ESTRO 2025 - Abstract Book

S2000

Clinical - Urology

ESTRO 2025

2. Byrne, M., Archibald-Heeren, B. ...& Foroudi, F. (2022). Varian Ethos online adaptive radiotherapy for prostate cancer: Early results of contouring accuracy, treatment plan quality, and treatment time. Journal of Applied Clinical Medical Physics, 23(2), e13479. 3. Kibrom, A. Z., & Knight, K. A. (2015). Adaptive radiation therapy for bladder cancer: A review of adaptive techniques used in clinical practice. Journal of Medical Radiation Sciences, 62(4), 277 – 285.

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Digital Poster Primary endpoint analysis of the phase II DESTINATION-MRL trial for patients with favorable intermediate risk prostate cancer Mathijs G Dassen 1 , Alison C Tree 2 , Lisa Wiersema 1 , Ben Neijndorff 1 , Peter de Ruiter 1 , Joeke van der Linden 1 , Adam Mitchell 2 , Alex Dunlop 2 , Dylan Y Breitkreutz 3 , Sian Cooper 2 , Floris J Pos 1 , Tomas Janssen 1 , Danny Vesprini 3 , Uulke A van der Heide 1 1 Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, Netherlands. 2 Radiation Oncology, Royal Marsden NHS Foundation Trust, London, United Kingdom. 3 Radiation Oncology, Sunnybrook Health Sciences Centre, Toronto, Canada Purpose/Objective: Genitourinary toxicity and erectile dysfunction are the most commonly observed side effects in patients following external beam radiation therapy for localized prostate cancer (PCa). The rationale in the DESTINATION-MRL trial is that escalating dose to the gross tumor volume (GTV) whilst de-escalating dose to the prostate clinical target volume (CTV) can reduce these toxicities without compromising biochemical control in patients with favorable intermediate risk PCa. The primary endpoint of this study is the technical feasibility of this approach in online adaptive MRI guided stereotactic body radiation therapy (SBRT). Material/Methods: This trial ran as 3 parallel single-center phase II non-randomized trials in 3 different institutes (NCT06284304, NCT06177093, NCT05709496). Each institute enrolled 20 patients which were all treated on a 1.5T Unity MR-Linac. GTV was defined as tumor(s) visible on multi-parametric MRI. The CTV was defined as the whole prostate. The proximal 1- 2cm of seminal vesicles were included in the CTV at the clinician’s discretion. An intra -prostatic margin of 4mm was applied to the GTV to account for delineation uncertainty (GTV4mm) and no PTV margin was applied to the CTV. All patients were treated with 30Gy in 5 fractions to the CTV and an isotoxic boost of 45Gy to the GTV4mm. Dose accumulation was performed by deformable registration of the post-treatment MRI of fraction 2-5 to the post treatment MRI of fraction 1 to assess the dose delivered to the GTV and CTV over all treatment fractions. The primary endpoint was technical feasibility defined as accumulated GTV D90% of >42Gy in >90% of the patients. Results: Between May 2023 and September 2024, 60 patients were treated of which 54 were included for analysis. Six were excluded due to technical reasons. An accumulated GTV D90% of >42Gy was reached in 46 patients (85%). Analysis per institute showed that this criterion was reached in 10 of 14 patients (71%) in institute 1 and in 18 of 20 patients (90%) in both institute 2 and 3. Figure 1 summarizes the results of accumulated dose planned and delivered to the GTV and CTV. In the single institute that did not fulfill the criterion patients were actively made aware of the end of treatment delivery, which may have encouraged patient motion before post-treatment MRI acquisition.