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PURPOSE: To assess the cosmetic impact of breast conserving surgery (BCS), whole breast irradiation (WBI) fractionation and tumour bed boost (TBB) use in a phase III trial for women with ductal carcinoma in situ (DCIS) of the breast. MATERIALS AND METHODS: Baseline and 3-year cosmesis were assessed using the European Organization for Research and Treatment of Cancer (EORTC) Cosmetic Rating System and digital images in a randomised trial of non-low risk DCIS treated with postoperative WBI +/- TBB. Baseline cosmesis was assessed for four geographic clusters of treating centres. Cosmetic failure was a global score of fair or poor. Cosmetic deterioration was a score change from excellent or good at baseline to fair or poor at three years. Odds ratios for cosmetic deterioration by WBI dose-fractionation and TBB use were calculated for both scoring systems. RESULTS: 1608 women were enrolled from 11 countries between 2007 and 2014. 85-90% had excellent or good baseline cosmesis independent of geography or assessment method. TBB (16 Gy in 8 fractions) was associated with a >2-fold risk of cosmetic deterioration (p < 0.001). Hypofractionated WBI (42.5 Gy in 16 fractions) achieved statistically similar 3-year cosmesis compared to conventional WBI (50 Gy in 25 fractions) (p ≥ 0.18). The adverse impact of a TBB was not significantly associated with WBI fractionation (interaction p ≥ 0.30). CONCLUSIONS: Cosmetic failure from BCS was similar across international jurisdictions. A TBB of 16 Gy increased the rate of cosmetic deterioration. Hypofractionated WBI achieved similar 3-year cosmesis as conventional WBI in women treated with BCS for DCIS.

Theodora A Koulis, Tien Phan, Ivo A Olivotto Department of Oncology, University of Calgary, Tom Baker Cancer Centre, Calgary, AB, Canada Abstract: Adjuvant radiotherapy (RT) is an important part of breast cancer management but the dose and fractionation schedules used are variable. A total of 50 Gy in 25 daily fractions delivered over 5 weeks is often considered the "standard" adjuvant RT prescription. Hypofractionated regimes such as 42.5 Gy in 16 daily fractions or 40 Gy in 15 daily fractions following breast-conserving surgery have proven to be equally effective and achieve similar or better cosmetic and normal tissue outcomes for both invasive and in situ diseases and when treating the regional nodes. Hypofractionation is more convenient for patients and less costly. However, certain patients at higher risk of RT late effects may benefit from a less intense, even more extended fractionation schedule. This review describes the indications for whole breast hypofractionated adjuvant RT for patients with breast cancer following breast-conserving surgery and proposes that hypofractionation should be the new "standard" for adjuvant breast cancer RT. Keywords: fractionation, breast cancer, cosmesis, radiotherapy