological effectiveness (RBE) in proton and ion radiotherapy.
• To highlight the importance of considering secondary particle effects in radiobiological modeling.

Main Methods:

• Analysis of secondary particle spectra generated by proton and heavier ion beams interacting with different tissue compositions.
• Quantitative study comparing dose-averaged LET values with and without the inclusion of secondary particles.
• Evaluation of the effect of these spectral differences on RBE calculations.

Main Results:

• Secondary particle spectra significantly influence averaged LET values.
• The inclusion or exclusion of secondary particles leads to variations in calculated RBE.
• Trends observed for microdosimetry-based quantities and LET-based parameters are similar, suggesting fluence-averaged quantities warrant closer investigation.

Conclusions:

• Secondary particles generated during radiotherapy play a critical role in determining LET and RBE.
• Accurate radiobiological modeling requires explicit consideration of secondary particle spectra.
• Further investigation into fluence-averaged quantities is recommended for improved predictive models in particle therapy.