Extranodal lymphomas (ENLs) comprise about a third of all non-Hodgkin lymphomas (NHL).Radiation therapy (RT) is frequently used as either primary therapy (particularly for indolent ENL),consolidation after systemic therapy,salvage treatment,or palliation.The wide range of presentations of ENL,involving any organ in the body and the spectrum of histological sub-types,poses a challenge both for routine clinical care and for the conduct of prospective and retrospective studies.This has led to uncertainty and lack of consistency in RT approaches between centers and clinicians.Thus far there is a lack of guidelines for the use of RT in the management of ENL.This report presents an effort by the International Lymphoma Radiation Oncology Group (ILROG) to harmonize and standardize the principles of treatment of ENL,and to address the technical challenges of simulation,volume definition and treatment planning for the most frequently involved organs.Specifically,detailed recommendations for RT volumes are provided.We have applied the same modern principles of involved site radiation therapy as previously developed and published as guidelines for Hodgkin lymphoma and nodal NHL.We have adopted RT volume definitions based on the International Commission on Radiation Units and Measurements (ICRU),as has been widely adopted by the field of radiation oncology for solid tumors.Organ-specific recommendations take into account histological subtype,anatomy,the treatment intent,and other treatment modalities that may be have been used before RT.