S525
Clinical - Haemotology
ESTRO 2026
1 Radiation Oncology, H.U. La Princesa, Madrid, Spain. 2 Physics, H.U. La Princesa, Madrid, Spain
Purpose/Objective: Total Body Irradiation (TBI) is a standard treatment used for conditioning regimens before Hematopoietic Cell Transplantation (HCT). However, it is technically complex and requires several hospital resources. Consequently, some centers are transitioning away from TBI in preference for chemotherapy regimens. The aim of this study was to analyze TBI results in terms of toxicities and survival to evaluate if it remains a competitive treatment. Material/Methods: We conducted a single-center retrospective observational study of forty patients who received TBI as conditioning regimen before HCT between January 2015 and July 2025. Principal clinical dates included: hematological diagnosis, donor type, average age, oncological response, disease recurrence, fractionation dose and acute and late toxicities. In addition, a survival analysis was performed using Kaplan-Meier and Log-Rank statistics. Results: The average age at transplant of the forty patients treated with TBI was 41.7 years and the most common diagnosis was Acute Lymphoblastic Leukemia (ALL). Among the complications analyzed, hypothyroidism and renal dysfunction were the most frequent, with 13% and 10%, respectively. With a median follow-up of 1131 days, the mean overall survival was 1805 days (95% CI 1422 - 2187 days). Twelve patients are deceased (30%) and twenty-eight patients are alive (70%). Clinical data of patients are exposed in Figure
Results: Using the conventional approach, maximum deviations from the mean displacement reached 0.84 cm (lateral), 0.30 cm (vertical), and >1 cm (longitudinal). With CBCTExtended, these deviations decreased to 0.30 cm, 0.11 cm, and 0.45 cm, respectively. The inter-session variability was also significantly reduced, from more than 1 cm with the conventional method to 0.22 cm with CBCTExtended.Overall, these results represent accuracy improvements of 64% laterally, 63% vertically, and 55% longitudinally, demonstrating the superior precision and reproducibility of the CBCTExtended technique. The merged CBCT approach simplifies setup, minimizes manual corrections, and enhances dose delivery consistency, reducing the potential for positioning errors. Conclusion: CBCTExtended provides a faster, more accurate, and reproducible verification method for TBI positioning compared with the conventional multi-isocenter CBCT procedure. This guide supports its clinical implementation as a reliable and optimized alternative for daily TBI image verification. Keywords: TBI, Extended CBCT, Guide Digital Poster 4943 Long-term results and survival analysis in patients treated with Total Body Irradiation María Isabel Nafría 1 , María Sol Talaya 1 , Rosario Rubiato 1 , Margarita Casado 1 , Susana Gonzalo 1 , Diego Aldave 1 , Almudena Zapatero 1 , Alexandra Elena Stoica 1 , Alicia Marín 1 , José Alfonso Cruz 1 , María Carmen Martín 1 , Mario López 1 , Mariela Rojas 1 , Carmen Pilar Villalba 1 , Pablo Chamorro 2 , Pablo Castro 2 , Guillermo Paradela 2 , María Teresa Murillo 1
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