Calibration of PET/CT scanners for multicenter studies on differentiated thyroid cancer with 124I

Abstract

BackgroundStudies on imaging of differentiated thyroid cancer (DTC) using 124I often require a multicenter approach, as the prevalence of DTC is low. Calibration of participating scanners is required to obtain comparable quantification. As determination of a well-defined range of recovery coefficients is complicated for various reasons, a simpler approach based on the assumption that the iodine uptake is highly focal with a background that significantly lacks radioactivity might be more efficient. For each scanner, a linear conversion between known and observed activity can be derived, allowing quantification that can be traced to a common source for all scanners within one study-protocol. The aim of this paper is to outline a procedure using this approach in order to set up a multicenter calibration of PET/CT scanners for 124I.MethodsA cylindrical polyethylene phantom contained six 2-ml vials with reference activities of ~2, 10, 20, 100, 400, and 2000 kBq, produced by dilution from a known activity. The phantom was scanned twice on PET/CT scanners of participating centers within 1 week. For each scanner, the best proportional and linear fit between measured and known activities were derived and based on statistical analyses of the results of all scanners; it was determined which fit should be applied. In addition, a Bland-Altman analysis was done on calibrated activities with respect to reference activities to asses the relative precision of the scanners.ResultsNine Philips (vendor A) and nine Siemens (vendor B) PET/CT scanners were calibrated in a time period of 3 days before and after the reference time. No significant differences were detected between the two subsequent scans on any scanner. Six fitted intercepts of vendor A were significantly different from zero, so the linear model was used. Intercepts ranged from −8 to 26 kBq and slopes ranged from 0.80 to 0.98. Bland-Altman analysis of calibrated and reference activities showed that the relative error of calibrated activities was smaller than that of uncalibrated activities.ConclusionsA simplified multicenter calibration procedure for PET/CT scans that show highly focal uptake and negligible background is feasible and results in more precise quantification. Our procedure can be used in multicenter 124I PET scans focusing on (recurrent) DTC.

Quantitative PET-Bildgebung für die Dosimetrie an Beispielen von 124I, 86Y, 68Ga und 44Sc

“…Bei den heuristischen Verfahren handelt es sich um Bild-basierte Techniken [34,36,41,43]. Sie beruhen auf Phantommessungen mit Aktivitätsverteilungen, wie sie bei der PET-Bildgebung bei Patienten beobachtet wurden.…”

“…An dieser Stelle ist erwähnenswert, dass weitere Radioscandium-Isotope, 43 Sc und 47 Sc, auch in den Fokus geraten sind [74]. Der Positronenstrahler 43 Sc besitzt ähnliche Eigenschaften wie 44 Sc. Der Vorteil von 43 Sc liegt darin, dass es einen deutlich geringeren PGC-Anteil besitzt.…”

“…Der Positronenstrahler 43 Sc besitzt ähnliche Eigenschaften wie 44 Sc. Der Vorteil von 43 Sc liegt darin, dass es einen deutlich geringeren PGC-Anteil besitzt. Jedoch kann 43 Sc nur im Zyklotron produziert werden, woraus eine geringere Verfügbarkeit und ein höherer Preis resultieren.…”

A phantom study: Should 124I‐mIBG PET/CT replace 123I‐mIBG SPECT/CT?

“…This protocol allows comparison with other studies conducted in our institution. [12][13][14][15] SPECT/CT images were acquired on a dual-headed Siemens Symbia T16 (Siemens Healthcare, Erlangen, Germany) with a Low and Medium Energy General Purpose (LMEGP) (Nuclear Fields BV, Vortum-Mullem, The Netherlands) collimator. The LMEGP collimator has 24785 holes, a hole length of 37 mm, hole diameter of 2.5 mm and septal thickness of 0.6 mm.…”

“…The reconstructions were performed in accordance with the clinical protocol. [12][13][14] This method is defined as the PSF TOF method.…”