Abstract

Purpose: This prospective study aims to assess the diagnostic test characteristics of Na[18F]F PET/CT for the skeletal staging of cancer in morbidly obese patients compared with 99mTc-methylene diphosphonate (MDP), whole-body planar (WBS), SPECT, and SPECT/CT acquisitions.

Material and methods: One hundred seventeen obese patients (BMI 46.5 ± 6.1 kg/m2 and mean age, 59.0 years; range 32-89 years) with BMI > 40 kg/m2 were prospectively enrolled and underwent [99mTc]Tc-MDP WBS, SPECT, SPECT/CT, and Na[18F]F PET/CT within two weeks for the osseous staging of a malignancy. Images were assessed qualitatively using a 3-point scale. Patient and lesion-based diagnostic test characteristics were estimated using an optimistic and pessimistic dichotomization method.

Results: Bone metastases were confirmed in 44 patients. Patient-based optimistic diagnostic test characteristics were (sensitivity, specificity, overall accuracy): Na[18F]F PET/CT (95.5%, 95.9%, 95.7%), [99mTc]Tc-MDP WBS (52.3%, 71.2%, 64.1%), SPECT (61.4%, 80.8%, 73.5%) and SPECT/CT (65.9%, 91.8%, 82.1%). Lesion-based optimistic diagnostic test characteristics were: Na[18F]F PET/CT (97.7%, 97.9%, 97.7%), [99mTc]Tc-MDP WBS (39%, 67%, 48.9%), SPECT (52.9%, 93.6%, 67.3%) and SPECT/CT (65.9%, 91.8%, 82.1%). There was no significant difference in the specificity of Na[18F]F and SPECT/CT. All other pairwise comparisons were significant (p<.001). ROC curve analysis showed a high overall accuracy of Na[18F]F with significantly higher AUCs for Na[18F]F PET/CT compared to [99mTc]Tc-MDP WBS, SPECT, and SPECT/CT on both patient and lesion-based analysis (p<.001). Moreover, Na[18F]F PET/CT changed patient management in 38% of patients.

Conclusions: Na[18F]F PET/CT may be the preferred imaging modality for skeletal staging in morbidly obese patients. The technique provides excellent diagnostic test characteristics superior to [99mTc]Tc-MDP bone scan (including SPECT/CT), impacts patient management, has an acceptable radiation exposure profile, and is well-tolerated. Further cost-effectiveness evaluations are warranted.

Keywords: 18F-NaF PET-CT; 99mTc-MDP; SPECT/CT; metastatic bone disease; obesity.