OBJECTIVES: Boost-dose radiation during breast-conserving surgery (BCS), followed by whole breast external beam radiotherapy (WB-EBRT), is associated with a reduced risk of recurrence. This systematic review aimed to evaluate the safety and effectiveness of intraoperative radiotherapy with low-energy X-ray (boost IORT) for breast cancer patients.

METHODS: Ovid-MEDLINE, Ovid-EMBASE, Cochrane library and five Korean databases were searched on February 19, 2021, for studies comparing conventional radiotherapy [EBRT, interstitial brachytherapy, intraoperative electron radiotherapy (IOERT)]. The target patient population for boost IORT comprised patients with breast cancer undergoing breast-conserving surgery. The risk of bias was assessed using the SIGN methodology checklist. The entire process was conducted in collaboration with experts in breast surgery, radiation oncology, and hemato-oncology.

RESULTS: 10 articles, including 5 randomized controlled trials (RCTs) and 5 cohort studies, were selected. The review found that local recurrence was slightly higher in the boost IORT group (1.2–9.9%) compared to the comparison group (0.7–8.3%), but there were no significant differences between the two groups. Recurrence-free survival did not significantly differ between the boost IORT and comparison groups (HR 0.61–1.19). Five-year disease-free survival did not significantly differ between the boost IORT group (81.0–88.5%) and the comparison group (68.0–86.0%). Most procedure-related complications such as hematoma/seroma, fat necrosis, edema occurred early after surgery and were not severe.

CONCLUSIONS: Boost IORT has been found to have an acceptable level of safety. Despite the fact that most of the included studies assessing effectiveness were retrospective, the outcomes were not clinically different from those of the group that received EBRT and IOERT as boost therapy. Hence, IORT is safe and effective as a boost therapy for patients undergoing BCS and WB-EBRT.