A phantom for testing of 4D-CT for radiotherapy of small lesions

Dunn, L, Kron, T, Taylor, M, Callahan, J and Franich, R 2012, 'A phantom for testing of 4D-CT for radiotherapy of small lesions', Medical Physics, vol. 39, no. 9, pp. 5372-5383.


Document type: Journal Article
Collection: Journal Articles

Title A phantom for testing of 4D-CT for radiotherapy of small lesions
Author(s) Dunn, L
Kron, T
Taylor, M
Callahan, J
Franich, R
Year 2012
Journal name Medical Physics
Volume number 39
Issue number 9
Start page 5372
End page 5383
Total pages 12
Publisher American Association of Physicists in Medicine
Abstract Purpose: The use of time-resolved four-dimensional computed tomography (4D-CT) in radiotherapy requires strict quality assurance to ensure the accuracy of motion management protocols. The aim of this work was to design and test a phantom capable of large amplitude motion for use in 4D-CT, with particular interest in small lesions typical for stereotactic body radiotherapy. Methods: The phantom of see-saw design is light weight, capable of including various sample materials and compatible with several surrogate marker signal acquisition systems. It is constructed of polymethylmethacrylate (Perspex) and its movement is controlled via a dc motor and drive wheel. It was tested using two CT scanners with different 4D acquisition methods: the Philips Brilliance Big Bore CT (helical scan, pressure belt) and a General Electric Discovery STE PETCT (axial scan, infrared marker). Amplitudes ranging from 1.5 to 6.0 cm and frequencies of up to 40 cycles per minute were used to study the effect of motion on image quality. Maximum intensity projections (MIPs), as well as average intensity projections (AIPs) of moving objects were investigated and their quality dependence on the number of phase reconstruction bins assessed. Results: CT number discrepancies between moving and stationary objects were found to have no systematic dependence on amplitude, frequency, or specific interphase variability. MIP-delineated amplitudes of motion were found to match physical phantom amplitudes to within 2 mm for all motion scenarios tested. Objects undergoing large amplitude motions (>3.0 cm) were shown to cause artefacts in MIP and AIP projections when ten phase bins were assigned. This problem can be mitigated by increasing the number of phase bins in a 4D-CT scan.
Subject Medical Physics
Keyword(s) 4D-CT
motion
motion management
phantom
quality assurance
tumour motion
DOI - identifier 10.1118/1.4742053
Copyright notice © 2012 American Association of Physicists in Medicine
ISSN 0094-2405
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