Room: Stars at Night Ballroom 1
Purpose: This work aims to develop PodPhantom, a compact dosimetric data collection system, enabling automatic, accurate, and efficient data collection on a special radiation unit GammaPod.
Methods: PodPhantom is designed to use remote control to automatically move an ion chamber in a cylindrical coordinate, with translation in vertical and horizontal directions and rotation around a mechanical isocenter. Translations are accomplished by automatically movement of stepper motors (51Âµm step resolution), while rotation is achieved by manually turning the stage along mechanically constructed spokes. A customized plastic jig is fabricated to hold and register the motion stage to GammaPod radiation axes. A cylindrical chamber holder is installed on the motion stage with a home-made plastic block. The motion stage is controlled with a Raspberry Pi microcomputer and wireless connected to a controlling computer from outside the vault. The prototype operates in two modes: a step-and-shoot mode with 30-second integration between for beam scanning and a static positioning mode for point-dose measurement. The performance of PodPhantom was evaluated through initial mechanical assessment and later dosimetry data collection.
Results: Horizontal and vertical straightness were validated by measuring the light field projection of the device against a flat surface and plumb line, respectively, over the range of motion to be less than 0.1 degrees. Positioning and reproducibility of the system was validated using a caliper to be less than 0.1 mm. Profile scanning was conducted in a water-filled breast cup using a Standard Imaging A16 chamber and PTW UNIDOS electrometer. PodPhantom reduced the collection of a single profile from hours to minutes and overall data collection for commissioning from weeks to days.
Conclusion: PodPhantom has been constructed and used in GammaPod commissioning. Future evolution of the system would include automated rotation of the stage and refinement of the existing system.