Count-rate Management in I SPECT/CT Calibration

Overview

Journal EJNMMI Phys

Date 2025 Jan 26

PMID 39864022

Authors

Staffan Jacobsson Svard

Cecilia Hindorf

Joachim N Nilsson

Affiliations

Soon will be listed here.

Abstract

Background: System calibration is essential for accurate SPECT/CT dosimetry. However, count losses due to dead time and pulse pileup may cause calibration errors, in particular for I, where high count rates may be encountered. Calibration at low count rates should also be avoided to minimise detrimental effects from e.g. background counts and statistical fluctuations. This paper aims to present experimental data illustrating count-rate dependencies and to propose practical routines to mitigate errors in the I calibration procedure without needing advanced analysis tools.

Results: The sensitivities of two General Electric (GE) Discovery 670 Pro systems were assessed using two Jaszczak phantom geometries. SPECT/CT data were collected over two months, starting with an initial I content of > 2 GBq, decaying to approximately 20 MBq. This allowed for a detailed analysis of count losses due to dead time and pulse pileup. From the sensitivity analysis, it was shown that robust calibration was obtained for I phantom activities ranging between 250 and 1500 MBq.

Conclusions: The results show that adequate corrections for dead-time and pulse-pileup counting losses are essential for accurate calibration. It is argued that loss corrections should be based on total spectrum count rates in projections and not only on the 364.5 keV energy window data. The measurement campaigns presented in this paper, using basic tools and equipment, may serve as a model for establishing routines for count-loss corrections as well as for system calibration and regular control of system sensitivity. The data suggest that analysis of source and count concentration in a homogeneous Jaszczak phantom offers robust calibration, whereas analysis of source strength and counts in a delineated phantom insert offers a practical and robust method for regular quality control.

References

Ferrer L, Delpon G, Lisbona A, Bardies M . Dosimetric impact of correcting count losses due to deadtime in clinical radioimmunotherapy trials involving iodine-131 scintigraphy. Cancer Biother Radiopharm. 2003; 18(1):117-24. DOI: 10.1089/108497803321269395. View

Gregory R, Murray I, Gear J, Leek F, Chittenden S, Fenwick A . Standardised quantitative radioiodine SPECT/CT Imaging for multicentre dosimetry trials in molecular radiotherapy. Phys Med Biol. 2019; 64(24):245013. DOI: 10.1088/1361-6560/ab5b6c. View

Iwashita Y, Goto S, Tahara K, Kawano K, Chen C, Kitano S . Potent stimuli combined with lipopolysaccaride and IFNgamma may improve immunotherapy against HCC by increasing the maturation and subsequent immune response of the dendritic cells. Cancer Biother Radiopharm. 2003; 18(1):1-6. DOI: 10.1089/108497803321269278. View

Marin G, Vanderlinden B, Karfis I, Guiot T, Wimana Z, Flamen P . Accuracy and precision assessment for activity quantification in individualized dosimetry of Lu-DOTATATE therapy. EJNMMI Phys. 2017; 4(1):7. PMC: 5267757. DOI: 10.1186/s40658-017-0174-7. View

Dickson J, Armstrong I, Minguez Gabina P, Denis-Bacelar A, Krizsan A, Gear J . EANM practice guideline for quantitative SPECT-CT. Eur J Nucl Med Mol Imaging. 2022; 50(4):980-995. PMC: 9931838. DOI: 10.1007/s00259-022-06028-9. View

Epelbaum R, Frenkel A, Haddad R, Sikorski N, Strauss L, Israel O . Tumor aggressiveness and patient outcome in cancer of the pancreas assessed by dynamic 18F-FDG PET/CT. J Nucl Med. 2012; 54(1):12-8. DOI: 10.2967/jnumed.112.107466. View

Dewaraja Y, Ljungberg M, Green A, Zanzonico P, Frey E, Bolch W . MIRD pamphlet No. 24: Guidelines for quantitative 131I SPECT in dosimetry applications. J Nucl Med. 2013; 54(12):2182-8. PMC: 3970715. DOI: 10.2967/jnumed.113.122390. View

Vij R, Fowler K, Shokeen M . New Approaches to Molecular Imaging of Multiple Myeloma. J Nucl Med. 2015; 57(1):1-4. PMC: 5673073. DOI: 10.2967/jnumed.115.163808. View

Ljungberg M, Celler A, Konijnenberg M, Eckerman K, Dewaraja Y, Sjogreen-Gleisner K . MIRD Pamphlet No. 26: Joint EANM/MIRD Guidelines for Quantitative 177Lu SPECT Applied for Dosimetry of Radiopharmaceutical Therapy. J Nucl Med. 2015; 57(1):151-62. DOI: 10.2967/jnumed.115.159012. View

Dewaraja Y, Frey E, Sgouros G, Brill A, Roberson P, Zanzonico P . MIRD pamphlet No. 23: quantitative SPECT for patient-specific 3-dimensional dosimetry in internal radionuclide therapy. J Nucl Med. 2012; 53(8):1310-25. PMC: 3465844. DOI: 10.2967/jnumed.111.100123. View

Desy A, Bouvet G, Croteau E, Lafreniere N, Turcotte E, Despres P . Quantitative SPECT (QSPECT) at high count rates with contemporary SPECT/CT systems. EJNMMI Phys. 2021; 8(1):73. PMC: 8557232. DOI: 10.1186/s40658-021-00421-3. View

Gear J, Chiesa C, Lassmann M, Minguez Gabina P, Tran-Gia J, Stokke C . EANM Dosimetry Committee series on standard operational procedures for internal dosimetry for I mIBG treatment of neuroendocrine tumours. EJNMMI Phys. 2020; 7(1):15. PMC: 7060302. DOI: 10.1186/s40658-020-0282-7. View

10.

Heemskerk J, Defrise M . Gamma detector dead time correction using Lambert W function. EJNMMI Phys. 2020; 7(1):27. PMC: 7214567. DOI: 10.1186/s40658-020-00296-w. View

11.

Frezza A, Desport C, Uribe C, Zhao W, Celler A, Despres P . Comprehensive SPECT/CT system characterization and calibration for Lu quantitative SPECT (QSPECT) with dead-time correction. EJNMMI Phys. 2020; 7(1):10. PMC: 7021856. DOI: 10.1186/s40658-020-0275-6. View