18F-Fluoride PET/CT in the detection of bone metastases in clear cell renal cell carcinoma: discordance with bone scintigraphy

Prospective study evaluating the relative sensitivity of 18F-NaF PET/CT for detecting skeletal metastases from renal cell carcinoma in comparison to multidetector CT and 99mTc-MDP bone scintigraphy, using an adaptive trial design

BACKGROUND

The detection of occult bone metastases is a key factor in determining the management of patients with renal cell carcinoma (RCC), especially when curative surgery is considered. This prospective study assessed the sensitivity of (18)F-labelled sodium fluoride in conjunction with positron emission tomography/computed tomography ((18)F-NaF PET/CT) for detecting RCC bone metastases, compared with conventional imaging by bone scintigraphy or CT.

PATIENTS AND METHODS

An adaptive two-stage trial design was utilized, which was stopped after the first stage due to statistical efficacy. Ten patients with stage IV RCC and bone metastases were imaged with (18)F-NaF PET/CT and (99m)Tc-labelled methylene diphosphonate ((99m)Tc-MDP) bone scintigraphy including pelvic single photon emission computed tomography (SPECT). Images were reported independently by experienced radiologists and nuclear medicine physicians using a 5-point scoring system.

RESULTS

Seventy-seven lesions were diagnosed as malignant: 100% were identified by (18)F-NaF PET/CT, 46% by CT and 29% by bone scintigraphy/SPECT. Standard-of-care imaging with CT and bone scintigraphy identified 65% of the metastases reported by (18)F-NaF PET/CT. On an individual patient basis, (18)F-NaF PET/CT detected more RCC metastases than (99m)Tc-MDP bone scintigraphy/SPECT or CT alone (P = 0.007). The metabolic volumes, mean and maximum standardized uptake values (SUV mean and SUV max) of the malignant lesions were significantly greater than those of the benign lesions (P < 0.001).

CONCLUSIONS

(18)F-NaF PET/CT is significantly more sensitive at detecting RCC skeletal metastases than conventional bone scintigraphy or CT. The detection of occult bone metastases could greatly alter patient management, particularly in the context when standard-of-care imaging is negative for skeletal metastases.

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.

PET/Computed Tomography in Renal, Bladder, and Testicular Cancer

Imaging plays an important role in the clinical management of cancer patients. Hybrid imaging with PET/computed tomography (CT) is having a broad impact in oncology, and in recent years PET/CT is beginning to have an impact in urooncology. In both bladder and renal cancers, there is a need to study the efficacy of other tracers than F-18 fluorodeoxyglucose (FDG), particularly tracers with limited renal excretion. Thus, new tracers are being introduced. This review focuses on the clinical role of FDG and other PET agents in renal, bladder, and testicular cancers.

Quantification of 18F-Fluoride Kinetics: Evaluation of Simplified Methods

(18)F-fluoride PET is a promising noninvasive method for measuring bone metabolism and bone blood flow. The purpose of this study was to assess the performance of various clinically useful simplified methods by comparing them with full kinetic analysis. In addition, the validity of deriving bone blood flow from K1 of (18)F-fluoride was investigated using (15)O-H2O as a reference.

METHODS

Twenty-two adults (mean age ± SD, 44.8 ± 25.2 y), including 16 patients scheduled for bone surgery and 6 healthy volunteers, were studied. All patients underwent dynamic (15)O-H2O and (18)F-fluoride scans before surgery. Ten of these patients had serial PET measurements before and at 2 time points after local bone surgery. During all PET scans, arterial blood was monitored continuously. (18)F-fluoride data were analyzed using nonlinear regression (NLR) and several simplified methods (Patlak and standardized uptake value [SUV]). SUV was evaluated for different time intervals after injection and after normalizing to body weight, lean body mass, and body surface area, and simplified measurements were compared with NLR results. In addition, changes in SUV and Patlak-derived fluoride influx rate (Ki) after surgery were compared with corresponding changes in NLR-derived Ki. Finally, (18)F-fluoride K1 was compared with bone blood flow derived from (15)O-H2O data, using the standard single-tissue-compartment model.

RESULTS

K1 of (18)F-fluoride correlated with measured blood flow, but the correlation coefficient was relatively low (r = 0.35, P < 0.001). NLR resulted in a mean Ki of 0.0160 ± 0.0122, whereas Patlak analysis, for the interval 10-60 min after injection, resulted in an almost-identical mean Ki of 0.0161 ± 0.0117. The Patlak-derived Ki, for 10-60 min after injection, showed a high correlation with the NLR-derived Ki (r = 0.976). The highest correlation between Ki and lean body mass-normalized SUV was found for the interval 50-60 min (r = 0.958). Finally, changes in SUV correlated significantly with those in Ki (r = 0.97).

CONCLUSION

The present data support the use of both Patlak and SUV for assessing fluoride kinetics in humans. However, (18)F-fluoride PET has only limited accuracy in monitoring bone blood flow.