Ultrahypofractionated Whole Breast Radiation Therapy Using a Novel Boost Regimen for Early-Stage Breast Cancer.

Abstract

The 5-year results of the FAST-Forward trial demonstrated noninferiority of local tumor control using a 26 Gy in 5 fraction regimen compared with 40 Gy in 15 fractions for breast cancer patients receiving adjuvant whole breast radiation therapy (WBRT) with or without a sequential conventionally fractionated tumor bed boost (2 Gy per fraction). Here, we reported our institutional experience using the FAST-Forward regimen with a novel sequential boost regimen of 5.2 Gy in 1 fraction or 10.4 Gy in 2 fractions. Patients with nonmetastatic invasive breast cancer or ductal carcinoma in situ treated with adjuvant WBRT of 26 Gy in 5 fractions from January 7, 2019, to January 6, 2022, were identified from an institutional database. Clinical outcomes, including adverse events, disease control, and patient-reported outcomes, were collected. Survival outcomes were estimated using the Kaplan-Meier method. Associations between toxicities and clinicopathologic and treatment characteristics were assessed using logistic regression. A total of 311 consecutive patients were included; the use of a 1- or 2-fraction boost was left to the discretion of the treating physicians (54% 1-fraction, 8.7% 2-fraction, and 38% no boost). Median follow-up was 32 months. Overall survival and local recurrence-free survival probabilities at 36 months were 96% (95% CI, 94-99) and 93% (95% CI, 90-97), respectively. Acute and late toxicities occurred at a higher rate in the 2-fraction versus 1-fraction and no boost groups (37.4%, 10.8%, and 12.2% [acute] and 22.7%, 8.6%, and 7.9% [late], respectively). Boost receipt, greater boost volume, 15× energy, increasing breast V95%, and bolus use were associated with the risk of acute grade ≥ 2 toxicities. A 5-fraction ultrahypofractionated WBRT regimen for early-stage breast cancer with either no boost or a single-fraction boost of 5.2 Gy resulted in excellent disease control and acceptable toxicity. Increased toxicity was observed with a boost of 10.4 Gy in 2 fractions and is no longer used at our institution.