Response of Osteosarcoma to Chemotherapy. Evaluation with F-18 FDG-PET Scans.

Objective: Positron emission tomography (PET) using fluorine-18-fluoro-2-D-deoxyglucose (FDG) is increasingly being used to evaluate and manage oncology patients. Several reports have documented its utility in diagnosis, staging, response to treatment, and tumor viability assessment. There is, however, a paucity of literature on PET scanning in patients with osteosarcoma. We report results of serial F-18 FDG-PET scans in 16 untreated patients with osteosarcoma who underwent chemotherapy prior to surgical resection of the primary tumor site.Procedure: Changes in tumor fluoro-2-D-deoxyglucose (FDG) uptake were correlated with percent tumor necrosis on histopathology. PET studies were analyzed by visual assessment of tumor uptake of FDG by 3 independent observers, calculating a tumor to normal background activity ratio (TBR) by drawing regions of interest (ROIs) around the tumor and background activity in the contralateral normal limb, and percent change in TBR values between baseline and presurgical study.Results: All patients had positive baseline scans. Baseline TBRs ranged between 2.5-8.7 and visual assessment of intensity of FDG uptake was 2-3 on a scale of 0-3. At histopathologic examination, 8 patients were classified as good responses with more than 90% tumor necrosis and 8 patients as poor responses with less than 90% necrosis. Tumor necrosis was accurately predicted on PET scan in 15/16 patients by visual assessment, 14/15 patients by final TBR value on presurgery scans, and 7/15 patients using percent change of TBR on serial scans.Conclusions: The results of this small series suggest that FDG-PET scanning is fairly accurate in evaluating the response of osteosarcoma to chemotherapy. Visual assessment and TBR are more accurate in predicting tumor necrosis than percent change in TBR on serial scans.

Normal thymic uptake of 2-deoxy-2[F-18]fluoro-D-glucose.

Whole-body 2-deoxy-2-[F-18]fluoro-D-glucose (FDG) positron emission tomography (PET) of a 54-year-old woman with a history of recurrent thyroid follicular cancer and an elevated thyroglobulin level showed significant FDG uptake in the thyroid bed and anterior mediastinum. A previous scan after high-dose I-131 therapy also showed iodine uptake in these regions. Because of a lack of response to iodine therapy, the patient had surgery. Recurrent thyroid cancer was found in the neck, but the mediastinal lesion was shown to consist of normal thymus tissue. In repeated examinations performed after surgery, there was no uptake of FDG or I-131 in the anterior mediastinum. Previous treatment with a high dose of radioiodine may have contributed to visualization of a normal adult thymus with FDG PET.

Hematopoietic cytokine-mediated FDG uptake simulates the appearance of diffuse metastatic disease on whole-body PET imaging.

FDG-PET is increasingly being used to assess malignant tumors. However, leukocyte colony-stimulating factors (CSFs), which promote the expansion of hematopoietic bone marrow, have also been demonstrated to cause increased bone-marrow FDG uptake. Three hundred FDG-PET studies conducted over a 1-year period were reviewed for diffuse bone-marrow uptake. Elevated bone-marrow uptake on PET was correlated with pathological findings and courses of granulocyte-CSF (G-CSF) therapy. These results demonstrate that G-CSF mediated FDG uptake in bone marrow is often indistinguishable from that caused by disseminated metastatic disease. However, the bone-marrow response to G-CSF decreases rapidly following the last CSF administration. Therefore, FDG-PET in patients receiving G-CSF should be delayed, when possible, until 5 days after the end of G-CSF therapy.

Normal thymic uptake of FDG on PET imaging.

Assessment and characterization of the thymus by various imaging methods have been extensively described. The authors report increased uptake of 2-(18)Fluoro-2-deoxy-D-glucose (FDG) in the normal thymus gland of patients between the ages of 2 and 13 years. Most of these patients had PET scans for various oncologic conditions and had no clinical problems referable to the thymus gland. This uptake assumes an important role when evaluating mediastinal uptake in whole-body PET scans in pediatric oncology patients to avoid false-positive interpretation.