Evaluation of the magnitude of EBT Gafchromic film polarization effects

  • M. J. Butson
  • T. Cheung
  • P. K. N. Yu
Scientific Note


Gafchromic EBT film, has become a main dosimetric tools for quantitative evaluation of radiation doses in radiation therapy application. One aspect of variability using EBT Gafchromic film is the magnitude of the orientation effect when analysing the film in landscape or portrait mode. This work has utilized a >99% plane polarized light source and a non-polarized diffuse light source to investigate the absolute magnitude of EBT Gafchromic films polarization or orientation effects. Results have shown that using a non-polarized light source produces a negligible orientation effect for EBT Gafchromic film and thus the angle of orientation is not important. However, the film exhibits a significant variation in transmitted optical density with angle of orientation to polarized light producing more than 100% increase, or over a doubling of measured OD for films irradiated with x-rays up to dose levels of 5 Gy. The maximum optical density was found to be in a plane at an angle of 14 °±7 ° (2SD) when the polarizing sheet is turned clockwise with respect to the film. As the magnitude of the orientation effect follows a sinusoidal shape it becomes more critical for alignment accuracy of the film with respect to the polarizing direction in the anticlockwise direction as this will place the alignment of the polarizing axes on the steeper gradient section of the sinusoidal pattern. An average change of 4.5 % per 5 ° is seen for an anticlockwise polarizer rotation where as the effect is 1.2 % per 5 ° for an clockwise polarizer rotation. This may have consequences to the positional accuracy of placement of the EBT Gafchromic film on a scanner as even a 1 ° alignment error can cause an approximate 1 % error in analysis. The magnitude of the orientation effect is therefore dependant on the degree of polarization of the scanning light source and can range from negligible (diffuse LED light source) through to more than 100 % or doubling of OD variation with a fully linear polarized light source.

Key words

Gafchromic EBT Radiochromic film densitometry orientation 


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  1. 1.
    Currie, M., Bailey, M. and Butson, Martin. J.,Verification of nose irradiation using orthovoltage x-ray beams, Australas. Phys. Eng. Sci. Med., 30, 105–110, 2007.Google Scholar
  2. 2.
    Damrongkijudom, N., Butson, Martin. J. and Rosenfeld, A.Extrapolated surface dose measurements using a NdFeB magnetic deflector for 6 MV x-ray beams. Australas. Phys. Eng. Sci. Med. 30, 46–51, 2007.CrossRefPubMedGoogle Scholar
  3. 3.
    Damrongkijudom, N., Oborn, B., Butson, Martin. J. and Rosenfeld, A.Measurement of magnetic fields produced by a “magnetic deflector” for the removal of electron contamination in radiotherapy. Australas. Phys. Eng. Sci. Med., 29, 321–327, 2006.CrossRefPubMedGoogle Scholar
  4. 4.
    Butson, M.J., Yu, K.N. and Metcalfe, P.E.,Extrapolated surface dose measurements with radiochromic film, Medical Physics, 26, 485–488, 1999.CrossRefGoogle Scholar
  5. 5.
    Butson, M.J., Cheung, T. and Yu, K.N.,Radiochromic film: the new x-ray dosimetry and imaging tool, Australasian Physical & Engineering Sciences in Medicine, 27, 230, 2004.CrossRefGoogle Scholar
  6. 6.
    Cheung, T., Butson, M.J. and Yu, K.N.,Multilayer Gafchromic film detectors for breast skin dose determination in vivo, Physics in Medicine and Biology, 47, N31–37, 2002.CrossRefPubMedGoogle Scholar
  7. 7.
    Butson, M.J., Yu, K.N., Cheung, T. and Metcalfe, P.,High sensitivity radiochromic film dose comparisons, Physics in Medicine and Biology, 47, N291-N295, 2002.CrossRefPubMedGoogle Scholar
  8. 8.
    Cheung, T., Butson, M.J. and Yu, K.N.,Evaluation of a fluorescent light densitometer for radiochromic film analysis, Radiation Measurements, 35, 13–16, 2002.CrossRefGoogle Scholar
  9. 9.
    He, C.F., Geso, M., Ackerly, T. and Wong, C.J.,Stereotactic dose perturbation from an aneurysm clip measured by Gafchromic EBT film, Australas. Phys. Eng. Sci. Med., 31, 18–23, 2008.CrossRefPubMedGoogle Scholar
  10. 10.
    Butson, M.J., Cheung, T. and Yu, P.K.,Measuring energy response for RTQA radiochromic film to improve quality assurance procedures, Australas. Phys. Eng. Sci. Med., 31, 203–206, 2008.PubMedGoogle Scholar
  11. 11.
    Butson, M.J., Cheung, T. and Yu, P.K.,Radiochromic film for verification of superficial x-ray backscatter factors, Australas. Phys. Eng. Sci. Med., 30, 269–273, 2007.PubMedCrossRefGoogle Scholar
  12. 12.
    Gotanda, R., Katsuda, T., Gotanda, T., Eguchi, M., Takewa, S., Tabuchi, A. and Yatake, H.,Computed tomography phantom for radiochromic film dosimetry. Australas. Phys. Eng. Sci. Med., 30, 194–199, 2007.PubMedGoogle Scholar
  13. 13.
    Price, S., Williams, M., Butson, M., Metcalfe, P.,Comparison of skin dose between conventional radiotherapy and IMRT, Australas. Phys. Eng. Sci. Med., 29, 272–277 2006.PubMedCrossRefGoogle Scholar
  14. 14.
    Butson, M.J., Cheung, T., Yu, P.K.,Megavoltage x-ray skin dose variation with an angle using grid carbon fibre couch tops, Phys. Med. Biol., 52, N485–92, 2007.CrossRefPubMedGoogle Scholar
  15. 15.
    Butson, M.J., Cheung, T. and Yu, P.K.,Spatial resolution of a stacked radiochromic film dosimeter, Radiother. Oncol., 61, 211–3, 2001.CrossRefPubMedGoogle Scholar
  16. 16.
    Butson, M.J., Cheung, T. and Yu, K.N.,Weak energy dependence of EBT Gafchromic film dose response in the 50 kVp – 10 MVp X-ray range, Applied Radiation and Isotopes, 64, 60–62, 2006.CrossRefPubMedGoogle Scholar
  17. 17.
    Butson, M.J., Cheung, T. and Yu, K.N.,Absorption spectra variations of EBT radiochromic film from radiation exposure, Physics in Medicine and Biology, 50, N135-N140, 2005.CrossRefPubMedGoogle Scholar
  18. 18.
    Saur, S. and Frengen, J.,GafChromic EBT film dosimetry with flatbed CCD scanner: a novel background correction method and full dose uncertainty analysis, Med. Phys., 35, 3094–3101, 2008.CrossRefPubMedGoogle Scholar
  19. 19.
    Zeidan, O.A., Stephenson, S.A., Meeks, S.L., Wagner, T.H., Willoughby, T.R., Kupelian, P.A. and Langen, K.M.,Characterization and use of EBT radiochromic film for IMRT dose verification. Med. Phys., 33, 4064–4072, 2006.CrossRefPubMedGoogle Scholar
  20. 20.
    Lynch, B.D., Kozelka, J., Ranade, M.K., Li, J.G., Simon, W.E. and Dempsey, J.F.,Important considerations for radiochromic film dosimetry with flatbed CCD scanners and EBT GAFCHROMIC film. Med. Phys., 33, 4551–4556, 2006.CrossRefPubMedGoogle Scholar
  21. 21.
    Dini, S.A., Koona, R.A., Ashburn, J.R. and Meigooni, A.S.,Dosimetric evaluation of GAFCHROMIC XR type T and XR type R films. J. Appl. Clin. Med. Phys., 6, 114–134, 2005.CrossRefPubMedGoogle Scholar
  22. 22.
    Butson, M.J., Cheung, T. and Yu, P.K.,Scanning orientation effects on Gafchromic EBT film dosimetry, Australas. Phys. Eng. Sci. Med., 29, 281–284, 2006.PubMedCrossRefGoogle Scholar
  23. 23.
    Mack, A., Mack, G., Weltz, D., Scheib, S.G., Bottcher, H.D. and Seifert, V.,High precision film dosimetry with GAFCHROMIC films for quality assurance especially when using small fields, Med. Phys. 30, 2399–2409, 2003.CrossRefPubMedGoogle Scholar
  24. 24.
    Klassen, N., Zwan, L. and Cygler, J.,Gafchromic MD-55: investigated as a precision dosimeter, Med. Phys., 24, 1924–1934, 1997.CrossRefPubMedGoogle Scholar
  25. 25.
    Butson, M.J., Yu, K.N., Cheung, T. and Inwood, D.,Polarization effects on a high sensitivity radiochromic film, Physics in Medicine and Biology, 48, N207–211, 2003.CrossRefPubMedGoogle Scholar
  26. 26.
    Rink, A., Vitkin, I. and Jaffray, D.,Characterization and realtime optical measurements of the ionizing radiation dose response for a new radiochromic medium, Med. Phys., 32, 2510–6, 2005.CrossRefPubMedGoogle Scholar
  27. 27.
    Butson, M., Yu, P. and Metcalfe, P.,Effects of readout light sources and ambient light on radiochromic film, Phys. Med. Biol., 43, 2407–2412, 1998.CrossRefPubMedGoogle Scholar
  28. 28.
    Cheung, T., Butson, M.J. and Yu, K.N.,Post irradiation coloration of Gafchromic EBT radiochromic film, Physics in Medicine and Biology, 50, N281-N285, 2005.CrossRefPubMedGoogle Scholar
  29. 29.
    Yu, P.K., Butson, M. and Cheung, T.,Does mechanical pressure on radiochromic film affect optical absorption and dosimetry?, Australas. Phys. Eng. Sci. Med., 29, 285–287, 2006.PubMedCrossRefGoogle Scholar
  30. 30.
    Cheung, T., Yu, P.K. and Butson, M.J.,Source and detector polarization effects on radiographic film dosimetry, Phys. Med. Biol., 48, N329-N334, 2003.CrossRefPubMedGoogle Scholar

Copyright information

© Australasian College of Physical Scientists and Engineers in Medicine 2009

Authors and Affiliations

  1. 1.Dept. of Physics and Materials ScienceCity University of Hong KongKowloon TongHong Kong
  2. 2. Department of Medical PhysicsIllawarra Cancer Care CentreWollongongAustralia

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