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

Abstract

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.

Brentuximab Vedotin Combined With Chemotherapy in Patients With Newly Diagnosed Early-Stage, Unfavorable-Risk Hodgkin Lymphoma

“…In cohorts 1 and 2, ISRT was administered per standard guidelines and under the direction of lymphoma radiation oncologists (J.Y., J.Y., L.S.C., R.T.H., and S.V.D.). 4,24 Typical ISRT fields were designed with consideration of the prechemotherapy and postchemotherapy gross tumor volume. This volume was then expanded in a nonisotropic way to account for microscopic disease spread to create a clinical target volume (CTV).…”

Radiation Therapy Across Pediatric Hodgkin Lymphoma Research Group Protocols: A Report From the Staging, Evaluation, and Response Criteria Harmonization (SEARCH) for Childhood, Adolescent, and Young Adult Hodgkin Lymphoma (CAYAHL) Group

“…Involved site radiotherapy (ISRT) is conceptually similar to INRT, but permits some uncertainty in interpreting diagnostic imaging for CTV definition. The key difference between ISRT and INRT lies in the quality and accuracy of pre-chemotherapy imaging and the concordance of patient positioning and image registration to the treatment planning CT. First, ISRT permits the physician to use their own clinical judgment when considering potential dose to an adjacent OAR, such that the CTV can be tailored to spare nearby critical structures like the heart [26][27][28]. Second, additional margins are permitted to allow for uncertainties regarding the anatomic location of involved nodes in delineating the CTV.…”

Primary Mediastinal B Cell Lymphoma in the Positron-Emission Tomography Era Executive Summary of the American Radium Society Appropriate Use Criteria

“…Involved-site RT (ISRT) treatment volumes are guided by the International Lymphoma Radiation Oncology Group guidelines, although substantial variations in interpretation exist with ISRT. [33][34][35][36] Given these variations, the radiation oncologist developing the radiation treatment plan should be knowledgeable and experienced in ISRT field design. Patients with stage I/II disease should receive radiation to all sites of initial involvement.…”

“…For patients who demonstrate an excellent response to chemotherapy (Deauville 1-3), coverage of the target volume can be compromised to reduce radiation exposure to the OARs. 35,36 Conversely, patients with an incomplete response to chemotherapy (Deauville 4 or 5) might require less strict dose constraints to obtain appropriate target coverage. The International Lymphoma Radiation Oncology Group guidelines for proton therapy for mediastinal lymphomas provides a good table for radiation dose constraints for normal tissue.…”