Robotic Stereotactic Boost in Early Breast Cancer, a Phase 2 Trial

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 Kaplan-Meier 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.