Quality control within the multicentre perfusion CT study of primary colorectal cancer (PROSPeCT): results of an iodine density phantom study
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To assess the cross-centre consistency of iodine enhancement, contrast-to-noise ratio and radiation dose in a multicentre perfusion CT trial of colorectal cancer.
Materials and methods
A cylindrical water phantom containing different iodine inserts was examined on seven CT models in 13 hospitals. The relationship between CT number (Hounsfield units, HU) and iodine concentration (milligrams per millilitre) was established and contrast-to-noise ratios (CNRs) calculated. Radiation doses (CTDIvol, DLP) were compared across all sites.
There was a linear relationship between CT number and iodine density. Iodine enhancement varied by a factor of at most 1.10, and image noise by at most 1.5 across the study sites. At an iodine concentration of 1 mg ml−1 and 100 kV, CNRs ranged from 3.6 to 4.8 in the 220-mm phantom and from 1.4 to 1.9 in the 300-mm phantom. Doses varied by a factor of at most 2.4, but remained within study dose constraints. Iterative reconstruction algorithms did not alter iodine enhancement but resulted in reduced image noise by a factor of at most 2.2, allowing a potential dose decrease of at most 80 % compared to filtered back projection (FBP).
Quality control of CT performance across centres indicates that CNR values remain relatively consistent across all sites, giving acceptable image quality within the agreed dose constraints.
• Quality control is essential in a multicentre setting to enable CT quantification.
• CNRs in a body-sized phantom had the recommended value of at least 1.5.
• CTDIs and DLPs varied by factors of 1.8 and 2.4 respectively.
KeywordsComputed tomography Perfusion CT Colorectal cancer Phantom study Quality control
We would like to acknowledge Nick Keat (Imanova Ltd) for writing the IDL image analysis modules and Paul Woodburn (GSTT) for preparing the iodine solutions.
We would like to acknowledge the following for their contribution to the PROSPeCT study:
Principal investigators: M Betts, I Britton, D Breen, J Brush, P Correa, N Dodds, C Grierson, N Griffin, S Gourtsoyianni, J Hampton, A Higginson, A Lowe, R Mannion, C Oliver, A Slater, M Strugnell, D Tolan, R Vinayagam, I Zealley
Site radiographers & research staff: (in alphabetical order):
D Barrie, G Cattini, N Cowan, M Dodds, S Dundas, N Gibbons, A Green, M Harris, G Haley, L Houston, K Jones, L Jones, C Marsh, E Ngandwe, B Pharoah, V Ritchie, C Roe, R Smith, D Tew, K Wallace, A Williams, P Woodburn, N Wragg
Trial management group, steering committee, data monitoring committee, and advisors (in alphabetical order):
D Altman, C Bartram, R Glynne-Jones, A Groves, A Hackshaw, S Halligan, P Hoskin, S Mallett, D Miles, K Miles, A Rockall, M Rodriguez-Justo, SA Taylor
The scientific guarantor of this publication is Professor Vicky Goh. The authors of this manuscript declare relationships with the following companies: Vicky Goh: Research Agreement Siemens Healthcare, GE Healthcare. Other authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article. This study has received funding from the UK National Institute of Health Research (NIHR) HTA programme: Funding NIHR HTA 09/22/49. Dr Susan Mallett (Oxford) is providing statistical expertise for the trial. No complex statistical methods were necessary for this paper. Institutional review board approval was obtained. Methodology: prospective, experimental: phantom study, multicentre study.
The authors also acknowledge financial support from the Department of Health via the National Institute for Health Research Comprehensive Biomedical Research Centre award to Guy's & St Thomas' NHS Foundation Trust in partnership with King's College London and King's College Hospital NHS Foundation Trust; and from the King's College London/University College London Comprehensive Cancer Imaging Centre funded by Cancer Research UK and Engineering and Physical Sciences Research Council in association with the Medical Research Council and Department of Health.
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