99mTc-MDP scintigraphy vs. 18F-NaF PET/CT for detection of skeletal metastases

Objectives ^99mTc-MDP bone scanning (BS) is highly sensitive and cost-effective, thus having been for decades the standard method for nuclear imaging of the skeletal system. Owing to the pharmacokinetic properties of ¹⁸F-NaF and better resolution of PET/CT, ¹⁸F-NaF PET/CT has attracted clinical interest. Several published studies reported the value of ¹⁸F-NaF PET/CT for skeletal imaging and indicated that it might be superior over ^99mTc-MDP BS in detecting bone metastases. However, ¹⁸F-NaF PET/CT did not replace ^99mTc-MDP BS in routine clinical practice for a variety of reasons. Here we reviewed our clinical experience with ^99mTc-MDP BS and ¹⁸F-NaF PET/CT for detection of bone metastases.

Methods This is a retrospective study (Sep 2007 - Oct 2015) of 77 patients with proven malignancy (51 prostate cancer, 12 sarcoma, 7 breast cancer, 7 other cancers), who had ^99mTc-MDP BS and ¹⁸F-NaF PET/CT for evaluation of skeletal metastases. There were 65 men and 12 women, 19-88 year-old (average: 62.8±15.1). ^99mTc-MDP BS and ¹⁸F-NaF PET/CT were performed within 2-30 days (average: 22±9.7). The lesions detected with each test were tabulated and the results compared.

Results Neither scan identified bone metastases in 27/77 patients (27%). Skeletal metastases were detected by ^99mTc-MDP BS in 41/77 patients (53%) and by ¹⁸F-NaF PET/CT in 50/77 patients (65%). For the group with skeletal metastases on both scans, the extent of disease was greater by ¹⁸F NaF-PET/CT over ^99mTc-MDP BS in 27/41 patients (66%) and the same in 14/41 patients (34%). ¹⁸F-NaF PET/CT showed skeletal metastases not seen on ^99mTc-MDP BS in 9/77 patients (12%).

Conclusions The evaluation of the extent of skeletal metastases with ¹⁸F-NaF PET/CT was superior over ^99mTc-MDP BS in our cohort. In addition, 12% of the patients had bone metastases seen only on ¹⁸F-NaF PET/CT. However, given the concordance between the results of the two scans, it may be possible to create a clinical workflow to evaluate patients referred for bone scintigraphy with a ^99mTc-MDP BS first, followed by ¹⁸F-NaF PET/CT only for patients with negative or equivocal ^99mTc-MDP BS who continue to have high clinical suspicion for bone metastases.