Comparison of Gating Algorithms in 4D-PET for Mobile Tumor Segmentation
S Jani*, M Dahlbom, B White, D Thomas, S Gaudio, D Low, J Lamb, University of California, Los Angeles, Los Angeles, CASU-D-500-5 Sunday 2:05PM - 3:00PM Room: 500 Ballroom
Purpose: To quantitatively compare the accuracy of tumor volume segmentation in four different gating algorithms in gated 4D-PET.
Methods: Four acrylic spheres with inner diameters ranging from 1cm to 4cm were filled with a 11-C solution and affixed inside a cylindrical bath of 18-FDG. The system was attached to a robotic arm that underwent 1D motion according to large-amplitude trajectories based on measured patient breathing trajectories. Two trajectories were used: one with and one without baseline drift. List-mode data was split into two-minute images at different source-to-background ratios (SBRs), which were gated into eight bins using two amplitude-based (equal amplitude bins (A1) and equal counts per bin (A2)) and two temporal phased-based gating algorithms. All gated images were segmented using a commercially available gradient-based technique. Internal target volumes (ITVs), generated by taking the union of all eight contours per gated image, were compared to their respective ground truths. The ground-truth ITV was defined as the volume subtended by the tumor model positions covering 99% of breathing amplitude. Superior-inferior distances between sphere centroids in the end-inhale and end-exhale phases were also calculated.
Results: Averaged over all sphere sizes, both trajectories, and high and low SBRs, A2 was the closest in accuracy of ITV segmentation, with a measured-to-expected ratio of 1.002 vs. 0.920 and 0.964 for temporal phase-based methods (p<0.05). A1 consistently recovered the greatest volume and had the highest accuracy in the presence of irregular breathing, while A2 performed the best in accurately representing the smallest (1cm) sphere. Amplitude-based methods consistently produced more distance between end-inhale and end-exhale phases than phase-based methods (27.5% more on average), with A1 recovering up to 94% of peak-to-peak separation (p<0.01).
Conclusion: Target volumes in images generated from amplitude-based gating are more accurate, potentially at clinically significant levels, than those from temporal phase-based gating.
Funding Support, Disclosures, and Conflict of Interest: NIH R01 CA096679
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