A phase II trial to determine the cosmetic outcomes and toxicity of 27 Gy in five-fraction accelerated partial breast irradiation: the ACCEL trial

Accelerated partial breast irradiation (APBI) has been investigated in randomized controlled trials with the goals of reducing side effects and treatment burden. There is accumulating evidence that local control for multi-fraction APBI is not inferior to whole breast irradiation (WBI) but an external beam prescription that can be safely delivered in five consecutive days has not been reported. The aim of this study is to investigate an APBI prescription delivered once per day in 1 week. This is a single-arm, phase II, prospective cohort study. Two hundred seventy-four eligible women with newly diagnosed, early-stage, invasive, or in situ ductal carcinoma treated with breast-conserving surgery and sentinel lymph node biopsy or axillary dissection who are candidates for whole breast radiation without a boost will be recruited. Twenty-seven Gray (Gy) in five fractions will be delivered once daily over five consecutive working days to the target volume. The primary outcome is the rate of global cosmetic deterioration from an excellent or good score at baseline (prior to radiation therapy) to a fair or poor score at 2 years after treatment. The study is powered to demonstrate non-inferiority compared to the use of WBI arm in the RAPID trial. The ACCEL trial aims to demonstrate the safe and effective delivery of a five-fraction APBI treatment using IMRT or 3D-conformal radiation. The study is designed to account for an updated alpha/beta ratio for breast tissue and compares cosmesis to the WBI arm of the RAPID trial. The ACCEL trial was registered in February 2016 and began accrual in the subsequent May. This trial will assess the cosmetic and normal tissue outcomes of external beam APBI delivered in 1 week for early-stage breast cancer.