Hybrid FDG PET-MRI: Comparison of dedicated MRI with PET for distant and local extent of sarcomas

Objectives: Sarcomas comprise a heterogeneous group of mesenchymal derived tumors. Limb-sparing operative procedures combined with external radiation therapy and chemotherapy provide an acceptable local tumor control. In the preoperative work up conventional MRI offers excellent soft-tissue contrast which is essential for local therapy planning. However, oncologic monitoring after treatment remains challenging. We wish to compare dedicated MRI with FDG PET in hybrid PET-MRI for evaluating distant and local extent of sarcomas to aid in surgical and medical planning. Methods: In this retrospective study, we identified 16 patients with soft tissue sarcoma who underwent FDG PET-MR imaging with whole body and dedicated MRI sequences, from January 2014 to November 2017. Average age was 35 with 5 males and 11 females. A radiologist and a nuclear medicine physician reviewed each study individually and then by consensus. Tumor and metastases were evaluated in terms of size, extent of local invasion, and SUVmax. Medical chart was reviewed. Results: Both PET and MRI had equal efficiency at detection of the primary tumor. Sarcoma showed high FDG activity (avg SUVmax 11.8). Combined fusion images show better delineation of tumor than MRI or PET alone since peritumoral inflammation can affect interpretation. Both MRI and PET detected regional metastatic spread in same number of patients, although PET had higher number of lesions due to MRI having difficulty with post-surgical changes (p