A model for the relative biological effectiveness of protons: The tissue specific parameter α/ β of photons is a predictor for the sensitivity to LET changes.

Wedenberg, Minna; Lind, Bengt K.; Hårdemark, Björn

Background. The biological effects of particles are often expressed in relation to that of photons through the concept of relative biological effectiveness, RBE. In proton radiotherapy, a constant RBE of 1.1 is usually assumed. However, there is experimental evidence that RBE depends on various factors. The aim of this study is to develop a model to predict the RBE based on linear energy transfer (LET), dose, and the tissue specific parameter α/ β of the linear-quadratic model for the reference radiation. Moreover, the model should capture the basic features of the RBE using a minimum of assumptions, each supported by experimental data. Material and methods. The α and β parameters for protons were studied with respect to their dependence on LET. An RBE model was proposed where the dependence of LET is affected by the ( α/ β)phot ratio of photons. Published cell survival data with a range of well-defined LETs and cell types were selected for model evaluation rendering a total of 10 cell lines and 24 RBE values. Results and Conclusion. A statistically significant relation was found between α for protons and LET. Moreover, the strength of that relation varied significantly with ( α/ β)phot. In contrast, no significant relation between β and LET was found. On the whole, the resulting RBE model provided a significantly improved fit (p-value phot as input parameters. Hence, no proton specific biological parameters are needed.

CELL lines; CONFIDENCE intervals; STATISTICAL correlation; RADIOTHERAPY; RESEARCH funding; DATA analysis software; STATISTICAL models; DESCRIPTIVE statistics; IN vitro studies

Acta Oncologica, 2013, Vol 52, Issue 3, p580

0284-186X

Academic Journal

10.3109/0284186X.2012.705892