Comparison of three high-resolution digitizers for radiochromic film dosimetry

A recently introduced radiographic film scanner from Howtek is evaluated and compared to two other commercially available densitometry systems for its use in radiochromic (RC) film dosimetry in the clinical dose range 0-100 Gy. It has a high-intensity red LED light-source centered at 662 nm (near the major absorption peak for RC film), and is coupled to a CCD linear array detector. This new densitometry system is directly compared to two high-resolution film scanners commonly employed in RC film dosimetry, namely the Lumiscan 75 digitizer (He-Ne laser light source) and the Vidar VXR-16 digitizer (fluorescent light source). A spot densitometer (Nuclear Associates Radiochromic Densitometer) with a filtered 671 nm laser-diode light source is also included as a reference for comparison. The response of the spot densitometer and three high-resolution digitizers is characterized by the dose required to reach a net optical density of 1 (DNOD1), and is 16.0, 37.3, and 46.4 Gy for the Nuclear Associates Radiochromic Densitometer, Howtek MultiRAD 460 and Lumiscan 75 digitizer, respectively. The Vidar VXR-16 does not reach a net optical density of 1. The minimum usable dose at which a 2% level of uncertainty can be achieved (MUD2%) on the three digitizers are 2.6, 6.0, and 38.5 Gy for the Howtek MultiRAD 460, Lumiscan 75, and Vidar VXR-16, respectively. The Howtek MultiRAD 460 shows the greatest sensitivity, lowest MUD2% and best signal-to-noise ratio in the clinical dose range 0-100 Gy. Furthermore, it has no apparent interference (moiré) artifacts that severely limit the low optical density region of the He-Ne laser digitizer. For high-resolution radiochromic dosimetry in the clinical dose range 0-100 Gy, the high-intensity red LED light-source digitizer proves to be the superior modality.