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Communication Dans Un Congrès Année : 2021

Accuracy of thyroid uptake calibration method: a multi-centric study with realistic phantoms.

Résumé

Aim/Introduction: measurement of the thyroid uptake is of interest in diagnostic and for treatment of benign thyroid disease. The sensitivity obtained from measurement in air or in a standard neck phantom does not take into account the real thyroid anatomy. The goal of this multi-centric study was to assess the accuracy of thyroid uptake measurement using a set of realistic thyroid phantoms of varying size. These measurements were carried-out according to the site-specific local procedure (Local) and according to a standardized protocol (Std). In this preliminary report sensitivities obtained with routine calibration objects were compared with those obtained with the set of phantoms, for both protocols. Material and methods: measurements were carried-out from October 2020 to June 2021 on 20 NaI gamma-cameras and 3 CZT cameras with parallel and pinhole collimators. Radionuclides were Tc-99m and I-123. Five thyroid phantoms between 3 and 30 mL were used. Images were centrally analyzed, a 3DSlicer module has been developed for automatic segmentation and calculation of the sensitivity. The mean sensitivity over five thyroid volumes was compared with the routine calibration factor (Srout) and with the sensitivity in air, obtained with a unique syringue (Sair). The three sensitivities were measured for both protocols. Results: 25 configurations have been analyzed (58% of final set). For pinhole Tc-99m measurements, the mean sensitivities Sair were 101 ±45 counts/MBq/s (Std, n=7) and 148 ±91 counts/MBq/s (Local, n=7). The difference being mainly due to different measurement distances in the protocols. For I-123 measurements with parallel collimators, the mean sensitivities Sair were 73 ±13 counts/MBq/s (Std, n=10) and 72 ±14 counts/MBq/s (Local, n=9). Sair was almost independent of radionuclides and protocol. For pinhole collimator the sensitivity decreased when the thyroid volume increased, whatever the radionuclide and protocol. For the 30 mL phantom, on mean, the sensitivity was 12% lower than . Considering the local protocol and both radionuclides the relative difference between Srout and was greater than 15% in 43% of the cases. The standard protocol did not reduce this difference. For parallel collimators the difference between Srout and was always less than 17%, almost independently of the protocol, radionuclide and parallel collimator model. Conclusion: with parallel collimators, the sensitivity was relatively independent of the thyroid volume and the routine calibration was suitable for thyroid uptake estimation. For pinhole collimators the calibration was strongly influenced by the volume and quantitative measurement were of limited accuracy.
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Dates et versions

hal-04022239 , version 1 (09-03-2023)

Identifiants

  • HAL Id : hal-04022239 , version 1

Citer

Mathilde Demonchy, T. Beaumont, David Broggio, Bardia Farman, Aurélie Forbes, et al.. Accuracy of thyroid uptake calibration method: a multi-centric study with realistic phantoms.. 34th Annual Congress of the European Association of Nuclear Medicine, Oct 2021, Vienne (Online), Austria. ⟨hal-04022239⟩
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