Accelerated Partial Breast Irradiation (APBI) Using Five Daily Fractions: A Prospective, Phase II, Multi-Centre Trial of Cosmetic Outcomes and Toxicity (The Accel Trial): Final Results

ABSTRACT

Purpose: To report final results of a clinical trial of APBI using intensity modulated radiotherapy (IMRT) to deliver 27 Gy in 5 daily fractions following breast conserving surgery (BCS) prospectively designed to assess the efficacy and cosmetic outcomes of a oneweek, APBI regimen among women with early breast cancer. Material(s) and Method(s) Women >= 50 years, with lymph nodenegative, ER positive, HER-2 negative breast cancer or ductal carcinoma in situ (DCIS), <= 3cm diameter, following BCS with margins >= 2mm, and excellent or good baseline cosmesis received 27 Gy in 5 daily fractions to the seroma plus 1 cm CTV and 0.7 cm PTV margins. Clinical photographs, patient and provider cosmetic scores, breast fibrosis, telangiectasia and pain were collected prospectively, prior to RT and at 6 weeks, 1 and 2 years after RT. The primary endpoint was the proportion of women who retained Excellent or Good cosmesis at 2 years using the EORTC Cosmetic Rating System. Cosmetic failure was deterioration from Excellent or Good to Fair or Poor. A panel of 5 radiation oncologists independently assessed the cosmetic photographs. Secondary endpoints were rates and grades of breast fibrosis, telangiectasia, breast pain, ipsilateral breast tumour recurrence (IBRT), overall (OS), breast cancer-specific survival (BCSS) and subsequent mastectomy. Efficacy outcomes were assessed at clinic visits and by review of charts. ClinicalTrials.gov registration NCT02681107. Result(s) A total of 298 patients were treated between April 25, 2016, and October 31, 2019. At a median follow-up of 48 months, the four-year OS was 98.5% (95% CI 96.1% - 99.5%) and BCSS was 99.7% (95% CI 97.6% - 99.9%). The four-year IBRT rate was 3.3% (95% CI 1.1% - 6.4%). There were 10 contralateral breast events for a four-year rate of 3.9% (95% CI 2.2% - 6.9%). There were 10 ipsilateral and six contralateral mastectomies. Two patients died of unrelated causes prior to two years;79 patients declined inclinic attendance due to COVID or competing comorbidities and 217 women had two-year cosmetic photographs and clinical assessments performed. Consensus of the photo-panel cosmesis at baseline was Excellent n=116 (53%), Good n=102 (47%), Fair n=1 (0.5%) and Poor n=0. Consensus overall cosmesis at two years was Excellent n= 141 (65%), Good n=78 (35%), Fair n=0 and Poor n=0. Most patients had either improved (n=168;77%) or no change (n=43;20%) in cosmesis at two years. No patient had cosmetic failure but 6 (3%) had a change from Excellent to Good at two years. Most patients reported either no (79%) or mild (21%) pain, with no moderate or severe pain. Two patients (0.9%) had Grade 2 fibrosis and five patients (2%) had visible telangiectasia that did not detract from overall cosmesis. Conclusion(s) APBI using 27 Gy in 5 fractions using a conformal IMRT technique, achieved excellent two-year cosmesis with minimal toxicity. The IBRT risk was comparable to the contralateral new breast cancer risk and to local recurrence rates of recently published early breast cancer trials. Copyright © 2022 Elsevier Ireland Ltd. This is an open access article under the CC-BY-NC-ND license (http//creativecommons.org/licenses/by-nc-nd/4.0/).