ESTRO 2021 Abstract Book

S899

ESTRO 2021

Conclusion LDRT is effective and well tolerated in patients affected by MALT or nodal MZLs and achieved high response rates and LC at 2 years. This strategy has the potential to be curative while reducing the risk of toxic effects and could be an alternative strategy for the radical treatment of early-stage tumors. Future randomized trials should define the role of 2 Gy x 2 regimens in the curative setting of MALTs and MZLs. PO-1081 Effectiveness and tolerability of radiotherapy for patients with diffuse large cell B-cell lymphoma I. Hadi 1 , S.N. Hartoyo 2 , R. Bodensohn 2 , M. Dreyling 3 , M. Niyazi 1,4 , C. Belka 1,4 , M. Li 1 1 LMU Munich University Hospital, Radiation Oncology, Munich, Germany; 2 LMU Munich University Hospital , Radiation Oncology, Munich, Germany; 3 LMU Munich University Hospital , Hematology/Oncology, Munich, Germany; 4 German Cancer Consortium (DKTK), Radiation Oncology, Munich, Germany Purpose or Objective To analyze the effectiveness and toxicities of radiotherapy in diffuse large cell B-cell lymphoma (DLBCL) patients treated in our institution. Materials and Methods Patients with DLBCL treated with radiotherapy between 1996 and 2017 and a follow up of more than 3 months were included. The primary endpoint was progression-free survival (PFS). Secondary endpoints were local control (LC), overall survival (OS) and toxicities. PFS, LC, and OS were analyzed using Kaplan-Meier method. Log-rank test was used to investigate the differences between subgroups. Cox proportional hazard model was used for univariate continuous analysis. Results This is an interim analysis of 60 patients out of 137 patients, who were identified in our institutional database between 1996 and 2017 and matched aforementioned criteria. Thirteen patients (21.7%) had stage I after Ann- Arbor, 21 patients (35.0%) had stage II, 13 patients (21.7%) stage III, and 13 patients (21.7%) stage IV. Extranodal involvement was observed in 50 patients (83.3%), 15 patients among them had bone lesions (30%). The median follow-up was 57 months (95%-CI: 46 – 67 months). Consolidation radiation therapy (RT) at the first diagnosis was performed in 53 patients (88.3%) and 7 patients (17.7%) received RT at the relapse situation. Prior to RT, 18 F-FDG-PET/CT was taken into planning consideration in 41 patients (68.3%) and not performed in 19 patients (31.7%). Median single dose per fraction was 2.0 Gy (range, 1.8 – 3.0 Gy) and median total dose was 36.0 Gy (range, 12.0 – 45.0 Gy). The estimated PFS after 5 and 10 years were 70.0% and 64.1% in Kaplan-Meier analysis, respectively. The 5- and 10-year LC were 84.2% and 76.5%, respectively. The 5- and 10-year OS were 79.8% and 74.1%. In univariate analyses of PFS, younger patients (≤ 60 years old) had significantly superior PFS to those older than 60 years old (5-year PFS 83.1% vs. 56.9%, p= 0.029). Bone lesions and stage had no prognostic impact on PFS. Depending on the site of lymphomas, the most common acute side effects were: dermatitis CTCAE °I - II (35.0%), dysphagia CTCAE °I - II (21.6%), diarrhea CTCAE °I -II (15.0%), mucositis CTCAE °I-II (8.3%), and xerostomy CTCAE °I - II (6.7%). No adverse event CTCAE °III or higher was reported. Most acute side effects recovered at 3 to 6 months after radiotherapy.