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Dose calibrator dial settings reported by NIST in 2010 (ARI, v. 68, p. 1367) are now known to give erroneously low (by 10%) activity readings. The original determinations were based on a chain of calibrations; a broken link in this chain was recently discovered. New calibration factors (i.e., dial settings), directly linked to updated NIST primary standards, are reported here. In addition, the raw data used to derive the factors reported in 2010 are revisited. The validity of the reevaluation is established via comparison with the new experiments and revised calibration factors for numerous clinical geometries are reported. The main conclusions of the 2010 report regarding geometry effects remain valid. [ABSTRACT FROM AUTHOR]

Abstract: Calibration factors for commercial ionization chambers (i.e. dose calibrators) were determined for a solution of 123I; the activity was based on the 1976 NBS standard. A link between the NIST standard and the International Reference System (SIR) was established. The two major U.S. dose calibrator manufacturers recommend oppositely biased calibration factors, giving a spread of 11.3% in measured activities. With modern quantitative imaging techniques capable of ≤10% accuracy, this bias for a SPECT nuclide is highly significant. [Copyright &y& Elsevier]

Source self-attenuation for solutions of 57 Co of varying density and carrier concentration was measured in nine re-entrant ionization chambers maintained at NIST. The magnitude of the attenuation must be investigated to determine whether a correction is necessary in the determination of the activity of a source that differs in composition from the source used to calibrate the ionization chamber. At our institute, corrections are currently made in the measurement of 144 Ce, 109 Cd, 67 Ga, 195 Au, 166 Ho, 177 Lu, and 153 Sm. This work presents the methods used as recently applied to 57 Co. A range of corrections up to 1% were calculated for dilute to concentrated HCl at routinely used carrier concentrations. [ABSTRACT FROM AUTHOR]

A suspension of 224Ra adsorbed onto CaCO 3 microparticles shows promise for α-therapy of intracavitary micro-metastatic diseases. To facilitate accurate activity administrations, geometry-specific calibration factors for commercially available reentrant ionization chambers (ICs) have been developed for 224RaCl 2 solutions and 224Ra adsorbed onto CaCO 3 microparticles in suspension in ampoules, vials, and syringes. Ampoules and vials give IC responses consistent with each other to <1%. Microparticles attenuation leads to a ≈1% to ≈2.5% reduction in response in the geometries studied. • Determination of geometry-specific calibration factors for solutions containing 224Ra. • Evaluation of attenuation for 224Ra adsorbed onto CaCO 3 microparticles. • Monte Carlo calculations support interpretation of the underlying physics. [ABSTRACT FROM AUTHOR]

Abstract: Ra-223 is a bone-seeking alpha emitter currently being evaluated as a radiopharmaceutical. Concurrent with the primary standardization, NIST established that calibration factors currently used for radionuclide calibrators in the clinical setting give readings 5.7–8.7% higher than the NIST calibrated activity. This work describes the determination of calibration factors specific to dose vials and syringes. Using the calibration factors derived with standard ampoules to measure syringe activities can give readings up to 3.6% too high. [Copyright &y& Elsevier]

The national metrology institutes for the United Kingdom (UK) and the United States of America (USA) have compared activity standards for 224Ra, an α-particle emitter of interest as the basis for therapeutic radiopharmaceuticals. Solutions of 224RaCl 2 were assayed by absolute methods, including digital coincidence counting and triple-to-double coincidence ratio liquid scintillation counting. Ionization chamber and high-purity germanium (HPGe) γ-ray spectrometry calibrations were compared; further, a solution was shipped between laboratories for a direct comparison by HPGe spectrometry. New determinations of the absolute emission intensity for the 241 keV γ ray (I γ = 4.011(16) per 100 disintegrations of 224Ra) and of the 224Ra half-life (T 1/2 = 3.6313(14) d) are presented and discussed in the context of previous measurements and evaluations. • NIST and NPL activity standards for 224Ra are demonstrated to be in accord. • The absolute emission intensity for the 241 keV γ ray is evaluated as I γ = 4.011(16) per 100 disintegrations of 224Ra. • The 224Ra half-life is evaluated as T 1/2 = 3.6313(14) d. [ABSTRACT FROM AUTHOR]