(Mis)use of 133 Ba as a calibration surrogate for 131 I in clinical activity calibrators

Abstract

Using NIST-calibrated solutions of 131Ba and 131I in the 5 mL NIST ampoule geometry, measurements were made in three NIST-maintained Capintec activity calibrators and the NIST Vinten 671 ionization chamber to evaluate the suitability of using 133Ba as a calibration surrogate for 131I. For the Capintec calibrators, the 133Ba response was a factor of about 300% higher than that of the same amount of 131I. For the Vinten 671, the Ba-133 response was about 7 % higher than that of 131I. These results demonstrate that 133Ba is a poor surrogate for 131I. New calibration factors for these radionuclides in the ampoule geometry for the Vinten 671 and Capintec activity calibrators were also determined.

An update on ‘dose calibrator’ settings for nuclides used in nuclear medicine

“…The use of 68 Ge sources as surrogates for short-lived positron emission tomography (PET) radionuclides is now firmly established [9, 35]. However, some approaches, such as the use of 133 Ba as a surrogate for 131 I can lead to errors [15].…”

Active and passive dosimetry for beta-emitting radiopharmaceutical therapy agents in a custom SPECT/CT compatible phantom

“…The largest sources of uncertainty for the MC simulations were in the modeling of the experiment and determination of the source activity. An approximated uncertainty in the activity measurement of 5% was used based on a combination of manufacturer recommendations and previous publications using dose calibrators for measurements with 131 I and 177 Lu (Capintec Inc. 2010, Zimmerman and Bergeron 2016, Tiwari et al 2020, Staanum et al 2021, Van et al 2022. The type B uncertainty implicit to the EGSnrc code was assumed to be negligible compared to the dominant sources of uncertainty in the experiments.…”