Pediatric Oncology

Abstract

In pediatric oncology 18F-FDG PET-CT imaging is used mainly for staging and restaging of lymphoma and bone tumors. In this special patient collective minimizing the radiation dose is one of the major goals. With the introduction of PET-MR, the CT exposure component previously produced in PET-CT studies potentially can be eliminated [1]. Preliminary reports state that compared to PET-CT the radiation exposure from a single hybrid imaging PET-MR-scan is reduced by around 80 %, to only one effective dose of 4.6 mSv) [2, 3]. In addition, especially in bone tumors (e.g. Ewing-sarcoma, multifocal osteosarcoma) patient require both whole-body MR and 18F-FDG PET and, therefore, the combination of both examinations in one single ­session has also substantial logistical advantages (e.g. only one anesthesia). Furthermore, compared to PET-CT this technique also enables whole-body diffusion-weighted imaging (DWI) providing additional information about cellularity and nuclear/cytoplasmic ratio of tumors. Recent studies in pediatric patients with lymphoma demonstrated high sensitivity for the detection of lesions and allows quantitative assessment of diffusion that may aid in the evaluation of malignant lymphomas [4]. For soft-tissue and bone tumors the advantage of PET-MR compared to PET-CT also lies in its high soft-tissue contrast [5]. 18F-FDG PET-CT does not provide exact information as MRI for T-staging in sarcomas, however it can give additional prognostic information [6, 7]. e.g. in one study assessing therapy response in pediatric osteosarcomas 18F-FDG PET could discriminate responders from nonresponders [8]. In regards of the advantages of both modalities integrated PET/MRI can replace PET-CT for these indications with a focus of the 18F-FDG PET component for prognostic questions and assessment of N-stage and M-stage and the MR-examination on local staging.