Abstract P093

Definition of independent lymph node regions in pediatric HL. An expert consensus by an International Collaboration on Staging Evaluation and Response Criteria Harmonization (SEARCH) for Children, Adolescent, and Young Adult Hodgkin Lymphoma (CAYAHL)

Background/Purpose: Currently, the Ann Arbor classification and the Lugano criteria are used to stage pediatric Hodgkin lymphoma. The pattern of involvement, along with other individual risk factors, determines the treatment strategy. The increased anatomical detail provided by modern imaging modalities needs to be reflected in a consistent lexicon for lymph node level definitions. The presented atlas is intended to provide regional criteria for nodal involvement and to serve as a standardized guide for anatomic assignment of lymph node involvement.

Methods: An expert consensus from the Children's Oncology Group (COG), the European Network for Pediatric HL (EuroNet-PHL) and the Pediatric Hodgkin Consortium (PHC) defined typical involved lymph node regions in pHL using anatomic landmarks visible on modern staging CT and MRI based on other published consensus guidelines for delineating lymph node levels. These definitions were then validated in the central review process of the C2 trial.

Results: 12 regions and an additional 7 subregions were defined with their cranial, caudal, medial, lateral, ventral, and dorsal borders. The regions were then delineated on a typical neck and torso CT scan of an adolescent male patient in complete remission with no significant anatomic variations or residual tumor volume. Also discussed are recurring situations that typically lead to questions for central review by local investigators, such as the location of axillary and infraclavicular lymph nodes in relation to arm position, inspiration-dependent assignment of lymph nodes, and the retrocrural region.

Conclusions: The atlas presented provides anatomic criteria for nodal involvement and can serve as a standardized guide to the anatomic location of lymph node involvement in pHL, which is essential for accurate and reproducible disease staging, and radiation treatment planning.