Adjuvant Breast Radiotherapy Using a Simultaneous Integrated Boost for Early-Stage Breast Cancer: Results from a Phase II Trial

Abstract

The purpose of the study was to report outcome analysis of a prospective institutional phase 2 trial of patients undergoing postoperative whole breast irradiation with inversely intensity modulated radiotherapy (IMRT) and a simultaneous integrated boost following breast-conserving surgery (BCS). This prospective cohort study (NCT01394575) included 532 patients treated with RT for invasive breast cancer (T1-2, N1-2M0) or carcinoma in situ after BCS. Patients received whole-breast radiation therapy to 45 Gy in 25 weekly fractions with a simultaneous integrated boost to the tumor bed of 60Gy in 25 fractions. The primary endpoint was ipsilateral breast tumor recurrence, development of distant metastatic disease, and overall survival. Patients were also evaluated for acute toxicity (Common Terminology Criteria for Adverse Events version 3.0). Between 2010 and 2014, 532 eligible patients (65 DCIS and 467 invasive breast cancer) underwent whole breast irradiation with intensity modulated radiotherapy and simultaneously integrated boost (IMRT-SIB) following BCS. The median age was 46 years old (range, 22-74 years), and the median follow-up period was 5.06 years. The most common grade 1 or 2 acute toxicities were breast pain, radiation dermatitis, and fatigue. There was only one patient presenting a grade 3 event (0.18%). Ipsilateral breast tumor recurrence developed in a total of two patients (0.3%), one in conjunction with widespread metastatic disease. Distant metastatic disease developed in eight patients (1.5%), and the five-year disease-free survival and overall survival rates were 98.1% and 99.2%, respectively. Five-year disease-specific outcomes for adjuvant breast radiotherapy using a simultaneous integrated boost are favorable in early-stage breast cancer.