Abstract P3-19-19: Intraoperative Radiation Therapy (IORT) : A large integrated healthcare system’s approach and outcomes

Abstract Background: With TARGIT-R(Retrospective) showing a higher-than-expected ipsilateral breast tumor recurrence (IBTR) the community setting for intraoperative radiation therapy (IORT), we evaluated IORT outcomes in an integrated health care system.Methods: A retrospective review of early breast cancer patients who received IORT between February 2014-February 2020 was performed. IORT was offered at a single medical center within a large integrated healthcare system. Criteria for IORT included patients ≥50 years with T1, low to intermediate grade, endocrine-responsive HER2- invasive ductal carcinoma. All breast cancer patients were reviewed at weekly multidisciplinary breast conferences, and IORT was offered when patients met the eligibility criteria. Primary outcomes include IBTR, mortality, and complications. Results: Of 5,731 potentially eligible patients, 245 patients (4.3%) underwent IORT. Mean age was 65.4 ± 0.4 years with median follow-up 3.5 years ± 2.2 months. Based on American Society of Radiation Oncology guideline, 51% were suitable, 38.4% cautionary, and 10.6% unsuitable candidates based on the final pathology. The patients were reassigned to the cautionary group because of the margin width and/or extensive DCIS. Unintended boost (primary IORT followed by whole-breast radiation) was given in 6.5% of IORT patients. At median follow-up of 3.5 years, IBRT was 3.7% for all patients. There was one breast-cancer-related mortality (0.4%), and 7 mortality (2.9%) from other causes. Although not statistically significant, there was a trend towards higher recurrence in those not adherent with endocrine treatment than those who were (7.4% vs 1.9%, p=0.07). The overall complication rate was 14.7% with seroma as the most common.Conclusions: At 3.5-year follow-up, our IORT IBTR rate of 3.7%. Our protocol subsequently was modified to require all IORT patients to receive surgical shave margins, WBI for all cautionary patients on the final pathology, and requirement of endocrine treatment. Citation Format: Annie Tang, Jason Kelly, Elizabeth Cureton, Jonathan Svahn, Eva Thomas, Liisa Lyon, Veronica Shim. Intraoperative Radiation Therapy (IORT) : A large integrated healthcare system’s approach and outcomes [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-19-19.