S1201
Clinical - Urology
ESTRO 2026
conventional pelvic drainage pathways and are variably classified as regional (N1) or distant (M1a) metastases in prostate cancer, leading to uncertainty in staging and management[1]. With increasing adoption of PSMA PET/CT, sub-centimetre MRNs are more frequently detected, yet their clinical relevance and optimal treatment remain unclear. This study reports the largest single-centre cohort of prostate cancer patients with MRN involvement treated with radiotherapy (RT), evaluating nodal distribution, survival outcomes, and gastrointestinal (GI) toxicity rates, with a focus on predictors of GI toxicity. Material/Methods: All consecutive patients receiving prostate and pelvic nodal RT (PNRT) between January 2022 and January 2025 were retrospectively reviewed. MRN involvement was confirmed using PSMA PET, CT, and MRI. Clinical and treatment data, including radiation doses, systemic therapy, PSA, and GI toxicity (CTCAE v7), were collected for those with MRN involvement. RT plans were analysed for MRN–rectal wall distance and rectal dosimetry. Statistical analyses were performed in SPSSv31 with non-parametric tests (Mann–Whitney U, Fisher’s exact test); p<0.05 was considered significant. Results: Among 2,379 patients treated with prostate RT, 568 (24%) received PNRT, of whom 35 (6%) had MRN involvement. Review of these 35 patients showed in 25% MRN was the only nodal site. Systemic therapy comprised ARTA in 7 (20%) and Docetaxel in 4 (11%) patients. Median age was 67 years, median follow-up 20 months, and mean PSA 33 ng/mL. Grade 2 GI toxicity (G2GI) occurred in 2 patients (6%): one during RT and one 23 months post-RT; no grade ≥ 3 events occurred. Nineteen (54%) received an MRN boost (median 58Gy; range 51–61Gy), with G2GI observed in 2 (11%); neither received systemic therapy. Among those without G2GI toxicity, median MRN–rectal wall distance was 6mm (range 1–29mm). Two of five patients (40%) with MRN–rectal distance ≤ 1 mm who received a boost doses (60 Gy/37fr and 51 Gy/20fr) developed G2GI toxicity (p=0.017 Fisher’s exact). Fractionation schedules, boost dose, mean rectal dose, and systemic therapy were not significantly associated with G2GI toxicity. Two patients progressed; one died of metastatic disease.
fraction fluctuations averaged 73.1 ml (33.6%). Larger planning bladder volumes were significantly associated with greater bladder volume variability (p<0.001). A higher baseline water intake (p=0.043) and a greater fluctuation in water intake during treatment (p=0.037) were also correlated with increased volume variability. A water intake exceeding 875 ml at planification was predictive of a volumetric variability beyond -30% (AUC=0.773). No significant associations were found with treatment timing, prostate gland volume, or the other clinical parameters.
Conclusion: Large bladder volumes at planification, as well as excessive and inconsistent hydration are the main predictive factors of bladder volume variability during prostate radiotherapy. Maintaining a stable and moderate water intake, below 875 ml, throughout treatment, combined with enhanced patient education, may improve bladder reproducibility and treatment precision. Keywords: Bladder volume, Predictive factors, Hydration Digital Poster 1914 Radiotherapy Toxicity in Prostate Cancer with Mesorectal Node Involvement: Balancing Coverage and Complications — Large UK Academic Centre Results Mehrshad Sultani Tehrani 1 , Emily Orgovanyi 1 , Muskan Sardana 1 , Kirsty Blythe 2 , Barbara Fuller 2 , Isaac Arthur 2 , Gurdip Azad 2 , Kirsty Morrison 2 , Victoria A Harris 2 , Vinod Mullassery 2 , Vishal Manik 2 , Stephen Morris 2 , Ajay Aggarwal 2 , Sindu Vivekanandan 1,2 1 Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom. 2 Guy's Cancer Centre, Guy's and St Thomas' NHS Trust, London, United Kingdom
Purpose/Objective: Mesorectal lymph nodes (MRNs) lie outside
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