Short-Term Outcomes of Re-Irradiation to the Chest Wall Using Intensity-Modulated Proton Therapy (IMPT) in Women with Breast Cancer

Re-irradiation is defined by ASTRO as a group 1 indication for proton beam therapy due to proton therapy’s superior ability to spare excess dose to critical organs while maintaining high doses of radiation to the target. Thus far, no data has been published regarding the tolerance and acute/short term toxicities of chest/breast re-irradiation with proton therapy. Here we present our initial experience with the use of IMPT for re-irradiation. We hypothesized that IMPT is well tolerated with acceptable acute toxicities in women receiving re-irradiation of the chest wall for a diagnosis of breast cancer. A retrospective analysis was performed of consecutive breast cancer patients treated from 2/2016 to 2/2019 at a single proton center. Demographic, cancer related, treatment related and follow up variables were collected. Descriptive statistics were performed. Eighteen women completed re-irradiation during this timeframe. Two of 18 women had prior mantle field radiation for Hodgkin’s lymphoma, while the remainder was previously radiated for breast cancer. One patient received re-irradiation for an angiosarcoma of the chest wall. One patient received concurrent systemic therapy while seven received concurrent hyperthermia. Five women received bilateral chest wall radiation due to the presence of a contralateral breast cancer. Seven women had breast reconstruction: two with previous flaps and the remainder with permanent breast implants. A median of 6 years elapsed between initial receipt of radiation and re-irradiation (range: 1 – 29). The most common dose/fractionation used was 50.4 Gy (range: 37.5 Gy – 66.6 Gy) in 1.8 Gy fractions +/- a scar boost (10 Gy in 2 Gy fractions). Hyperfractionation was utilized in 3 cases. Grade 2 dermatitis was seen in 78% (n=14/18/9 patients and grade 3 in 5% (n=1/18); there was no grade 4 dermatitis. There were no other reported acute grade 2 toxicities. Other common grade 1 toxicities were observed including hyperpigmentation, fatigue, and breast pain. At a median follow up of 7.5 months, two patients developed distant progression of disease while the re-irradiated area remained controlled. Three patients died – all from progression of breast cancer. With short term follow up in the cohort, one patient developed a non-healing ulcer along the mastectomy scar. One other patient continues to experience skin ulceration; however, this was present prior to initiation of re-irradiation and has continued to improve clinically. Re-irradiation with IMPT was well tolerated by this unique cohort of women. Expected acute toxicities were seen which were similar to those reported by our group previously. While long term follow up is lacking, only one patient has developed a non-healing ulcer since completion of therapy. Chest wall re-irradiation appears to be safe and feasible with the use of IMPT. Future studies are needed to determine the optimal dose and fractionation schedule for breast/chest wall re-irradiation.