Dynamic PET/CT imaging of ¹⁸F-(2S, 4R)4-fluoroglutamine in healthy volunteers and oncological patients

Objectives: ¹⁸F-(2S, 4R)4-fluoroglutamine (¹⁸F-FGln) was developed as a PET tracer for mapping glutaminolytic tumors. The purpose of this study was to compare dynamic PET/CT imaging of ¹⁸F-FGln between healthy volunteers and oncological patients and explore the optimal imaging time in different cancer types.

Methods: Two groups of subjects (13 healthy volunteers, 25 untreated cancer patients) underwent dynamic and/or static whole-body PET/CT after intravenous injection of ¹⁸F-FGln (3.7MBq per kilogram), followed by a whole body ¹⁸F-FDG/PET performed in the same week. Whole-organ volumes of interest (VOI) were drawn manually on every section of major organs/tissues in the reconstructed PET/CT images to explore the characteristic of ¹⁸F-FGln radiotracer distribution in different organs. The average standardized uptake values (SUVmean) across all scans, the coefficient of variation (CV) and the Total Activity for each organ were calculated. Same parameters were also derived for sphere/ellipsoid VOI drawn according the organs. The distribution of ¹⁸F-FDG in healthy subject group were also be evaluated as control. The Organ Level Internal Dose Assessment/Exponential Modelling (OLINDA/EXM)software was used to calculate human dosimetry based on the biodistribution of the ¹⁸F-FGln.

Results: In this dynamic PET/CT imaging study of ¹⁸F-FGln, average dose was 16.90±2.13 μSv/MBq for male and 21.90±2.97 μSv/MBq for female both were below the recommended Food and Drug Administration limit for research studies. The calculated CVs of 20 organs/tissue across all healthy volunteers for SUVmean were included in this study, liver could be selected as the basis of quantitative reliability in ¹⁸F-FGln PET images given its low variability (14.70%), which was similar with ¹⁸F-FDG PET (13.35%). In addition, the ¹⁸F-FGln activity (SUVmean) of most normal organs in cancer patients were lower than that of healthy subjects, especially in lung, muscle, spleen and heart (p<0.05), supporting recent findings that proliferating cancer cells compete with normal cells for circulating glutamine. Furthermore, optimal imaging time for breast and thyroid was 10 min and 60 min post injection, respectively; while the melanoma cancer displayed similar results in three different time points (10, 30 and 60 min). ¹⁸F-FGln PET was a promising PET radiotracer for patients with breast cancer, although the SUVmax in 17 breast cancer were not associate with the Ki-67 level of the lesions.

Conclusions: Dynamic imaging of ¹⁸F-FGln PET/CT in cancer patients can be useful for detection of various tumor subtypes. Optimal imaging time for ¹⁸F-FGln PET/CT in different cancer types may need to be optimized to improve tumor to background ratios. This study suggested that 18F-FGln PET imaging might be able to assist in diagnosing the presence of tumor, but by itself alone might not be sufficient to monitor the cell invasion ability of cancer.

• Download figure
• Open in new tab
• Download powerpoint