Susan Sharp

123I-MIBG Scintigraphy and 18F-FDG PET in Neuroblastoma

The purpose of this study was to compare the diagnostic utility of 123I-metaiodobenzylguanidine (123I-MIBG) scintigraphy and 18F-FDG PET in neuroblastoma. Methods: A total of 113 paired 123I-MIBG and 18F-FDG PET scans in 60 patients with neuroblastoma were retrospectively reviewed. Paired scans were acquired within 14 days of each other. Results: For stage 1 and 2 neuroblastoma (13 scans, 10 patients), 18F-FDG depicted more extensive primary or residual neuroblastoma in 9 of 13 scans. 123I-MIBG and 18F-FDG showed equal numbers of lesions in 1 of 13 scans, and 3 of 13 scan results were normal. For stage 3 neuroblastoma (15 scans, 10 patients), 123I-MIBG depicted more extensive primary neuroblastoma or local or regional metastases in 5 of 15 scans. 18F-FDG depicted more extensive primary neuroblastoma or local or regional metastases in 4 of 15 scans. 123I-MIBG and 18F-FDG were equal in 2 of 15 scans, and 4 of 15 scan results were normal. For stage 4 neuroblastoma (85 scans, 40 patients), 123I-MIBG depicted more neuroblastoma sites in 44 of 85 scans. 18F-FDG depicted more neuroblastoma sites in 11 of 85 scans. 123I-MIBG and 18F-FDG were equivalent or complementary in 13 of 85 scans, and 17 of 85 scan results were normal. Conclusion: 18F-FDG is superior in depicting stage 1 and 2 neuroblastoma, although 123I-MIBG may be needed to exclude higher-stage disease. 18F-FDG also provides important information for patients with tumors that weakly accumulate 123I-MIBG and at major decision points during therapy (i.e., before stem cell transplantation or before surgery). 18F-FDG can also better delineate disease extent in the chest, abdomen, and pelvis. 123I-MIBG is overall superior in the evaluation of stage 4 neuroblastoma, especially during initial chemotherapy, primarily because of the better detection of bone or marrow metastases.

Pediatrics: Diagnosis of Neuroblastoma

Neuroblastoma is the most common pediatric extracranial soft-tissue tumor, accounting for approximately 8% of childhood malignancies. Its prognosis is widely variable, ranging from spontaneous regression to fatal disease despite multimodality therapy. Multiple imaging and clinical tests are needed to accurately assess patient risk with risk groups based on disease stage, patient age, and biological tumor factors. Approximately 60% of patients with neuroblastoma have metastatic disease, most commonly involving bone marrow or cortical bone. Metaiodobenzylguanidine (mIBG) scintigraphy plays an important role in the assessment of neuroblastoma, allowing whole-body disease assessment. mIBG is used to define extent of disease at diagnosis, assess disease response during therapy, and detect residual and recurrent disease during follow-up. mIBG is highly sensitive and specific for neuroblastoma, concentrating in >90% of tumors. mIBG was initially labeled with (131)I, but (123)I-mIBG yields higher quality images at a lower patient radiation dose. (123)I-mIBG (AdreView; GE Healthcare, Arlington Heights, IL) was approved for clinical use in children by the Food and Drug Administration in 2008 and is now commercially available throughout the United States. The use of single-photon emission computed tomography and single-photon emission computed tomography/computed tomography in (123)I-mIBG imaging has improved certainty of lesion detection and localization. Fluorodeoxyglucose positron-emission tomography has recently been compared with mIBG and found to be most useful in neuroblastomas which fail to or weakly accumulate mIBG.

SPECT/CT imaging in children with papillary thyroid carcinoma

BackgroundSPECT/CT improves localization of single photon-emitting radiopharmaceuticals.ObjectiveTo determine the utility of SPECT/CT in children with papillary thyroid carcinoma.Materials and methods20 SPECT/CT and planar studies were reviewed in 13 children with papillary thyroid carcinoma after total thyroidectomy. Seven studies used I-123 and 13 used I-131, after elevating TSH by T4 deprivation or intramuscular thyrotropin alfa. Eight children had one study and five children had two to four studies. Studies were performed at initial post-total thyroidectomy evaluation, follow-up and after I-131 treatment doses. SPECT/CT was performed with a diagnostic-quality CT unit in 13 studies and a localization-only CT unit in 7. Stimulated thyroglobulin was measured (except in 2 cases with anti-thyroglobulin antibodies).ResultsIn 13 studies, neck activity was present but poorly localized on planar imaging; all foci of uptake were precisely localized by SPECT/CT. Two additional foci of neck uptake were found on SPECT/CT. SPECT/CT differentiated high neck uptake from facial activity. In six studies (four children), neck uptake was identified as benign by SPECT/CT (three thyroglossal duct remnants, one skin contamination, two by precise anatomical CT localization). In two children, SPECT/CT supported a decision not to treat with I-131. When SPECT/CT was unable to identify focal uptake as benign, stimulated thyroglobulin measurements were valuable. In three of 13 studies with neck uptake, SPECT/CT provided no useful additional information.ConclusionSPECT/CT precisely localizes neck iodine uptake. In small numbers of patients, treatment is affected. SPECT/CT should be used when available in thyroid carcinoma patients.

MIBG in Neuroblastoma Diagnostic Imaging and Therapy

Neuroblastoma is a common malignancy observed in infants and young children. It has a varied prognosis, ranging from spontaneous regression to aggressive metastatic tumors with fatal outcomes despite multimodality therapy. Patients are divided into risk groups on the basis of age, stage, and biologic tumor factors. Multiple clinical and imaging tests are needed for accurate patient assessment. Iodine 123 ((123)I) metaiodobenzylguanidine (MIBG) is the first-line functional imaging agent used in neuroblastoma imaging. MIBG uptake is seen in 90% of neuroblastomas, identifying both the primary tumor and sites of metastatic disease. The addition of single photon emission computed tomography (SPECT) and SPECT/computed tomography to (123)I-MIBG planar images can improve identification and characterization of sites of uptake. During scan interpretation, use of MIBG semiquantitative scoring systems improves description of disease extent and distribution and may be helpful in defining prognosis. Therapeutic use of MIBG labeled with iodine 131 ((131)I) is being investigated as part of research trials, both as a single agent and in conjunction with other therapies. (131)I-MIBG therapy has been studied in patients with newly diagnosed neuroblastoma and those with relapsed disease. Development and implementation of an institutional (131)I-MIBG therapy research program requires extensive preparation with a focus on radiation protection.

Spondylolysis and Beyond: Value of SPECT/CT in Evaluation of Low Back Pain in Children and Young Adults

Single photon emission computed tomography (SPECT)/computed tomography (CT) is ideally suited for assessment of low back pain in children and young adults. Spondylolysis is one of the most common structural causes of low back pain and is readily identified and characterized in terms of its chronicity and likelihood to heal. The value of SPECT/CT extends to identification and characterization of other causes of low back pain, including abnormalities of the posterior elements, developing vertebral endplate, transverse processes, and sacrum and sacroiliac joint. Some of the disease processes that are identifiable at SPECT/CT are similar to those that occur in adults (eg, facet hypertrophy) but may be accelerated in young patients by high-level athletic activities. Other processes (eg, limbus vertebrae) are more unique to children, related to injury of the developing spine. The authors review the spectrum of pars interarticularis abnormalities with emphasis on the imaging features of causes of pediatric low back pain other than spondylolysis.

Estimated cumulative radiation dose from PET/CT in children with malignancies

Sir, The article by Chawla et al. [1] calculates effective doses for [F-18]FDG PET/CT studies performed at their hospital. This paper provides interesting data with respect to the numbers of PET/CT scans performed in their patients and an estimate of the resulting cumulative dose. However, a careful reading discloses that the effective dose from the PET radiopharmaceutical does not represent optimal clinical practice in 2010 and that it also no longer represents clinical practice at the authors’ hospital. The CT doses attributed to PET/CT represent the full diagnostic CT doses in use at their hospital. The authors state that it was their practice to perform the diagnostic CT required by the patient as part of the PET/CT scan. Therefore, the only added effective dose from the PET/CT scan is due to the addition of PET imaging. The amount of [F-18]FDG (administered activity) that a pediatric patient receives is usually calculated from a reference adult administered activity. The authors’ administered activity of 0.21 mCi/kg (7.8 MBq/kg) indicates that they used a reference activity of 15 mCi (555 MBq), which is commonly used at adult hospitals. However, a survey of North American children’s hospitals in 2008 indicated the median administered activity at these specialty hospitals surveyed was 0.145 mCi/kg (5.4 MBq/kg), corresponding to a reference activity of 10.1 mCi (373 MBq). An FDG administered activity of 0.14 mCi/kg (5.2 MBq/kg) has been used or recommended by other authors [2–5]. The authors indicate in a single sentence in the Discussion section that, after completion of PET/CT studies in this study’s patient cohort, they reduced the administered activity at their hospital to 0.14 mCi/kg. At an administered activity of 0.14 mCi/kg, the effective dose attributable to [F-18]FDG is reduced by 33%. Recent studies indicate that administered activities can be reduced further in pediatric patients younger than 5 to 10 years of age and for brain imaging [6, 7]. In the authors’ estimation of an average effective dose of 24.8 mSv per PET/CT, 80% of this dose is due to the CT acquisition. In general, the CT acquisition was performed with a rather high technique over the entire body. In contrast to the presented cohort, the CT component of the PET/CT study can be performed using any of three approaches. One approach is to perform a full diagnostic CT scan, usually with intravenous contrast agent, integrated into the PET/CT protocol. The authors appear to have used this approach. In a patient with neoplasm, this diagnosticquality CT scan would typically be the only diagnostic CT scan performed at this time point in the patient’s care. The added effective dose for the CT part of the PET/CT study at this time point is, therefore, zero. A second approach to the use of CT during PET/CT is to perform a reduced dose localization CT scan during free breathing as part of the PET/CT scan. This scan is typically performed at less than half of the exposure settings used for a diagnostic CT scan. This results in an effective dose attributable to CT of about 4–6 mSv. M. J. Gelfand (*) : S. E. Sharp Department of Radiology, Cincinnati Children’s Medical Center, 3333 Burnet Ave., Cincinnati, OH 45215-3039, USA e-mail: Michael.gelfand@cchmc.org

Optimization of Pediatric PET/CT

PET/CT, the most common form of hybrid imaging, has transformed oncologic imaging and is increasingly being used for nononcologic applications as well. Performing PET/CT in children poses unique challenges. Not only are children more sensitive to the effects of radiation than adults but, following radiation exposure, children have a longer postexposure life expectancy in which to exhibit adverse radiation effects. Both the PET and CT components of the study contribute to the total patient radiation dose, which is one of the most important risks of the study in this population. Another risk in children, not typically encountered in adults, is potential neurotoxicity related to the frequent need for general anesthesia in this patient population. Optimizing pediatric PET/CT requires making improvements to both the PET and the CT components of the procedure while decreasing the potential for risk. This can be accomplished through judicious performance of imaging, the use of recommended pediatric 18fluorine-2-fluoro-2-deoxy-d-glucose (18F-FDG) administered activities, thoughtful selection of pediatric-specific CT imaging parameters, careful patient preparation, and use of appropriate patient immobilization. In this article, we will review a variety of strategies for radiation dose optimization in pediatric 18F-FDG-PET/CT focusing on these processes. Awareness of and careful selection of pediatric-specific CT imaging parameters designed for appropriate diagnostic, localization, or attenuation correction only CT, in conjunction with the use of recommended radiotracer administered activities, will help to ensure image quality while limiting patient radiation exposure. Patient preparation, an important determinant of image quality, is another focus of this review. Appropriate preparative measures are even more crucial in children in whom there is a higher incidence of brown fat, which can interfere with study interpretation. Finally, we will discuss measures to improve the patient experience, the resource use, the departmental workflow, and the diagnostic performance of the study through the use of appropriate technology, all in the context of minimizing procedure-related risks.

Detection of lymph node metastases in pediatric and adolescent/young adult sarcoma: Sentinel lymph node biopsy versus fludeoxyglucose positron emission tomography imaging—A prospective trial

Lymph node metastases are an important cause of treatment failure for pediatric and adolescent/young adult (AYA) sarcoma patients. Nodal sampling is recommended for certain sarcoma subtypes that have a predilection for lymphatic spread. Sentinel lymph node biopsy (SLNB) may improve the diagnostic yield of nodal sampling, particularly when single‐photon emission computed tomography/computed tomography (SPECT‐CT) is used to facilitate anatomic localization. Functional imaging with positron emission tomography/computed tomography (PET‐CT) is increasingly used for sarcoma staging and is a less invasive alternative to SLNB. To assess the utility of these 2 staging methods, this study prospectively compared SLNB plus SPECT‐CT with PET‐CT for the identification of nodal metastases in pediatric and AYA patients.

The Role of PET/CT in assessing pulmonary nodules in children with solid malignancies

OBJECTIVE. The purpose of this article is to assess the feasibility and utility of PET/CT in distinguishing benign from malignant pulmonary nodules in patients with solid childhood malignancies. SUBJECTS AND METHODS. This prospective study was conducted between March 2008 and August 2010. We enrolled 25 subjects 21 years old or younger with solid childhood malignancies and at least one pulmonary nodule measuring 0.5-3.0 cm. PET/CT was performed within 3 weeks of diagnostic chest CT. Three panels of three reviewers each reviewed diagnostic CT only (panel 1), PET/CT only (panel 2), or diagnostic CT and PET/CT concurrently (panel 3) and predicted each nodules histologic diagnosis as benign, malignant, or indeterminate. Interreviewer agreement was assessed with the kappa statistic. Using nodule biopsy or clinical follow-up as reference standards, the sensitivity, specificity, and accuracy for each panel was assessed. Logistic regression was used to assess the nodules maximum standardized uptake value (SUVmax) association with its histologic diagnosis. RESULTS. There were 75 nodules with a median size of 0.74 cm (range, 0.18-2.38 cm); 48 nodules were malignant. Sensitivity was 85% (41/48) for panel 1, 60% (29/48) for panel 2, and 67% (32/48) for panel 3. All panels had poor specificities. Interreviewer agreement was moderate for panel 1 (0.43) and poor for panels 2 (0.22) and 3 (0.33). SUVmax was a significant predictor of histologic diagnosis (p = 0.004). CONCLUSION. PET/CT assessment of pulmonary nodules is feasible in children with solid malignancies but may not reliably improve our ability to predict a nodules histologic diagnosis. The SUVmax may improve the performance of PET/CT in this setting.

[F-18]2-fluoro-2-deoxyglucose (FDG) positron emission tomography after limb salvage surgery: post-surgical appearance, attenuation correction and local complications

BackgroundMetal endoprostheses and internal fixation devices cause significant artifacts on CT after limb salvage surgery; positron emission tomography (PET) images should be evaluated for artifacts.Objective(1) To describe [F-18]2-fluoro-2-deoxyglucose (FDG) PET uptake patterns after limb salvage surgery. (2) To determine whether metal endoprostheses and fixation hardware cause significant artifacts on CT attenuation-corrected PET that interfere with diagnostic use of PET/CT after limb salvage surgery.Materials and methodsWe reviewed 92 studies from 18 patients ages 5–21 years. Diagnoses were osteogenic sarcoma in 14, Ewing sarcoma in 3, and malignant peripheral nerve sheath tumor originating in bone in 1. Nine patients had distal femur/knee endoprostheses, five had lower-extremity bone allografts secured by large metal plates and four had upper-extremity limb salvage procedures. Maximum standardized uptake value was calculated at lower-extremity soft-tissue–endoprosthesis interfaces. In 15 patients with PET/CT imaging, the first PET/CT scan after limb salvage surgery was reviewed for metal artifacts on CT images and for artifacts at locations on PET corresponding to the CT metal artifacts.ResultsIncreased FDG uptake was consistently present at soft-tissue interfaces with endoprostheses, allografts and internal fixation devices, with little or no FDG uptake at cemented endoprosthesis–bone interfaces. Maximum standardized uptake value at margins of femur/knee endoprostheses ranged from 1.4 to 5.7. In four patients with distal femur/knee endoprostheses, minimal artifact was noted on attenuation-corrected PET images, but image interpretation was not affected. In the other 11 patients who had CT attenuation correction, we detected no artifacts caused by the attenuation correction.ConclusionCT attenuation correction did not cause artifacts that affected interpretation of attenuation-corrected PET images.