Intraoperative radiation therapy for early-stage breast cancer: a single-institution experience

Abstract

Background: To assess outcomes and toxicity after low-energy intraoperative radiotherapy (IORT) for early-stage breast cancer (ESBC).

Materials and methods: We reviewed patients with unilateral ESBC treated with breast-conserving surgery and 50-kV IORT at our institution. Patients were prescribed 20 Gy to the surface of the spherical applicator, fitted to the surgical cavity during surgery. Patients who did not meet institutional guidelines for IORT alone on final pathology were recommended adjuvant treatment, including additional surgery and/or external-beam radiation therapy (EBRT). We analyzed ipsilateral breast tumor recurrence, overall survival, recurrence-free survival and toxicity.

Results: Among 201 patients (median follow-up, 5.1 years; median age, 67 years), 88% were Her2 negative and ER positive and/or PR positive, 98% had invasive ductal carcinoma, 87% had grade 1 or 2, and 95% had clinical T1 disease. Most had pathological stage T1 (93%) N0 (95%) disease. Mean IORT applicator dose at 1-cm depth was 6.3 Gy. Post-IORT treatment included additional surgery, 10%; EBRT, 11%; adjuvant chemotherapy, 9%; and adjuvant hormonal therapy, 74%. Median total EBRT dose was 42.4 (range, 40.05-63) Gy and median dose per fraction was 2.65 Gy. At 5 years, the cumulative incidence of ipsilateral breast tumor recurrence was 2.7%, the overall survival rate was 95% with no breast cancer-related deaths, and the recurrence-free survival rate was 96%. For patients who were deemed unsuitable for postoperative IORT alone and did not receive recommended risk-adapted EBRT, the IBTR rate was 4.7% versus 1.7% (p = 0.23) for patients who were either suitable for IORT alone or unsuitable and received adjuvant EBRT. Cosmetic toxicity data was available for 83%, with 7% experiencing grade 3 breast toxicity and no grade 4-5 toxicity.

Conclusions: IORT for select patients with ESBC results in acceptable outcomes in regard to ipsilateral breast tumor recurrence and toxicity.

Keywords: Intrabeam; breast cancer; clinical outcomes; intraoperative radiation; radiation toxicity.

Figure 1

Kaplan-Meier curves. A. 5-year ipsilateral breast tumor recurrence; the 5-year rate was 2.7%. B. Ipsilateral breast tumor recurrence rates by radiation received and suitability group; the 5-year ipsilateral breast tumor recurrence for patients who completed recommended radiation therapy (i.e., patients who were suitable for intraoperative radiotherapy (IORT) alone according to 2016 ASTRO Consensus Criteria or patients who were unsuitable and also received adjuvant external-beam radiation therapy (EBRT) was 1.7% versus 4.7% for patients who did not meet suitability criteria post-operatively and did not receive adjuvant EBRT (p = 0.23)

Figure 2

Incidence of adverse events (n = 167); only the highest-grade toxicity for each adverse event was counted for each patient