Variable biological effectiveness of proton beams
In plain words
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 statement
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.
What would settle it
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.
Status in the literature
Unverified 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.
Related problems
- More general than Effective range extension at the distal falloff