A Recommendation for Revised Dose Calibrator Measurement Procedures for 89Zr and 124I

Abstract

Because of their chemical properties and multiday half lives, iodine-124 and zirconium-89 are being used in a growing number of PET imaging studies. Some aspects of their quantitation, however, still need attention. For 89Zr the PET images should, in principle, be as quantitatively accurate as similarly reconstructed 18F measurements. We found, however, that images of a 20 cm well calibration phantom containing 89Zr underestimated the activity by approximately 10% relative to a dose calibrator measurement (Capintec CRC-15R) using a published calibration setting number of 465. PET images of 124I, in contrast, are complicated by the contribution of decays in cascade that add spurious coincident events to the PET data. When these cascade coincidences are properly accounted for, quantitatively accurate images should be possible. We found, however, that even with this correction we still encountered what appeared to be a large variability in the accuracy of the PET images when compared to dose calibrator measurements made using the calibration setting number, 570, recommended by Capintec. We derive new calibration setting numbers for 89Zr and 124I based on their 511 keV photon peaks as measured on an HPGe detector. The peaks were calibrated relative to an 18F standard, the activity level of which was precisely measured in a dose calibrator under well-defined measurement conditions. When measuring 89Zr on a Capintec CRC-15R we propose the use of calibration setting number 517. And for 124I, we recommend the use of a copper filter surrounding the sample and the use of calibration setting number 494. The new dose calibrator measurement procedures we propose will result in more consistent and accurate radioactivity measurements of 89Zr and 124I. These and other positron emitting radionuclides can be accurately calibrated relative to 18F based on measurements of their 511 keV peaks and knowledge of their relative positron abundances.

Biodistribution and Radiation Dosimetry of 124I-DPA-713, a PET Radiotracer for Macrophage-Associated Inflammation

“…Images were acquired in 3-dimensional mode at 5 min per bed position and were reconstructed as described previously (13), using 3-dimensional orderedsubset expectation maximization with time of flight and a correction for the prompt g-emissions by 124 I. To obtain images in Bq/cm 3 , the scanner was calibrated with a 20-cm-diameter, 20-cm-long 124 I-NaI water phantom using a Capintec CRC 15W dose calibrator with calibration 788 (14).…”

An international multi-center investigation on the accuracy of radionuclide calibrators in nuclear medicine theranostics

“…In particular, these radionuclides ( 111 In, 123 I and 124 I) show a large dependence on sample geometry (particularly sample container) caused by self-absorption of the emitted low-energy X-rays within the sample itself. Consequently, accurate activity measurement of these radionuclides requires speci c calibration or correction factors for the sample geometry [16,17]. When factory settings dedicated to speci c sample con gurations are available, they must be experimentally veri ed prior to clinical use, as they might not be accurate for the speci c containers used locally.…”

“…When factory settings dedicated to speci c sample con gurations are available, they must be experimentally veri ed prior to clinical use, as they might not be accurate for the speci c containers used locally. This was the case for many activity measurements of 123 I, 111 In and 124 I. Alternatively, selective absorption of low-energy X-rays using a copper/aluminum lter is an effective method to minimize the variability in activity measurements caused by sample geometry [17,18].…”

Molecularly specific detection of bacterial lipoteichoic acid for diagnosis of prosthetic joint infection of the bone

“…Radiolabeled antibodies were prepared as detailed above, and injectate was assayed using a well counter with a calibration factor of 517, as determined previously. 29 In a volume of 150 µL, 225 µCi of radiolabeled antibody (approximately 100 µg) was administered intravenously via the retro-orbital sinus. Mice were serially scanned (10-20 min acquisitions, 350-750 keV energy window) on days 1, 3, 5, and 7 on a microPET R4 system (Concorde Microsystems Inc., Knoxville, TN) followed by Faxitron MX-20-DC12 digital X-ray imaging system (Faxitron Bioptics, LLC, Tucson, AZ).…”