Sci-Fri PM: Delivery - 12: Scatter-B-Gon: Implementing a fast Monte Carlo cone-beam computed tomography scatter...

A fast and accurate MC-based scatter correction algorithm was implemented on real cone-beam computed tomography (CBCT) data. An ACR CT accreditation 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. 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 three regions of interest centered on material inserts in the ACR phantom, the reconstructed CT numbers agreed with clinical CT scan data to within 35 Hounsfield units after 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 adaptive on the fly dose calculations on individual fractions, as well as vastly improved image registration.