This trial studies the effectivity of low-dose radiation therapy with 10x2Gy for the treatment of patients with stage I-II stomach or duodenal Lymphoma (Marginal Zone or Follicular)

• Prove the effectiveness of 20 Gy (and non-inferiority to actually recommended 30 Gy) with respect to response rate 6 months after radiotherapy.
• Correlation of blood serum biomarker levels with lymphoma response to radiation treatment
• Recording of survival rates, quality of life (QoL), radiogenic toxicities and inflammation relevant molecules in blood serum.

Primary Objective:

Response rate 6 months after end of treatment, 4 categories according to GELA-criteria: CR (complete remission) = CR or pMRD (probable minimal residual disease), PR (partial remission) = rRD (responding residual disease), NC (no change), PD (progressive disease)

Secondary Objectives:

QoL according to EORTC (QLQ C30 and STO22). EFS=Event-free survival (time to any failure or death from any cause, patients in CR or PR), LSS=lymphoma-specific survival (time to death related to lymphoma or associated with the treatment, all patients), PFS=Progression-free survival (time to progression of lymphoma or death from any cause, all patients), OS=overall survival (time to death from any cause, all patients). Level of cytokines IL-1β, IL-4, IL-8, TNFalpha and other inflammation relevant molecules Syndecan1, MMP-2 and S100 proteins. Acute toxicities during treatment according to NCI-CTC, chronic toxicities according to NCI-CTC/ LENT-SOMA.

Monitoring of Adverse Events (AEs) and Serious Adverse Events (SAEs)

-Assessment of safety: Monitoring of Adverse Events (AEs) and Serious Adverse Events (SAEs)

Inclusion Criteria:

• primary indolent gastric or duodenal lymphoma
• pathology: marginal zone lymphoma (MZL) or follicular lymphoma (FL)
• stage: clinical stage I or II (Ann Arbor classification)
• H. pylori negative or antibiotic resistant lymphoma
• IPI or FLIPI score low - high (0-4)
• any size of tumor or affected lymph nodes
• male or female with age ≥ 18 years
• performance status ECOG 0 - 3
• written informed consent by the patient

Exclusion Criteria:

• prior radiation treatment of the gastrointestinal lymphoma
• stage: clinical stage III or IV (Ann Arbor classification)-unability to understand the informed consent or unwillingness to participate in the study
• severe comorbidity or organ dysfunction contraindicating the use of RT (liver cirrhosis Child-Pugh C, chronic obstructive pulmonary disease GOLD 4, heart insufficiency NYHA IV, dialysis dependent renal insufficiency, uncontrolled epilepsy)
• known seropositivity for HIV
• acute hepatitis B or C infection
• chronic inflammatory bowel disease
• prior malignant disease (exclusion: basalioma, non-metastasized solid tumor in constant remission diagnosed >3 years ago)
• pregnancy or breastfeeding
• active substance abuse or severely compromised compliance