Radiotherapy is an effective tool for local control of non-Hodgkin’s lymphoma (NHL) and an important component of comprehensive treatment, however, with the development of modern radiotherapy techniques and chemotherapy, the past principles of target definition and dose are no longer applicable to current radiotherapy plans. The International Lymphoma Radiation Oncology Collaborative Group (ILROG) has reached an expert consensus on the principles of radiotherapy for NHL, taking into account the available evidence, and published in the April 2014 issue of the International Journal of Radiation Oncology * Biology * Physics. Patient selection: With chemotherapy and targeted therapy playing an increasingly important role in B-cell NHL, radiotherapy is mainly used for local control of early-stage NHL and for patients with advanced disease with large masses (>10 cm) and extra-nodal invasion. Also radiotherapy is the only treatment for most early inert NHL. Target area definition: In view of the fact that recurrence of NHL is mainly concentrated at the original site of involvement and radiotherapy brings certain side effects, we advocate the use of invoved-site RTISRT instead of the previous involved-field RT (IFRT). Large-field irradiation is mainly used as a remedy for chemotherapy failure. GTV: Any abnormal site suggestive of lymphoma invasion on the initial imaging data prior to any intervention is within the scope of GTV, combined with PET-CT imaging when available. CTV: The accuracy of imaging, the extent of lymphatic drainage, foci of subclinical invasion, and the impact of adjacent organs should be considered, and if two lymph nodes are <5 cm apart, they may be considered for inclusion in the same cTV. ITV: internal irradiation target area mainly considers the uncertainty of size, shape and location of CTV, such as masses in the chest and upper abdomen often move with breathing, ITV in these areas should be externalized 1.5-2.0cm on the basis of CTV, of course, the most ideal way is to use 4D-CT simulation for positioning. PTV: The planned target area should also consider the positional error and the systematic error of the machine during each treatment on top of the CTV and ITV. OAR: Organs at risk mainly refer to normal tissues and organs that may be irradiated and should be outlined and protected, which can be combined with histogram of dose volume distribution. The target area of a stage IIA mediastinal invasive diffuse large B-cell lymphoma is outlined (GTV in red) Dose of irradiation: The dose of irradiation for NHL is between 30-50 Gy, usually in 1.8 or 2.0 Gy fractions. Radical doses of 45-50Gy can be chosen. A recent prospective study in the UK showed that no significant difference in efficacy was observed between the two groups for patients after chemotherapy for diffuse large B lymphoma, irradiated at 30Gy or 40Gy. With the development of modern tumor radiotherapy technology and imaging, the involved site irradiation (ISRT) can further reduce the irradiation range, thus reducing the damage to the usual tissues and improving the survival quality of patients. Radiotherapists should actively participate in the MDT discussion of NHL treatment and encourage patients to receive pre-chemotherapy imaging and evaluation.