Linear approximation of variable relative biological effectiveness models for proton therapy

The McNamara (MCN) and Wedenberg (WED) RBE weighted dose (D(RBE)), dose and dose-weighted average LET (LET(d)) were calculated in twenty brain cancer patients. A linear approximation was made for each RBE model to give best agreement to clinically relevant dosimetric parameters. Additional evaluations were done on twenty head and neck and twenty breast cancer patients.The R(2) of the fits was ≥0.94 and ≥0.91 for MCN and WED respectively for α/β values ≥1.0 Gy. The graphs derived in this work can be used to convert RBE-LET slopes derived from clinical data to α/β values in the MCN or WED models.