Intraoperative Radiation Therapy for Early-Stage Breast Cancer: A Single-Institution Experience

Abstract

We assessed patient outcomes and toxicity after the use of intraoperative low-energy photon radiotherapy for select early-stage breast cancer (ESBC) patients. This is a retrospective review of patients with unilateral ESBC treated with breast-conservation surgery followed by low-energy photon intraoperative radiotherapy (IORT) at a single institution between 2010 and 2017. Institutional suitability guidelines included: age ≥ 50 years, invasive ductal carcinoma (IDC) with or without DCIS, grade 1 – 2 tumors < 3 cm, ER and or PR positive, Her2 negative, clinically node negative, no lymphovascular space invasion (LVSI), and negative margins (>2 mm). 20 Gy was prescribed to the surface of the spherical applicator fitted to the surgical cavity at surgery. Postoperative patients who did not meet institutional guidelines for IORT alone were recommended adjuvant treatment, including possible additional surgery, external-beam radiotherapy (EBRT), chemotherapy, and/or endocrine therapy. Kaplan-Meier estimates and Cox regression analysis were used to assess ipsilateral breast tumor recurrence (IBTR), overall survival (OS), and relapse-free survival (RFS). 201 patients were included with a median follow up of 5.1 years. Most patients met institutional guidelines for IORT for ESBC. The median age was 67 years; 88% were Her2 negative and ER positive and/or PR positive, 97% had IDC, 87% had grade 1 or 2 disease on biopsy, and 95% had T1 disease. On final pathology, 8% had LVSI, 25% had close (<2 mm) margins, and 3% had positive margins. Most had pathological T1 (93%) N0 (95%) disease. The median IORT applicator size was 4.5 cm with a mean dose at 1 cm depth of 6.3 Gy delivered over an average of 37 minutes. 10% of patients completed additional surgery, 11% additional EBRT, 9% adjuvant chemotherapy, and 74% received adjuvant hormonal therapy. The median total EBRT dose was 42.4 Gy (range 40.05 - 63 Gy) with a median dose of 2.65 Gy/fraction. The 5-year cumulative risk of IBTR was 2%. There was no statistically significant difference in IBTR between patients considered unsuitable by our institutional guidelines (p = 0.93) or by the 2016 ASTRO consensus guidelines (p = 0.26) compared to patients who were considered suitable for IORT alone, by respective guidelines. Of the 98 patients who did not meet institutional criteria based on final surgical pathology, 32% received adjuvant EBRT. Of the 9 patients who experienced IBTR, 5 patients did not undergo indicated EBRT. The 5-year OS rate was 95% with no breast cancer-related deaths. The 5-year RFS rate was 96%. 83% of patients had documented toxicity information and the overall highest reported grade 3 toxicity was 8%; seroma was the most common grade 3 toxicity (4%). IORT for select patients with ESBC has led to acceptable outcomes in regards to ipsilateral breast tumor recurrence and toxicity. We continue to recommend adjuvant EBRT for patients who do not meet IORT suitability criteria upon review of final pathology.