ESTRO 2025 - Abstract Book

Brachytherapy - Gastro-intestinal, paediatric brachytherapy, miscellaneous

S186

ESTRO 2025

Conclusion: HDRBT appears to preserve lymphocyte counts more effectively than EBRT in rectal cancer nRT, suggesting a benefit to the host immune response. Elevated ALC following nRT is associated with higher pCR rates and favourable oncological outcomes, supporting ALC's potential role in anticancer processes. This study highlights the importance of lymphocyte preservation in optimizing cancer treatment responses and suggests that HDRBT is a promising lymphocyte-sparing modality. Future prospective studies could further explore HDRBT’s role in enhancing immunotherapy efficacy in rectal cancer. References: 1. Feeney G, Sehgal R, Sheehan M, et al. Neoadjuvant radiotherapy for rectal cancer management. World J Gastroenterol . 2019;25(33):4850-4869. doi:10.3748/wjg.v25.i33.4850 2. Påhlman L, Bohe M, Cedermark B, et al. The Swedish rectal cancer registry. Br J Surg . 2007;94(10):1285-1292. doi:10.1002/bjs.5679 3. Campian JL, Ye X, Sarai G, Herman J, Grossman SA. Severe Treatment-Related Lymphopenia in Patients with Newly Diagnosed Rectal Cancer. Cancer Invest . 2018;36(6):356-361. doi:10.1080/07357907.2018.1499028 4. Vuong T, Garant A, Vendrely V, Martin AG, Devic S. Clinical applications of high dose rate endorectal brachytherapy for patients with rectal cancer. Cancer Radiother . 2022;26(6-7):879-883. doi:10.1016/j.canrad.2022.07.001 Proffered Paper Target volume definition and organ at risk delineation in HDR brachytherapy for rectal cancer - consensus based GEC-ESTRO guidelines Anne Valkenburg 1 , Evert-Jan Van Limbergen 1 , Ane Appelt 2,3 , Johannes Knoth 4 , Maximilian A. Schmid 5 , Nikos Tselis 6 , Peter Hass 7 , Rahul Krishnatry 8,9 , Reena Engineer 8,9 , Bruno Fionda 10 , Maria Antonietta Gambacorta 10 , Baukelien van Triest 11 , Claudia Schuurhuizen 12 , Karen J. Neelis 13 , Mateusz Bilski 14,15 , Rajaram Sripadam 16 , Alexandra Stewart 17,18 , Maaike Berbée 1 1 Department of Radiation Oncology (Maastro), GROW Research Institute for Oncology and Reproduction, Maastricht University Medical Centre+, Maastricht, Netherlands. 2 Leeds Institute of Medical Research, University of Leeds, Leeds, United Kingdom. 3 Department of Medical Physics, Leeds Cancer Centre, Leeds Teaching Hospitals NHS Trust, Leeds, United Kingdom. 4 Department of Radiation Oncology, Comprehensive Cancer Center, Medical University/General Hospital of Vienna, Vienna, Austria. 5 Department of Radiation Oncology, Comprehensive Cancer Keywords: Rectal Cancer, Lymphocytes 3396