THE ROLE OF STRONTIUM 85 IN THE DETECTION OF BONE DISEASE.

Abstract

Strontium is metabolized by the body in a manner closely paralleling calcium (7, 10). The use of radioactive strontium 85 (Sr85), a gamma ray emitter, permits detection of focal areas of increased calcium turnover by external scintillation counting or automatic scintillation scanning. Increased Sr85 uptake was shown by Bauer and Wendeberg (1) to occur in both osteolytic and osteoblastic tumors, fractures, osteomyelitis, and Paget's disease. Other authors (3–6, 9) have since confirmed these findings and have demonstrated the presence of skeletal metastases before they were visualized roentgenographically. The growing interest in this potentially useful technic has prompted us to investigate a wide variety of bone lesions, including benign and malignant neoplasms and non-neoplastic conditions. During a sixteen-month period we have performed about 300 Sr85 determinations and have arrived at certain conclusions regarding the usefulness, indications and sources of error of this procedure. The results of our investigation will be presented in three sections. In Section 1 are determinations of the normal uptake of Sr85 in the axial skeleton. Section 2 deals with the detection of malignant bone disease, and Section 3 contains a number of illustrations of nonmalignant osseous lesions which concentrate Sr85. Material Sr85 decays by electron capture to rubidium 85, and this is followed by an emission of a single gamma photon of 0.51 Mev. It is administered as a strontium chloride solution either by intramuscular or intravenous injection. The total body dose by the parenteral route has been variously reported from 1.5 to 2.3 rads per 100 µc (3, 12). We inject between 50 and 100 µc. External spot counting is performed with a 5 cm straight-bore lead collimator which is placed in contact with the body surface. The 2 × 2-in. sodium iodide scintillation crystal is 15 cm distant from the skin, and the discriminator is set just below the knee of the integral spectrum. Spot counting is performed between two and seven days after injection. Average activity over the spine in normal patients is 1,800 c.p.m. for 100 µc Sr85 and background is about 375 c.p.m. The standard deviation due to counting statistics has been calculated to be 2 to 4 per cent of the net count. Referring to Tables I and II it can be seen that counting statistics account for only a small part of the experimental standard deviations. A 19-hole lead focusing collimator is employed on the automatic scintillation scanner (Nuclear-Chicago) which is associated with a 1.5 × 3-in. diameter sodium iodide crystal. The spectrometer settings accept the full width of the 0.51 Mev photopeak. Scanning may be performed after routine spot counting to better localize an area of high activity or investigate a specific region of bone pain.