238 - Single-Institution Phase 1/2 Prospective Trial Evaluating Three-Fraction Partial Breast Irradiation: Four Year Outcomes Including Quantitative Cosmesis and Patient-Reported Outcomes
S. C. Raju1, M. Mahmood2, J. E. Zoberi3, M. A. Thomas4, L. L. Ochoa4, J. L. Garcia-Ramirez5, and I. Zoberi4; 1Washington University in St. Louis, St. Louis, MO, 2Washington University School of Medicine in St. Louis, Department of Radiation Oncology, St. Louis, MO, 3Washington University School of Medicine, Department of Radiation Oncology, St. Louis, MO, 4Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 5Washington University School of Medicine, Springfield, MO
Purpose/Objective(s): To report the four year failure rates, toxicity, cosmesis and quality-of-life (QoL) outcomes from a single institutional prospective phase I/II clinical trial of three-fraction accelerated partial breast irradiation (Tri-APBI). Materials/
Methods: Eligible breast cancer patients were at least 50 years old, postmenopausal, with hormone sensitive, HER-2 negative breast cancers, stage pTis-1N0M0 (=2cm) treated with breast conserving surgery to negative margins. HDR brachytherapy using a Strut-Adjusted Volume Implant (SAVI) applicator (22.5 Gy in 3 fractions) or external beam radiation therapy (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 surgical beds considered 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 by 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. Results: From August 2018 to March 2021, 75 patients were treated. Stage I disease was present in 79% and EBRT was used in 60%. Median follow-up was 49 months from completion of Tri-APBI (IQR 42 – 55 months). There were two IBTRs: one in a patient who did not receive endocrine therapy, and another in a patient who was compliant with endocrine therapy. Both patients underwent salvage mastectomy resulting in cure. There were no axillary or distant recurrences. There were three CTCAEv4.0 adverse events attributable to treatment, all Grade 1 and all of which self-resolved. Qualitative cosmesis, as measured by the Aaronson-modified Harris scale, was evaluated by patients and providers, respectively, as good-to-excellent in 94% and 99% pre-treatment, and in 91% and 98% at latest follow-up. Quantitative cosmesis was assessed by percentage of breast retraction assessment (pBRA) and showed that breast asymmetry did not worsen compared to pre-treatment, with a baseline mean pBRA of 7.5% (IQR 3.5% - 8.5%) and a 24-month mean pBRA of 6.1% (IQR 3.0% - 7.1%). QoL scores remained stable following APBI, as assessed by the EORTC score (QLQ-C30) and breast cancer-specific (QLQ-BR23) QoL questionnaires. Conclusion: Tri-APBI as delivered with EBRT or SAVI in this trial was safe and effective, with low IBTR rates at 4 years and minimal impact on patient-reported quality of life, qualitative, and quantitative cosmesis. Further follow-up is needed to evaluate long-term efficacy.
