Radiochromic film explained

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". Several types of gafchromic film are marketed with differing properties.^[3] One type, MD-55, is made up of layers of polyester substrate with active emulsion layers adhered (approximately 16μm thick). 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".^[4] ^[5]

Usage

Radiochromic films have been in general use since the late 1960s, although the general principle has been known about since the 19th century.^[6]

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.

Dosimetry

Unlike many other types of radiation detector, radiochromic film can be used for absolute dosimetry where information about absorbed dose is obtained directly.^[7] 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]

Notes and References

Book: Jones. Deric P.. Biomedical sensors. 2010. Momentum Press. New York. 9781606500569. 177. 1st.
Book: Pawlicki. Todd. Scanderbeg. Daniel J.. Starkschall. George. Hendee's Radiation Therapy Physics. John Wiley & Sons. 9781118575260. 68. en. 2016. 4th.
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.. Radiochromic film dosimetry: Recommendations of AAPM Radiation Therapy Committee Task Group 55. Medical Physics. November 1998. 25. 11. 2093–2115. 10.1118/1.598407. 9829234. 1998MedPh..25.2093N .
Book: Clough. Roger L.. Irradiation of polymers: fundamentals and technological applications. 620. 152–166. 1995. American Chemical Society. Washington, DC. 9780841233775. 2nd. Radiochromic Solid-State Polymerization Reaction. 10.1021/bk-1996-0620.ch011. ACS Symposium Series.
Ali. I.. Costescu. C.. Vicic. M.. Dempsey. J. F.. Williamson. J. F.. Dependence of radiochromic film optical density post-exposure kinetics on dose and dose fractionation. Medical Physics. 9 July 2003. 30. 8. 1958–1967. 10.1118/1.1587611. 12945961. 2003MedPh..30.1958A .
McLaughlin. W.L.. Yun-Dong. Chen. Soares. C.G.. Miller. A.. Van Dyk. G.. Lewis. D.F.. 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. April 1991. 302. 1. 165–176. 10.1016/0168-9002(91)90506-L. 1991NIMPA.302..165M .
Butson. Martin J. Yu. Peter K.N. Cheung. Tsang. Metcalfe. Peter. Radiochromic film for medical radiation dosimetry. Materials Science and Engineering: R: Reports. September 2003. 41. 3–5. 61–120. 10.1016/S0927-796X(03)00034-2. 10.1.1.705.3331.
Devic. Slobodan. Radiochromic film dosimetry: Past, present, and future. Physica Medica. July 2011. 27. 3. 122–134. 10.1016/j.ejmp.2010.10.001. 21050785.