This Japanese prospective series describes outcomes for 23 patients treated with definitive focal proton beam irradiation for locally-recurrent rectal cancer without a history of prior radiation. All tumors and/or patients were not amenable to salvage surgery, and tumors were located in the presacrum (n=11), pelvic sidewall (n=7) or anastomosis (n=4). The goal was to deliver >70 Gy in >2.2 Gy per fraction (if bowel tolerance allowed) to gross disease with 0.5 cm-CTV and 0.5 cm-PTV margins. Everyone had a PET before and after treatment and metabolic responses were complete (n=11), partial (n=8), stable (n=2), and progressive (n=2). At 5 years, 47% had local control and 38% were alive without any disease progression. Those with a complete metabolic response proved to indeed have much better long term local control (HR 4.49). | Takagawa, Adv Radiat Oncol 2023
