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Accepted · first revision · record

Title: Variable biological effectiveness of proton beams
Plain: Clinics assume protons are a fixed 10 percent more damaging than x-rays, but laboratory data show the factor rises near the end of the particle range. How much it rises in patients is unknown.
Precise: Determine the proton relative biological effectiveness as a function of dose-averaged linear energy transfer $\mathrm{LET}_{d}$ from $1 \text{ to } 15\,\mathrm{keV}/\mathrm{micron}$, dose per fraction from $100 \text{ to } 1000\,\mathrm{rad}$, and tissue $\alpha/\beta$ from $200 \text{ to } 1000\,\mathrm{rad}$, for clinically relevant normal-tissue endpoints. The clinical standard $\mathrm{RBE} = 1.1$ is constant. An answer is a validated RBE model with uncertainty bands usable in treatment planning.
Settled by: Clinical outcome data correlating observed normal-tissue changes with planned $\mathrm{LET}_{d}$ distributions, combined with in vivo endpoint measurements along a spread-out Bragg peak.
Kind: phenomenon
Answer type: value
References: (empty)
Literature status: contested
Status note: Imaging-based evidence of elevated effect at the distal edge in brain accumulated through 2024, but no variable-RBE model had been clinically adopted.
Posed since: 1990