Interpolation Method for Calculation of Computed Tomography Dose from Angular Varying Tube Current

Abstract

The scope and magnitude of radiation dose from computed tomography (CT) examination has led to increased scrutiny and focus on accurate dose tracking. The use of tube current modulation (TCM) results complicates dose tracking by generating unique scans that are specific to the patient. Three methods of estimating the radiation dose from a CT examination that uses TCM are compared: using the average current for an entire scan, using the average current for each slice in the scan, and using an estimation of the angular variation of the dose contribution. To determine the impact of TCM on the radiation dose received, a set of angular weighting functions for each tissue of the body are derived by fitting a function to the relative dose contributions tabulated for the four principle exposure projections. This weighting function is applied to the angular tube current function to determine the organ dose contributions from a single rotation. Since the angular tube current function is not typically known, a method for estimating that function is also presented. The organ doses calculated using these three methods are compared to simulations that explicitly include the estimated TCM function.