N Correa*, I Barreto, M Arreola, University of Florida College of Medicine, Gainesville, FL

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  N Correa

(Saturday, 3/26/2022)   [Central Time (GMT-5)]

Purpose: This study measured computed tomography dose index volume (CTDIvol) for single and dual-energy scans in wide-beam CT scanners. The conventional ACR method does not consider the scatter tails from the dose profile in a volume acquisition. Therefore, CTDIvol must be measured for wide-beams to display an accurate representation of radiation output.

Methods: The IEC method for CTDIfree in air measurements was followed. First, the PMMA CTDI phantom along with a 100 mm pencil chamber was used to measure CTDI100 for a beam width of 40 mm. The pencil chamber was then used alone for in-air measurements using a beam width of 40 mm and 160 mm. Three contiguous scans were conducted along the z-axis using the pencil chamber at isocenter, 100 mm superior and inferior to isocenter for 160 mm beam width. A correction factor was calculated as the ratio from the first measurement with the CTDI phantom and the three contiguous scans. A second method was also investigated where 3 contiguous scans were conducted using the CTDI phantom with the pencil chamber at isocenter, 100 mm superior and inferior to isocenter for a beam width of 160 mm. All measurements were performed for volumetric single and dual-energy acquisitions in a 320-slice Canon CT scanner.

Results: Single-energy and dual-energy scans resulted in a 39.9% and 45.2% increase in CTDIvol using the IEC and phantom method, respectively. The highest measured CTDIvol was 30.76 mGy and 31.36 mGy for single and dual-energy compared to a reported CTDIvol of 18.60 mGy and 18.80 mGy.

Conclusion: Both methodologies for measuring CTDI for wide-beam CT scanners show substantial increase greater than ± 20% required by the ACR. These findings must be accounted for when using CTDIvol for beams widths greater than 100 mm.

Keywords

CT, Dosimetry, Dual-energy Imaging

Taxonomy

IM- CT: Dual Energy and Spectral

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