Investigation of Rotational Deviations on Single Fiducial Tumor Tracking with Simulated Respiratory Motion using Synchrony® Respiratory Motion Tracking for Cyberknife® Treatment

It is hypothesized that the uncertainty of the Synchrony® model from the rotation of a
geometrically asymmetrical single fiducial shall be non-zero during the motion tracking.
To validate this hypothesis, the uncertainty was measured for a Synchrony® model built
for a respiratory motion phantom oriented at different yaw angles on a Cyberknife®
treatment table.
A Mini-ball Cube with three cylindrical GoldMark™ (1mmx5mm Au) numbered
fiducials was placed inside a respiratory phantom and used for all tests. The fiducial with
the least artifact interference was selected for the motion tracking. A 2cm periodic,
longitudinal, linear motion of the Mini-ball cube was executed and tested for yaw
rotational angles, 0° – 90°. The test was repeated over 3 nonconsecutive days. The
uncertainty increased with the yaw angle with the most noticeable changes seen
between20° and 60° yaw, where uncertainty increased from 23.5% to 57.9%. A similar test was performed using a spherical Gold Anchor™ fiducial. The uncertainties found
when using the Gold Anchor™ were statistically lower than those found when using the
GoldMark™ fiducial for all angles of rotation.
For the first time, it is found that Synchrony® model uncertainty depends on fiducial
geometry. In addition, this research has shown that tracking target rotation using a single
fiducial can be accomplished with the Synchrony® model uncertainty as it is displayed on
the treatment console.
The results of this research could lead to decreased acute toxicity effects related to
multiple fiducials.