Cellular parameters and RBE-LET dependences for modelling heavy-ion radiotherapy

Sets of four parameters (m, E0, sigma0 and kappa) of the cellular track structure model of Katz have been fitted to recently published data concerning human melanoma (AA) and mammalian (V79) cells exposed to a variety of lighter ions and to mixed ion-Co60 and ion-ion irradiation. Using these parameters, model predictions of V79 survival were verified against experimental data. RBE-LET dependences were calculated and compared with experimental data obtained for V79 cells after exposure to 3He, 12C and 20Ne ion beams. The presented track-segment approach used in track structure calculations, while satisfactory for heavier ions, may be of limited value for predicting the RBE-LET dependence of proton and helium radiotherapy beams in regions close to the distal range of these particles. We discuss the predictive capability of this model and propose standards in reporting cellular radiobiology data for application in modelling heavy ion beam radiotherapy.