Outcomes for APBI With Strut-Based Brachytherapy: 101 Patients at 4.5 Years Median Follow-up

Abstract

The SAVI Collaborative Research Group (SCRG), was created to study the long-term outcomes of women receiving accelerated partial breast irradiation (APBI) using strut-based applicators. The outcomes for the most mature subgroup of this study's patients (n = 101), accrued 3.5 to 6 years ago at 3 institutions, is presented. All patients were treated at least 42 months prior to abstract submission. Median follow-up of this cohort was 54 months. Patients were treated with APBI using the strut-based brachytherapy device with conventional dose and fractionation (3.4 Gy x 10 fx, BID). Treatment planning goals for the planning target volume were a V90 >90%, V150 <50 cc, and V200 <20 cc. Patients were followed regularly and outcome was graded based on the CTCAE v3.0 (common terminology criteria for adverse events, version 3.0). Seventy-one patients had invasive disease and 29 had ductal carcinoma in situ. The median age was 62 years (range, 40-82 years), with 82% post-menopausal. Median tumor size was 12.5 mm (range, 2-35 mm) with 92% being estrogen receptor positive. All patients completed APBI as planned with no serious adverse events. All patients met the dosimetric criteria with median V90 of 96%, V150 of 29 cc and V200 of 14 cc. Late toxicity (grade ≥2) rates were low; hyperpigmentation (0%), telangiectasias (2%), seroma (2%), fat necrosis (0%) and breast asymmetry secondary to radiation effects (3%). Statistically, tumor size had a weak association with fibrosis (21.7 cc vs 12.5 cc, p = 0.049) and surgical breast asymmetry (22 cc vs 12.7 cc, p = 0.089). There were no statistical associations (p < 0.05) between treatment parameters and toxicity, possibly due to the low event rates (≤3%). Local control was excellent with a true recurrence/marginal miss rate of 2% and an ipsilateral/elsewhere recurrence rate of 2%. These data will be updated and presented for 5 year median follow-up in October 2013. For these 101 patients with a median 4.5 years of follow-up (all with >3.5 years), strut-based brachytherapy appears to be a well-tolerated, effective treatment with low rates (<5%) of toxicities. With APBI an acceptable treatment for many women with early-stage breast cancer, strut-based brachytherapy continues on longer follow-up to be versatile, safe and effective.