Patterns of Recurrence Among Higher-Risk Patients Receiving Daily External Beam Accelerated Partial-Breast Irradiation to 40 Gy in 10 Fractions

PURPOSE: The 2016 American Society for Radiation Oncology consensus guidelines for the use of accelerated partial-breast irradiation (APBI) define “suitable,” “cautionary,” and “unsuitable” populations for this adjuvant breast radiation therapy technique. We sought to determine whether patients in the cautionary group exhibited adverse outcomes after APBI compared with their suitable counterparts. METHODS AND MATERIALS: We identified 252 consecutively treated patients from a single institution with in situ or early-stage invasive breast cancer who underwent APBI between 2008 and 2017. Treatment technique was uniform throughout the population, consisting of 3-dimensional conformal radiation therapy to 40 Gy administered in 10 daily fractions. RESULTS: One hundred seventy-eight patients (70%) were classified as suitable, 69 (27%) as cautionary, and 5 (2.0%) as unsuitable. Because unsuitable patients were few and had no recurrences, they were excluded from analysis. At a median follow-up time of 3.9 years, 97.2% of patients were free of recurrence. Four patients (1.5% overall; 3 suitable and 1 cautionary) experienced ipsilateral in-breast recurrences, and 1 cautionary patient developed an ipsilateral regional recurrence in an axillary lymph node. There was no significant difference in the rate of ipsilateral breast recurrence (2.4% vs 1.0%) between cautionary and suitable groups. CONCLUSIONS: Local recurrences are rare among guideline-defined cautionary patients with in situ or invasive breast cancer treated with APBI delivered via daily 3-dimensional conformal radiation therapy to 40 Gy. At a median follow-up of 3.9 years, no significant differences in local control were noted between cautionary and suitable patient groups. Further study is needed to characterize long-term disease outcomes among various risk groups.