S726
Clinical – Lower GI
ESTRO 2026
cancer centre, following the UK national rectal cancer IMRT guidance, with peritoneal space (‘bowel space’) and bladder as organs-at-risk (OAR). Patients were prospectively evaluated for acute side-effects, using a standardised bowel and urinary questionnaire, at two time points: at baseline (before radiotherapy) and 2–3 weeks after radiotherapy finished, before delayed surgery at 8-12 weeks after radiotherapy. Structured side effect data and radiotherapy metrics were collected retrospectively for analysis. Results: 231 patients were analysed, with the majority being T3 (129, 56%) and/or N+ (152, 66%). Three-quarters (74%) were male, the median age was 69 years (IQR 60-75), 48% were PS1+, and 12% had a pre-treatment stoma.The median volumes of bowel space receiving 10Gy, 15Gy, 20Gy and 23Gy were 320cm3 (IQR 216- 429cm3), 227cm3 (151-331cm3), 185cm3 (116- 260cm3), and 160cm3 (104-234cm3), respectively. The median of the mean bladder doses was 19.4Gy (16.1- 23.0Gy), and the median relative volume of bladder receiving 21Gy was 39.5% (26.3-52.7%).At baseline, 19.9% of patients reported moderate to severe impact of bowel symptoms on their Quality of Life, increasing to 33.8% post-radiotherapy, see Table 1. Symptom burden also increased across specific bowel domains, with worsening in 32.9% of patients for painful bowel movements (34%) and 31.8% with urgency/tenesmus. Urinary symptoms worsened for 28.7% of patients after SCRT. However, although the overall symptom burden increased, a substantial number of patients also saw improved symptoms, as illustrated for one questionnaire item (“Impact of bowel function on Quality of Life”) in Figure 1. Overall, only 2 (0.9%) of the 231 patients required admission for toxicities post SCRT. One was due to urinary retention secondary to constipation, while the other was due to severe constipation. Change in bowel opening frequency weakly correlated with V23Gy (OR=1.17 per 50cm3), but no other relationships between OAR doses and symptom change were identified.
mesorectum, including perirectal and presacral lymph nodes, with an upper boundary at the S2/S3 interspace.Treatment consisted of 50.4 Gy of conventional fractionated radiation, combined with fluoropyrimidine-based chemotherapy. Follow-up was performed every six months for two years, annually for the subsequent three years, and continued based on patient condition. The study endpoints included local control, disease-free survival (DFS), overall survival(OS), and cancer-specific survival (CSS). Results: With a median follow-up of 9.1 years (range 1.8-17.4), only three patients (5.7%) developed local recurrence. DFS rates at 10 and 15 years were 82.4%, while local progression-free survival was 93.6% at all time points. OS rates were 76% at 10 and 15 years, with CSS reaching 87.4%.Notably,despite the prolonged follow- up, loco-regional recurrences remained low, and gastrointestinal late adverse event was minimal (only one case of grade 3 anal/rectal pain). Conclusion: With over 10 years of follow-up,this study confirms that reducing radiation volumes inselected patients with locally advanced rectal cancer without lateral node metastases, does not compromise clinical outcomes.These findings support a more tailored approach to radiotherapy that minimises unnecessary exposure while maintaining excellent long-term disease control Keywords: reducede volume; radiochemotherapy; rectal cancer Digital Poster Highlight 3494 Acute Side Effects of Short-Course Radiotherapy in Rectal Cancer Nagendran Balaramal 1 , Paul Khoo Li Zhi 1 , Pang Yan Ling 1 , Christopher Hooper 1 , Thomas Pigott 1 , Alexandra Gilbert 1,2 , Ane Appelt 2,3 , Mark Teo 1,2 1 Leeds Cancer Centre, St James's University Hospital, Leeds, United Kingdom. 2 Leeds Institute of Medical Research at St James’s, University of Leeds, Leeds, United Kingdom. 3 Department of Oncology, Rigshospitalet, Technical University Hospital of Greater Copenhagen, Copenhagen, Denmark Purpose/Objective: Data on acute side effects after short-course radiotherapy (SCRT) for rectal cancer, especially for intensity-modulated radiotherapy (IMRT), are sparse. We report prospectively collected patient-reported acute side effects of SCRT for a large cohort of rectal cancer patients treated with IMRT. Material/Methods: Patients with locally advanced rectal cancer were treated with 25Gy in 5 fractions at a large tertiary
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