SU-E-I-04: Implementation of a Fast Monte Carlo Scatter Correction for Cone- Beam Computed Tomography

To improve image quality in cone-beam computed tomography (CBCT) scans by implementation of a fast and accurate MC-based scatter correction algorithm.

A Solid WaterTM phantom was imaged on a Varian OBI CBCT scanner using the standard-dose head protocol (100 kVp, 151 mAs, partial-angle). A fast Monte Carlo simulation developed in the EGSnrc framework was used to transport photons through the uncorrected CBCT scan. From the simulation output, the contribution from both primary and scattered photons for each projection image was estimated. Using these estimates, a subtractive scatter correction was performed on the CBCT projection data. This correction procedure was repeated iteratively, using the previous scatter corrected scan as input to the Monte Carlo simulation.

Implementation of the scatter correction algorithm on real CBCT data was shown to help mitigate scatter-induced artifacts, such as cupping and streaking. The scatter corrected images were also shown to have improved accuracy in reconstructed attenuation coefficient values. In a region of interest centered on the Solid Water phantom, the number of voxels agreeing to within 10% of the theoretical attenuation coefficient increased from 46% to 97% after two iterations of the scatter correction.

These results suggest that the proposed scatter correction algorithm is successful in improving image quality in real CBCT images. The accuracy of the attenuation coefficients extracted from the corrected CBCT scan renders the data suitable for on-the-fly dose recalculations, as well as vastly improved image registration.