Revision of the NIST Standard for 223 Ra: New Measurements and Review of 2008 Data

Abstract

After discovering a discrepancy in the transfer standard currently being disseminated by the National Institute of Standards and Technology (NIST), we have performed a new primary standardization of the alpha-emitter 223Ra using Live-timed Anticoincidence Counting (LTAC) and the Triple-to-Double Coincidence Ratio Method (TDCR). Additional confirmatory measurements were made with the CIEMAT-NIST efficiency tracing method (CNET) of liquid scintillation counting, integral γ-ray counting using a NaI(Tl) well counter, and several High Purity Germanium (HPGe) detectors in an attempt to understand the origin of the discrepancy and to provide a correction. The results indicate that a −9.5 % difference exists between activity values obtained using the former transfer standard relative to the new primary standardization. During one of the experiments, a 2 % difference in activity was observed between dilutions of the 223Ra master solution prepared using the composition used in the original standardization and those prepared using 1 mol·L−1 HCl. This effect appeared to be dependent on the number of dilutions or the total dilution factor to the master solution, but the magnitude was not reproducible. A new calibration factor (“K-value”) has been determined for the NIST Secondary Standard Ionization Chamber (IC “A”), thereby correcting the discrepancy between the primary and secondary standards.

The potential of 223Ra and 18F-fluoride imaging to predict bone lesion response to treatment with 223Ra-dichloride in castration-resistant prostate cancer

“…Following a revision of the primary standard for radionuclide calibrators [18,19], it was retrospectively acknowledged that, in fact, patients received 110 kBq/kg. Ra organ dosimetry in these patients has previously been reported [8].…”

Establishment of the Primary Activity Standard of ²²³Ra in Japan

“…After the inter-comparison study, NIST again performed a standardization study using several different technical approaches and updated the primary standard. 8) As a consequence, the discrepancy disappeared; however, the reason for such a large difference observed originally remains unclear. The updated report by NIST pointed out that care must be taken to verify the activities of citrate solutions whenever transfer or dilution of 223 Ra so- 223 Ra radiopharmaceuticals in such a situation in Japan, the National Metrology Institute of Japan (NMIJ) has developed a national primary standard.…”

“…In the present study, the detection efficiencies for β-emitters were determined using the CIEMAT/NIST efficiency tracing method. This method has been previously adopted for 223 Ra standardization by several authors 4,[6][7][8] and is known A 3 H quenched set was also fabricated using the standardized 3 H water described in subclause 2.2.…”

Ra-223 dichloride management in a Nuclear Medicine Unit: experience of a referral institution

“…In 2015, primary NIST dose calibrator standards for Ra-223 have been revised due to erroneously activity readings, about 10% lower than expected [25]. Updated secondary NIST reference standards have been introduced into clinical practice from January 2016 [26].…”