Robust Four‐Field and Arc LET-Optimized Proton Prostate Cancer Treatment Plans With Urethral Sparing

Purpose: To create LET-optimized pencil beam scanning proton prostate cancer treatment plans with clinically acceptable range robustness and urethral sparing. Methods: , target volume and organs at risk (OAR) relative biological effectiveness (RBE)-doses, minimum average RBE-doses, target-to-OAR dose ratios (TODRs), and OAR volumes receiving at least 80% of the CTV PSV D95 dose (V80%). Results: in the periurethral prostate prevented underdosage with urethral sparing. V80%s were statistically decreased in four-beam and most arc comparisons relative to SFO. While increased TODRs were demonstrated in a test patient, lack of statistical significance (or superiority in SFO over arc in the case of the rectum) in the 12 patient cohort occurred due to some patients already having low OAR RBE-doses in SFO plans, which could be addressed with additional optimization objectives at lower doses. Conclusion: and clinically acceptable robustness with the potential to increase the therapeutic ratio and implemented urethral sparing without underdosing the periurethral prostate.