Phenomenon-based prediction of relative biological effectiveness of ion beams by means of the MultiScale Approach

TL;DR

This paper introduces the MultiScale Approach (MSA) for predicting the relative biological effectiveness (RBE) of ion beams, demonstrating its accuracy and predictive power through comparison with experimental data and exploring effects at high linear energy transfer (LET).

Contribution

It is the first application of MSA to analyze RBE of ion beams, providing a molecular-level understanding and accurate predictions relevant for ion-beam cancer therapy.

Findings

MSA accurately predicts RBE for carbon-ion irradiation.

Good agreement with experimental data validates the model.

RBE varies significantly at high LET due to the overkill effect.

Abstract

Relative biological effectiveness (RBE) is a key quantity for the description of radiobiological effects induced by charged-particle irradiation in the context of ion-beam cancer therapy. Since RBE is a complex function that depends on different physical, chemical and biological parameters, a fundamental understanding of these effects becomes increasingly important for clinical applications. The phenomenon-based MultiScale Approach to the physics of radiation damage with ions (MSA) provides a tool for a molecular-level understanding of physical and chemical mechanisms of radiation biodamage and allows to quantify macroscopic biological effects caused by ion irradiation. This study reports the first application of the MSA for the analysis of RBE of ion beams. As a case study, we quantify the response of human normal tissue cell lines to carbon-ion irradiation at different values of linear energy transfer. RBE corresponding to different biological endpoints as well as other radiobiological parameters, such as clonogenic cell survival as a function of dose and inactivation cross section, are analyzed and compared with experimental data. Good agreement with an extensive data set emphasizes the predictive power of the MSA. The method is also used to make predictions of RBE at high values of LET where RBE decreases due to the "overkill" effect. In this regime, the dose needed to achieve a given biological effect is deposited by a few ions. The fact that a given number of ions may produce more damage than needed for a given effect leads to a significant (up to 20%) variation in RBE. This effect should be taken into consideration in the analysis of experimental data on irradiation with high-LET ions.