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<h5 class="section-title" id="d482568e146">Purpose:</h5>
<p id="d482568e148">External tracking systems used for patient positioning and motion
monitoring during
radiotherapy are now capable of detecting both translations and rotations. In this
work, the authors develop a novel technique to evaluate the 6 degree of freedom 6(DOF)
(translations and rotations) performance of external motion tracking systems. The
authors apply this methodology to an infrared marker tracking system and two 3D optical
surface mapping systems in a common tumor 6DOF workspace.
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<h5 class="section-title" id="d482568e151">Methods:</h5>
<p id="d482568e153">An in-house designed and built 6DOF parallel kinematics robotic
motion phantom was
used to perform motions with sub-millimeter and subdegree accuracy in a 6DOF workspace.
An infrared marker tracking system was first used to validate a calibration algorithm
which associates the motion phantom coordinate frame to the camera frame. The 6DOF
positions of the mobile robotic system in this space were then tracked and recorded
independently by an optical surface tracking system after a cranial phantom was rigidly
fixed to the moveable platform of the robotic stage. The calibration methodology was
first employed, followed by a comprehensive 6DOF trajectory evaluation, which spanned
a full range of positions and orientations in a 20 × 20 × 16 mm and 5° × 5° × 5° workspace.
The intended input motions were compared to the calibrated 6DOF measured points.
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<h5 class="section-title" id="d482568e156">Results:</h5>
<p id="d482568e158">The technique found the accuracy of the infrared (IR) marker tracking
system to have
maximal root-mean square error (RMSE) values of 0.18, 0.25, 0.07 mm, 0.05°, 0.05°,
and 0.09° in left–right (LR), superior–inferior (SI), anterior–posterior (AP), pitch,
roll, and yaw, respectively, comparing the intended 6DOF position and the measured
position by the IR camera. Similarly, the 6DOF RSME discrepancy for the HD optical
surface tracker yielded maximal values of 0.46, 0.60, 0.54 mm, 0.06°, 0.11°, and 0.08°
in LR, SI, AP, pitch, roll, and yaw, respectively, over the same 6DOF evaluative workspace.
An earlier generation 3D optical surface tracking unit was observed to have worse
tracking capabilities than both the IR camera unit and the newer 3D surface tracking
system with maximal RMSE of 0.69, 0.74, 0.47 mm, 0.28°, 0.19°, and 0.18°, in LR, SI,
AP, pitch, roll, and yaw, respectively, in the same 6DOF evaluation space.
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<h5 class="section-title" id="d482568e161">Conclusions:</h5>
<p id="d482568e163">The proposed technique was found to be effective at evaluating
the performance of
6DOF patient tracking systems. All observed optical tracking systems were found to
exhibit tracking capabilities at the sub-millimeter and subdegree level within a 6DOF
workspace.
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