Shuai Leng PhD, Presenter: Nothing to Disclose

Thomas J. Vrieze RT(R), Abstract Co-Author: Nothing to Disclose

Lifeng Yu PhD, Abstract Co-Author: Nothing to Disclose

Cynthia H. McCollough PhD, Abstract Co-Author: Research grant, Siemens AG

To determine skin dose from the existing console report of scanner output (CTDIvol) in CT scans without table motion, such as interventional and perfusion CT, and to investigate the influence of patient size, kV, beam collimation and scanner type.

Skin doses were measured using small dosimeters (a 0.6cc ion chamber and a solid state detector) placed on the lateral side of a series of tissue-equivalent body-shaped phantoms. Sizes ranged from 20 to 50cm wide, representing children, small, medium and large size adults. Phantoms were scanned using sequential mode (without table translation) on two different model scanners (Siemens Sensation 64 and Siemens Definition Flash). Skin dose was also measured at 3 different tube potentials (80, 100 and 120kV) and 5 different beam collimations. For each scan, console CTDIvol was recorded and the ratio between measured surface dose and console CTDIvol was calculated. Regression analysis was used to determine the dependence of skin dose on patient size.

Skin dose was exponentially related to patient size (R2>0.97). The fitting coefficients depended on the kV and scanner type, with slight differences between 100kV & 120 kV and large differences for 80 kV. The dependence on scanner type (bow tie filter, source to isocenter distance, etc) and beam collimation was significant. Surface dose expressed as a percentage of CTDIvol at 120kV varied from 49% to 65% on the 64 slice scanner at 12x0.6mm collimation, from 86% to 116% on the 128 slice dual source scanner at 32x1.2mm collimation across patient sizes. On the 64 slice scanner, skin dose was 68%, 53%, 78%, 74%, 74%, and 89% of the console CTDIvol for beam collimations of 1×5mm, 12×0.6mm, 1×10mm, 12×1.2mm, 32×0.6mm, and 24×1.2 mm, respectively.

The surface dose from CT scans without table increment could be accurately estimated from console CTDIvol for different patient sizes using an exponential curve. The dependence changed slightly with tube potential but changed significantly with scanner type and beam collimation. Look up tables for each kV and collimations could be generated and to be used for skin dose estimation for different size patients.

Skin dose estimation is critical in perfusion study to avoid deterministic effects, e.g. skin burn due to the higher dose level compared with routine CT scans.

Leng, S, Vrieze, T, Yu, L, McCollough, C, Skin Dose Estimation from CT Perfusion Studies: Influence of Patient Size, Beam Collimation, and Scanner Type.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9006850.html