Intraoperative radiotherapy in early-stage breast cancer: Multidiciplinary management and analysis of outcome.

Abstract

e12036 Background: The TARGIT-A trial investigated the efficacy of using single-dose targeted intraoperative radiotherapy (IORT) in place of whole-breast external beam radiotherapy (EBRT) for treating breast cancer. IORT is an effective alternative to EBRT for adjuvant treatment of select patients with estimated conversion rate of 15%, who required additional EBRT following complete pathologic staging. An institutional study was performed to evaluate the rate of patients who received IORT but still required EBRT, in-breast-tumor recurrence rate (IBTR) and overall survival (OS). Methods: Institutional retrospective review of patients treated with IORT was performed, including age at the time of IORT, histology, AJCC stage, margin, and clinical features as outlined in ASTRO and ABS guideline. Conversion rate, IBTR and OS was calculated. Reason for conversion to EBRT assessed. Results: From 1/1/2016 to 1/1/2019, 35 patients underwent IORT concurrent with lumpectomy and sentinel node biopsy within the ASTRO and ABS guideline. Patients median age 60 (51-79 yo) and all had ER+, clinical T(0.5 -2.5cm)N0 with intraoperative sentinel node frozen section evaluation. Zeiss IORT consisted 50 KV x-rays with spherical applicators, and a dose of 20Gy was prescribed at the surface of the applicator. 14.2% (5/35) were recommended EBRT. Conversion was due to microscopic disease found on final surgical pathology (3 node positive and 2 positive surgical margin). 4 patients successfully completed EBRT and 1 patient declined EBRT. 100% underwent adjuvant endocrine treatment. IBTR was 0% and OS was 100% with a median follow-up of 18.6 months (range of 2 – 35 months). Conclusions: Pathologic false negative rate contributed to EBRT conversion rate but remained below 15% TARGIT-A threshold. IORT concurrent with lumpectomy within a risk adapted approach is a good option for eligible patients using evidence-based guideline and multidisciplinary team model. Continued cohort assessment for IBTR, OS and toxicity outcome will be prospectively assessed.