ESTRO 2023 - Abstract Book

S931

Digital Posters

ESTRO 2023

as higher doses. We sought to evaluate and compare the outcomes of an Asian patient population treated with different radiotherapy (RT) regimens for orbital MALT lymphoma. Materials and Methods This was a retrospective cohort study of patients diagnosed with orbital MALT lymphoma from 1999 to 2021 at the National Cancer Centre Singapore. Patients were treated with RT according to their physician’s preference. The endpoints were local control rate (LCR), progression free survival (PFS) and overall survival (OS). Results A total of 64 patients were analysed, with a median age of 58 years. The most common tumour location was within the orbital cavity (58%), and 80% of patients had stage 1 disease. A majority of treatments were delivered with a curative intent (88%) using 3D conformal RT (91%). Seven patients received 4Gy (5 of which were for palliation), 39 patients received 24Gy, and the remaining 18 patients received a range of doses from 23.4-35.8Gy in 13-20 fractions. Treatment compliance was high (97%). With a median follow up of 6.4 years, the 5-year LCR, PFS and OS were 96.1% (95% CI 87.9-99.3%), 87.7% (95% CI 74.0-94.4%) and 96.8% (95% CI 87.7-99.2%) respectively. The PFS of patients who received 4Gy vs those who received 24Gy and above were comparable (Hazard ratio [HR]=0.42, 95% CI 0.11-1.53, p=0.173) The OS of patients who received 24Gy was superior to those who received 4Gy (HR=0.10, 95% CI 0.02-0.52, p=0.001), although it is worth noting that the 5yr OS for those who received 4Gy was 100% compared to 96.5% for patients who received 24Gy and above. Age at diagnosis (HR=1.10, 95% CI 1.03-1.18) and RT duration (HR=0.89, 95% CI 0.82-0.97) were also found to be significantly associated with OS. Exploratory multivariable analysis with adjustment to account for model overfitting suggested that age at diagnosis was the only independent predictor of OS (HR=1.09, 95% CI 1.02-1.17). Conclusion This study in an Asian cancer centre showed that RT for orbital MALT lymphoma provided excellent LCR, PFS and OS. Analyses suggested that outcomes of patients treated with 4Gy were comparable with those who received higher doses of 24Gy and above. Hence it would be worth prospectively evaluating these associations in future studies with a larger number of patients. Purpose or Objective Extranodal non-Hodgkin's lymphoma (NHL) is a rare entity, occurring most frequently in the gastrointestinal (GI) tract, representing 5 - 20% of all NHL, and 30 - 45% of extranodal NHL. Lesions can appear along the entire GI tract, with the stomach being the most frequent organ (60 - 75%). Primary duodenal lymphoma (PDL) is extremely rare, and there is currently no scientific evidence to support the best therapeutic approach. The information available in the literature is very scarce, consisting mainly of isolated case reports, and case series with small number of patients, mostly in the Eastern population. This study aimed to describe the experience of an external radiation therapy department in the treatment of patients with PDL. Materials and Methods We retrospectively reviewed electronic files and treatment plans of patients treated with radiotherapy for PDL, between January 2011 and December 2021. Oncological outcomes and toxicities were collected and described for each patient. Results Eight patients (4 men, median age 58.5 years, range 31 to 66 years) were considered for analysis. The median follow-up time was 30.3 months (range 6 to 60 months). Half of the patients had stage Ann Arbor IE. In two patients, lymphoma was incidentally diagnosed during endoscopy. Otherwise, the most frequent circumstances of diagnosis were epigastric pain (n=3) and dyspepsia (n=2). None of the patients included in the study had B symptoms. The portion of the duodenum where lymphoma occurred most frequently was at the DI/DII transition (62.5 %). The most frequent histological subtype was follicular lymphoma (75%). Very low-dose radiotherapy (VLDRT), 4 Gy in two fractions, was performed in 75% of patients in combination with Rituximab. Before being observed at our department, one patient was proposed for the Watch and Wait (WW) strategy, having progressed after 3 years. One patient had nausea grade 2 during treatment (evaluated using the CTCAE v5.0), and there were no late toxicities reported. All patients had a complete response at endoscopic duodenal biopsies. At the end of the study, all patients were alive without relapse or progression of the disease. Conclusion PDL is a rare disease, with an indolent course and a good prognosis, however rare cases of histological transformation may occur, mainly to diffuse large B cell lymphoma. There are no established therapeutic guidelines for optimal treatment. Despite the small size and heterogeneity of our sample, this retrospective observational study suggests that VLDRT with Rituximab provides a potential good local control with minimal toxicity for patients with PDL. A more conservative approach with a WW strategy could also be an appropriate and safe treatment option. There are no methods to predict prognosis or progression in PDL. Therefore, an appropriate long-term follow-up strategy is important in patients with PDL, especially those selected for the WW strategy. PO-1164 Primary non-Hodgkin´s lymphoma of the duodenum: experience from a radiation oncology department S. Sarandão 1 , S. Costa 1 , F. Fernandes 1 , Â. Oliveira 1 , L. Carvalho 1 1 Instituto Português de Oncologia do Porto, External Radiation Oncology Department, Porto, Portugal

PO-1165 Efficacy of residual site RT in patients with primary mediastinal lymphoma with DS 4 following R-CHT