Intraoperative breast radiation therapy with image guidance: Findings from CT images obtained in a prospective trial of intraoperative high-dose-rate brachytherapy with CT on rails

Purpose: Intraoperative radiation therapy (IORT) is an increasingly popular approach to breast conserving therapy in the treatment of early-stage breast cancer. A drawback to IORT compared with postoperative adjuvant radiation therapy is that it is not performed using image guidance. Our aim was to report on how our institution's unique IORT workflow integrates CT image guidance and how these CT images were used intraoperatively to change applicator positioning. Methods and Materials: We retrospectively reviewed the first 29 patients who participated in a prospective clinical trial of breast IORT at our institution. All patients underwent lumpectomy, multicatheter balloon placement, intraoperative CT scan, and high-dose-rate brachytherapy treatment delivery to 12.5 Gy to 1 cm from the balloon surface. This report focuses on the intraoperative CT findings that led to clinical changes, followed by repeat CT for IORT treatment planning. Results: After initial intraoperative CT, 7 patients underwent an additional intraoperative CT scan (24.1%). In 6 patients, the initial intraoperative CT scan identified large air cavities and/or poor tissue conformity. This defect could be improved in all patients with adjustment of the balloon applicator before planning and delivering IORT. Intraoperative CT scan was used in one patient to localize a biopsy clip and aided in excision to negative margin. Conclusions: In our study, intraoperative CT identifies actionable findings in breast IORT, including residual tumor or errors in applicator positioning, in almost 25% of patients. Clinical results of the described trial will serve to further validate this image-guided approach to IORT.