ESTRO 2025 - Abstract Book

S378

Brachytherapy - Urology

ESTRO 2025

198,32 Gy. This observation might advise some caution with regard to the expected real late toxicity in ultrahypofractionation.

Conclusion: Our calculations suggest a potential value of incorporating (radio)biological parameters for different prostate cancers in the planning process in order to individualize treatment choice and dose prescription. However the actual calculation models are not perfect and have to be optimized by further correlating them with clinical data.

Keywords: Prostate Cancer, Biological Equivalent dose, EQD2

References: 1. The application of the linear-quadratic dose-effect equation to fractionated and protracted radiotherapy. R.G. Dale 1985, The British Journal of Radiology, 58, 515-528 2. Phase 3 Trial of Stereotactic Body Radiotherapy in Localized Prostate Cancer. van As N. et al., NEJM 2024;391:1413-25 3. A radiobiological study of the schemes with a low number of fractions in high-dose-rate brachytherapy as monotherapy for prostate cancer. Guirado D et al., J. Contemp.Brachytherapy 2020,12,2,193-200

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Digital Poster Long-term outcomes of external beam radiation therapy with high-dose-rate brachytherapy boost in very high-risk prostate cancer Ana L. Rivero Pérez 1 , Pedro J. Prada Gómez 1 , Joaquin A. Carballido Rodríguez 2 , Javier T. Anchuelo Latorre 3 , Marina Gutierrez Ruiz 4 , Rosa Fabregat Borras 4 , Cristina Rodriguez-Acosta Caballero 1 , Carlos F. Carrascal Gordillo 5 , Frandeina Pinto Guevara 1 , Mara Garcia Lamela 1 , Francisco J. Olloqui Urroz 1 , Alejandra Perez Gonzalo 1 , Maria Piedad Galdos Barroso 1 , Paola A. Navarrete Solano 1 , Patricia Sarrion Rubio de la Torre 1 , Amaia Ilundain Idoate 1 , Paula Delgado Tapia 4 , Noelia Suarez Alvarez 4 , Jose A. Vazquez Rodríguez 4 , Javier Albendea Roch 1 , Ivan Diaz de Cerio Martínez 1 , Marian A. Cobo Belmonte 1 , Uriel A. Corro Verde 1 , Enrique Capon Saez 1 , Juan I. Raba Diez 1 1 Radiation Oncology department, Marqués de Valdecilla University Hospital, Santander, Spain. 2 Radiation Oncology department, Puerta de Hierro University Hospital, Madrid, Spain. 3 Radiation Oncology department, Miguel Servet University Hospital, Zaragoza, Spain. 4 Medical Physics Department, Marqués de Valdecilla University Hospital, Santander, Spain. 5 Radiation Oncology department, Karolinska University Hospital, Estocolmo, Sweden Purpose/Objective: Given the demonstrated local control benefits of high-dose-rate brachytherapy (HDR-BT) boost in very high-risk prostate cancer (VHR PCa), this study aimed to evaluate the long-term durability of these benefits and associated toxicity profile in patients treated with external beam radiation therapy (EBRT) to an equivalent dose in 2 Gy fractions (EQD2) of 281-366 Gy. Material/Methods: This retrospective study analyzed 87 patients with histologically confirmed VHR PCa treated with a combination of EBRT and HDR-BT between 1999 and 2006. Patients received 46 Gy to the whole pelvis in 23 fractions. Concurrently, two HDR-BT boosts of 11.5 Gy each were delivered during weeks 5 and 15 of EBRT, resulting in a total HDR-BT dose of 23 Gy. Biochemical control, based on Phoenix criteria, and late toxicity, graded using Common Terminology Criteria for Adverse Events (CTCAE) v5.0, were the primary and secondary endpoints, respectively. Patient characteristics are presented in Table 1.