Search

18F-2-fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) shows tumor activity in most neuroblastomas, but the role of 18F-FDG PET/CT in neuroblastoma remains to be defined. This study explored the prognostic significance of 18F-FDG PET in newly diagnosed neuroblastic tumors. This retrospective study reviewed all 18F-FDG PET/CT examinations performed for a new diagnosis of suspected neuroblastoma. MYCN amplification status, tumor recurrence and survival were abstracted from the medical record. Primary tumors were manually segmented to measure maximum standardized uptake value (SUVmax), mean standardized uptake value (SUVmean), tumor volume and total lesion glycolysis. Univariate and multivariable analyses using Cox proportional hazards regression testing assessed the predictive performance of PET indices for event-free survival and overall survival with thresholds determined using receiver operating characteristic curve analysis. Fifty-five children were included, with a median age of 2.9 years (interquartile range [IQR] 1.8–3.0 years). SUVmax, tumor volume and total lesion glycolysis were higher in MYCN-amplified tumors (P=0.012, P 4.77) vs. >2,957 days (SUVmax≤4.77). No PET parameters were independently significantly associated with overall survival or event-free survival after controlling for MYCN status, stage or treatment risk stratification. Tumor metabolic activity is higher in higher-stage MYCN-amplified neuroblastic tumors. Higher SUVmax and SUVmean were associated with worse overall survival but were not independent of other prognostic markers.

Osteosarcoma is the most common pediatric malignant bone tumor, frequently surgically managed with limb salvage rather than amputation. Local recurrences are seen in up to 9% of osteosarcoma patients, with CT and MRI imaging often limited by metal artifacts. To describe the [F-18]2-fluoro-2-deoxyglucose (FDG) PET/CT appearance of local osteosarcoma recurrences with correlation to findings on other imaging modalities. A retrospective review of pediatric osteosarcoma patients imaged with FDG PET/CT was performed in patients with pathologically proven local recurrences. FDG PET/CT findings were reviewed and correlated with available comparison imaging studies. Ten local osteosarcoma recurrences in eight pediatric osteosarcoma patients were imaged with FDG PET/CT. All eight patients had a local recurrence after limb salvage; two patients had a second local recurrence after amputation. All local recurrences were seen with FDG PET/CT, demonstrating solid (n=5) or peripheral/nodular (n=5) FDG uptake patterns. Maximum standard uptake values (SUVs) ranged from 3.0 to 15.7. In five recurrences imaged with FDG PET/CT and MRI, MRI was limited or nondiagnostic in three. In four recurrences imaged with FDG PET/CT and bone scan, the bone scan was negative in three. Local osteosarcoma recurrences are well visualized by FDG PET/CT, demonstrating either solid or peripheral/nodular FDG uptake with a wide range of maximum SUVs. FDG PET/CT demonstrates the full extent of local recurrences, while MRI can be limited by artifact from metallic hardware. PET/CT appears to be more sensitive than bone scan in detecting local osteosarcoma recurrences.

Metal endoprostheses and internal fixation devices cause significant artifacts on CT after limb salvage surgery; positron emission tomography (PET) images should be evaluated for artifacts. (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. We 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. Increased 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. CT attenuation correction did not cause artifacts that affected interpretation of attenuation-corrected PET images.

Granulocyte colony-stimulating factors (G-CSF) speed recovery from chemotherapy-induced myelosuppression but the marrow stimulation they cause can interfere with interpretation of F-18 fluorodeoxyglucose positron emission tomography (F-18 FDG PET) exams. To assess the frequency of interfering G-CSF-induced bone marrow activity on FDG PET imaging in children and young adults with Ewing sarcoma and rhabdomyosarcoma and to define an interval between G-CSF administration and FDG PET imaging that limits marrow interference. Blinded, retrospective review of FDG PET exams performed in patients treated with long-acting G-CSF as part of their chemotherapeutic regimen. Exams were subjectively scored by two reviewers (R1 and R2) who assessed the level of marrow uptake of FDG and measured standardized uptake values in the marrow, liver, spleen and blood pool. FDG PET findings were correlated with time since G-CSF administration and with blood cell counts. Thirty-eight FDG PET exams performed in 17 patients were reviewed with 47.4% (18/38) of exams having marrow uptake of FDG sufficient to interfere with image interpretation. Primary predictors of marrow uptake of FDG were patient age (P = 0.0037) and time since G-CSF exposure (P = 0.0028 for subjective marrow uptake of FDG, P = 0.008 [R1] and P = 0.004 [R2] for measured maximum standardized uptake value (SUVmax)). The median interval between G-CSF administration and PET imaging in cases with marrow activity considered normal or not likely to interfere was 19.5 days (range: 7–55 days). In pediatric and young adult patients with Ewing sarcoma and rhabdomyosarcoma, an interval of 20 days between administration of the long-acting form of G-CSF and FDG PET imaging should limit interference by stimulated marrow.

Altered FDG uptake patterns were noted in certain lymphoblastic lymphoma patients during therapy. To describe these altered FDG uptake patterns and their relationship to chemotherapy. Thirty-five FDG PET or PET/CT scans obtained in 11 children with lymphoblastic lymphoma were retrospectively reviewed. FDG uptake patterns were recorded. SUV measurements were performed in liver and facial soft tissues. Results were correlated with induction chemotherapy regimens. Six of the children had transiently altered FDG uptake with increased uptake in the superficial soft tissues, most notably involving the face. Altered uptake was noted approximately 1 month after initiation of chemotherapy and subsequently resolved. Hepatic uptake was transiently reduced on the 1-month scan in all six children with increased facial uptake. No significant FDG uptake in lymphoma was seen on five of six scans with altered uptake; however, two of these five affected children had FDG uptake in lymphoma on the next follow-up examination. Blood glucose levels in the affected children were in the normal range. All six children with altered FDG uptake received the same induction chemotherapy regimen, which included very high doses of corticosteroids. Children with lymphoblastic lymphoma on induction chemotherapy protocols including very high doses of corticosteroids transiently demonstrated altered FDG uptake patterns, including increased superficial facial uptake and reduced hepatic uptake. The facial uptake is probably the FDG PET equivalent of Cushingoid facies. Caution in interpreting scans with this altered FDG uptake pattern is suggested, as uptake at sites of lymphomatous involvement may potentially be affected.

Positron emission tomography (PET) has transformed nuclear medicine imaging technology. PET is an inherently tomographic technique that utilizes the simultaneous detection of 180-degree opposed 511 keV photons emitted by positron annihilation. Collimation can be eliminated, greatly improving sensitivity and spatial resolution. By placing PET and CT scanners on the same gantry, co-registered PET/CT images can be obtained, allowing normal and abnormal physiology to be accurately depicted in a high-resolution spatial context. The CT part of the PET/CTscanner can be used in any of three modes: as a diagnostic CT scanner at appropriate diagnostic settings for pediatric CT, at reduced non-diagnostic localization settings, and at extremely low non-imaging settings for attenuation correction only. PET/CT has improved the accuracy of PET imaging in 10–30% of patients in adult and pediatric studies. With precise localization of PET abnormalities on PET/CT images and the anatomical information obtained from the co-registered diagnostic or localization CT, interpretative errors are reduced in frequency.

In Langerhans cell histiocytosis (LCH), FDG PET demonstrates active disease in bone. Other imaging modalities show the effects of bone destruction by LCH.To evaluate a selective CT method for reducing effective dose from FDG PET/CT in LCH, using whole-body modified attenuation correction CT at extremely low exposure settings, with repeat selective limited-volume CT at typical localization settings.Fifty-one PET/CT scans were performed in 23 LCH patients, median patient age 8.5 years (range: 1-25 years). Thirty-four were performed with modified attenuation correction CT settings, with bed positions (excluding head and neck) repeated at localization CT settings in regions with abnormal or difficult to interpret PET findings.Of 34 modified attenuation correction PET/CT scans, 10 required repeat localization CT of 1 to 3 bed positions (total: 17 bed positions). Lytic bone lesions were easily recognized at modified attenuation correction settings. Calculated average effective dose for the 34 whole-body CT scans at modified attenuation correction settings was 1.65 mSv. Average effective dose per patient for repeat imaging of 17 bed positions at localization settings was 1.19 mSv. Average total effective dose from CT for all 34 scans performed at the modified attenuation correction CT settings, including the 10 repeat localization CT scans, was 2.0 mSv. High-quality PET scans were consistently obtained with reduced FDG-administered activities of 3.7 MBq/kg (0.10 mCi/kg). In active LCH, abnormal FDG uptake was seen in all lytic bone lesions ≥9 mm, including cranial vault lesions.Substantial reduction in effective dose is possible using selective CT techniques for FDG PET/CT.

SPECT/CT improves localization of single photon-emitting radiopharmaceuticals. To determine the utility of SPECT/CT in children with papillary thyroid carcinoma. 20 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). In 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. SPECT/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.

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