Impact of PET-CT on involved field radiotherapy design for pediatric Hodgkin lymphoma

Purpose: To determine how the incorporation of PET-CT changes radiotherapy treatment in pediatric Hodgkin lymphoma. Procedure: Fifty-three Hodgkin lymphoma patients with a median age of 14 years (6-21 years) underwent multiagent chemotherapy followed by involved field radiotherapy (IFRT) to initial sites of disease. All patients had conventional staging which included CT scan of the neck, chest, abdomen and pelvis, bone marrow biopsy±MRI, Gallium scan and bone scan. All had an initial 18-F-fluoro-deoxy-D-glucose (FDG) PET-CT. When there was discordance between conventional staging and PET-CT staging, true sites of disease were determined either by biopsy or response to multiagent chemotherapy. Results: In 19 of 53 (35.8%) patients, there was discordance between conventional staging and PET-CT findings. The most common location for the 23 sites of discordance were the spleen in 6 (26.1%), neck in 3 (13%), inguinal nodes in 3 (13%) and mediastinum in 3 (13%). A change in stage occurred in 5 (9.4%) as a result of PET-CT imaging. A change in IFRT fields occurred in 9 (17%); eight were more extensive while one was less extensive. For PET-CT, the specificity, sensitivity, positive predictive value and accuracy were 99.5%, 96.3%, 97.9%, and 98.9%. Conclusion: Incorporation of PET-CT information was found to influence IFRT design in 17% of patients, with most having more extensive radiotherapy fields.