S2968
Late-Breaking
ESTRO 2026
Liverpool, United Kingdom. 18 Radiotherapy Quality Assurance, Mount Vernon Cancer Centre, London, United Kingdom. 19 Radiotherapy Physics, Addenbrookes Hospital, Cambridge, United Kingdom. 20 Radiotherapy Physics, Mount Vernon Hospital, London, United Kingdom Purpose/Objective: IMPORT HIGH is a randomised phase 3 trial testing dose escalated simultaneous integrated boost (SIB) against sequential boost using intensity modulated radiotherapy and image guided radiotherapy (IGRT) for early-stage breast cancer with high local relapse risk. We report results of updated efficacy analyses at 10 years and 10-year adverse effects (AE). Material/Methods: Women aged ≥ 18 after breast conservation surgery for pT1-3pN0-pN3aM0 invasive carcinoma were randomised (1:1:1) between 40Gy/15F to whole breast (WB) + 16Gy/8F sequential photon boost to tumour bed (40+16Gy; control), 36Gy/15F to WB, 40Gy to partial breast + 48Gy (48Gy) or + 53Gy (53Gy) in 15F SIB to tumour bed. In all patients, boost planning target volume (PTV) was the clip-defined tumour bed + 5mm. AE were assessed annually by clinicians (all patients). Primary endpoint was ipsilateral breast tumour relapse (IBTR). The focus at 10 years is on estimation of effects; no formal test of non-inferiority was conducted given this was the focus at the 5 year primary endpoint. Results: 2617 women consented from 03/2009-09/2015 from 76 UK centres. With a median follow-up of 120.6 months (IQR 119.8, 121.9), 105 IBTR events have been reported to date (40+16Gy: 28, 48Gy: 32, 53Gy: 45). Estimated unadjusted 10-year IBTR incidence was 3.5% (95%CI 2.4, 5.0) for 40+16Gy, 3.7% (2.6, 5.3) for 48Gy, 5.5% (4.1, 7.3) for 53Gy. Estimated absolute differences in 10-year IBTR incidence vs 40+16Gy were 0.4% (-1.1, 2.9) for 48Gy – still lower than the 3% non- inferiority criterion for the difference at 5 years; - and 2.0% (0.0, 5.2) for 53Gy. A total of 1497 patients had at least one radiotherapy related AE assessed at 10 years. Clinician reported moderate/marked AEs at 10 years are low in all groups and full results will be presented. Conclusion: At 10 years, IBTR event incidence is low in this higher- than-average risk breast cancer group treated with small boost PTVs and image-guided radiotherapy, whether the boost is delivered sequentially or simultaneously. Incidence in both 40+16Gy and 48Gy groups at 10 years remains lower than the 5% estimate for the control group at 5 years in original sample size calculations. SIB is a safe treatment with reduced patient visits. Further escalation of boost dose does not appear advantageous. These results
randomised controlled trial of prostate and pelvis versus prostate alone radiotherapy with or without prostate boost (CRUK/16/018). Clin Transl Radiat Oncol, 2020. 25: p. 22-28.2. Murthy, V., et al., Prostate- Only Versus Whole-Pelvic Radiation Therapy in High- Risk and Very High-Risk Prostate Cancer (POP-RT): Outcomes From Phase III Randomized Controlled Trial. J Clin Oncol, 2021. 39(11): p. 1234-1242.3. van As, N., et al., Phase 3 Trial of Stereotactic Body Radiotherapy in Localized Prostate Cancer. N Engl J Med, 2024. 391(15): p. 1413-1425. Keywords: Prostate cancer, SBRT, randomised controlled trial Proffered Paper 5570 Ten-year results of the IMPORT HIGH trial (ISRCTN47437448): Dose escalated simultaneous integrated boost radiotherapy in early breast cancer Charlotte E Coles 1 , Lucy Kilburn 2 , Anna M Kirby 3,4 , Mark A Sydenham 2 , Bahareh Khosravi 2 , Joanne S Haviland 5 , Gillian Barnett 6 , Indrani S Bhattacharya 6 , A Murray Brunt 7 , Charlie Chan 8 , Emma Harris 9 , Monica Jefford 10 , Cliona Kirwan 11 , Sara Lightowlers 12 , Andrew Poynter 13 , Elena Provenzano 14 , Elinor Sawyer 15 , Navita Somaiah 3,16 , Isabel Syndikus 17 , Yat Man Tsang 18 , Nicola
Twyman 19 , Karen Venables 20 , Judith M Bliss 2 1 Clinical Oncology, University of Cambridge,
Cambridge, United Kingdom. 2 ICR-CTSU, The Institute of Cancer Research, Sutton, United Kingdom. 3 Breast Unit, Royal Marsden NHS Foundation Trust, Sutton, United Kingdom. 4 Academic Radiotherapy, The Institute of Cancer Research, Sutton, United Kingdom. 5 Wolfson Institute of Population Health, Queen Mary University of London, London, United Kingdom. 6 Department of Oncology, Cambridge University Hospitals NHS Foundation Trust, Cambridge, United Kingdom. 7 School of Medicine, University of Keele, Keele, United Kingdom. 8 Department of Breast Surgery, Nuffield Hospital, Cheltenham, United Kingdom. 9 Physics, The Institute of Cancer Research, Sutton, United Kingdom. 10 Patient Advocate, Independent Cancer Patients' Voice, London, United Kingdom. 11 Division of Cancer Sciences, University of Manchester, Manchester, United Kingdom. 12 Oncology, North West Anglia Foundation Trust, Peterborough, United Kingdom. 13 Department of Medical Physics and Biomechanical Engineering, University College, London, United Kingdom. 14 Department of Histopathology, Addenbrookes Hospital, Cambridge, United Kingdom. 15 Precision and Population Oncology, Kings College, London, United Kingdom. 16 Division of Radiotherapy and Imaging, The Institute of Cancer Research, Sutton, United Kingdom. 17 Department of Radiotherapy, Clatterbridge Centre for Oncology,
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