Answer to Question #908 Submitted to "Ask the Experts"

A film dosimeter is comprised of a film packet, filters, and a holder. Film dosimetry is unique in that each processor can use a specific type of film, varying number of filters with varying mg/cm^-2 thicknesses, and varying types of holder configurations. ICN Biomedicals, Inc. (ICN) utilizes Kodak Type 2 film that is assembled in a plastic holder and contains five specific areas of filtration for assessment of dose.

Dose from film is assessed in many ways. ICN's film algorithm is based on over 2,000 irradiations at Battelle Pacific Northwest Laboratories. Dozens of curves have been developed and incorporated in the algorithm, comparing Optical Density (OD), how a film is read, compared to dose, for each monoenergetic photon energy, NIST Beam Codes, based on ANSI N13.11-1993, beta and mixture combinations. This is a very sophisticated dose algorithm, and provides very accurate and precise dose determinations. An unirradiated film packet is clear (similar to film used in an x-ray facility in a medical office. When film is irradiated, there is a darkening of the film and, based on each of the five filtered areas, there is a different response in OD) based on the type of radiation, be it gamma, low-energy x ray, or beta, and the level of exposure. These filtered images are visible after the film is developed. If a film is irradiated while not in the holder, there is a uniform darkening across the entire film packet. If a film is worn during times of radiation exposure, the filter image on the film will be distinct, but blurred. Remember, the radiation is constant, and the person is moving. Think of this as if it were a time-lapse picture being taken of traffic on a busy street at night. The motion is one long colorful blur. If the film is irradiated in a stationary position, the filter patterns are very distinct and crisp, with no blurring whatsoever.

If you are interested, I can provide a file that contains various film images based on varying photon energies and for beta as well. If the film is irradiated on an angle, the filter patterns are also very distinct, and the processor can tell if the exposure came from the top, bottom, or side and even at what angle the incident irradiation was. The film dosimeter is an excellent dosimeter if a facility is interested in knowing how its staff is being exposed and can be used to modify work habits. It is also an excellent dosimeter when a facility needs to mitigate a potential regulatory notice of violation, by providing evidence that the high dose on the film was not an actual occupational exposure, but rather a stationary exposure. The facility would then have to provide a dose estimate for the person since the film cannot be used.

If more information is required, please contact the editor of this website and she will put you in touch with me.

Sandy Perle,
Technical Director,
ICN Worldwide Dosimetry Service