Best metric to represent proton beam quality and reliability of LET

Determine the most appropriate physical quantity to represent variations in proton beam quality for clinical treatment optimization and evaluate whether linear energy transfer (LET), including dose‑averaged LET (LETd), is sufficiently reliable across the proton range in ocular proton therapy and other clinical contexts.

Background

Proton therapy often uses a constant relative biological effectiveness (RBE) of 1.1, yet substantial evidence indicates RBE varies with depth and linear energy transfer (LET). As a result, there is growing interest in using physical metrics such as LET or dose‑averaged LET (LETd) to capture changes in radiation quality along the proton path for treatment optimization.

This paper measures LET and compares experiments with TOPAS simulations on the Clatterbridge ocular beamline, contributing LETd data. However, the authors emphasize that the choice of which physical quantity best captures beam quality variations—and the reliability of LET-based metrics—remains unresolved and of clinical importance.