Comparison of two radiation boost schedules in postlumpectomy patients with breast cancer

We have been practicing hypofractionation, 40 Gy in 16 fractions over 3 weeks for whole breast irradiation (WBI) for the past five decades with or without boost at our center. In this study, we compared two boost schedules of 10 Gy/5#/1 week with 16 Gy/8#/1.5 weeks in postlumpectomy patients with breast cancer after WBI.

From June 2012 to June 2016, the study included 87 breast cancer patients postbreast conservation surgery. The institutional ethics committee approved the study, which was registered with ClinicalTrials.gov (ClinicalTrials.gov identifier no. CT02142907). All patients were treated with WBI of 40 Gy/16#/3 weeks. WBI was followed by tumor bed boost of 10 Gy/5#/1 week in 44 patients and 16 Gy/8#/1.5 weeks in 43 patients, either with electron beam therapy or 3D CRT with photons. The primary endpoint of the study was the comparison of local control between two schedules. Secondary endpoints were acute and late radiation toxicities, cosmetic score analysis, disease-free survival (DFS), and overall survival (OS). The assessment of acute and late skin toxicity was made as per RTOG scores and LENT-SOMA scale. The cosmetic assessment was made with Harvard/NSABP/RTOG Breast Cosmesis Grading Scale.

Median follow-up was 55 months (range 18-78 months). Local recurrence was seen in 1 (2.3%) patient in the 16 Gy boost only. Acute Grade 2 skin toxicity was 33% in 16 Gy boost arm compared to 23% in 10 Gy boost arm. Late skin toxicities were also high in patients with 16 Gy boost. Grade ≥2 induration was seen in 4.5% and 14% of patients with 10 Gy and 16 Gy boost, respectively. None of the patients with 10 Gy boost had Grade 2 edema as compared to 5% with 16 Gy. Pigmentation was observed in 9% and 23% patients with 10 Gy and 16 Gy boost, respectively. Grade 1 fibrosis was 2% versus 12% in patients with 10 Gy and 16 Gy boost, respectively. The cosmetic score was good/excellent in 91% and 84% of patients with 10 Gy and 16 Gy boost, respectively. Distant metastasis occurred in 2 (4%) and 3 (7%) patients in 10 Gy and 16 Gy boost, respectively. DFS and OS at 5 years were comparable between the two boost schedules.

Local control was comparable with 10 Gy and 16 Gy boost. Acute and late skin toxicities were higher with 16 Gy boost dose. The cosmetic score was better with 10 Gy boost. DFS and OS was comparable with the two boost schedules. Hence, a boost of 10 Gy/5# after WBI may be adequate in patients with breast cancer.