Single-Institution Phase 1/2 Prospective Trial Evaluating Three-Fraction Partial Breast Irradiation: Safety and Patient-Reported Outcomes of TRI-APBI

Abstract

To report the initial tolerance, quality-of-life (QoL), and cosmetic outcomes from a single institutional prospective phase I/II clinical trial of three fraction accelerated partial breast irradiation (Tri-APBI).Eligible breast cancer patients were treated with breast conserving surgery to negative margins and were at least 50 years old, postmenopausal, with hormone sensitive, HER-2 negative cancers, and stage pTis-1N0M0 (2 cm or less in size). HDR brachytherapy using a SAVI applicator (22.5 Gy in 3 fractions) or external beam radiation (EBRT) (25.5 Gy in 3 fractions) over 2-3 days was used to deliver Tri-APBI. APBI modality was chosen by the treating physician, based on physical exam and ultrasound assessment of the surgical bed. In general, those surgical beds suitable for brachytherapy were treated with SAVI. EBRT was delivered using MR-guidance, unless contraindicated. The PTV for all patients was created using a 1-cm expansion of breast tissue around the surgical bed limited 0.5 cm from the skin surface, and for SAVI patients excluded the applicator. Coprimary endpoints were grade 3+ CTCAEv4.0 toxicity and ipsilateral breast tumor recurrence (IBTR). Patient-reported QOL and cosmesis via qualitative and quantitative methods were also assessed.From August 2018 to January 2021, 73 of a planned 75 patients have been treated. Stage I disease was present in 78% and EBRT was used in 59%. Median follow-up was 14 months from completion of Tri-APBI (range, 1 - 28). There has been no grade 3+ CTCAEv4.0 toxicities, and no cancer recurrences. Qualitative cosmesis, as measured by the Aaronson-modified Harris scale, was evaluated by patients and providers respectively as good-to-excellent in 94% and 98% pre-treatment and 94% and 95% at latest follow-up. Quantitative cosmesis was assessed by percentage of breast retraction assessment (pBRA) and showed that breast asymmetry did not significantly worsen compared to pre-treatment, with a baseline mean pBRA of 7.2% (range 2.1 - 22.6%) and a 12-month mean pBRA of 6.9% (range 1.6 - 26.8%). There was no significant decline in QOL over time after APBI as assessed by the EORTC core (QLQ-C30) and breast cancer-specific (QLQ-BR23) QOL questionnaires.Tri-APBI as delivered with EBRT or SAVI in this trial was safe, with a minimal initial impact on patient-reported quality of life, qualitative and quantitative cosmesis. Further follow-up is needed to evaluate efficacy.