Author: Christopher J. Mart, Daniel G. McDonald, Inna V. McGowin, Sean A. Roles 👨🔬
Affiliation: Medical University of South Carolina 🌍
Purpose: To improve the efficiency and accuracy of the positioning process for electron treatments by providing a pointer system for patient alignment to central axis (CAX) of the field at the correct SSD.
Methods: The pointer system was designed for the TrueBeam accelerator (Varian Medical Systems) and is comprised of two parts. The baseplate fits in an electron applicator tray like a Cerrobend block. A separate pointer fits into the baseplate. This pointer is customizable and provides a physical indication of CAX at the desired SSD. The pointer fits tightly into the baseplate but is not locked. In the event of pressure on the tip of the pointer, it will dislodge from the baseplate for patient safety. This system was designed in free web-based cad software (TinkerCAD) and printed with polylactic acid (PLA) using standard 3D-printing methods. The system was validated by comparing the location and SSD indicated by the pointer tip to the light field graticule and SSD indicated by the vendor-supplied calibrated front-pointer for the TrueBeam. Each unique pointer designed and printed for a specific SSD was validated prior to clinical use.
Results: The pointer system’s accuracy was validated against the TrueBeam CAX and front-pointer and found to match within 1mm in all directions. Additionally, the setup time to align CAX and set SSD on a patient was found to be reduced from 3-5 minutes to under 1 minute for each treatment fraction.
Conclusion: Positioning of electron patients is a tedious process involving aligning to CAX with the light field graticule and adjusting patient SSD using the optical distance indicator in a cyclical process whereby each adjustment affects the other. The use of a custom designed, printed and validated pointer system allows the patient to be positioned quickly and accurately.