Long-term outcomes of patients with conserved breast cancer treated with adjuvant hypofractionated prone breast intensity-modulated radiation therapy

Introduction New techniques for adjuvant radiation therapy after breast conservation include prone positioning, hypofractionation and intensity-modulated radiation therapy (IMRT). Long-term evaluations of this combination are lacking, and we report our own experience. Methods Patients with invasive breast cancer followed for a minimum 36 months post-IMRT were eligible. Dose used was 40 Gray in 15 fractions over 3 weeks to the whole breast via forward-planned prone, whole breast IMRT. A 10 Gy in 5 fraction supine boost was offered. Results Between January 2012 and January 2020, 2199 patients had breast conservation and adjuvant radiation: 489 received hypofractionated prone breast IMRT, with 155 eligible for our evaluation. Median follow-up was 52 months. Median age was 62 (range 36-80), 78.7% were T1, 20.6% were T2, and 12.3% were node-positive. Grade was 1 in 26.5%, 2 in 43.9% and 3 in 29.7%; 87.1% were oestrogen receptor positive, 3.2% were HER2 positive, and 11.0% were triple negative. 58.6% received a boost, 74.8% endocrine therapy and 32.3% chemotherapy. No patient developed local recurrence. One regional recurrence was successfully salvaged. Six patients (3.9%) developed metastases, and 1.9% died. Five-year actuarial local recurrence-free, regional recurrence-free and breast cancer-specific survival rates were 100.0%, 98.2% and 94.8%. Late grade 1 and 2 breast pain occurred in 20.0% and 1.3% of patients. Only 11.0% had new pain compared to pre-radiation. No patient developed radiation-induced pneumonitis, pulmonary fibrosis, rib fracture or cardiac toxicity. All patients scored cosmesis as 'good' or better. Conclusion Adjuvant hypofractionated prone breast IMRT has excellent locoregional control and minimal toxicity.