Isotope Scanning with 18F for the Early Detection of Bone Tumours

The metabolic processes leading to bone deficits or accretions go on for a substantial period before an appreciable change in bone density can be seen on roentgenograms. Since isotope localization is a function of these metabolic processes, early visualization of bone tumours can be achieved by scanning. The mechanism of uptake of the isotope in osteolytic or osteoblastic lesions is by ion exchange with exposed bone crystals. Any small ion which can take the place of Ca2+, OH-, or PO43 in bone salt will localize. 47Ca and 85Sr ions have been used in bone scanning. The gamma-ray energy of 47Ca (1.3 MeV) is too high for use with scanning equipment found in most hospitals, and the half-life of 85Sr (65 days) prevents the administration of adequate doses of this isotope. The 18F fluoride ion is rapidly taken up in bone lesions and the non-localized isotope is quickly cleared from the blood and soft tissue. The short physical half-life of 18F permits the use of large doses with little radiation to the patient. Over 350 patients have been studied. Lesions visible on roentgenograms have almost invariably shown abnormal uptake of the isotope. In over 10% of the cases it has been possible to demonstrate bone metastases on the isotope scans before X-ray changes have appeared. (author)