Intraoperative Radiation Therapy (IORT): A Series of 1000 Tumors.

Background: Two prospective, randomized trials, TARGIT-A and ELIOT, have shown intraoperative radiation therapy to be a safe alternative, with a low-risk of local recurrence, compared with whole breast radiation therapy, following breast-conserving surgery, for selected low-risk patients. We report the first 1000 tumors treated with this modality at our facility.

Methods: A total of 1000 distinct breast cancers in 984 patients (16 bilateral) were treated with breast conserving surgery and X-ray IORT from June 2010 to August 2017. Patients were enrolled in an IORT registry trial. Local recurrence was the primary endpoint.

Results: There have been 28 ipsilateral local recurrences, ten DCIS and 18 invasive. Four local recurrences were within the IORT field, 13 outside of the IORT field but within the same quadrant as the index cancer, and 11 were new cancers in different quadrants. There have been four regional nodal recurrences and one distant recurrence. There have been no breast cancer related deaths and 14 non-breast cancer deaths. With a median follow-up of 36 months, Kaplan-Meier analysis projects 3.9% of patients will recur locally at 4 years. This includes all ipsilateral events in all quadrants.

Conclusions: The local, regional, and distant recurrence rates observed in this trial were comparable to those of the prospective randomized TARGIT-A and ELIOT trials. The low complication rates previously reported by our group as well as the low recurrence rates reported in this study support the cautious use and continued study of X-ray IORT in women with low-risk breast cancer.