Intraoperative radiotherapy versus whole breast radiotherapy in early-stage breast cancer: a retrospective outcome analysis based on ASTRO guidelines on PBI.

Background: Intraoperative radiotherapy (IORT) is a convenient treatment techniques for patients with early-stage breast cancer. We aimed to compare the outcome of IORT to that of whole-breast external beam radiotherapy (EBRT) in highly selected breast cancer patients based on the 2023 American Society for Radiation Oncology (ASTRO) Clinical Practice Guideline for Partial Breast Irradiation (PBI).

Patients and methods: We reviewed patients who underwent breast-conserving surgery (BCS) and received either IORT or EBRT for early-stage breast cancer between 2014 and 2019. The outcomes of these patients were analyzed and compared across different risk stratifications according to the 2023 ASTRO Clinical Practice Guideline for PBI, which categorized the patients into "recommended", "conditionally recommended", or "conditionally not recommended" groups.

Results: A total of 732 patients were enrolled with a mean follow-up time of 5.1 years. Among patients in the recommended group, the locoregional recurrence rates were 2.0% for IORT and 2.3% for EBRT (p = 0.978). Conversely, in the conditionally recommended or conditionally not recommended groups, IORT exhibited significantly higher locoregional recurrence rates compared to EBRT: in the conditionally recommended group, IORT had a recurrence rate of 11.1% versus 3.0% for EBRT (p = 0.044), and in the conditionally not recommended group, IORT had a rate of 13.8% versus 2.5% for EBRT (p = 0.010).

Conclusions: The locoregional recurrence rate in the IORT group was comparable to that of the EBRT group for patients recommended for PBI. However, for patients categorized as conditionally recommended or conditionally not recommended for PBI, the IORT group showed a higher locoregional recurrence rate, highlighting the need for careful patient selection.