18F-fluoride PET/CT in clinical practice

Radiol Bras. 2015 Jul/Ago;48(4):VII–VIII The presence of bone metastasis is a relevant prognostic factor for cancer patients, and the skeleton is a common site of distant metastasis in cases of advanced-stage neoplasias. Recent developments in oncological treatments have led to a significant increase in patients’ survival. On the other hand, much of the morbidity and disability in such patients is caused by metastatic bone disease. Thus an appropriate assessment of the skeleton for early detection of bone metastasis is essential for correct clinical decisions making in order to provide patients with appropriate treatment and better quality of life. Bone scintigraphy (BS) with Tc-labeled radiopharmaceuticals, such as Tc-MDP, has been extensively utilized for the diagnosis of bone metastasis, and plays a relevant role in the initial assessment and follow-up of cancer patients. In spite of its relatively high sensitivity, the accuracy of BS is compromised by its limited spatial resolution. The specificity is frequently low as the skeleton may be affected by different diseases with no specific scintigraphic findings. For this reason, about one third of BSs present inconclusive results for bone metastasis, which implies the necessity of additional procedures for a definite diagnosis or for anatomical correlation, namely radiography, computed tomography, magnetic resonance imaging and biopsy. The routine use of tomographic images such as SPECT/CT (single photon emission computed tomography/computed tomography) is also helpfull, but it significantly increases imaging acquisition time, particularly in cases where several segments of the skeleton must be scanned. Positron emission tomography/computed tomography (PET/CT) with the radiopharmaceutical sodium fluoride labeled with fluorine18 (F-NaF) has been utilized in the assessment of bone metastasis in a variety of malignancies. The fast and intense F-fluoride uptake by active osteoblastic lesions and by the osteoblastic component of osteolytic lesions occurs due F-fluoride ions exchange with the hydroxyl groups in hydroxyapatite crystals. The method accuracy is quite high and several studies demonstrate that F-fluoride PET/CT is more sensitive and specific than BS to identify bone metastases due its higher spatial resolution and to the more favorable biokinetics of the radiopharmaceutical. In Brazil the availability of F-fluoride is limited, in spite of being produced for many years by Instituto de Pesquisas Energéticas e Nucleares (Ipen). Except for Ipen, all the other ten centers involved in the production of F-fluorodeoxyglucose (F-FDG) do