Validating robotic couch isocentricity with 3D surface imaging.

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Technology

Background:

• Proton therapy utilizes 190° gantries with robotic couch rotations for treatment beam adjustments.
• Clinical validation of couch rotations traditionally relies on post-rotation radiographic imaging.

Purpose of the Study:

• To assess the sensitivity and specificity of the AlignRT 3D surface imaging system for validating robotic couch rotations in proton therapy.
• To determine if AlignRT can reliably detect deviations in patient positioning after couch movements.

Main Methods:

• AlignRT was used to capture reference surface images post-setup, with the couch at 270°.
• The couch was rotated ±90°, and AlignRT reported 3D displacement vectors, accounting for patient motion and system variations.
• Sensitivity was tested using volunteers and phantoms with intentional translations (2-8 mm) and rotations, totaling 300 measurements.

Main Results:

• Mean AlignRT displacement vectors were 0.1 ± 0.1 mm (phantom), 0.8 ± 0.1 mm (immobilized), and 1.1 ± 0.2 mm (non-immobilized).
• 95% of measurements for immobilized and non-immobilized subjects were within 1 mm and 2 mm of actual displacement, respectively.
• The system flagged positional deviations exceeding 4 mm with 90% sensitivity and 100% specificity.

Conclusions:

• The three-pod AlignRT system effectively identifies gross non-isocentric patient rotations following couch adjustments.
• Significant positional deviations detected by AlignRT warrant radiographic imaging and potential repositioning.
• AlignRT serves as a reliable tool for verifying patient positioning after couch rotations in proton therapy setups.