Definitive hyperfractionated, accelerated proton reirradiation for patients with pelvic malignancies.

Pelvic reirradiation (re-RT) presents challenges due to concerns for late toxicity to tissues-at-risk including pelvic bone marrow (PBM). We routinely utilize a hyperfractionated, accelerated re-RT for recurrent rectal or anal cancer in the setting of prior radiation. We hypothesized that proton beam radiation (PBR) is uniquely suited to limit doses to pelvic non-target tissues better than photon-based approaches. All patients who received hyperfractionated, accelerated PBR re-RT to the pelvis from 2007 to 2017 were identified. Re-RT was delivered twice daily with a 6 h minimum interfraction interval at 1.5 Gray Relative Biological Effectiveness (Gy(RBE)) per fraction to a total dose of 39-45 Gy(RBE). Concurrent chemotherapy was given to all patients. Comparison photon plans were generated for dosimetric analysis. Dosimetric parameters compared using a matched-pair analysis and the Wilcoxon signed-rank test. Survival analysis was performed Kaplan Meier curves. Fifteen patients were identified, with a median prior pelvic RT dose of 50.4 Gy (range 25-80 Gy). Median time between the initial RT and PBRT re-RT was 4.7 years (range 1.0-36.1 years). In comparison to corresponding photon re-RT plans, PBR re-RT plans had lower mean PBM dose, and lower volume of PBM getting 5 Gy, 10 Gy, 20 Gy, and 30 Gy (p < 0.001, p < 0.001, p < 0.001, and p = 0.033, respectively).With median 13.9 months follow-up after PBR re-RT, five patients had developed local recurrences, and four patients had developed distant metastases. One-year overall survival following PBR re-RT was 67.5% and one-year progression free survival was 58.7%. No patients developed acute or late Grade 4 toxicity. PBR re-RT affords improved sparing of PBM compared with photon-based re-RT. Clinically, PBR re-RT is well-tolerated. However, given modest control rates with definitive re-RT without subsequent surgical resection, a multidisciplinary approach should be favored in this setting when feasible.

Déclaration de conflit d'intérêts

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.