Quantitative Sensitivity Validation of a Novel Device for Radiation Therapy Machine Quality Assurance
Abstract
Purpose
Routine radiation therapy machine quality assurance (QA) relies on multiple independent devices and subjective manual measurements, which can limit efficiency and sensitivity to small mechanical deviations. The purpose of this work was to quantitatively evaluate the geometric and mechanical sensitivity of a novel compact QA device (nüFilm) to demonstrate its accuracy and objectivity in radiation therapy machine QA.
Methods
Sensitivity testing was performed in two phases. Phase 1 consisted of simulation-based laboratory experiments designed to establish ground truth using controlled geometric offsets applied to light fields. Custom 3D-printed fixtures were used to introduce known spatial displacements, and collimator star-shot and collimator walk-out measurements were acquired with offsets ranging from 0.5 to 3.0 mm. Phase 2 consisted of clinical measurements performed on a Varian TrueBeam linear accelerator using radiation fields. Controlled jaw shifts and field-edge displacements (0 - 5 mm) were introduced to evaluate radiation-based collimator star-shot sensitivity and light-radiation field coincidence. Measured nüFilm responses were compared to applied offsets using linear regression to assess sensitivity and linearity.
Results
Laboratory light-field sensitivity testing demonstrated a linear response between applied offsets and measured displacement, with a slope of approximately 1.0 mm per mm of applied offset (R² = 0.99). Clinical radiation-based collimator star-shot measurements showed comparable performance, with measured responses of approximately 0.9-1.0 mm per mm of applied offset (R² = 0.99). These results validate the sensitivity of the device down to 0.1 mm.
Conclusion
The nüFilm QA system demonstrates robust, linear sensitivity to small geometric and mechanically induced deviations under both laboratory and clinical conditions, with validated sub-millimeter sensitivity. This level of precision is critical for reliably assessing machine performance relative to the QA tolerances specified in TG-142.