S1177
Clinical - Urology
ESTRO 2026
University Health Network, Toronto, Canada. 8 Radiation oncology, Centre Hospitalier de l’Université de Montréal, Montreal, Canada Purpose/Objective: To evaluate focal dose escalation to the gross intra- prostatic tumour/s with external beam radiotherapy (EBRT) and either an integrated boost (IB) or high-dose rate brachytherapy (HDR). Material/Methods: Patients with localised prostate cancer with gross tumour volume (GTV) identified on multiparametric magnetic resonance imaging (mpMRI), were eligible to participate in this phase 2 non-randomised clinical trial. All patients received prostate whole gland VMAT, 76Gy in 38 fractions (Fr). The boost strategy involved either an IB of 95Gy in 38fr (IB-VMAT) or HDR boost of 10Gy in a 1fr (HDR-boost). The primary end-point was 3-year local control assessed by MR-guided biopsy and/or MRI alone. Secondary outcomes include biochemical failure-free survival (bFFS), toxicity and health-related quality of life (HRQoL) using Common Terminology for Adverse Events version 4.0 (CTCAE v.4), the American Urological Association Symptom Score (AUASS), and Expanded Prostate Index Composite (EPIC). Results: Eighty patients (5% low-risk, 75% intermediate-risk and 20% high-risk) were enrolled from November 2012 to August 2016. The median (IQR) follow-up was 55.2 months (48.1-71.4 months). Sixty-six patients underwent a 3-year MRI and/or MRI-guided biopsy. Of these, one patient in the IB-VMAT arm demonstrated persistent disease on GTV biopsy. During follow-up, five patients developed biochemical recurrence (1 IB- VMAT; 4 HDR-boost), four of them had intraprostatic failures outside the boost volume (1 IB-VMAT; 3 HDR- boost) and 2 patients developed regional/distant metastases. The 5-year bFFS was 92% (95% CI, 85-99). No differences were found in bFFS or late toxicities between both arms. Grade (G) 2 genitourinary (GU) toxicity was comparable, 27.5% in the HDR-boost and 22.5% in the IB-VMAT arm; and G2 gastrointestinal (GI) toxicity was 5% in both arms. Two G3 (1 GI, 1 GU) toxicities were seen in the IB-VMAT arm, a rectal fistula and haematuria secondary to a new diagnosis of bladder cancer. A significant difference was found in AUASS at 2 years in favour of HDR-boost (p = 0.04), however this was not maintained at 3 years (p = 0.11). There was a significant difference in Sexual domain (p 0.05) and bother (p 0.04) were significantly higher at 1 month in favour to IB-VMAT however this was not maintained over time. Conclusion: Dose escalation to intraprostatic lesions, with either IB-VMAT or HDR-boost, provided high rates of local and biochemical control with limited impact in HRQoL
frequent early GI effects were diarrhoea, proctitis, both more frequently reported with PPN. At 2 years, G2+ rates were low with no differences between groups: P 3%, PPN 5%; p=0.28. Cumulative incidence of 2-year late GI CTCAE G2+ events were P: 8.5% (95%CI: 6.4-11.3%), PPN: 10.8% (8.4-13.9%), logrank p=0.21. RTOG GI G2+ 2-year cumulative incidence was P: 6.1% (4.4-8.6%, 31 events), PPN: 8.0% (5.9-10.7%, 40 events); p=0.24.There were no differences in early GU CTCAE G2+ side effects (P 46.5%, PPN 50.3%, p=0.22) or late effects at 2 years (P 10.3%, PPN 10.8%, p=0.82). Cumulative incidence of late GU CTCAE G2+ was P: 20.6% (17.4-24.4%), PPN: 24.6% (21.1-28.6%); logrank p=0.10. Late GU RTOG G2+ events were less frequent than CTCAE; cumulative incidence P: 12.4% (9.8-15.6%, 63 events), PPN: 12.7% (10.1-15.9%, 64 events); p=0.84. Conclusion: Early GI, but not GU, side effects were more common with PPN than P. Cumulative late GI and GU events and absolute rates at 2 years were similar. Nodal radiotherapy (47Gy/20f) is safe. References: 1. Syndikus I, Cruickshank C, Staffurth J, Tree A, Henry A, Naismith O, Mayles H, Snelson N, Hassan S, Brown S, Porta N, Griffin C, Hall E, on behalf of the PIVOTALboost Trial Management Group (2020). PIVOTALboost: A phase III randomised controlled trial of prostate and pelvis versus prostate alone radiotherapy with or without prostate boost (CRUK/16/018). Clinical & Translational Oncology. 25:22-8. Keywords: Prostate; Pelvic Node Radiotherapy, RCT Poster Discussion 1234 Tumor-targeted dose escalation for localized prostate cancer using MRguided HDR brachytherapy or integrated VMAT boost: Long- term outcomes Noelia Sanmamed Salgado 1 , Jerusha Padayachee 2 , Amy Liu 3 , Philip Ye 4 , Jenny Lee 5 , Alejandro Berlin 4 , Warren Foltz 4 , Bernadeth Lao 4 , Alexandra Rink 4 , Andrew Bayley 4 , Charles Catton 6 , Sangeet Ghai 7 , Andrew McPartling 6 , Rachel Glicksman 4 , Cynthia Ménard 8 , Peter Chung 6 1 Radiation Oncology, Hospital Clinico San Carlos, Madrid, Spain. 2 Radiation oncology, Auckland City Hospital, Auckland, New Zealand. 3 Radiation Oncology, University Health Network, Toronto, Canada. 4 Radiation Oncology, Princess Margaret Cancer Centre, University Health Network, Toronto, Canada. 5 Radiation, Princess Margaret Cancer Centre, University Health Network, Toronto, Canada. 6 Radiation oncology, Princess Margaret Cancer Centre,
University Health Network, Toronto, Canada. 7 Radiology, Princess Margaret Cancer Centre,
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