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University Hospital Münster 48149 Münster, Germany
We congratulate Dr. McCarville and colleagues [1] on their article reviewing their experience with PET/CT in the evaluation of childhood sarcoma. The authors performed PET/CT with low-dose CT in 28 pediatric patients with sarcoma for staging, therapy monitoring, and detection of recurrence. They nicely showed the usefulness of PET/CT in these indications. We appreciate this work as being one of the very few articles about this new coregistration technology in pediatric patients. We would like to add our own experience with more than 150 pediatric patients with various malignancies, including 67 patients with sarcomas: Our experience [2, 3] shows that not only low-dose CT but also diagnostic CT with IV and oral contrast media is feasible in these patients using PET/CT.
McCarville et al. [1] mentioned that the current evaluation of patients with sarcomas includes MRI of the primary tumor site, CT of the chest to evaluate pulmonary metastases, and bone scanning to identify osseous metastases. Because 18F-FDG PET is not adequate to exclude pulmonary metastases in bone and soft-tissue sarcomas [4, 5], we suggest that a diagnostic chest CT examination be performed during the PET/CT examination.
In soft-tissue sarcoma, with its propensity for nodal spread, diagnostic CT is often performed for lymph node evaluation. If diagnostic CT is required in patients with soft-tissue sarcoma, we encourage radiologists to obtain cervical, thoracic, abdominal, and pelvic CT images with IV and oral contrast media also during the PET/CT examination. The coregistration of the diagnostic CT and the 18F-FDG PET is time saving (for both patients and physicians) and offers high-quality PET, CT, and fused PET/CT images in one single examination. As stated by McCarville et al. [1], additional trials are needed to evaluate the clinical benefit of various PET/CT protocols in pediatric patients with sarcoma.
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St. Jude Children's Research Hospital Memphis, TN 38105
We thank Drs. Franzius, Juergens, and Vormoor for their kind comments regarding our recent article titled "PET/CT in the Evaluation of Childhood Sarcomas" [1], and we share their enthusiasm for the value of PET/CT in assessing children with cancer. We agree with their observation that performing diagnostic quality CT with oral and IV contrast media rather than low-dose unenhanced CT when performing PET/CT may benefit patients. This is especially true for patients who are scheduled to undergo either MRI or diagnostic CT for the detection of nodal or hematogenous metastases.
We are familiar with the work of Franzius [2] regarding 18F-FDG PET versus helical CT for the evaluation of pulmonary nodules in children with sarcomas. In that retrospective review, Franzius found that helical CT was superior to PET alone for the detection of pulmonary nodules. We, too, are hopeful that PET/CT will improve our ability to evaluate pulmonary nodules in these children by combining the anatomic information gained from CT with the metabolic information attained with 18F-FDG PET. In the future, we will prospectively evaluate the accuracy of diagnostic CT alone versus PET/CT alone versus concurrent review of diagnostic CT and PET/CT in predicting nodule histology in this patient population.
When considering whether to obtain diagnostic quality and relatively higher dose CT scans during PET/CT, it is important to consider how the PET/CT examination is performed. Because the CT scan is used for attenuation correction of PET images, both scans must include the same body parts. Unlike many institutions, we scan patients from the skull vertex to the toes, as a true whole-body staging examination. Currently, it is not possible to perform a diagnostic quality CT of one body part—for example, of the chest—while scanning the remainder of the body with a lower radiation dose. Therefore, one must consider whether it is truly beneficial to expose the entire patient to the higher radiation dose needed to obtain diagnostic quality CT scans of a specific area of interest to eliminate the need for a separate diagnostic CT of that body part.
Another issue of concern is the positioning of the arms during image acquisition for PET/CT. Patients must remain in the same position throughout both the CT and PET portions of the examination. Because these examinations can become lengthy, often 45 min or longer, the patient must be positioned to reduce discomfort and motion. Often, this requires placing the arms at the patient's sides, which results in some streak artifact through the chest and upper abdomen, thus somewhat compromising the diagnostic quality of the CT scans of those areas.
This is an exciting time for our discipline, and we look forward to learning more about the work of Franzius and others regarding PET/CT in pediatric oncology. Carefully designed clinical trials and collaboration between clinical investigators and the manufacturers of PET/CT equipment will allow us to fine-tune the application of PET/CT in the management of children with sarcomas.
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