MRI-Guided Accelerated Partial Breast Irradiation: Treatment Outcomes and Patient Reported Cosmesis

Abstract

<h3>Purpose/Objective(s)</h3> Accelerated Partial Breast Irradiation (APBI) is a valid treatment option for women with early-stage breast cancer (BC) who meet the "suitable" criteria per ASTRO APBI guidelines. Magnetic Resonance Imaging guided APBI (MRgAPBI) results in less set up uncertainty and possibly tighter planning target volume (PTV) margins. This study aims to report MRgAPBI treatment outcomes and patient reported cosmesis. <h3>Materials/Methods</h3> This IRB approved retrospective study included early-stage BC patients who underwent lumpectomy with or without sentinel lymph node biopsy and were treated consecutively at our institution with MRgAPBI between 2018 and 2020, with a minimum follow up of 6 months. Charts were reviewed for patient and tumor characteristics, APBI induced adverse events, and treatment outcomes. Patients reported their breast appearance as "Poor, Fair, Good, or Excellent", two weeks after APBI completion and at their last follow up. <h3>Results</h3> The study included 19 eligible patients. Mean patients age was 72 years old (range 51 – 89), 68% had invasive ductal carcinoma (IDC), and 32% had ductal carcinoma in-situ. Mean tumor size was 9 mm (range 4-16 mm), 53%, 37%, and 10% had grade 1, 2, and 3 disease respectively. All patients had ER / PR positive disease, all IDC patients had HER2 negative disease, and a median Ki67 of 5% (range 1 – 60%). In patients with IDC, 8%, 69%, and 23% had stage pT1a, pT1b, and pT1c respectively. All patients had lymph node negative disease. Mean closest surgical margin was 5.75 mm (range 3-11 mm). 32% of patients received 30 Gy in 5 once daily fractions of 6 Gy given every other day, and 68% received 38.5 Gy in twice daily fractions of 3.85 Gy. All patients' plans met the dose constraints including the ratio of volume receiving at least 95% of the prescription dose to the whole breast target volume (< 15%). Median on-table treatment time was 30 minutes (range 23-40 minutes). All patients had a 1 cm expansion from the lumpectomy cavity to clinical target volume (CTV). CTV expansion to PTV ranged from 0-3 mm. Acute treatment induced adverse events included grade 1 dermatitis (16%), grade 1 breast pain (11%), and grade 1 fatigue (11%). All acute adverse events were resolved within 3 months. No patients experienced late adverse events. At a median follow up of 18 months (range 6 – 24 months), no patient had local-regional recurrence or distant metastases. At 2 weeks post treatment, 6%, 65%, and 29% of women described their breast appearance as "Fair", "Good", and "Excellent" respectively. At their last follow up, 41%, and 59% of women described their breast appearance as "Good", and "Excellent" respectively. <h3>Conclusion</h3> MRgAPBI in our early single institution experience is an effective and well tolerated treatment modality for women with early-stage BC who meet "suitable" criteria per ASTRO APBI guidelines. All patients reported their cosmetic outcomes as good or excellent and none had local, regional or distant recurrence at a median follow up of 18 months. Longer follow up and larger cohorts are required.