Early Stage Follicular LymphOma and RadioTherapy PLUS Anti-CD20 Antibody

Inclusion Criteria: * • Centrally reviewed CD20-positive follicular lymphoma grade 1/2 or 3a based on WHO classification (2008) * Untreated (radiation-, chemo- or immunotherapy) nodal follicular lymphoma (including involvement of Waldeyer´s ring) * Age: ≥18 years * ECOG: 0-2 * Stage: clinical stage I or II (Ann Arbor classification) based on FDG-PET Staging * Risk profile: Largest diameter of the lymphoma ≤ 7 cm (sectional images) * Written informed consent and willingness to cooperate during the course of the trial * Adequate bone marrow capacity: ANC ≥ 1.5 x 103/ml, thrombocytes ≥ 100000 x 10 3/ml, hemoglobin ≥ 10 g/dL * Capability to understand the intention and the consequences of the clinical trial * Adequate contraception for men and women of child-bearing age during therapy and 18 months thereafter Exclusion Criteria: * Extra nodal manifestation of follicular lymphoma * Secondary cancer in the patient's medical history (exclusion: basalioma, spinalioma, melanoma in situ, bladder cancer T1a, non-metastasized solid tumor in constant remission, which was diagnosed \>3 years ago) * Serious disease interfering with a regular therapy according to the study protocol, e.g: congenital or acquired immune-deficiency syndromes, active infections including viral hepatitis, uncontrolled concomitant diseases including significant cardiovascular or pulmonary disease * Severe psychiatric disease * Pregnancy / lactation * Known hypersensitivity against Obinutuzumab or Rituximab drugs with similar chemical structure or any other additive of the pharmaceutical formula of the study drug * Active hepatitis B infection (inactive hepatitis B infections require additional prophylactic anti-viral medication for 1 year (e.g. Lamivudin, Entecavir, Tenofovir) * Participation in another interventional trial or follow-up period of a competing trial which can influence the results of this current trial * Creatinine \> 1.5 times the upper limit of normal (ULN) (unless creatinine clearance normal), or calculated creatinine clearance \< 40 mL/min * AST or ALT \> 2.5 × ULN * Total bilirubin ≥ 1.5 × ULN * INR \> 1.5 × ULN * PTT or aPTT \> 1.5 × the ULN