Biophysical modelling of proton radiation effects based on amorphous track models

Area of Science:

• Medical Physics
• Radiation Biology
• Computational Biology

Background:

• Accurate Relative Biological Effectiveness (RBE) is crucial for charged particle therapy dose calculation.
• Estimating RBE is challenging due to uncertainties in physical (LET distributions) and biological (cell nucleus size, local response) parameters.
• Track structure theory offers a framework for predicting particle irradiation dose-response curves.

Purpose of the Study:

• To compare the Amorphous Track Partition (ATP) and Amorphous Track Local effect (ATL) models for predicting proton radiation effects.
• To investigate the predictive power of these track structure models for proton therapy applications.
• To evaluate the general dependencies of model predictions on input parameters.

Main Methods:

• Comparison of the principles and computational procedures of the ATP and ATL track structure models.
• Investigation of model dependencies on physical and biological input parameters.
• Comparison of model predictions for V79 cell survival with experimental data for proton irradiation.

Main Results:

• ATP model uses equations and average doses in subtargets; ATL model uses Monte Carlo simulations and local doses in infinitesimal compartments.
• Both models predict proton survival curves reasonably well but lack agreement with experimental data across a range of proton energies and absorbed doses.
• Conceptual differences include empirical scaling in ATP and parameter adjustment for high local dose regions in ATL.

Conclusions:

• Track structure models, primarily designed for heavy ions, exhibit limitations in predicting proton radiation effects.
• Questionable assumptions regarding subtargets, multitarget/single-hit response, radial dose parameterization, and high-dose cellular response impact model accuracy for protons.
• Further refinement of track structure models is needed for reliable application in proton therapy.