Involved Site Radiation Therapy in Adult Lymphomas: An Overview of International Lymphoma Radiation Oncology Group Guidelines

Involved node radiation therapy for lymphoma was introduced with the aim of using the smallest effective treatment volume, individualized to the patient's disease distribution, to avoid the potentially unnecessary normal tissue exposure and toxicity risks associated with traditional involved field radiation therapy. The successful implementation of involved node radiation therapy requires optimal imaging and precise coregistration of baseline imaging with the radiation therapy planning computed tomography scan. Limitations of baseline imaging, changes in patient position, and anatomic changes after chemotherapy may make this difficult in routine practice. Involved site radiation therapy (ISRT) was introduced by the International Lymphoma Radiation Oncology Group as a slightly larger treated volume, intended to allow for commonly encountered uncertainties. In addition to imaging considerations, the optimal ISRT treatment volume also depends on disease histology, stage, nodal or extranodal location, and the type and efficacy of systemic therapy, which in turn influence the distribution of macroscopic and potential subclinical disease. This article presents a systematic overview of ISRT, updating key evidence and highlighting differences in the application of ISRT across the lymphoma clinical spectrum.