18F-NaF-PET/CT and 99mTc-MDP Bone Scintigraphy in the Detection of Bone Metastases in Prostate Cancer

99mTc-MDP whole-body bone scintigraphy is a highly sensitive imaging method that has been used for decades to evaluate prostate cancer bone metastasis based on its availability and low cost; however, because of accumulation of this radiotracer in degenerative, traumatic, and inflammatory lesions, it suffers from noncomparable specificity. The modality is also used to monitor response to therapy and to predict patients' prognosis. As planar imaging may not give enough information for lesion detection or anatomical localization, it can be supplemented with SPECT to increase image contrast particularly in the evaluation of small and complex skeleton. In addition, hybrid SPECT/CT can be used to assess both functional and morphologic changes leading to more accurate detection of the metastatic bone lesions in a single-section test. 18F-NaF-PET/CT offers excellent advantages in investigating bone metastases. It provides greater spatial resolution and better image quality, resulting in better sensitivity and specificity. Furthermore, 18F-NaF-PET/CT is able to evaluate response to therapy more accurately and to detect occult bone metastases in lower prostate-specific antigen levels when comparing with conventional 99mTc-labeled whole-body bone scan. Owing to smaller administered dose and shorter half-life of 18F-NaF, the total actual radiation absorbed dose is almost comparable with 99mTc-labeled conventional bone scintigraphy. Hence, we believe that conventional bone scintigraphy would be replaced by 18F-NaF-PET/CT in the assessment of metastatic bone disease where PET/CT scanners are available.