Gold coated contact lens-type ocular in vivo dosimeter (CLOD) for monitoring of low dose in computed tomography: A Monte Carlo study.

Abstract

This study reports a sensitivity enhancement of gold-coated contact lens-type ocular in vivo dosimeters (CLODs) for low-dose measurements in computed tomography (CT). Monte Carlo (MC) simulations were conducted to evaluate the dose enhancement from the gold (Au) layers on the CLODs. The human eye and CLODs were modeled, and the X-ray tube voltages were defined as 80, 120, and 140 kVp. The thickness of the Au layer attached to a CLOD ranged from 100nm to 10μm. The thickness of the active layer ranged from 20 to 140μm. The dose ratio between the active layer of the Au-coated CLOD and a CLOD without a layer, i.e., the dose enhancement factor (DEF), was calculated. The DEFs of the first 20-μm thick active layer of the 5-μm thick Au-coated CLOD were 18.4, 19.7, 20.2 at 80, 120, and 140 kVp, respectively. The DEFs decreased as the thickness of the active layer increased. The DEFs of 100-nm to 5-μm thick Au layers increased from 1.7 to 5.4 for 120-kVp X-ray tube voltage when the thickness of the active layer was 140μm. The MC results presented a higher sensitivity of Au-coated CLODs (∼20-times higher than that of CLODs without a gold layer). Au-coated CLODs can be applied to an evaluation of very low doses (a few cGy) delivered to patients during CT imaging.