Guiding Sole Intraoperative Radiotherapy in Breast Cancer According to ASTRO Guidelines: Mitigating Adverse Outcomes in a Taiwan Single-Center

Background: Intraoperative radiotherapy (IORT) is considered a de-escalating adjuvant treatment for breast cancer low-risk patients. However, the broader criteria applied by the Taiwan IORT Study Cooperative Group led to an increased rate of locoregional recurrence (LRR) among patients receiving only IORT. Consequently, we revised the criteria for sole IORT treatment to include patients who meet the American Society for Radiation Oncology (ASTRO) eligibility standards. This study aims to investigate how aligning treatment strategies with ASTRO guidelines impacts oncological outcomes in patients receiving IORT.

Methods: From September 2014 to March 2022, a retrospective review of 632 patients with invasive breast cancer undergoing breast-conserving surgery assessed outcomes following External Beam Radiation Therapy (EBRT), sole IORT, or IORT combined with supplemental EBRT (IORT+boost), with a mean follow-up period of 4.71 ± 2.10 years. Strategic modifications following the ASTRO guidelines were implemented in April 2021 for sole IORT recipients.

Results: ASTRO-suitable patients had significantly lower rates of LRR (0.00% vs. 10.64%), distant metastasis (0.00% vs. 4.00%), and any recurrence (0.00% vs. 7.79%) than non-suitable patients (p < 0.05). After adjusting for confounders, the overall and non-suitable patients in the IORT group both exhibited significantly higher hazard ratios for LRR than those in the EBRT group, with values of 5.79 (95% confidence intervals (CI) = 1.75-19.18) and 5.48 (95% CI = 1.66-18.02), respectively.

Conclusions: Aligning treatment criteria with ASTRO guidelines for sole IORT significantly reduces locoregional recurrence rates in patients with invasive breast cancer, highlighting the efficacy of these strategic modifications in improving oncological outcomes.