ESTRO 2024 - Abstract Book

S483

Clinical - Breast

ESTRO 2024

intraoperative radiotherapy versus external beam radiation in suitable breast cancer patients

Tanun Jitwatcharakomol 1 , Jiraporn Setakornnukul 1 , Kullathorn Thephamongkhol 1 , Suebwong Chuthapisith 2 , Adune Ratanawichitrasin 2 1 Faculty of Medicine, Siriraj Hospital, Mahidol University, Radiation oncology, Bangkok, Thailand. 2 Faculty of Medicine, Siriraj Hospital, Mahidol University, Surgery, Bangkok, Thailand

Purpose/Objective:

Intraoperative radiotherapy (IORT) with electron method has higher ipsilateral breast tumor recurrence (IBTR) rates in early-stage breast cancer patients than external beam radiation (EBRT). Few randomized studies and retrospective studies with limited data suggested that this approach may be appropriate for a suitable subset of patients according to the ASTRO/ESTRO definitions. The objective of this study is to compare the oncological outcomes of an appropriate group of breast cancer patients.

Material/Methods:

This was a retrospective, single-center cohort study. Radiation treatments were employed to separate patients into two groups (IORT or EBRT). The primary goal was five-year local control, whereas the secondary outcomes were five year disease-free survival and breast cancer-specific survival.

Results:

From January 2011 to December 2022, 237 eligible patients following ASTRO/ESTRO definitions were assessed (IORT, 74 patients; EBRT, 163 patients). The median follow-up period was 5.5 years. The 5-year local control rates (LC) were as follows: 98.46% for IORT (95% confidence interval [CI], 89.6%-99.8%) and 100%(no incident) for EBRT (log-rank test P=.033). The 5-year disease-free survival (DFS) rates for IORT were 95.58% (95% CI, 86.9%-98.6%) and 98.67% (95% CI, 90.9%- 99.8%) for EBRT, respectively; log-rank test P=.026. The two groups' 5-year breast cancer-specific survival rates (BCSS) were comparable. The 5-year breast cancer-specific survival rates were 98.61% (95% CI, 90.5%-99.8%) for IORT and 100%(no event) for EBRT, with a log-rank test P-value of 0.175.

Conclusion:

IORT was associated with a small but statistically significant worse in 5-year LC and DFS in the suitable patient population. With absolute differences of 1.54 % for LC and 3.09 % for DFS without compromising BCSS, IORT with electron method should be applied with caution.

Keywords: IORT, Suitable patients, APBI