Accuracy of rapid radiographic film calibration for intensity-modulated radiation therapy verification

A single calibration film method was evaluated for use with intensity-modulated radiation therapy film quality assurance measurements. The single-film method has the potential advantages of exposure simplicity, less media consumption, and improved processor quality control. Potential disadvantages include cross contamination of film exposure, implementation effort to document delivered dose, and added complication of film response analysis. Film response differences were measured between standard and single-film calibration methods. Additional measurements were performed to help trace causes for the observed discrepancies. Kodak X-OmatV (XV) film was found to have greater response variability than extended dose range (EDR) film. We found it advisable for XV film to relate the film response calibration for the single-film method to a user-defined optimal calibration geometry. Using a single calibration film exposed at the time of experiment, the total uncertainty of film response was estimated to be <2% (1%) for XV (EDR) film at 50 (100) cGy and higher, respectively.