Molecular Imaging Insight - May 2008 - (Page 13) great interest in integrating PET into the evaluation of children and adolescents with cancer to help adjust treatment strategies and possibly improve outcomes, says Edita Kabickova, MD, pediatric oncologist and assistant professor, department of pediatric hematology and oncology, Charles University, Prague, Czech Republic. PET with 18F-fluorodeoxygluclose allows for a functional assessment of tumor metabolism and has increased sensitivity for lesions that may be undetectable by anatomic-based methods of imaging. “PET is now widely used in our patients and is helpful in the primary staging, treatment and follow-up of children with cancer,” Kabickova says. “Today, PET/CT is incorporated into the diagnostic work-up of our patients with lymphomas, germ cell tumors, sarcomas and some types of rare pediatric malignancies, such as colorectal carcinoma, thyroid cancer and melanoma.” Using PET with FDG allows a physician to ascertain the extent of cancer in the body in rather unique ways because it does not rely on anatomic changes or the detection of masses, says Treves. “Instead, it allows the physician to portray the actual [metabolic] activity of the tumors. It has really been a powerful tool to give us a more complete picture of disease.” Kabickova adds that small cancer manifestations, for example, normal size lymph nodes in children with lymphomas or sarcomas, can be visualized due to high FDG uptake. This can improve the clinical staging of untreated patients. PET/CT also is being used to evaluate tumor viability after chemotherapy and to identify children at risk for early relapse. “The current treatment strategy for childhood malignancies is risk-based and the rapidity of response to the first few cycles of chemotherapy is used to determine the subsequent treatment intensity,” says Kabickova. “PET/CT imaging allows identification of responding and non-responding tumors early in the course of therapy. With this information, we can rapidly modify ineffective therapies for these patients and thereby potentially improve their outcomes.” While PET/CT is effective in staging lymphomas, bone, and soft-tissue tumors, and for evaluating tumor response, it is not helpful for routine follow-up on surveillance of children for bone and soft-tissue tumors with no evidence of recurrent or metastatic disease and no symptoms, according to Nadel. “We have determined in a series of studies that the least value of PET/CT is in surveillance monitoring in the absence of symptoms, where we get a very low rate of abnormality,” Nadel says. “Where we do get a high rate of pick-up and change in management is either at diagnosis for staging and picking up unexpected, more widespread, disease at the time of assessment for local control before surgical planning and at the end of treatment.” Other studies have shown value in surveillance monitoring. Another area of growth in pediatrics is infection imaging, or inflammation, particularly in musculoskeletal disease and fever of unknown origins. “PET/CT can help us to look at infections in children more easily and avoid the need to label their white blood cells,” Wahl says. MolecularImaging.net Clinical indications for SPECT/CT SPECT/CT is relatively new in pediatrics—it has not penetrated the field to the degree PET/CT has, but it holds promise. “SPECT/ CT has a growing role within pediatrics, but it is going to be a more limited role compared to PET/CT,” says Wahl. Currently, the technology is being used more for Meta-Iodo-Benzyl-Guanidine (MIBG) scans for neuroblastoma, and in some patients with osteosarcoma, he adds. With SPECT/CT, a physician gains improved anatomical localization and the acquisition of attenuation maps for attenuation correction. “It is the uniqueness of the information that studies provide that make the technology so desirable,” says Treves. SPECT/CT is used for imaging of the brain and the body in routine applications for epilepsy, tumors and whole-body imaging, including myocardial perfusion imaging. British Columbia Children’s Hospital has slowly been increasing its SPECT/CT workload over the last nine months, Nadel says. The hospital is utilizing the technology to do diagnostic CT scans and correlated imaging tests when the child was already scheduled to have a CT scan, for example, in patients with neuroblastoma. By doing SPECT MIBGs with contrast enhanced CT scans, Nadel says they have found economies of time—the child is saved an extra trip; economies of radiation exposure—minimizing radiation dosing; and economies of efficiency, reading both diagnostic scans simultaneously. “Two heads are better than one,” she says. “When you put the two studies together, you can see things that could not be matched up alone.” For example, a child at the Children’s Hospital had an initial SPECT/CT study done, Nadel says, for staging; the next study done prior to reaching a treatment decision point was done as one modality; the next time as the other modality. Although done correctly, they each missed one observation. A fourth combined study was done. “It was clear that the stand-alone studies showed what they could, the best they could,” she says. “However, the combined study of SPECT and CT clearly helped in disease evaluation and was better than the two [separately].” Another area where SPECT/CT is found to be beneficial is in small bone lesion localization and diagnosis. “We are finding things hot on bone scans that we did not know exactly where they were, but in finding their location, we were able to better suggest the correct diagnosis,” Nadel adds. Assessing future potential The recent proliferation of hybrid imaging systems has been revolutionary and has added a new and important dimension in imaging, Treves says. Molecular imaging has helped to highlight the great advantages of radionuclide imaging in the diagnosis and monitoring of disease in children. Ongoing research will continue to expand the effectiveness and potential of value of PET/CT and SPECT/ CT in pediatric care. May 2008 | Molecular Imaging Insight 13 http://MolecularImaging.net
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