Comparison of dose response of radiochromic film measured with He‐Ne laser, broadband, and filtered light densitometers

Dose response curves for GAFChromic MD‐55‐2 film were measured using three different densitometer systems: a He‐Ne laser densitometer, a broadband (white light) densitometer, and a filtered red light densitometer. These were found to differ significantly; the dose needed to achieve a net optical density of 1 (DNOD1) was greater than 100 Gy for the white light densitometer, 56 Gy for the He‐Ne densitometer, and only 14.8 Gy for the filtered red light densitometer. This represents approximately a fourfold increase in response for the filtered red light versus the He‐Ne laser densitometer, which is a significant improvement. For some patient prescriptions this enables us to achieve an accuracy and precision sufficient to verify daily dose to within 5%.