Proton Re-Irradiation with Concurrent Hyperthermia in Patients with Recurrent Breast Cancer

Abstract

The aim of this study is to evaluate the safety and effectiveness of proton re-irradiation with concurrent hyperthermia in the treatment of recurrent breast cancer. We retrospectively identified patients previously treated with photon whole breast or chest wall irradiation for a primary breast cancer at our institution, who subsequently developed a histologically-confirmed locoregional recurrence or new ipsilateral primary breast cancer and underwent proton chest wall re-irradiation with concurrent hyperthermia as part of definitive treatment. Acute toxicity was evaluated once weekly while on-treatment and at 2 weeks and 3 months post-treatment. Toxicities were graded according to CTCAE v4.0. Fifteen patients received proton re-irradiation with concurrent superficial hyperthermia at our institution from August 2018 to December 2022. Median interval between radiation treatment courses was 7.7 years (range 1-30 years). Four patients (26%) had gross, unresected disease at the time of re-treatment. The median initial radiation dose, re-irradiation dose, and cumulative EQD2 was 60.4 Gy (50.6-61.2 Gy), 60 Gy (RBE) (45-66 Gy (RBE)), and 120 Gy (RBE) (103-126 Gy (RBE)), respectively. Patients received a median of 9 (3-14) concurrent hyperthermia treatments delivered twice weekly, and 13 patients (87%) received seven or more hyperthermia treatments. Median toxicity follow-up was 9 months (0-36 months). Acute grade 3 toxicities included two patients (13%) with grade 3 dermatitis, both of which resolved with conservative management within 3 months of treatment completion. Chronic grade 2 or higher toxicities included two grade 2 hyperpigmentation, one grade 3 induration, one grade 2 telangiectasia, and one grade 2 rib fracture. There were no grade 4-5 acute or late toxicities. There was one in-field local recurrence and one regional recurrence outside of the re-irradiation field. Both patients had gross, unresected disease at the time of re-irradiation. Two patients (13%) developed distant disease. Proton re-irradiation with concurrent hyperthermia is feasible and well-tolerated in the re-treatment of breast cancer. Further studies are warranted to determine long-term toxicity and oncologic outcomes.