Abstract P4-12-16: A seven year single institution experience with IntrabeamTM intraoperative radiation therapy:recurrence rates and predictors of recurrence

Abstract

Objectives: Patients undergoing single fraction intraoperative radiation therapy (IORT) for early stage breast cancer were analyzed to determine rates of local recurrence and to identify predictors of local recurrence. Materials and Methods: Patients who underwent intraoperative radiotherapy (IORT 20 Gray at 50kV using the INTRABEAMTM IORT system) have been analyzed over a 7 year period. The procedures were performed at a single institution by a single surgical and radiation oncology group. Post-operative whole breast radiotherapy (WBRT) was generally recommended in high risk patients with positive sentinel lymph nodes (SLN), lymphovascular invasion (LVI), extensive intraductal component (EIC), or positive margins requiring re-excision. Local recurrence was defined as any same breast recurrence during the follow-up period. Results: A total of 438 patients were included in the analysis. Median follow-up was 35 months. Median age was 68 years, mean tumor size on preoperative ultrasound was 1.2 cm. Patient characteristics are listed below: Patient/Tumor CharacteristicnGrade 1-232474.5%Grade 311125.5%Presence of LVI429.9%Presence of EIC4811.6%ER Negative429.7%PR Negative7918.4%DCIS only6514.4%Invasive Lobular only102.2%Positive SLN276.9%Re-excision performed6013.7% A total of 16 patients (3.7%) had a local or simultaneous local/regional recurrence. Median time to recurrence was 24.5 months. When analyzing associations between predictor variables and local recurrence using logistic regression, it was found that high tumor grade, EIC, LVI, DCIS or DCIS component, and need for re-excision were significant (p<0.05) predictors of local recurrence. Furthermore, there was a strong association with local recurrence and time to local recurrence when adjuvant endocrine therapy was recommended but the patient was either non-compliant or discontinued use due to side-effects (odds ratio 0.064, p<0.0005). Conclusions: INTRABEAMTM IORT can be used in select breast cancer patients with low local recurrence rates. Unfavorable tumor features and non-compliance with adjuvant endocrine therapy result in the highest risk of local recurrence. Better patient selection and pre-treatment education should minimize this risk. Citation Format: Christina Munford, William E Burak Jr, Krista Miller, Jennifer Davis, Nicole Neal, Caleb Price, Matthew Bertke, Michael Hasselle, Aaron Pederson. A seven year single institution experience with IntrabeamTM intraoperative radiation therapy:recurrence rates and predictors of recurrence [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-12-16.