ESTRO 36 Abstract Book

S161 ESTRO 36 2017 _______________________________________________________________________________________________

5 Beatson West of Scotland Cancer Centre, Oncology Department, Glasgow, United Kingdom 6 Royal Stoke Hospital, Oncology Department, Stoke-on- Trent, United Kingdom 7 Aukland Hospital, Physics Department, Aukland, New Zealand 8 Nuffield Health Cheltenham Hospital, Department of Surgery, Cheltenham, United Kingdom 9 Norfolk and Norwich University Hopsitals NHS Foundation Trust, Oncology Department, Norwich, United Kingdom 11 Kings College London, Oncology Department, London, United Kingdom 12 Clatterbridge Cancer Centre, Oncology Department, Bebington, United Kingdom 13 Mount Vernon Cancer Centre, Radiotherapy Department, Northwood, United Kingdom 14 Royal Cornwall Hospital, Oncology Department, Truro, United Kingdom 15 Independent Cancer Patient Voice, London, United Kingdom 16 Institute of Cancer Research, Academic Department of Radiotherapy, London, United Kingdom Background: Local cancer relapse rates after breast conservation surgery followed by radiotherapy have fallen sharply in many countries with risk influenced by patient age and clinico-pathological factors. In women at lower than average risk of local relapse, partial breast radiotherapy restricted to the vicinity of the original tumour is hypothesised to improve the balance of beneficial versus adverse effects compared with whole breast radiotherapy. Methods: The IMPORT LOW trial (ISRCTN12852634) recruited women aged ≥50 years after breast conserving surgery for invasive ductal adenocarcinoma pT≤3cm, pN0- 3, G1-3 and ≥2mm resection margins. Using 15 daily treatments, patients were randomly allocated (1:1:1) to 40 Gy whole breast radiotherapy (control), 36 Gy whole breast plus 40 Gy to partial breast (reduced dose) or 40 Gy partial breast only (partial breast). Primary endpoint was ipsilateral local relapse rate (80% power to exclude a +2.5% non-inferiority margin at 5 years for each test group). Findings: Between May 2007 and October 2010, 2018 women were recruited (control n=675, reduced dose: n=674, partial breast: n=669). With a 72.2 month median follow-up (IQR 61.7-83.2), 5-year local relapse rates were 1.1% (95%CI 0.5-2.3), 0.2% (0.02-1.2) and 0.5% (0.2-1.4) in control, reduced dose and partial breast groups. Absolute differences in local relapse rate compared with the control group were -0.73% (-0.99, 0.22) for the reduced dose and -0.38% (-0.84, 0.90) for the partial breast groups, demonstrating non-inferiority for both test groups. Photographs, patients and clinicians reported similar or lower levels of adverse effects after reduced dose or partial breast radiotherapy compared with whole breast radiotherapy (see Table 1).

Conclusion Arm function in patients treated with ALND was worse compared to patients without ALND. Patients reported significant more arm symptomatology after ALND followed by local RT compared to non-ALND patients treated with local RT and axillary irradiation in the first 3 months after start of RT. Updated results on PROMs with increased patient numbers, longer follow-up and multivariable analyses will be available at the 36 th ESTRO conference. SP-0314 Partial breast radiotherapy after breast conservation: 5 year outcomes from the IMPORT LOW (CRUK/06/003) phase III trial C. Coles 1 , C. Griffin 2 , A. Kirby 3 , R. Agrawal 4 , A. Alhasso 5 , I. Bhattacharya 2 , A.M. Brunt 6 , L. Ciurlionis 7 , H. Chan 8 , E. Donovan 3 , M. Emson 2 , A. Harnett 9 , J. Haviland 2 , P. Hopwood 2 , M. Jefford 10 , R. Kaggwa 2 , E. Sawyer 11 , I. Sybdikus 12 , Y. Tsang 13 , D. Wheatley 14 , M. Wilcox 15 , J. Yarnold 16 , J. Bliss 2 1 Cambridge Cancer Centre, University of Cambridge, Cambridge, United Kingdom 2 Clinical Trials and Statistics Unit, Institute of Cancer Research, London, United Kingdom 3 Royal Marsden NHS Foundation Trust, Department of Radiotherapy, London, United Kingdom 4 Shrewsbury and Telford Hospitals NHS Trust, Oncology Department, Shrewsbury, United Kingdom

Interpretation: At 5 years, partial breast and reduced dose radiotherapy showed local relapse rates non-inferior to that observed following whole breast radiotherapy and