Intraoperative Radiation Therapy Versus Hypofractionated Whole Breast Irradiation in T1N0, ER Positive Patients

Abstract

The aim of this study was to compare local recurrence between intraoperative radiotherapy (IORT) and hypofractionated whole breast irradiation. Recently, new suitability criteria regarding accelerated partial breast irradiation (APBI) was published in an ASTRO consensus statement, which included IORT. This study utilized the new suitability criteria to conduct an analysis between IORT and hypofractionated whole breast irradiation. Intraoperative radiotherapy has been compared to whole breast irradiation in the past, but these studies have included conventional whole breast fractionation. In this single institution, retrospective cohort study, patients aged 50 or greater with T1N0, ER positive breast cancer were examined. Patients aged 50 or greater with T1N0, ER positive breast cancer were identified who received lumpectomy with IORT or lumpectomy followed by external beam radiation therapy at a single institution between January 2008 - June 2016. A total of 357 patients were included in the study. Of these, 45 patients received IORT with 20 Gy given at the time of surgery to the lumpectomy cavity. 312 patients received hypofractionated radiation therapy with 42.56 Gy given in 16 fractions of 266 cGy with or without a 1-3 fraction boost. Treatment groups were compared using Pearson chi-squared and Fisher’s exact test. Univariate Cox regression was used to determine factors associated with recurrence. Multivariate logistic regression was used to compare both treatment groups while adjusting for possible confounders. After a mean follow up of 3.4 years (range 0.1 - 9.1 years), the incidence of local recurrence was 2.2% in the IORT group compared to 1.6% in the hypofractionated group (p=0.17). No patients had distant recurrence in the IORT group compared to 1.3% in the hypofractionated group (p=0.66). The 5-year overall survival for the entire cohort was 98%, and there was no statistically significant difference in overall survival between the two groups (p=0.44). Treatment groups were similar with respect to histology (p=0.14), tumor grade (p=0.08), and adjuvant chemotherapy (p=0.40). The two treatment groups had different distributions of age (p=0.01), positive margin status (p=0.01), and adjuvant hormonal therapy (p=0.01), but this was addressed in the multivariate analysis. After adjusting for age, positive margin status, and adjuvant hormonal therapy, there was no statistically significant difference in local recurrence between IORT and hypofractionated whole breast irradiation (OR 0.17; 95% CI: 0.01, 1.87; p=0.15). Outcomes were similar between intraoperative radiotherapy and hypofractionated whole breast irradiation in this single institution cohort consisting of patients meeting suitability criteria for APBI (age 50 or greater with T1N0, ER positive breast cancer).