[Validation of Changes over Time in Sensitivity Calibrations of SPECT Quantification for Different Radionuclides]

In single-photon emission computed tomography (SPECT), the standardized uptake value requires a becquerel calibration factor (BCF). The changes over time in BCF due to different radionuclides and collimators was examined.

The BCF (cps/MBq) was monthly calculated from the radioactivity of syringe formulations and dispensed sources measured with a dose calibrator, and planar acquisition counts. In addition, relative errors with respect to the maximum BCF over 44 months were calculated.

The average BCF was 46.0 for ¹²³I with a low-penetration high-resolution collimator (¹²³I-LPHR) and 124.1 for ¹³¹I with a medium-energy low-penetration collimator (¹³¹I-MELP). The standard deviation of the BCF for any radionuclides and collimators was less than 3.4 and the differences between detectors were small. Relative errors of the BCF were less than 10% for ^99mTc with a low-energy high-resolution collimator (^99mTc-LEHR), ¹²³I-MELP, ⁶⁷Ga-MELP, and ¹³¹I-MELP, and less than 5% for ¹²³I-MELP. Relative errors for ¹²³I-LEHR and ¹²³I-LPHR were initially slightly higher but decreased to less than 10% after 7 months.

The BCF measured by planar acquisition were stable and reproducible over time with a wide variety of nuclides and collimators.