S2958
Late-Breaking
ESTRO 2026
boost (p=0.7405). Conclusion: Boost dose significantly improves long-term LTC and CSS in patients treated with BCS and WBI, while causing only a non-significant increase in late side effects. Young age ( ≤ 40 years), positive or close margin status, and the presence of EIC should be considered as absolute indications for tumour bed boost. Keywords: breast cancer, tumour bed boost, randomised trial Proffered Paper 5479 HERMES: 2-year outcomes of a randomised phase II trial of 2-fraction and 5-fraction MRI-guided adaptive radiotherapy for prostate cancer Sian Cooper 1 , Katie Biscombe 2 , Alex Dunlop 3 , Rosalyne L Westley 1 , Adam Mitchell 4 , Uwe Oelfke 3 , Simeon Nill 3 , Julia Murray 1 , Derek Price 5 , Aidan Adkins 5 , Angela Pathmanathan 1 , Shaista Hafeez 1 , Chris Parker 1 , Georgina Manning 2 , Stephanie Burnett 2 , Sophie Alexander 6 , Trina Herbert 6 , Emma Hall 2 , Alison C Tree 1 1 Clinical Oncology, The Royal Marsden Hospital NHS Foundation Trust, Sutton, United Kingdom. 2 CTSU, The Institute of Cancer Research, Sutton, United Kingdom. 3 The Joint Department of Physics, The Royal Marsden Hospital/ The Institute of Cancer Research, Sutton, United Kingdom. 4 PPI, The Royal Marsden Hospital NHS Foundation Trust, Sutton, United Kingdom. 5 Patient and Public Involvement, The Royal Marsden Hospital NHS Foundation Trust, Sutton, United Kingdom. 6 Radiotherapy, The Royal Marsden Hospital NHS Foundation Trust, Sutton, United Kingdom Purpose Stereotactic body radiotherapy (SBRT) for localised prostate cancer is standard of care [1]. Short to medium term urinary adverse events (AE) remain a primary concern [2,3], with no difference in 5-year adverse events. The HERMES trial (NCT04595019) aimed to leverage the low alpha/beta ratio of prostate cancer and delivered 2-fraction (F) SBRT and 5F SBRT [4,5], facilitated by the precision afforded by MR-Linac delivery [6]. Two-year outcomes are reported. Methods
Proffered Paper 5468
Electron and brachytherapy boost after breast- conserving surgery and whole breast irradiation: 30-year results of the randomized Budapest Boost Trial Csaba Polgar 1,2 , Zoltan Takacsi-Nagy 1,2 , Tibor Major 1,2 , Janos Fodor 1 1 Department of Radiotherapy, National Institute of Oncology, Budapest, Hungary. 2 Department of Radiotherapy, Semmelweis University, Budapest, Hungary Purpose/Objective: To evaluate the long-term effect of electron and high- dose-rate (HDR) brachytherapy (BT) boost on local tumour control (LTC), survival, late side effects and cosmetic results after breast-conserving surgery (BCS) and whole breast irradiation (WBI) in a prospective Between 1995 and 1998, 620 women with stage I–II breast cancer who had undergone BCS were treated with 50 Gy WBI and then randomly assigned to receive either a boost to the tumour bed (n=303) or no further radiotherapy (n=317). Boost treatments consisted of either 16 Gy electron beam irradiation (n=237) or 8– 14.25 Gy HDR BT (n=66). Breast cancer-related events, late side effects, and cosmetic results were assessed. Results: At a median follow-up of 27.9 years for surviving randomized study. Material/Methods: patients, the crude rate of ipsilateral breast recurrence (IBTR) was 13.9% (42/303) with and 19.2% (61/317) without boost. The 5-, 10-, 20-, and 30-year actuarial rate of IBTR was 4.6% vs 11.9%, 12.6% vs 16.7%, 20.7% vs 26.3%, and 23.9% vs 32.5%, respectively (p=0.0289; RR:0.65). There was no significant difference in the 30- year rate of IBTR between patients treated with electron or HDR BT boost (21.1% vs 31.8%; p=0.1180). On univariate analysis, patient age ≤ 40 years (p=0.0001; RR:2.93), and positive or close (<2 mm) margin status (p=0.0366; RR:1.32) were found to be significant risk factors for IBTR, and in patients with an extensive intraductal component (EIC), there was a tendency toward a higher IBTR rate (p=0.0694; RR:1.50). The 30-year probability of relapse-free (RFS), cancer-specific (CSS), and overall survival according to boost irradiation was 45.4% vs 38.9% (p=0.0806; RR:0.82), 62.0% vs 51.5% (p=0.0282; RR:0.73), and 33.4% vs 27.9% (p=0.1182). A non-significant trend toward a higher incidence of grade 2–3 late side effects was observed in the boost arm (23.7% vs 16.6%; p=0.0826). However, the rate of excellent/good cosmetic results was similar in the two groups (54.7% vs 60.0%; p=0.3526). Cosmesis was rated as excellent/good in 51.7% of patients treated with HDR BT and in 56.5% of patients treated with electron
HERMES is a single-centre non-comparative randomised phase 2 trial. Participants with
intermediate or lower high-risk prostate cancer were randomised between 24 Gy in 2F over 8 days, with a 27 Gy integrated boost to the MRI defined tumour, and 36.25 Gy in 5F over 2 weeks to PTV, with 40 Gy to the prostate+proximal 1cm seminal vesicles. MRI guided adaptive radiotherapy (MRIgART) was delivered on the Unity MR-Linac (Elekta AB, Sweden) with daily online adaption. All participants had androgen deprivation treatment for at least 6 months. AE point
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