ESTRO 2025 - Abstract Book

S2029

Clinical - Urology

ESTRO 2025

recovery where available. Patients were dichotomised by median pre-SBRT PSA level of 2.34. Median time to distant metastasis was 33months for pre- SBRT PSA≤2.34 compared to 13months with pre -SBRT PSA>2.34 (p=0.002). OS was 91 months for oligometastatic vs 70 months for oligoprogressive patients (p=0.007). Conclusion: In this PCa cohort, VCF rate was 8%, mostly asymptomatic, and more common in those over 70 and no radiation myelopathy occurred with spinal SBRT over 12 years. Local control rates were excellent. Pre-SBRT PSA was predictive for time to DM.

Keywords: Prostate cancer, SBRT

References: 1.

Glicksman RM, Tjong MC, Neves-Junior WFP, Spratt DE, Chua KLM, Mansouri A, et al. Stereotactic Ablative Radiotherapy for the Management of Spinal Metastases: A Review. JAMA Oncology. American Medical Association; 2019. 2. Chalkidou A, Macmillan T, Grzeda MT, Peacock J, Summers J, Eddy S, et al. Stereotactic ablative body radiotherapy in patients with oligometastatic cancers: a prospective, registry-based, single-arm, observational, evaluation study. Lancet Oncol [Internet]. 2021 Jan 1 [cited 2023 May 9];22(1):98 – 106.

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Digital Poster TWO- versus Five-fraction DOminant-TArgeted Boost with MRgART in Localized Prostate Cancer (DOTA-2): Interim Acute Toxicity Analysis of Phase II RCT Ratchapas Romrattaphan, Pittaya Dankulchai, Tissana Prasartseree, Wiwatchai Sittiwong, Wajana Thaweerat Division of Radiation Oncology, Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand Purpose/Objective: “DOTA - 2” is a single-center phase II RCT comparing two ultra-hypofractionated radiotherapy regimens with simultaneous integrated boost (SIB) to the dominant intraprostatic lesion (DIL): 26 Gy/2 fractions SIB to 32 Gy versus 36.25 Gy/5 fractions SIB to 40 Gy without androgen deprivation therapy (ADT) for prostate cancer. Interim analysis of acute toxicity was reported. Material/Methods: Patients with low- to favorable intermediate-risk prostate cancer were randomly assigned (1:1) to receive either 2 fractions (26 Gy/2F SIB 32 Gy) over 8 days or 5 fractions (36.25 Gy/5F SIB 40 Gy) over 10-11 days. No ADT was allowed. DIL was defined by multiparametric MRI. The CTV include whole prostate gland and whole seminal vesicles. The PTV was expanded isotopically by 2 mm in all directions and 3 mm superoinferiorly from DIL and CTV. MR guided adaptive radiotherapy (MRgART) was delivered by Unity MR-Linac with Adapt-to-Shape (ATS) method in every fractions. Primary endpoint was acute genitourinary (GU) toxicity using Common Terminology Criteria for Adverse Events version 5.0 toxicity (CTCAE v5.0). Secondary endpoints were acute gastrointestinal (GI) toxicity and quality of life in urinary and sexual domains using the International Prostate Symptom Score (IPSS) and International Index of Erectile Function (IIEF-5) Questionnaire, respectively. We perform an interim analysis in acute GU and GI toxicities in the first 19 patients from the total planned 44 patients. Results: Between December 2023 and October 2024, 19 patients were randomly assigned to 2-fraction (n=9) or 5-fraction arm (n=10), stratified by risk group, prostate volume and DIL location. Median age was 74 years. Four (21%) patients were NCCN low risk and 15 (79%) were favorable-intermediate risk (Table1). Median follow up time was 13 weeks.