2926 - Efficacy and Safety of Intraoperative Radiotherapy (IORT) as a Tumor Bed Boost Combined with Whole Breast Irradiation in Chinese Patients with Breast Cancer

Purpose/Objective(s): Intraoperative Radiation Therapy (IORT) has gained significant attention due to its precise definition of the tumor bed, avoidance of postoperative radiation therapy delays, and ability to deliver single high-dose irradiation. However, data from Chinese population are scarce, and the optimal dose remains undetermined. This study aims to observe the safety and efficacy of IORT as an alternative to conventional postoperative external beam radiation (EBRT) in Chinese breast cancer patients undergoing breast-conserving surgery (BCS).

Materials/Methods: A retrospective analysis was conducted on female breast cancer patients diagnosed pathologically with non-metastatic disease between May 2020 and December 2023 in our hospital. Patients underwent BCS with or without neoadjuvant treatment, followed by IORT and whole-breast EBRT afterward. Adjuvant systemic treatments were administered as needed. The incidence of disease recurrence and metastasis, disease-free survival (DFS), overall survival (OS), postoperative wound healing time were observed. Factors affecting efficacy were analyzed.

Results: A total of 217 patients were included. Except for 1 patient with poor wound healing, 1 with local recurrence before EBRT, and another who discontinued treatment due to personal reasons, all patients completed the standard treatment as described. Patient aged 20~67 years old (median 48 years), 77 patients aged under 45 years old. Most cases (208) were invasive ductal carcinomas, while 3 were special types of invasive cancers, and 6 were non-invasive cancers. For IORT doses, 189 patients received 10 Gy, and 28 received 10 Gy~20 Gy. 18 patients had received neoadjuvant chemotherapy. As for Luminal subtypes, 56 were Luminal A, 73 were Luminal B, 15 were Her-2 positive & HR negative, 28 were Her-2 positive & HR positive, and 45 were triple-negative. By the end of the last follow-up in December 2024, all patients were alive, with a median follow-up of 20 months (OS range: 12~55 months). 5 patients (2.3%) experienced local recurrence or metastasis. Fisher's exact test indicated that age <45 years (p=0.044) and T > +2cm (p=0.040) were significant influencing factors for recurrence and metastasis. DFS rates at 1 and 2 years were 99.1% (215/217) and 98.2% (213/217), respectively. Most patients (207/217) achieved wound healing within 4 weeks, with IORT dose significantly affecting wound healing time (p=0.000). The incidence of delayed wound healing was significantly higher in the high-dose group (20 Gy, 15.8%), compared to the intermediate-dose group (10-20 Gy, 0%) and the low-dose group (10 Gy, 2.6%).

Conclusion: IORT followed by postoperative EBRT is generally effective and safe in Chinese breast cancer patients. Age and tumor size significantly affect treatment outcomes. In this population, 20 Gy IORT dose notably impacted wound healing. 10 Gy~20 Gy IORT dose may be a better option. Further exploration into individualized IORT dose stratification based on risk factors is recommended.