ESTRO 2025 - Abstract Book

S3304

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2025

Conclusion: OART allows for reduced CTV-to-PTV margins in prostate cancer, potentially decreasing radiation exposure to organs at risk while maintaining sufficient tumor coverage.

Keywords: Margin reduction, Organ motion, Prostate cancer

References: 1. Vásquez Osorio EM, et al. A novel flexible framework with automatic feature correspondence optimization for nonrigid registration in radiotherapy. Med Phys 2009;36:2848-2859. 2. Bondar L, et al. A symmetric nonrigid registration method to handle large organ deformations in cervical cancer patients. Med Phys 2010;37:3760-3772. 3. Brand VJ, et al. Seminal vesicle inter- and intra-fraction motion during radiotherapy for prostate cancer: A review. Radiother Oncol 2022;169:15–24. 4. De Boer HC, Heijmen BJ. A protocol for the reduction of systematic patient setup errors with minimal portal imaging workload. Int J Radiat Oncol Biol Phys 2001;50:1350–1365. 5. Van Herk M. Errors and margins in radiotherapy. Sem Rad Onc 2004;14:52–64. Digital Poster Is the reduction of margin possibly with Adaptive Online Radiotherapy for Rectal Cancer? Mario Martin Veganzones 1 , Maria Isabel Martínez Fernández 2 , Patricia Lorenzana Moreno 2 , Victor De La Llana Granja 3 , Laura Bragado Álvarez 1 , Naiara Fuentemilla Urío 1 , Fernando Mañeru Cámara 1 , Rodrigo Astudillo Olalla 1 , Miren Lamaison Vidarte 1 , Aitor Gorrochategui Susperregui 1 , Nicolas García Iglesias 1 , Amaya Sola Galarza 2 , Marta Barrado Los Arcos 2 , Sonia Flamarique Andueza 2 , Ujue Ruiz Martinez de Azagra 2 , Libe Amondarain Elgarresta 2 , Darwin Pozo Jimenez 2 , Sara Lopez Garcia 2 , Mikel Rico Oses 2 , Elena Villafranca Iturre 2 , Santiago Pellejero Pellejero 1 1 Servicio de Radiofísica y Protección Radiológica, Hospital Universitario de Navarra, Pamplona, Spain. 2 Servicio de Oncología Radioterápica, Hospital Universitario de Navarra, Pamplona, Spain. 3 Servicio de Radiofísica y Protección Radiológica, Hospital Universitario de Leon, Leon, Spain Purpose/Objective: This study explores the feasibility of reducing the clinical target volume (CTV) to planning target volume (PTV) margins from 5 mm to 3 mm in rectal cancer patients undergoing adaptive radiotherapy (ART). ART allows for daily plan adjustments to compensate for anatomical variations, improving target coverage and minimizing dose to organs at risk (OARs). The aim is to assess whether narrower margins maintain adequate CTV coverage while reducing treatment volume. 3361

Material/Methods: 19 patients diagnosed with rectal cancer were treated with a short-course radiotherapy regimen (25 Gy in 5