Author: Jonathan Dowell, Wei Luo, Shane McCarthy, Janelle A. Molloy, Markus Murphy 👨🔬
Affiliation: University of Kentucky, Department of Radiation Medicine, Iridesce Solutions, Inc. 🌍
Purpose: The novel machine quality assurance (QA) device nüFilm (Iridesce Solutions, Lexington KY) allows for an objective assessment of light and radiation fields independent of setup. Herein, the ability of the device to make precise measurements of the two isocenters and their corresponding coincidence is verified across five different setup conditions.
Methods: nüFilm was placed on a TrueBeam LINAC couch in the recommended orientation. The couch was then shifted to five pseudo random positions. At each position, a collimator walkout and radiation starshot were performed to assess the mechanical and radiation central axis of rotation, respectively. Additionally, a “Gantry Flex Shot” was performed for both radiation and light fields to determine the vertical distance to the respective isocenter relative to the nüFilm device. With the positions of mechanical and radiation isocenter, relative to the device, the isocenter coincidence was calculated. The resulting five measurements of isocenter coincidence were compared to the recommended ±1 mm for an SRS/SBRT LINAC from Task Group 142. Error propagation was performed using the suggested error values for each associated vendor software test.
Results: The average isocenter coincidence was found to be 0.30 ± 0.07 mm, within agreement of the aforementioned criteria. Values ranged from 0.22 – 0.38 mm. On average, measurements of both radiation and mechanical isocenter took less than 15 minutes for each position.
Conclusion: nüFilm’s ability to objectively assess both radiation and light fields is, to our knowledge, the only marketable QA device to do so. Removing the subjective assessment of a light field’s alignment to the QA device being used, allows for more precise and accurate measurements of a LINAC. Furthermore, this device opens the avenue for a physicist to perform remote QA without relying on someone else to verify the device’s setup, ensuring high level QA at remote and underserved clinics.