ESTRO 2021 Abstract Book

S898

ESTRO 2021

PO-1080 Low-dose radiotherapy (4 Gy) in the treatment of marginal zone B- cell lymphomas M. Cerrato 1 , E. Orlandi 1 , A. Vella 1 , S. Bartoncini 1 , G.C. Iorio 1 , D. Bongiovanni 1 , F. Capriotti 1 , C. Boccomini 2 , F. Vassallo 2 , C. Cavallin 1 , V. De Luca 1 , F.R. Giglioli 3 , U. Ricardi 1 , M. Levis 1 1 University of Torino, Department of Oncology, Torino, Italy; 2 Azienda Ospedaliero Universitaria Città della Salute e della Scienza di Torino, Hematology Unit, Torino, Italy; 3 Azienda Ospedaliero Universitaria Città della Salute e della Scienza di Torino, Medical Physics Unit, Torino, Italy Purpose or Objective Low-dose radiotherapy (LDRT) with 4 Gy regimens (2 Gy x 2) proved to be effective for palliation in advanced stage and relapsed indolent lymphomas. In the curative setting, LDRT is generally inferior to the standard schedule for most indolent lymphomas. However, mucosa-associated lymphoid tissue (MALT) and nodal marginal zone lymphomas (MZL) showed high response rates with durable remission in preliminary retrospective studies, most with a limited number of patients. The purpose of this study was to investigate the efficacy of a LDRT schedule in the radical treatment of a cohort of unselected MALT or MZL patients. Materials and Methods We retrospectively collected stage I-IV histologically proven extranodal MALT or nodal MZL patients, treated at our institution with LDRT (4 Gy in 2 fractions) with either curative or palliative intent, between 2016 and 2020. For most patients, treatment was planned with a 3D conformal photon-based technique (93.3%). Response to LDRT was evaluated through clinical examination and appropriately selected radiographic studies, according to the Lugano criteria. Local control (LC), distant relapse-free survival (DRFS), progression-free survival (PFS) and overall survival (OS) were stratified for treatment intent (curative vs palliative) and estimated with the Kaplan-Meier product-limit. Results Of 45 consecutive patients enrolled in this study, 26 (58%) were female and the median age was 68 years (range 22-86). We identified 31 patients (69%) with early-stage MZLs and without any previous treatment, who received LDRT for a curative intent. Remaining 14 patients (31%) received palliative LDRT. The overall response rate (ORR) was 93%, without significant differences between patients receiving curative or palliative treatment (97% vs 86%, p = ns). With a median follow-up of 18 months, LC, DRFS, PFS and OS at 2 years were respectively 93%, 92%, 76% and 91%, in the overall population (Table1). Despite achieving similar LC rates, patients treated with curative LDRT had a better 2yPFS compared to patients receiving palliative treatment (85% vs 54%, p < 0.01) (Figure 1). Treatment intent did not impact in the same measure on OS. LDRT was well tolerated in all patients, without any significant acute or late side effects.