AbstractID: 8103 Title: Optimization of fiducial marker configurations in image-guided
radiotherapy
In image-guided radiotherapy of lung or liver lesions, a patient positioning system may
be used to track fiducial markers with stereoscopic infrared cameras. The 3D positions of
the markers provide reference information to determine the treatment plan isocenter
location and hence provide the ability to actively target the lesion. In current clinical
practice, however, placement of the fiducial markers is random, and the actual
registration error of the target inside the body may be up to 5.5 mm, given that typical
fiducial registration error (FRE) is 2.5 mm. The goal of this work is to develop methods
to design optimal configuration of fiducial makers to minimize the target registration
error (TRE), given the patient’s CT and the FRE. Floating genetic algorithm (GA)
optimization was used to optimize the positions of the skin markers. Given the preferred
number of markers N, the algorithm searches in 2N floating number space, representing
the left-right and super-inferior coordinates of the N markers. The anterior-posterior
coordinates are determined by the surface curve of the patient body, which is predetermined by an automatic segmentation algorithm from the CT image series. GA
algorithm terminates on a fixed number of generations. The searching bounds can be set
to the whole surface or different sub-areas for each marker. The evaluation function is the
TRE, or weighted average TRE for multiple lesions. When applied to patient data, this
optimization method was found to reduce the TRE significantly. Conclusion: A method
of optimizing fiducial configurations was developed for image-guided radiotherapy.