A Single-Institution Retrospective Study of Three-Fraction HDR Accelerated Partial Breast Irradiation

Abstract

Accelerated partial breast irradiation (APBI) delivered with high-dose-rate brachytherapy is a standard of care treatment typically delivered over 10 fractions. The TRIUMPH-T multi-institutional study recently demonstrated promising results using a shorter three fraction regimen, however there are limited additional published series using this regimen. Here, we report our experience and outcomes for patients treated as per the TRIUMPH-T regimen. This study was a retrospective single-institution analysis of patients who underwent lumpectomy followed by APBI (22.5 Gy in 3 fractions delivered over 2-3 days) using a Strut Adjusted Volume Implant (SAVI) applicator between November 2016 and January 2021. Dose-volume metrics were obtained from the clinically treated plan. Chart review was performed to determine locoregional recurrence and toxicities according to CTCAE v5.0. Between 2016 and 2021, 31 patients were treated per the TRIUMPH-T protocol. Median followup was 31 months from completion of brachytherapy. There were no acute/late Grade 3 or higher toxicities. Cumulative late Grade 1 and 2 toxicities were seen in 58.1% and 9.7% of patients, respectively. Of note, four patients experienced locoregional recurrence: three ipsilateral breast tumor recurrences and one nodal recurrence. All three ipsilateral breast tumor recurrences occurred in patients who would be classified as "cautionary" based on ASTRO consensus guidelines due to age ≤50, lobular histology, or high grade. Three-fraction HDR brachytherapy APBI was well-tolerated with no grade 3 or higher toxicities and an acceptably small percentage of grade 2 toxicities. Given the small sample size, the number of recurrences suggests that attention to appropriate patient selection is necessary until more long-term followup data is available.