Patient Preparation and Performance of PET/CT Scans in Pediatric Patients

Effect of Propranolol on 18F-Fluorodeoxyglucose Uptake in Brown Adipose Tissue in Children and Young Adults with Neoplastic Diseases

PURPOSE

To evaluate the effectiveness of propranolol at mitigating FDG uptake in brown adipose tissue (BAT) of pediatric patients with known or suspected malignancies.

METHODS

PET/CT scans of 3 cohorts of patients treated from 2005 to 2017 were scored for the presence of FDG uptake by BAT at 7 sites: right or left neck/supraclavicular area, right or left axilla, mediastinum, posterior thorax, and abdomen/pelvis. Uptake was scored as follows: 0, none; 1, mild uptake < liver; 2, moderate uptake = liver; and 3, intense uptake > liver. Group 1 consisted of 323 patients (630 scans) who had no specific preparation to mitigate FDG uptake by BAT. Group 2 consisted of 345 patients (705 scans) who underwent only warming in an uptake room with a fixed temperature at 24 °C. Group 3 consisted of 622 patients (1457 scans) who underwent warming. In group 3, patients 8 years and older, 471 patients (1114 scans), were also pre-medicated with oral propranolol 60 min before injection of FDG. Generalized estimation equation, using the logit link method, was used to model the relationship between the incidence of BAT score > 0, in any site, as a function of age, sex, seasonal effect, and body surface area (BSA).

RESULTS

In patients aged 8 years or older, the incidence of BAT uptake was 35-44 % and declined to 15 % with propranolol. BAT was most frequent in the neck (26 %), axilla (18 %), posterior thorax (18 %), mediastinum (14 %), and abdomen/pelvis (8 %); BAT was less common in warm months (p = 0.001). No substantial benefit was shown with pre-injection warming alone. No significant effect was found for age, sex, or BSA separately. When BAT uptake was present, it was usually intense.

CONCLUSION

Propranolol preparation minimizes FDG uptake by BAT and should be considered routine for pediatric FDG PET/CT cancer-related protocols in children, adolescents, and young adults.

18F-2-fluoro-2-deoxyglucose uptake in white adipose tissue on pediatric oncologic positron emission tomography (PET)/computed tomography (CT)

BACKGROUND

Altered biodistribution of [F-18]2-fluoro-2-deoxyglucose (FDG) is sometimes encountered in pediatric patients undergoing chemotherapy for lymphoma on post-induction positron emission tomography (PET) imaging. A characteristic pattern of increased FDG uptake in white adipose tissue can be seen, particularly in the buccal regions, body wall and gluteal regions, with a shift of radiotracer away from the blood pool and liver. This altered biodistribution has been attributed to effects of corticosteroids in pediatric and adult patients and is important to recognize because of its potential for limiting the diagnostic quality of the PET scan and interfering with therapeutic response assessment.

OBJECTIVE

In contrast to the well-known metabolically active brown fat seen on up to one-third of pediatric PET scans, white fat is usually non-metabolically active. We sought to determine the incidence of altered distribution of FDG in subcutaneous white adipose tissue in pediatric patients undergoing PET imaging and to assess the association with corticosteroid use.

MATERIALS AND METHODS

We reviewed the medical records and imaging for four children in whom altered biodistribution in white adipose tissue was present on post-induction FDG PET/CT, identified during routine clinical practice. All four were receiving corticosteroids as part of their chemotherapy. We then retrospectively reviewed oncology FDG PET/CT scans over a 2-year period (1,361 scans in 689 patients) to determine the incidence of uptake in white fat by qualitative visual assessment. In the children identified with altered biodistribution, we measured maximum standard uptake value (SUV_max) and mean standard uptake value (SUV_mean) in areas of subcutaneous white fat, the buccal regions, body wall or gluteal soft-tissue regions, liver and blood pool. We reviewed all medical records, including medication lists. We summarize the relevant clinical and imaging findings of 13 pediatric patients, including the 4 index patients.

RESULTS

We determined the incidence of FDG uptake in white fat to be rare, found in 9 of 1,361 (0.6%) PET scans performed for pediatric cancer evaluation. FDG uptake was increased in subcutaneous adipose tissue, particularly in the buccal regions, body wall and gluteal regions, with a shift of radiotracer away from the blood pool and liver. The degree of increased uptake in peripheral white fat varied from marked to mild, and the biodistribution was distinct from that of brown adipose tissue. Children with this altered biodistribution were uniformly receiving corticosteroids as part of induction treatment for their cancer, and these findings were only identified on post-induction PET/CT. Follow-up PET/CT documented resolution of this effect after treatment with corticosteroids ceased.

CONCLUSION

Our findings support the current understanding that characteristic uptake of FDG in white adipose tissue is mediated by corticosteroid effect. Although this altered biodistribution is rare (<1% of PET scans) it could impair the diagnostic quality of the scan, affecting image interpretation, and should be recognized when present.

Nuclear Medicine Procedures in Children: Special Considerations

Nuclear medicine imaging in children is best accomplished when a child-friendly environment is provided for patients and parents. An approach that minimizes patient anxiety and fear is described. International guidelines for administered activity should be used to minimize absorbed radiation doses from radiopharmaceuticals. CT exposure parameters may be reduced to pediatric best practice for diagnostic CT and further reduced when CT images are needed only for localization purposes.