TH-D-332-01: The Use of Dual-Energy CT Images for Monte Carlo Treatment Planning: Material Extraction and Metal Artifact Reduction

Abstract

Purpose: To investigate the feasibility of dual‐energy CT‐based material extraction (DECT) for Monte Carlo (MC)dose calculations, to evaluate metal streaking artifact reduction using DECT and to propose a novel scanning technique for motion artifacts reduction. Method and Materials: A phantom with 17 tissue equivalent materials was scanned at two tube voltages. The accuracy of mass density (ρ) extraction using DECT (ρdual) compared to the standard single‐energy CT technique (ρsingle) and the accuracy of the effective atomic number (Z) extraction was evaluated. A comparison of ρsingle and ρdual for a canine subject was made. The DECT extraction was also used on a prostate phantom and a patient with brachytherapy seeds in order to evaluate metal streaking artifact reduction. Moreover, a novel scanning technique with a moving copper filter is proposed. An optimal filter thickness is found and a MC simulation of DECT is performed. Results: The mean error on the relative electron density (ρ e ) and Z extraction is 1.8% and 3.2%. The improvement in ρdual compared to the standard ρsingle is significant, especially in soft bone materials where the ρ assignment error decreases from 8–10% to less than 2% when the DECT technique is used. Similar conclusions are drawn from the canine study where the comparison showed large differences (up to 12%) in bone marrow. The metal streaking artifacts caused by the brachytherapy seeds in the prostate phantom and the patient were significantly reduced. A 2 mm copper filter thickness was found to be optimal for the novel scanning technique. MC simulations of a CT scanner confirmed that with this filtration materials can be extracted with an accuracy of 1.8% in ρ e and 3.6% in Z. Conclusion: The dual‐energy CT technique results in improved tissue extraction and reduced metal artifacts, and is therefore a useful tool for MCdose calculations.