Single-Setup, Multi Angle Machine QA Framework for Proton Therapy Using Rotational Phantom
Abstract
Purpose
To develop a single-setup machine QA framework for multiple tests across different gantry angles in proton therapy. Current monthly QA procedures require separate setups to verify proton beam characteristics, including output consistency, scanning magnet performance, and beam collimated aperture accuracy. In addition, some of current tests are limited to point-based charge readings without spatial dose information.
Methods
A clinically used ion-chamber array detector (PTW Octavius 1500XDR) was inserted into a rotational phantom (PTW Octavius 4D). The phantom was synchronized with the gantry using an inclinometer, allowing it to rotate with the gantry and maintain the detector array perpendicular to the proton beam at all angles. Beam characteristics were measured over three consecutive days at multiple gantry angles. The evaluated tests included output consistency, as well as non-collimated and collimated Picket Fence patterns to verify scanning magnet performance and beam collimated aperture accuracy. The results were evaluated using multiple gamma analysis criteria.
Results
Output consistency results demonstrated an agreement within 1% across all tested gantry angles among different days. Picket Fence tests achieved 100% passing at 3%/3 mm for both collimated and non-collimated patterns. Non-collimated Picket Fence also passed 100% at 2%/2 mm, demonstrating highly accurate scanning magnet spot placement. For collimated Picket Fence, the passing rate dropped slightly, with minimal failing points at the field edge on one side, consistent with expected behavior of heavy-leaf collimator apertures trimming proton spots and possibly requires minor collimator alignment.
Conclusion
A single-setup rotational phantom enables comprehensive, multi-angle QA for proton therapy, providing spatially resolved verification of output, scanning magnet accuracy, and adaptive aperture performance. This approach streamlines QA, reduces setup complexity, and verifies machine performance across all gantry angles. Future work will expand this framework to include additional tests, such as range verification, toward more comprehensive and time-efficient proton therapy QA solution.