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Clinical experience with EBT2 GAFCHROMIC film at CCSI

Clinical experience with EBT2 at CCSI. 2. CCSI Renovation Project. Centre for the Southern Interior in Kelowna, BC opened in 19984 Elekta linacsWill be replaced by 5 Varian iXs by the end of 2011Current Status: 2 linacs installed. 3rd to arrive in April 2010.IMRT live since September 2009. IMRT

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Clinical experience with EBT2 GAFCHROMIC film at CCSI

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    1. March 28, 2012 1 Clinical experience with EBT2 GAFCHROMIC film at CCSI Dr. Jurgen Last BCCA Centre for the Southern Interior Kelowna, BC

    2. Clinical experience with EBT2 at CCSI 2 CCSI Renovation Project Centre for the Southern Interior in Kelowna, BC opened in 1998 4 Elekta linacs Will be replaced by 5 Varian iXs by the end of 2011 Current Status: 2 linacs installed. 3rd to arrive in April 2010. IMRT live since September 2009

    3. IMRT Film QA Components Clinical experience with EBT2 at CCSI 3

    4. CCSI IMRT QA 3 ion chamber measurements in cylindrical polystyrene phantom 2 films in coronal and sagittal plane Gamma criterion: 3% within 3 mm Dose difference criterion: 3% between calculation and measurement Analysis restricted to ROI containing the 70% isodose contour Typical results: More than 90% of dose points meet Gamma criterion, 70-80% meet dose difference criterion Some films register doses that can be off by as much as 15%! Clinical experience with EBT2 at CCSI 4

    5. Clinical experience with EBT2 at CCSI 5 Film Calibration

    6. Clinical experience with EBT2 at CCSI 6 Response Curve Variations

    7. Clinical experience with EBT2 at CCSI 7 Repeated Scans: Jumps in Scanner Output

    8. Clinical experience with EBT2 at CCSI 8 Grey Scale Correction

    9. Clinical experience with EBT2 at CCSI 9 Homogeneity of Dose Response Film was cut in 20 2x2 pieces Each film was exposed to 186 cGy Film was reassembled and scanned as one image

    10. Clinical experience with EBT2 at CCSI 10 Scanner Inhomogeneities Open platen scan Standard deviation of pixel values is 90 0.8 cGy @ 200 cGy or 0.4%

    11. Clinical experience with EBT2 at CCSI 11 Film Inhomogeneities

    12. Clinical experience with EBT2 at CCSI 12 Variations between Films 6 films: 3 packs of 2 film on top of each other Each pack exposed to 5 step pattern

    13. Clinical experience with EBT2 at CCSI 13 Variations between Films

    14. Clinical experience with EBT2 at CCSI 14 Error Roll-up for absolute dosimetry

    15. Clinical experience with EBT2 at CCSI 15 Conclusion Film QA with EBT2 has error sources that are not independent of each other. Scanner brightness should be monitored and eventually corrected. Some films show large shifts in overall sensitivity that can not be traced to scanner output variations or variations in the sensitive layer thickness. For relative dosimetry the combined total error from calibration variations and dose response inhomogeneities is about 4 % at 200 cGy.

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