Pre- and Intraoperative Factors Influencing Omission of Planned Intraoperative Radiation Therapy As a Boost for Breast Cancer Patients Undergoing Breast Conserving Treatment

Abstract

Ongoing trials are investigating the efficacy of intraoperative radiotherapy (IORT) using photon radiosurgery system as a tumor bed boost for high-risk breast cancer patients undergoing breast conserving treatment. We evaluated preoperative and intraoperative variables influencing the decision to abort the planned IORT boost. A phase II IORT boost trial began in August 2014, and eligible patients were women who were aged 20 years or older, were compatible for lumpectomy, and had ductal carcinoma in situ (DCIS) or invasive carcinoma (Stage I-III). All patients underwent MRI evaluation and were discussed in a multidisciplinary conference for eligibility. The presence of invasive carcinoma and DCIS in resection margins were intraoperatively assessed by the frozen pathologic examination. Optically stimulated luminescence dosimeter detected radiation dose delivered to the skin during IORT. Pre- and intraoperative variables were compared between patients undergoing IORT and those whose planned IORT was cancelled due to anatomical reasons. A total of 434 patients were eligible and underwent a surgery with intension to carry out IORT between August 2014 and December 2017. IORT was cancelled in 90 patients for anatomical reasons including repeated positive margins causing large tumor cavity or total mastectomy (n = 27), insufficient cavity-skin distance (n = 14), satellite lesions causing large tumor cavity or total mastectomy (n = 12), large primary tumor or uncertain tumor margins in MRI causing large tumor cavity (n = 6), tumor cavity geometry unsuitable for IORT (n = 6), subareolar extension (n = 6), tumor abutting pectoralis muscle (n = 3), and non-anatomical reasons including patient’s refusal (n = 5), bilateral breast cancer (n = 3) or benign pathology (n = 3) confirmed during surgery, device malfunction (n = 3), and scheduling difficulty (n = 2). The percentage of IORT omission was 23.8% in 2015, 20.9% in 2016, and 19.3% in 2017. Primary tumor >2.0 cm (n = 0.033) and positive frozen section (n = 0.013) were significantly associated with omission of planned IORT, while breast size, tumor location, DCIS pathology were not. The median skin dose measured during IORT was 2.10 Gy (range, 0.33-10.89 Gy), and acute toxicity after IORT and whole breast irradiation was observed in 16% of the patients (seroma requiring repeated aspiration 13.5% and wound complication 2.7%). A successful IORT procedure depended on preoperative imaging evaluation and status of surgical margins. MRI-based patient selection allowed restriction of skin dose and tolerable acute toxicity.