Radiochromic film

Radiochromic film is a type of self-developing film typically used in the testing and characterisation of radiographic equipment such as CT scanners and radiotherapy linacs. The film contains a dye which changes colour when exposed to ionising radiation, allowing the level of exposure and beam profile to be characterised.[1] Unlike x-ray film no developing process is required and results can be obtained almost instantly, while it is insensitive to visible light (making handling easier).[2]

Mechanism

For medical dosimetry "gafchromic dosimetry film (...) is arguably the most widely used commercial product".[3] Several types of gafchromic film are marketed with differing properties.[4] One type, MD-55, is made up of layers of polyester substrate with active emulsion layers adhered (approximately 16μm thick).[2] The active layer consists of polycrystalline, substituted-diacetylene and the colour change occurs due to "progressive 1,4-trans additions as polyconjugations along the ladder-like polymer chains".[5][3][6]

Usage

Radiochromic films have been in general use since the late 1960s, although the general principle has been known about since the 19th century.[3][7]

Profiling

Radiochromic film can provide high spatial resolution information about the distribution of radiation. Depending on the scanning technique, sub-millimetre resolution can be achieved.[4]

Dosimetry

Unlike many other types of radiation detector, radiochromic film can be used for absolute dosimetry where information about absorbed dose is obtained directly.[3] It is typically scanned, for example using a standard flat bed scanner, to provide accurate quantification of the optical density and therefore degree of exposure. Gafchromic film has been shown to provide measurements accurate to 2% over doses of 0.2-100 Gray (Gy).[8]

References

Jones, Deric P. (2010). Biomedical sensors (1st ed.). New York: Momentum Press. p. 177. ISBN 9781606500569.
Pawlicki, Todd; Scanderbeg, Daniel J.; Starkschall, George (2016). Hendee's Radiation Therapy Physics (4th ed.). John Wiley & Sons. p. 68. ISBN 9781118575260.
Butson, Martin J; Yu, Peter K.N; Cheung, Tsang; Metcalfe, Peter (September 2003). "Radiochromic film for medical radiation dosimetry". Materials Science and Engineering: R: Reports. 41 (3–5): 61–120. doi:10.1016/S0927-796X(03)00034-2.
Niroomand-Rad, Azam; Blackwell, Charles Robert; Coursey, Bert M.; Gall, Kenneth P.; Galvin, James M.; McLaughlin, William L.; Meigooni, Ali S.; Nath, Ravinder; Rodgers, James E.; Soares, Christopher G. (November 1998). "Radiochromic film dosimetry: Recommendations of AAPM Radiation Therapy Committee Task Group 55". Medical Physics. 25 (11): 2093–2115. doi:10.1118/1.598407. PMID 9829234.
Clough, Roger L. (1995). "Radiochromic Solid-State Polymerization Reaction". Irradiation of polymers: fundamentals and technological applications. ACS Symposium Series. 620 (2nd ed.). Washington, DC: American Chemical Society. pp. 152–166. doi:10.1021/bk-1996-0620.ch011. ISBN 9780841233775.
Ali, I.; Costescu, C.; Vicic, M.; Dempsey, J. F.; Williamson, J. F. (9 July 2003). "Dependence of radiochromic film optical density post-exposure kinetics on dose and dose fractionation". Medical Physics. 30 (8): 1958–1967. doi:10.1118/1.1587611. PMID 12945961.
McLaughlin, W.L.; Yun-Dong, Chen; Soares, C.G.; Miller, A.; Van Dyk, G.; Lewis, D.F. (April 1991). "Sensitometry of the response of a new radiochromic film dosimeter to gamma radiation and electron beams". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 302 (1): 165–176. doi:10.1016/0168-9002(91)90506-L.
Devic, Slobodan (July 2011). "Radiochromic film dosimetry: Past, present, and future". Physica Medica. 27 (3): 122–134. doi:10.1016/j.ejmp.2010.10.001.