ESTRO 2024 - Abstract Book

S1149

Clinical - Haematology

ESTRO 2024

1 Seoul National University Bundang Hospital, Department of Radiation Oncology, Seongnam, Korea, Republic of. 2 Seoul National University Hospital, Department of Radiation Oncology, Seoul, Korea, Republic of. 3 Yonsei Cancer Center, Department of Radiation Oncology, Seoul, Korea, Republic of

Purpose/Objective:

Definitive radiotherapy of 30Gy or higher is commonly recommended to treat H. pylori-independent gastric mucosa-associated lymphoid tissue lymphoma (GML) with excellent disease control rate. The efficacy of reduced dose (< 26Gy) radiotherapy has not been evaluated in a prospective cohort. This multi-institutional study aimed to define the role of reduced-dose radiotherapy in the treatment of stage IE GML.

Material/Methods:

From March 2017 to June 2022, 62 patients with histologically-confirmed stage IE GML without the evidence of H. pylori infection were enrolled. Patients were treated with reduced-dose radiotherapy to the whole stomach. Response to therapy was evaluated by endoscopy with biopsy on suspicious lesions if necessary.

Results:

Among 62 patients, 32 patients (51.6%) were previously treated with H. pylori eradication. Radiotherapy was delivered using 3D-conformal (n=20; 32.3%) or intensity-modulated radiotherapy (n=42; 67.7%) technique, with 25.5Gy in 17 fractions (n=47; 75.8%), 25.2Gy in 14 fractions (n=12; 19.4%), or 24Gy in 16 fractions (n = 3; 4.8%). The median follow-up duration was 27.6 months (range, 3.4-67.3 months). All but one patient showed complete response (CR) at endoscopic examination within a median of 2.7 months (range, 0.9-16.1 months) after radiotherapy, with the 6-month CR rate of 96.7%. Three patients exhibited residual disease at last endoscopic biopsy; two patients who initially showed CR later demonstrated residual disease at 13.9 and 27.6 months after radiotherapy. One patient manifested mucosa-associated lymphoid tissue lymphoma of the lung at post radiotherapy 16.1 months. Otherwise, no patients showed evidence of residual disease or relapse during follow-up. The 2-year overall survival, disease-free survival, and local control rates were 100.0%, 94.3%, and 96.5%, respectively. No patients experienced grade 3 or worse toxicity, and any grade 2 toxicities were reported in 17 patients (27.4%).

Conclusion:

Reduced-dose radiotherapy exhibited excellent response rates of stage IE GML, comparable to historical controls of standard dose (≥ 30Gy) radiotherapy, with minimal toxicity profile. The current prospective evidence strongly supports the use of definitive radiotherapy of 24-26Gy for treatment of H. pylori-independent stage IE GML.

Keywords: Gastric MALToma, radiotherapy, reduced-dose