Derivation of a comprehensive semi-empirical proton RBE model from published experimental cell survival data collected in the PIDE database.

We aimed to develop a comprehensive proton relative biological effectiveness (RBE) model based on accumulated cell survival data in the literature. Our approach includes four major components: (1) Eligible cell survival data with various linear energy transfers (LETs) in the Particle Irradiation Data Ensemble (PIDE) database (72 datasets in four cell lines); (2) a cell survival model based on Poisson equation, with and defined as the ability to generate and repair damage, respectively, to replace the classic linear-quadratic model for fitting the cell survival data; (3) hypothetical linear relations of and on LET, or and ; and (4) a multi-curve fitting (MCF) approach to fit all cell survival data into the survival model and derive the , , , and values for each cell line. Dependences of these parameters on cell type were thus determined and finally a comprehensive RBE model was derived. MCF showed that ( , , , ) = (1.09, 0.0010, 0.96, 0.033), (1.10, 0.0015, 1.03, 0.023), (1.12, 0.0025, 0.99, 0.0085), and (1.17, 0.0025, 0.99, 0.013) for the four cell lines, respectively. Thus, = 1.12 ± 0.04, = 0.0019 ± 0.0008, = 0.99 ± 0.03, and = 0.013 ∗ , and approximately and . Consequently, a relatively reliable and comprehensive RBE model with dependence on LET, , , and dose per fraction was finally derived for potential clinical application.