C-arm tracking by intensity-based registration of a fiducial in prostate brachytherapy

Motivation: In prostate brachytherapy, intra-operative dosimetry optimization can be achieved through reconstruction of the implanted seeds from multiple C-arm fluoroscopy images. This process requires tracking of the C-arm poses. Methodology: We compute the pose of the C-arm relative to a stationary radiographic fiducial of known geometry. The fiducial was precisely fabricated. We register the 2D fluoroscopy image of the fiducial to a projected digitally reconstructed radiograph of the fiducial. The novelty of this approach is using image intensity alone without prior segmentation of the fluoroscopy image. Experiments and Results: Ground truth pose was established for each C-arm image using a published and clinically tested segmentation-based method. Using 111 clinical C-arm images and ±10° and ±10 mm random perturbation around the ground-truth pose, the average rotation and translation errors were 0.62° (std=0.31°) and 0.73 mm (std= 0.55mm), respectively. Conclusion: Fully automated segmentation-free C-arm pose estimation was found to be clinically adequate on human patient data.