CALIBRATION OF TRANSFER IONIZATION CHAMBERS FOR SHORT-LIVED RADIONUCLIDES USED IN NUCLEAR MEDICINE DEVELOPED BY NIST.

One of the properties that makes most of the nuclides used in nuclear medicine so attractive for that purpose -- their short half-life--has the drawback of making it impractical to distribute these nuclides as Standard Reference Materials. Regulatory agencies such as the Nuclear Regulatory Commission and Food and Drug Administration (FDA), however, still require that users and producers of radiopharmaceuticals containing short-half-lived radionuclides demonstrate their ability to accurately measure the amount of radioactivity contained in a sample prior to administration. NIST is addressing this problem by developing calibration factors for commonly used, commercially available, re-entrant ionization chambers, or "dose calibrators." NIST has developed a measurement model that allows determination of uncertainties involved with the derivation of the calibration factor. Moreover, the group recently expanded the program to include the uncertainty due to variation between different individual chambers and variati ons among similar chambers from the same manufacturer. They are currently conducting a study, using the radiotherapy nuclide [Ho.sup.166], to evaluate the variability in measurements among several chambers. In collaboration with the Missouri University Research Reactor and three industrial partners, researchers from the Nuclear Energy Institute and NIST have been performing extensive calibrations of a bone-seeking radiopharmaceutical formulation of [Ho.sup.166]. This radionuclide is beginning beginning the FDA approval process for use in treating multiple myeloma. The derivation of calibration factors from measurements done on a series of chambers from several manufacturers will allow the producers and eventually the users to accurately measure this radiotherapy agent with dose calibrators in a clinical setting.