Stereotactic body radiation therapy (SBRT) for the treatment of primary breast cancer in patients not undergoing surgery

Purpose: The purpose was to explore the role of stereotactic body radiation therapy (SBRT) in providing local control (LC) for primary breast cancer in patients unable to undergo surgery. Materials/methods: Between 2015 and 2019, 13 non-surgical candidates with 14 lesions were treated with SBRT for primary breast cancer. In 4 cases, SBRT was used after whole breast radiation therapy (WBRT; 40-50 Gy/ 20-25 fractions). SBRT dose was 30-40 Gy in 5 fractions for patients treated with SBRT alone and 25-32 Gy in 4-5 fractions for those treated with SBRT + WBRT. LC and overall survival (OS) were estimated using KaplanMeier curves. Response was also assessed using RECIST guidelines. Results: Median follow-up was 32 (range: 3.4-70.4) months. Imaging at median 2.2 (0.6-8.1) months post-SBRT showed median 43.2 % (range: 2-100 %) decrease in the largest diameter and median 68.7 % (range: 27.9-100 %) SUV reduction. There were 3 cases of local progression at 8.7-10.6 months. Estimated LC was 100 % at 6 months and 71.6 % at 12, 24 and 36 months. Estimated median OS was 100 % at 6 months, 76.9 % at 12 months, and 61.5 % at 24 and 36 months. Acute toxicity (n = 13; 92.9 %) included grade (G)1 (n = 8), G2 (n = 4), and G4 (necrosis; n = 1). Late toxicity included G2 edema (n = 1) and G4 necrosis (n = 2, including 1 consequential late effect). Only patients treated with SBRT + WBRT experienced acute/late G4 toxicity, managed with resection or steroids. Conclusions: SBRT to primary breast cancer resulted in good LC in non-surgical/metastatic patients. Although necrosis (n = 2) occurred in the SBRT + WBRT group, it was successfully salvaged.