Comparison of PET-CT and conventional imaging in staging pediatric rhabdomyosarcoma

Background: Over the past decade, PET-CT has been used to assess rhabdomyosarcoma (RMS) in children. However, the role of PET-CT in staging RMS is unknown. Procedure: Thirty subjects with RMS, median age 7.3 years, underwent PET-CT before therapy. PET-CTs and conventional imaging (CI) were independently reviewed by two radiologists and two nuclear medicine physicians to determine the presence of metastases. Accuracy, sensitivity, and specificity of PET-CT for detecting metastases were compared to CI using biopsy and clinical follow-up as reference standards. Maximum standardized uptake values (SUV_max) of primary tumors, lymph nodes, and pulmonary nodules were measured. Results: Primary tumors had an average SUV_max of 7.2 (range, 2.5-19.2). Accuracy rates for 17 subjects with nodal disease were 95% for PET-CT and 49% for CI. PET-CT had 94% sensitivity and 100% specificity for nodal disease. Of seven pulmonary nodules detected by CI, three were not identified by PET-CT, two were indeterminate, and one was malignant with a SUV_max (3.4)>twice that of benign nodules. Two subjects had bone disease; both were identified by PET-CT but only one by CI. Four subjects had bone marrow disease, two had positive PET-CTs but none had positive CI. Two subjects had soft tissue metastases detected by PET-CT but not CI. Conclusions: PET-CT performed better than CI in identifying nodal, bone, bone marrow, and soft tissue disease in children with RMS. CI remains essential for detection of pulmonary nodules. We recommend PET-CT for staging of children with RMS. CI with Tc^99m bone scan can be eliminated.