Long-Term Outcome of Intraoperative Radiotherapy for Early-Stage Breast Cancer

Intraoperative radiotherapy (IORT) offers single-session treatment during breast-conserving surgery (BCS). Outcomes depend heavily on patient selection and tumor characteristics.

To assess local recurrence (LR) and prognosis using the 2024 American Society for Radiation Oncology (ASTRO) risk classification in IORT-treated patients.

This multicenter retrospective study analyzed 358 IORT cases (356 patients) treated between 2014 and 2018 using the Zeiss INTRABEAM system. Cases were classified per the 2024 ASTRO partial-breast irradiation guidelines. The primary endpoint was local recurrence-free survival (LRFS); secondary endpoints included overall survival (OS) and mastectomy-free survival (MFS).

The median age was 66 years (range 48-80); all tumors were invasive with a median tumor size of 10 mm. At a median follow-up of 7.1 years, LR occurred in 14/358 cases (3.9%) at a median of 5.2 years post-diagnosis. Five- and 8-year LRFS were 98.3% and 94.8%, respectively; 5- and 8-year OS were 99.4% and 97.7%; MFS at 8 years was 98.2%. Cases that were classified as "conditionally recommended" or "conditionally not recommended" had significantly higher LR than the "suitable" group (8.5% vs. 2.7%; HR 3.25, 95% CI 1.05-10.08, p = 0.041). Exploratory analysis showed that cases with ≥2 conditional criteria carried a markedly higher risk than those with 0-1 (21.4% vs. 3.2%; Firth-penalized Cox HR 8.26, 95% CI 2.06-26.06, p = 0.005).

In appropriately selected patients, IORT achieves local control consistent with contemporary series. The 2024 ASTRO risk classification effectively identifies high-risk cases, supporting its use for risk-adapted candidate selection.