Infrared Marker-Based Tracking and Quality Assurance Methods for Holographic Patient Alignment
Abstract
Purpose
To investigate infrared (IR) marker-based tracking for holographic patient alignment in radiation therapy and to establish quality assurance (QA) methods for the technique.
Methods
Applications utilizing IR marker tracking were developed for Microsoft HoloLens 2 to register a thorax phantom to a treatment machine isocenter. An IR marker array was designed to attach to the gantry of a linear accelerator, providing a known location to reference isocenter position. The thorax phantom surface, contoured from computed tomography (CT) images and converted to .obj format, was visualized relative to a planned treatment isocenter. The phantom was holographically aligned on the treatment couch, and offsets determined with surface guidance and evaluated against prior work with quick response (QR) marker-based alignment. Additionally, QA applications were developed to visualize a machine performance check (MPC) phantom and an array consisting of fifteen spheres, each having a radius of 5mm, placed 20cm apart horizontally, and 10cm apart vertically. Both applications visualize a crosshair to represent isocenter position.
Results
IR tracking root mean square (RMS) offsets ranged from 0.43cm to 0.69cm, consistent with QR alignment results. QA applications were effective at checking daily functionality against the MPC phantom and evaluating geometrical accuracy with the multi-sphere array against a field calibration plate. Virtual crosshairs can be quickly evaluated against room lasers.
Conclusion
Preliminary testing indicates that IR marker tracking provides similar alignment accuracy to QR marker tracking, but further testing is needed to validate this result. Daily holographic alignment verification can be conveniently performed using existing daily QA phantoms. More extensive QA with a multi-sphere array and crosshair visualization allows more precise confirmation of geometric alignment.