Evaluation of Calcium 47 in Normal Man and Its Use in the Evaluation of Bone Healing Following Radiation Therapy in Metastatic Disease

Abstract

The use of external counting technics for the study of problems in bone metabolism has been hampered in the past by the lack of suitable isotopes. Many radioactive compounds have been utilized in the study of bone metabolism, but without great success. These have included gallium 72 (3, 4) sodium 22, sodium 24, barium 140, etc. Dudley et. al (5) are presently working with radioactive yttrium in this study. Bauer and his associates (1) introduced calcium 47 as an agent for the evaluation of bone metabolism. The radioactive calcium was found to be selectively localized in areas of osteoblastic activities such as the epiphyses in young persons, healing fractures, metastatic areas of carcinoma to bone, eosinophilic granulomas, osteomyelitis, chondromas, etc. Radioactive calcium 47 has a half-life of 4.7 days and emits a high-energy gamma ray of 1.3 Mev as well as a beta particle in its decay to scandium 47. Scandium 47 is also radioactive with a half-life of 3.8 days, and decays by the emission of a beta particle and gamma photon to stable titanium 47. The physical characteristics of calcium 47 make it attractive for clinical studies of calcium metabolism. It is produced by neutron irradiation in a nuclear reactor of enriched calcium 46 in the form of calcium carbonate. The material is available from the Abbott Laboratories in Oak Ridge, Tenn., on a monthly schedule. Greenberg et al. (6) and Corey et al. (2) have recently pointed out the possibility of defining metastatic lesions in bone utilizing calcium 47. It was as a direct consequence of their work that we extended the evaluation of the material to further investigation of normal human values as well as to the appraisal of bone healing following radiation therapy to metastatic lesions. The patient, for study, received an intravenous dose of about 40 to 60 microcuries calcium 47 in the form of calcium chloride with aliquots of the administered solution being prepared as reference sources. It was intended that the external counting be done in as simple a manner as possible consistent with the physical characteristics of the material being utilized. For external counting the Picker Magnascanner with the ultraprobe A was employed. The probe had a sodium-iodide crystal measuring 3×2 inches and was surrounded by 2.5 cm. of lead shielding. In front of the crystal, there was a 7.5-cm. extension of the shield into which was inserted a 19-hole focusing lead collimator. The external counts were taken with the aperture of the collimator in direct contact with the skin overlying the volume of bone being counted. The isoresponse curve of the collimator was such that the volume of tissue being seen was in the range of 5 to 10 cm. below the surface of the skin. Blood and urine radioassays were also done at each time interval. The radioactive samples of each were counted in a well-type scintillation counter.