The aim of the trial is to evaluate the molecular characteristics and MDD/MRD of B-NHL in pediatric patients in order to identify on the one hand the very high risk group and to prescribe them more intensive treatment on the other hand to identify those patients who don't need very aggressive therapy. One more study question is to evaluate the role of PET/CT in assessment of the completeness of remission. The following primary study questions are going to be analyzed: * the effectiveness (event-free survival) in pediatric patients with very limited mature B-NHL (R1 - stage I and II R) of substituting anthracyclines and vincristine by the rituximab without compromising survival rates. * the effectiveness (event-free survival) in pediatric patients with limited mature B-NHL (R2 - stage I and II NR) of substituting anthracyclines by the rituximab without compromising survival rates. * the effectiveness (event-free survival) in pediatric patients with advanced VHR mature B-NHL (R4 - stages with unfavourable genetics of substituting standard chemotherapy by second-line block VICI in order to improve results Secondary study questions will address * additional parameters for immune reconstitution, lymphocyte subpopulations, immunoglobulin levels, vaccination titers and infection rates * kinetics of immune reconstitution after treatment