SU‐E‐T‐170: Development and Testing of a Single Exposure Film Calibration Procedure

Purpose: To develop and test the sensitivity of a single exposure film calibration procedure using a dynamic wedge. Method and Materials:A 60o dynamic wedge was used to expose EDR2 film and generate optical density (OD) to dose calibration curves in DoseLab Pro. Doses between 50 and 500 cGy were examined. Dosimetric data was generated from a Profiler2 diode array. This calibration curve was compared to one generated by the standard approach of irradiating 8 separate sheets of film to known doses. The sensitivity of the wedged‐film calibration procedure was also tested through the following 4 investigations. First, film measurements were repeated 10 times to determine the variability of the film response. Second, profiler measurements were repeated 10 times to determine the variability of the profiler response. Third, positional offsets of the profiler were investigated (up to 4mm off‐center — the size of the diode spacing). Fourth, different amounts of solid water build‐up were used (between 1 and 10cm) above the profiler and corresponding film. Results: The calibration curve generated with the wedge exposure compared very well to that generated with the standard 8‐film approach, being less than 2.5% locally different (0.8% relative to maximum) at doses above 50 cGy. Irradiation of multiple films introduced a maximum deviation of 1.2%, while multiple profiler measurements introduced a maximum deviation of 0.5%. Shifts in the position of the profiler introduced a maximum error of 3.0%. These deviations represent good robustness of the calibration procedure. Consistent calibration curves were generated regardless of the extent of build‐up material used. Each film exposure and software analysis was completed in 1 minute and 5 seconds, respectively. Conclusions: This work has developed a single exposure film calibration procedure. This offers physicists a rapid and robust film calibration method.