Critical considerations on the combined use of 18F-FDG and 18F-fluoride for PET assessment of metastatic bone disease

Emerging role of integrated PET-MRI in osteoarthritis

Osteoarthritis (OA) is a common degenerative disorder of the articular cartilage, which is associated with hypertrophic changes in the bone, synovial inflammation, subchondral sclerosis, and joint space narrowing (JSN). Radiography remains the first line of imaging till now. Due to the lack of soft-tissue depiction in radiography, researchers are exploring various imaging techniques to detect OA at an early stage and understand its pathophysiology to restrict its progression and discover disease-modifying agents in OA. As the OA relates to the degradation of articular cartilage and remodeling of the underlying bone, an optimal imaging tool must be sensitive to the bone and soft tissue health. In that line, many non-invasive imaging and minimally invasive techniques have been explored. Out of these, the non-invasive compositional magnetic resonance imaging (MRI) for evaluation of the integrity of articular cartilage and positron emission tomography (PET) scan with fluorodeoxyglucose (FDG) and more specific bone-seeking tracer like sodium fluoride (18F-NaF) for bone cartilage interface are some of the leading areas of ongoing work. Integrated PET-MRI system, a new hybrid modality that combines the virtues of the above two individual modalities, allows detailed imaging of the entire joint, including soft tissue cartilage and bone, and holds great potential to research complex disease processes of OA. This narrative review attempts to signify individual characteristics of MRI, PET, the fusion of these characteristics in PET-MRI, and the ongoing research on PET-MRI as a potential tool to understand the pathophysiology of OA.

18F-FDG PET/CT is a prognostic biomarker in patients affected by bone metastases from breast cancer in comparison with 18F-NaF PET/CT

Aim: To compare 18F-FDG PET/CT and 18F-NaF PET/CT with respect to disease prognostication and outcome in patients affected by bone metastases from breast cancer (BC). Patients, methods: We retrospectively investigated 32 women with BC and documented bone metastases. Semi-quantitative parameters were applied to 18F-FDG PET/CT and 18F-Na PET/CT in order to evaluate disease extent and tumour metabolism. We used time-to-event analyses (Kaplan Meier and COX proportional hazard methods) to estimate progression-free (PFS) and overall survival (OS) in order to assess the independent prognostic value of 18F-FDG PET/CT and 18F-Na PET/CT. Results: The sensitivity of 18F-NaF PET/CT (100%) was higher (p < 0.05) than that of 18F-FDG PET/CT (72% and 72%). None of the 18F-FDG PET/CT-negative patients showed disease progression at the end of follow-up. After adjustment for age, Ki-67 levels, presence of visceral metastases, hormone therapy, duration of bone disease and response to first-line therapy, only 18F-FDG SUV mean [HR 15.7, 95% confidence interval (CI) 1.15-214.5] and 18F-FDG whole-body bone metabolic burden (WB-B-MB) (HR 16.9; 95%CI 1.87-152.2) were independently and significantly associated with OS. None of the 18F-NaF PET/CT parameters were associated with OS. None of the conventional clinical prognostic parameters remained significantly associated with OS after the inclusion of PET/ CT parameters in the model. Conclusion: 18F-FDG PET/CT is independently associated with OS in BC patients with bone metastases and its prognostic impact seems to be higher than conventional clinical and biological prognostic factors. Although 18F-NaF PET/CT has a higher diagnostic sensitivity than 18F-FDG PET/ CT, it is not independently associated with OS.

Optimizing an 18F-NaF and 18F-FDG cocktail for PET assessment of metastatic castration-resistant prostate cancer

BACKGROUND

PET/computed tomography (CT) imaging with the sodium-(F)-fluoride/2-(F)-fluoro-2-deoxy-D-glucose (F-NaF/F-FDG) cocktail has been proposed for patients with osseous metastases. This work aimed to optimize the cocktail composition for patients with metastatic castration-resistant prostate cancer (mCRPC).

MATERIALS AND METHODS

The study was carried out on six patients with mCRPC, with a total of 26 analyzed lesions. The patients were injected with F-NaF and F-FDG at separate time points. Dynamic PET/CT imaging recorded the uptake time course for both the tracers into osseous metastases. F-NaF and F-FDG uptakes were decoupled by kinetic analysis, which enabled calculation of F-NaF and F-FDG standardized uptake values (SUVs) images. Peak, mean, and total SUVs were evaluated for both tracers and all visible lesions. The F-NaF/F-FDG cocktail was optimized under the assumption that the contribution of both tracers to image formation is equal. SUV images from PET/CT imaging with a combination of F-NaF and F-FDG were generated for cocktail compositions with an F-NaF : F-FDG ratio varying from 1 : 8 to 1 : 2.

RESULTS

The F-NaF peak and mean SUVs were on average four to five times higher than the F-FDG peak and mean SUVs, with an interlesion coefficient of variations of 20%. The total SUV for F-NaF was on average seven times higher than that for F-FDG. When the F-NaF : F-FDG ratio changed from 1 : 8 to 1 : 2, the typical SUV on the generated PET images increased by 50%, whereas the change in the uptake visual pattern was hardly noticeable.

CONCLUSION

F-NaF and F-FDG in the cocktail contribute equally to image formation when the F-NaF : F-FDG ratio is 1 : 5. Therefore, we propose this ratio as the optimal cocktail composition for mCRPC patients. We also urge to strictly control the cocktail composition during any F-NaF/F-FDG cocktail PET/CT examination.

18F-Fluoride PET/CT for detection of bone metastasis in patients with renal cell carcinoma: a pilot study

PURPOSE

The aim of this study was to evaluate the role of F-fluoride PET/computed tomography (CT) in the detection of bone metastasis in patients with renal cell carcinoma (RCC) and compare the results with fluorine-18 fluorodeoxyglucose (F-FDG) PET/CT and technetium-99m methylene diphosphonate bone scintigraphy (BS) when available.

MATERIALS AND METHODS

The data of 36 patients (mean age: 52.5±14.1 years; male/female: 27/9) with RCC who prospectively underwent F-fluoride PET/CT were analyzed. PET/CT images were analyzed by two nuclear medicine physicians in consensus, visually and semiquantitatively [maximum standardized uptake value (SUVmax)]. Results of F-fluoride PET/CT were compared with those of F-FDG PET/CT (n=16) and BS (n=22). Histopathology or clinical or imaging follow-up (minimum 6 months) were used as the reference standard.

RESULTS

Overall, F-fluoride PET/CT showed a sensitivity of 100%, specificity of 94.4%, positive predictive value of 94.7%, negative predictive value of 100%, and accuracy of 97.2%. It demonstrated a total of 134 skeletal lesions, of which 101 were characterized as metastasis and 33 as benign. Corresponding CT changes were seen for 129/134 lesions. The mean SUVmax of the lesions was 30.3±48.4. F-Fluoride PET/CT and F-FDG PET/CT showed similar accuracy for visualization of bone metastasis (93.7 vs. 100%; P=0.993). However, F-FDG PET/CT additionally demonstrated extraskeletal metastasis in 6/16 patients. No significant difference was seen between the accuracies of BS and F-fluoride PET/CT for visualization of bone metastasis (93.7 vs. 100%; P=0.115), but the former showed significantly more skeletal lesions (91 vs. 44; P<0.0001). In 4/22 patients (18%) with negative BS, F-fluoride PET/CT demonstrated skeletal metastasis.

CONCLUSION

F-Fluoride PET/CT shows high diagnostic accuracy for the detection of bone metastasis in patients with RCC. It shows comparable results to F-FDG PET/CT and detects more skeletal lesions compared to BS.

Combined Injection of (18)F-Fluorodeoxyglucose and 3'-Deoxy-3'-[(18)F]fluorothymidine PET Achieves More Complete Identification of Viable Lung Cancer Cells in Mice and Patients than Individual Radiopharmaceutical: A Proof-of-Concept Study

PURPOSE

The objective is to validate the combination of 3'-deoxy-3'-[(18)F]fluorothymidine ((18)F-FLT) and (18)F-fluorodeoxyglucose ((18)F-FDG) as a "novel" positron emission tomography (PET) tracer for better visualization of cancer cell components in solid cancers than individual radiopharmaceutical.

METHODS

Nude mice with subcutaneous xenografts of human non-small cell lung cancer A549 and HTB177 cells and patients with lung cancer were included. In ex vivo study, intratumoral radioactivity of (18)F-FDG, (18)F-FLT, and the cocktail of (18)F-FDG and (18)F-FLT detected by autoradiography was compared with hypoxia (by pimonidazole) and proliferation (by bromodeoxyuridine) in tumor section. In in vivo study, first, (18)F-FDG PET and (18)F-FLT PET were conducted in the same subjects (mice and patients) 10 to 14 hours apart. Second, PET scan was also performed 1 hour after one tracer injection; subsequently, the other was administered and followed the second PET scan in the mouse. Finally, (18)F-FDG and (18)F-FLT cocktail PET scan was also performed in the mouse.

RESULTS

When injected individually, (18)F-FDG highly accumulated in hypoxic zones and high (18)F-FLT in proliferative cancer cells. In case of cocktail injection, high radioactivity correlated with hypoxic regions and highly proliferative and normoxic regions. PET detected that intratumoral distribution of (18)F-FDG and (18)F-FLT was generally mismatched in both rodents and patients. Combination of (18)F-FLT and (18)F-FDG appeared to map more cancer tissue than single-tracer PET.

CONCLUSIONS

Combination of (18)F-FDG and (18)F-FLT PET imaging would give a more accurate representation of total viable tumor tissue than either tracer alone and would be a powerful imaging strategy for cancer management.