Orelabrutinib Followed by Response-adapted Ultra-low Dose 4Gy Radiation as First-line Treatment of MALT Lymphoma

Inclusion Criteria: * Age ≥ 18 years old * Histologically confirmed mucosa-associated lymphoid tissue (MALT) lymphoma * Lugano stage I-II * ECOG 0-2 * Signed informed consent * Having sufficient organ function: a) Hematopoietic function: Neutrophils ≥ 1.0 × 109/L, PLT ≥ 50 × 109/L, Hb ≥ 80g/L; b) Liver function: bilirubin ≤1.5 times the upper limit of normal (ULN), ALT and AST\<3 x ULN, serum albumin ≥ 30 g/L; c) Renal function: serum Cr\<1.5 × ULN, creatinine clearance rate ≥ 50mL/min (calculated according to the standard Cockcroft Gault formula, if renal dysfunction is caused by tumor compression, creatinine clearance rate ≥ 30mL/min); d) Coagulation function (unless the subject is receiving anticoagulant therapy and the coagulation parameters (PT/INR and APTT) are within the expected range of anticoagulant therapy at the time of screening): International standardized ratio (INR) ≤ 1.5 x ULN; Activated partial thromboplastin time (APTT) ≤ 1.5 x ULN. Exclusion Criteria: * Recent major surgery (within 4 weeks prior to enrollment), except for diagnostic surgery * Have uncontrolled intercurrent diseases (cardiovascular and cerebrovascular diseases, coagulation disorders, severe infectious diseases) including but not limited to: severe acute or chronic infection requiring systemic treatment, symptomatic congestive heart failure (NYHA III-IV) or symptomatic or poorly controlled arrhythmias, arterial hypertension (systolic blood pressure ≥ 160mmHg or diastolic blood pressure ≥1…