MultiRBE: Treatment planning for protons with selective radiobiological effectiveness.

Purpose: Clinical treatment planning protocols for protons recommend a uniform value radiobiological effectiveness (RBE) of protons of 1.1 throughout the treatment field, despite evidence from in-vitro and animal studies that proton RBE increases with linear energy transfer (LET), causing tissues placed distally to the target location to receive a presumably higher biological dose than estimated. While several voices in the medical physics community have advocated for variable RBE-based optimization, the uncertainties in RBE models have prevented its implementation in clinical practice, since an overestimation of RBE could cause significant target underdosage.