Author: David J. Carlson, Yiu-Hsin Chang, Zhe (Jay) Chen, Hyosung Cho, Dae Yup Han, MinYoung Lee, Weili Zhong 👨🔬
Affiliation: Department of Therapeutic Radiology, Yale University School of Medicine, Yonsei University 🌍
Purpose:
To compare the intra-fractional motion tracking sensitivity of prostate fiducial markers using triggered imaging and calypso tracking for prostate cancer cases.
Methods:
This study was conducted retrospectively with patients treated for prostate cancers at Yale New Haven Hospital since 2020. Randomly selected prostate cases (n=37) with standard prescription of 250cGyx28fx (24 cases) or SBRT of 725cGyx5fx (13 cases) were evaluated. All cases were treated with either triggered imaging (20 patients) or the Calypso system (17 patients). All patients have three fiducial markers implanted: either gold fiducial markers for triggered image cases or Calypso RF-transponders for the Calypso cases. Three-dimensional (lateral, vertical, and longitudinal) couch shift information was recorded for treatment delivery. Statistical analysis of the shift frequency and the average three-dimensional absolute shift distance were calculated. To evaluate systemic sensitivities of fiducial motion tracking by the triggered imaging and Calypso system, individual axes’ shift magnitude over the total shift magnitude was calculated.
Results:
In total, 683 fractional treatments were evaluated (356 fractions for triggered and 327 fractions for Calypso). The shift frequency was 20.2% for triggered imaging and 14.1% for Calypso cases. The maximum shift magnitude was 0.392±0.331cm (longitudinal direction) and 0.283±0.116cm (vertical direction) for triggered imaging and Calypso, respectively. Triggered imaging showed the most sensitivity in the longitudinal direction (28.9%), and the Calypso system showed the most sensitivity in the vertical directional motion (10.9%).
Conclusion:
Triggered imaging resulted in a higher shift frequency than the Calypso surveillance. Since the triggered images use the beam’s eye view kV image (2D) orthogonal to the treatment beam, it has a motion detection limitation in the lateral and vertical directions. Triggered imaging has pronounced longitudinal direction sensitivity, while the Calypso system shows vertical direction sensitivity.