Important considerations for radiochromic film dosimetry with flatbed CCD scanners and EBT GAFCHROMIC® film.

In this study, we present three significant artifacts that have the potential to negatively impact the accuracy and precision of film dosimetry measurements made using GAFCHROMIC® EBT radiochromic film when read out with CCD flatbed scanners. Films were scanned using three commonly employed instruments: a Macbeth TD932 spot densitometer, an Epson Expression 1680 CCD array scanner, and a Microtek ScanMaker i900 CCD array scanner. For the two scanners we assessed the variation in optical density (OD) of GAFCHROMIC EBT film with scanning bed position, angular rotation of the film with respect to the scan line direction, and temperature inside the scanner due to repeated scanning. Scanning uniform radiochromic films demonstrated a distinct bowing effect in profiles in the direction of the CCD array with a nonuniformity of up to 17%. Profiles along a direction orthogonal to the CCD array demonstrated a 7% variation. A strong angular dependence was found in measurements made with the flatbed scanners; the effect could not be reproduced with the spot densitometer. An IMRT quality assurance film was scanned twice rotating the film 90° between the scans. For films scanned on the Epson scanner, up to 12% variation was observed in unirradiated EBT films rotated between 0° and 90°, which decreased to approximately 8% for EBT films irradiated to 300cGy. Variations of up to 80% were observed for films scanned with the Microtek scanner. The scanners were found to significantly increase the film temperature with repeated scanning. Film temperature between 18 and 33°C caused OD changes of approximately 7%. Considering these effects, we recommend adherence to a strict scanning protocol that includes: maintaining the orientation of films scanned on flatbed scanners, limiting scanning to the central portion of the scanner bed, and limiting the number of consecutive scans to minimize changes in OD caused by film heating.

[1]  D. F. Lewis,et al.  Sensitometry of the response of a new radiochromic film dosimeter to gamma radiation and electron beams , 1991 .

[2]  W. Mclaughlin,et al.  Temperature and relative humidity dependence of radiochromic film dosimeter response to gamma and electron radiation , 1995 .

[3]  A. A. Abdel-Fattah,et al.  Temperature, humidity and time. Combined effects on radiochromic film dosimeters , 1996 .

[4]  G S Ibbott,et al.  Dosimetric characteristics of an improved radiochromic film. , 1996, Medical physics.

[5]  J Cygler,et al.  GafChromic MD-55: investigated as a precision dosimeter. , 1997, Medical physics.

[6]  J F Williamson,et al.  Quantitative evaluation of radiochromic film response for two-dimensional dosimetry. , 1997, Medical physics.

[7]  L. Reinstein,et al.  A rapid colour stabilization technique for radiochromic film dosimetry. , 1998, Physics in medicine and biology.

[8]  J. Galvin,et al.  Radiochromic film dosimetry: recommendations of AAPM Radiation Therapy Committee Task Group 55. American Association of Physicists in Medicine. , 1998, Medical physics.

[9]  D. Rogers,et al.  AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams. , 1999, Medical physics.

[10]  Optical density dependence on postirradiation temperature and time for MD-55-2 type radiochromic film , 1999 .

[11]  J. Dempsey,et al.  Validation of a precision radiochromic film dosimetry system for quantitative two-dimensional imaging of acute exposure dose distributions. , 2000, Medical physics.

[12]  Optical density changes of Gafchromic MD-55 film resulting from laser light exposure at wavelengths of 671 nm and 633 nm. , 2000, Medical physics.

[13]  J. Dempsey,et al.  Toward automated quality assurance for intensity- modulated radiation therapy. , 2002, International journal of radiation oncology, biology, physics.

[14]  M. Sohrabpour,et al.  Preparation of a new chemical radiochromic film dosimeter , 2002 .

[15]  S. Scheib,et al.  High precision film dosimetry with GAFCHROMIC films for quality assurance especially when using small fields. , 2003, Medical physics.

[16]  M. Butson,et al.  Polarization effects on a high-sensitivity radiochromic film. , 2003, Physics in medicine and biology.

[17]  David A Jaffray,et al.  Characterization and real-time optical measurements of the ionizing radiation dose response for a new radiochromic medium. , 2005, Medical physics.

[18]  C Ross Schmidtlein,et al.  Precise radiochromic film dosimetry using a flat-bed document scanner. , 2005, Medical physics.

[19]  M. Butson,et al.  Post-irradiation colouration of Gafchromic EBT radiochromic film , 2005, Physics in medicine and biology.

[20]  M. Butson,et al.  Absorption spectra variations of EBT radiochromic film from radiation exposure , 2005, Physics in medicine and biology.

[21]  S. Chiu‐Tsao,et al.  Energy dependence of response of new high sensitivity radiochromic films for megavoltage and kilovoltage radiation energies. , 2005, Medical physics.

[22]  F. Cremers,et al.  Evaluation of GafChromic EBT prototype B for external beam dose verification. , 2006, Medical physics.