The single emission spectrum densitometry for radiochromic films by flat-bed document scanner with transparency unit employing light emitting diode

We developed an infrared flat-bed scanner with a transparency unit (IR-4000, iMeasure, Inc.) in order to increase the sensitivity of the measuring density of Radiochromic film, Gafchromic film EBT model. Radiochromic film has been usedfor many years as a two-dimensional radiation detectorfor dosimetry in radiotherapy. One of the commercially available Radiochromic films today is the Gafchromic film EBT model (EBT) manufactured by ISP (International Speciality Products, Wayne, NJ). EBT has the absorption spectrum with a maximum absorption band centered at 636 nm. Consequently the response of EBT will be enhanced by measuring with a red light. The transparency unit of IR-4000 for EBT has a light emitting diode (LED) with a peak wavelength of 630 nm, and was produced by replacing a white light in the transparency unit for the flat-bed scanner (ES-2200, Seiko Epson Corp) with the LEDs. IR-4000 could improve the sensitivity for EBT in all dose ranges. However, we had to consider the methods for decreasing noise. We examined for IR-4000 how to keep the high sensitivity and reduce noise. Multiple scans and the reduction of the image resolution by pixel averaging, which was effective in noise reduction, were employed. IR-4000 is a useful densitometry device to GAFs since optional transparency units which have various single emission spectra are prepared.