51: A Phase II Trial of Brachytherapy Alone Following Lumpectomy for Select Breast Cancer: Tumor Control and Survival Outcomes of RTOG 95-17

Abstract

Accelerated partial breast irradiation (APBI) reduces the adjuvant radiotherapy treatment time for early stage breast carcinoma. RTOG 95-17 is a prospective Phase I-II cooperative group trial of APBI alone using multicatheter brachytherapy following lumpectomy in select early stage breast cancers. Tumor control and survival outcomes from this trial are reported. Eligibility criteria for this trial included stage I/II breast carcinoma confirmed to be unifocal, invasive non-lobular histology and <3cm in size. Patients with extensive intraductal component, residual suspicious micro-calcifications or collagen vascular disease were excluded. Negative surgical margins were required and patients with 0-3 positive axillary nodes without extracapsular extension were allowed. The target volume was defined as the lumpectomy cavity, delineated by 6 surgical clips, plus a 2 cm peripheral margin and 1 cm margin anteriorly and posteriorly. APBI treatment was delivered with either Low Dose Rate (LDR) (45 Gy in 3.5-5 days) or High Dose Rate (HDR) (34 Gy in 10 BID fractions over 5 days). A rapid review submission process with dosimetry review prior to treatment for each case was applied to assure optimal dose delivery. Chemotherapy (no earlier than 2 weeks following APBI) and/or tamoxifen could be given at the discretion of the treating physicians. Endpoints evaluated included in-breast control, mastectomy-free rate and regional control (estimated by the cumulative incidence method) and mastectomy-free survival, disease-free survival and overall survival (estimated by the Kaplan-Meier method). The study was designed to analyze the HDR and LDR groups separately and without comparison. Between 1997 and 2000, 100 patients were accrued and 99 were eligible; 66 treated with HDR and 33 treated with LDR. Eighty seven patients had T1 lesions and 12 had T2 lesions. Seventy nine were pathologically N0 and 20 were N1. Median follow-up in the HDR group is 6.14 years with the 5-year estimates of in-breast, regional and contralateral failure rates of 3%, 5% and 2%, respectively. In-breast failures include one true recurrence/marginal miss (in-breast failure located in the immediate vicinity of the lumpectomy cavity) and one reported as both true recurrence/marginal miss and elsewhere failure (in-breast failure located remote from the site of lumpectomy cavity). At five years, the mastectomy free rate is 95%, mastectomy-free survival is 88%, the disease-free survival 86% and the overall survival 92%. The LDR group experienced similar results with a median follow-up of 6.22 years. The 5-year estimates of in-breast, regional and contralateral failure rates of 6%, 0% and 6%, respectively. In-breast failures were reported as 3 true recurrence/marginal miss and 1 elsewhere failure. In this group the 5-year mastectomy-free rate was 87% and mastectomy-free survival was 88% with an 88% and 94% 5-year rate of disease-free survival and overall survival, respectively. Patients treated with multicatheter partial breast brachytherapy on this trial experienced excellent in-breast control rates and overall outcome that compare to reports from APBI studies with similar extended follow-up.