Di Zhang MS, Presenter: Nothing to Disclose

Christopher H. Cagnon PhD, Abstract Co-Author: Nothing to Disclose

John J. Demarco PhD, Abstract Co-Author: Nothing to Disclose

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

Dianna Cody PhD, Abstract Co-Author: Nothing to Disclose

Michael F. McNitt-Gray PhD, Abstract Co-Author: Institutional research agreement, Siemens AG

Adam Turner BS, Abstract Co-Author: Nothing to Disclose

Maryam Khatonabadi, Abstract Co-Author: Nothing to Disclose

In brain perfusion studies, the patient’s head is scanned repeatedly at one location over a short period of time to monitor contrast wash in and wash out. This may result in high radiation doses to the skin and the eye lens and possibly result in deterministic effects. The purpose of this study is to estimate the radiation dose to skin and eye lens from brain perfusion studies under a variety of scanning conditions.

Skin dose and eye lens dose were estimated using Monte Carlo simulations with a detailed patient model (GSF Model Irene) and CT scanner source models from all four major CT manufactures (Siemens Sensation 64, GE Lightspeed VCT, Toshiba Acquilion 64, and Phillips Brilliance 64). Brain perfusion scans were simulated with repeated axial scans using the widest available collimation from each scanner at four different scan locations. At one of these locations the x-ray primary beam completely covers the eye lens (location 4); and the beam is progressively further away from eye lens for the three other scan locations (location 1~3).

For all tube voltages and scan locations at four different scanners, the total mAs (mAs/rotation × number of rotations) that would cause the dose to eye lens and skin to reach 2 Gy were determined and a look up table was created. Using this information, the number of rotations to reach 2 Gy for the eye lens and skin dose can be easily calculated for any specific scanning protocol. With protocol specific information (scanner model, kVp, scan location), users can find the corresponding total mAs in the lookup table, divide it by their mAs/rotation to get number of rotations. For example, for a 300 mAs/rotation scan at 120 kVp for scanner B at scan location 4, 58 rotations would result in an eye lens dose of 2 Gy, and 47 rotations would result in a maximum skin dose of 2 Gy.

This study provides detailed information about the radiation dose to eye lens and skin from CT brain perfusion examinations at various scan locations on four CT scanner models from all major manufactures. The results from this study can be used by other institutions as a tool to calculate dose to eye lens and skin for any scanner and any kVp selected.

Clinical institutions can use these results to ensure that their neuro-perfusion protocols operate below the limits where deterministic effects may be seen from radiation dose to eye lens and skin.

Zhang, D, Cagnon, C, Demarco, J, McCollough, C, Cody, D, McNitt-Gray, M, Turner, A, Khatonabadi, M, Estimating Radiation Dose to Eye Lens and Skin from CT Brain Perfusion Examinations: A Monte Carlo Study.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9011544.html