ESTRO 2025 - Abstract Book

S891

Clinical - Haematology

ESTRO 2025

598

Poster Discussion Prognostic factors for low-dose total skin electron beam radiotherapy in stage IB - IIB mycosis fungoides Khaled Elsayad 1,2 , Isabel Falke 1 , David Rene Steike 1 , Christos Moustakis 1,3 , Burkhard Greve 1 , Hans Theodor Eich 1 1 Department of Radiation Oncology, University Hospital of Muenster, Muenster, Germany. 2 Department of Radiotherapy and Radiooncology, Marburg University Hospital, Marburg, Germany. 3 Department of Radiation Oncology, University Hospital Leipzig, Leipzig, Germany Purpose/Objective: Low-dose radiotherapy is very effective in primary cutaneous T-cell lymphomas due to their radiosensitivity. This study aims to assess the safety and effectiveness of different low-dose total skin electron beam therapy (TSEBT) schedules in mycosis fungoides (MF) and to identify prognostic factors. Material/Methods: In this prospective cohort, patients with stage IB to IIB MF underwent TSEBT with conventional low-dose or ultra hypofractionated TSEBT. The primary endpoint assessed was the overall response rate (ORR). The secondary endpoints were time to next treatment (TTNT), progression-free survival (PFS) and toxicity rates. Results: 118 patients (38 in stage IB-IIA and 80 in stage IIB) had received a median of 4 prior systemic therapies before low dose or ultra-hypofractioned TSEBT. 65 patients were treated with 12 Gy in 8 fractions and 53 patients were treated with 8 Gy in two fractions (ultra-hypofractionated TSEBT). The ORR at three months was 92%. At a median follow-up of 45 months (95% CI: 36-54) the median TTNT was 16 months (95% CI: 8-24) and the median PFS was 11 months (95% CI: 8-14). Almost all patients (94%) experienced grade 1 acute toxicities, while only 17% of patients experienced grade 2 toxicities. The rate of grade ≥3 toxicity was 4%. There were no significant differences in radiation-related toxicity grades based on radiation dose or fractionation scheme. However, a substantial reduction in the itching scale, skin disease burden, Skindex-29 score and EORTC QLQ-C30 global score improvement). In the translational part of the study, potential soluble biomarkers were assessed during baseline and follow-up visits. In the multivariate analysis, age, CD30 expression, lymphocyte count and administration of maintenance therapy were found to be correlated with TTNT and PFS. Additionally, better ECOG performance status and normal lactate dehydrogenase levels were also associated with longer PFS. Conclusion: Ultra-hypofractionated TSEBT with 8 Gy attains comparable clinical benefits with a similar toxicity profile while reducing hospital visits compared to a conventional low-dose TSEBT regimen with 12 Gy. Several prognostic factors as well as potential biomarkers were identified.

Keywords: Cutaneous Lymphoma, Quality of life, Biomarkers

991

Digital Poster Comprehensive analysis of uveal MALT lymphomas: epidemiological insights and radiotherapy utilization from the SEER database Pierre Loap 1 , Anne Loap 2 , Remi Dendale 1 , Youlia Kirova 1 1 Department of radiation oncology, Institut Curie, Paris, France. 2 Department of Hematologie, Institut Curie, Paris, France