Shohei Kudomi, Presenter: Nothing to Disclose

Yasuyuki Ueda PhD, Abstract Co-Author: Nothing to Disclose

Katsuhiko Ueda BS, Abstract Co-Author: Nothing to Disclose

Katsuhiro Ichikawa PhD, Abstract Co-Author: Nothing to Disclose

The purpose of this study was to evaluate the performance of the radiation dose reduction to the eye lens and the resulting image quality produced using a new organ-based dose modulation (ODM).

The study was performed on a 64-slice CT scanner (optima660, GE Healthcare). First, we scanned a 16 cm CT dose index phantom to investigate the dose distribution for a completely symmetric phantom by using a 10-cm ion chamber (Unfors Xi, RaySafe) for obtaining dose angular profile which indicate the fundamental performance of the new ODM. Second, we scanned an anthropomorphic head phantom (Kyoto Kagaku) to evaluate the radiation dose to the eye lens and the intracranial area by using radio-photoluminescence glass dosimeters (Dose Ace FDG 1000, Chiyoda Technol) with and without ODM in the head scanning protocols. The phantom was placed at the center of the gantry and at off-center positions in the y-direction at 50, 25, -50, and -75 mm. The quantitative image quality evaluation was performed by measuring the standard deviations (SD) in regions of interest placed on the eyes and the center of a selected intracranial area.

The dose profile indicated that the ODM reduced 16-19% of the dose to the midline of the anterior surface. Also, the dose angular profile showed no increased-dose region. Dose measurement results for the anthropomorphic head phantom placed at the center of the gantry showed 18% dose reduction to the eye lens and it corresponded to the dose profile. Dose to the intracranial area was reduced 5.5%. SD increases when using ODM of the eye and the intracranial area were 0.12 and 0.24, respectively. The increase of SD could be negligible in clinical settings. Furthermore, no artifacts were introduced by using the new ODM. The effects of ODM showed little position dependence and reduced the eye dose by 17.7% on average. 

Our results show that the new ODM is a robust dose reduction technique in cases where patients are placed at off-center positions without significantly degrading image quality.

Our results showed the performance of a new ODM. Because there is no increased-current region, the new ODM is safe for use when patients are placed at off-center position.

Kudomi, S, Ueda, Y, Ueda, K, Ichikawa, K, Radiation Dose Reduction to the Eye Lens in Head CT by Use of a New Organ-based Dose Modulation: A Phantom Study for Evaluation of the Dose Distribution and the off-center Effect.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14011656.html