SU-D-12A-03: Improve Scatter Correction in CBCT Reconstruction to Improve the Image Quality for Large Patients.
PURPOSE
CBCT images by pelvis scan of larger patients often have lower soft tissue perceptibility, larger amount of artifacts, and lower image intensity uniformity than images of smaller patients. We hypothesize that the poor image quality is related to inaccurate or non-optimal scattering correction during image reconstruction. To test the hypothesis, we implemented a new scattering correction algorithm and optimized its coefficients in order to understand if pelvis CBCT image qualities can be improved with better scattering correction methods and more optimal coefficients.


METHODS
A scatter correction algorithm using a fast scatter kernel superimposition with multiple kernel groups was implemented. The kernel parameters are the same as Varian TrueBeam machine, including 3 thickness groups, detector point-scatter function parameters. Detector scatter correction and bowtie filter correction were also implemented. A 48 cm wide phantom and another 43 cm wide phantom were simulated by enclosing a 38 cm pelvis phantom with 5 cm thick plastic flaps. A comparison was made between the phantom CBCT images reconstructed by the TrueBeam machine and the ones reconstructed by our in-house reconstruction program with the new scattering correction method.


RESULTS
CBCT images reconstructed using our in-house program with the new scattering correction method showed much less streaking artifacts, better intensity uniformity and comparative soft tissue contrast. The standard deviation of a soft tissue region is 17.1 HU for the 48 cm phantom and 16.8 for the 43 cm phantom using our program, compared to 36.9 HU for the 48 cm phantom and 25.9 for the 43 cm phantom using the TrueBeam machine.


CONCLUSION
Our results suggested that a better scattering algorithm could improve the pelvis CBCT scan image quality considerably for larger patients.