Using Radiochromic Film Tips and Techniques

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Eugene Tyler Barber
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1 Using Radiochromic Film Tips and Techniques David F. Lewis, Ph.D. Senior Science Fellow Advanced Materials Group International Specialty Products October 22, 2010

2 Topics Scanners and Scanning Cutting and Using Film Things to Avoid

3 Scanners What to choose Type: B&W, RGB, Flatbed, Drum, Laser? RGB Flatbed Maker: Vidar, Microtek, Epson? Epson Model: A4, A3? A3 Epson 10000XL preferred A2 Epson V700/750 acceptable for fields 10x10 cm

4 Epson vs Microtek Microtek 9800 Epson 1680

6 Scanner Essentials Scanner Driver Epson Scan SilverFast Turn Off all Image Adjustment Features They are provided to make images look good Dosimetry requires raw image data

8 Turn Off Color Correction

10 Optical Elements in a Flatbed Scanner

11 Scanner Practice Leave scanner always on Allow 30 minutes to warm up electronics Warm-up the lamp before each session Usually 3 preview scans is OK Do your own check

12 Scanner Response: An Important Distinction CCD rgb detector array Scan direction Parallel to the CCD the noise is dominated by variability between the individual detectors in the three arrays Parallel to the scan direction noise is dominated by the reproducibility of a single set of rgb detectors Noise parallel to the array>noise parallel to the scan direction

13 Quick Assessment of EBT2 Profiles look similar in all channels

14 Moisture Diffusion Has film equilibrated with ambient moisture condition? Diffusion rate: low Distance: short Diffusion rate: high Distance: long

15 Moisture Diffusion Moisture content of active layer equilibrates to RH of environment Changes possibly significant at extremes, e.g. >75% RH or <25% RH State of freshly manufactured film similar to equilibration at high humidity Film packaging can be consequential Film aging can be consequential

16 Moisture Equilibration From box After 5 days Effect might be observed with stacks of bare film Returned to use of interleaving with tissue Observation of moisture effects unlikely

17 Moisture Equilibration After Water-lamination Immediately after lamination After 15 days with interleaving

18 Cutting/Marking Film Not recommended Too small Less likely to represent average behavior More likely to have flatness issues Too much symmetry

19 Cutting/Marking Film Recommended Preserves original symmetry Large enough for 10cm x 10cm field

20 Scanning: The Calibration Window Scan direction Calibration Window Do not cover this area!!!

21 Scanning: Landscape Orientation Scan direction Short edge of film parallel to scan

22 Dose, cgy Orientation Dependence Effect of Film Orientation on EBT2 Response: Epson 10000XL Scanner Landscape orientation Portrait orientation Density

23 Cutting/Marking Film Recommended Preserves original symmetry Large enough for 10cm x 10cm field

24 Scanner response Angular Dependence Angular Dependence of EBT Red Channel Blue Channel Portrait orientation Landscape orientation Rotation Angle

25 Error from Misalignment During Scanning Response error is ~0.05% per degree Dose error ~0.15% per degree Misalignment of 5 in scan window Conclusion: Unlikely to create inadvertent measurement errors due to small misalignments of film

26 Red/Blue Angular Dependence Angular Dependence of EBT % 104.0% 103.0% 102.0% 101.0% 100.0% 99.0% 98.0% 97.0% 96.0% 95.0% Rotation Angle Relative red:blue response has an angular dependence

27 Scanning face-up or face-down? Polyester Laminate - 50 microns Adhesive Layer - 25 microns Topcoat - 4.5±0.5 microns Active Layer - 30±3 microns Polyester Base microns Original configuration (prior to January 2010)

28 Response difference Preferable to Use Landscape Orientation 10% Response Difference - Base side up vs. base side down Lot % 8% 7% 6% 5% Landscape orientation Portrait orientation 4% 3% 2% 1% 0% Dose, cgy Original recommendation - July 2009 Be consistent with placement Landscape orientation preferred

29 Which Side to scan? Examine the film surface in reflection Textured side Polyester Overlaminate - 50 microns Adhesive Layer - 25 microns Topcoat - 4.5±0.5 microns Active Layer - 30±3 microns Polyester Substrate microns Smooth side An ID mark has been added to lots now in production

30 The ID Mark Now Makes It Easy Small slit All lot numbers and higher

31 Does it still matter which side faces the glass? Polyester Overlaminate - 50 μm Adhesive Layer - 25 μm Active Layer - 28 μm Polyester Substrate μm A recent assessment says no Needs further validation Test and verify

32 Portrait Scan 180 Down web direction

33 Scanner response No Orientation Effect Orientation and Response Red Green Blue Red, flipped Green, flipped Blue, flipped RESPONSE DIFFERENCE Dose, cgy R G B % -0.15% 0.05% % 0.09% 0.08% % -0.37% -0.14% % -0.35% -0.35% % 0.13% 0.53% % 0.28% 0.22% % 0.24% 0.26% % 0.15% 0.19% Dose, cgy

34 Transmission vs Reflection Reflection More signal light passes through active layer twice No Newton s rings Transmission Less noise Lateral response effect is less

35 Transmission or Reflection? Reflection scan Transmission scan

36 Transmission or Reflection? ± 3.2 cgy ± 1.9 cgy

37 Film Calibration How many steps? 5-7 plus zero is sufficient for cgy Doses in a geometric progression How large? Key point capture the average behavior of the film Measurement area of at least 25 cm² Exposed area at least 50 cm²

38 Calibration Example

39 Exposure Value in Geometric Progression Step-to-step increase Dose/MU cgy/mu Step # MU Dose, cgy

40 Exposures on a Single Sheet Convenient, rapid method Use fewer, but taller steps Flatter dose profiles Step-to-step increase Dose/MU ~ cgy/mu Step # MU Dose, cgy

41 Dynamic Range of EBT2

EBT 2 Has a Large Dynamic Range Dose, cgy Scanner Response R G B 6102 5291 4081 6701 5157 5724 4792 7594 4281 6277 5624 8540 3427 7053 6800 9798 2577 8147 8650 11515 1929 9509 10861

42 EBT 2 Has a Large Dynamic Range Dose, cgy Scanner Response R G B

43 Density Post-Exposure Growth Post-exposure change 0.60 Red Green 0.55 Blue y = x R² = y = x R² = y = x R² = Log 10 (time after exposure, min)

44 Post-exposure Changes: Practical Considerations Calibration time (after exposure) 16 hours 16 hours Dose 161 cgy 161 cgy Read time (after exposure) 8 hours 24 hours Dose error -2.5 cgy 1.5 cgy Dose error -1.55% 0.93% Absolute dosimetry Establish a protocol and stick to it Scan calibration films at several times after exposure Relative dosimetry Time after exposure can be ignored

45 Keep Film Flat for Scanning Another reason to prefer larger films Weight of larger films tends to keep them flat

46 Film With a Curl

47 Film Kept Flat

48 Avoid Fingerprints Handle film at the edges Keep film clean Clean with a tissue and alcohol

49 Fingerprints: Triple Channel Dosimetry Helps Dose differences resulting from fingerprints Red channel dosimetry Triple channel dosimetry

50 Dose error Fingerprints: Triple Channel Dosimetry Helps 3% Dose profiles across EBT2 with fingerprints 2% 1% 0% -1% -2% Red channel dosimetry Triple channel dosimetry -3% Position, mm

51 Newton s Rings

52 Newton s Rings Interference pattern is color dependent Can intensify the artifact and make it worse

53 Dose, cgy Dose, cgy Newton s Rings Triple Channel Dosimetry Unhelpful Newton's Ring - Color dependence Dose profile corrupted by Newton's Rings Red channel dosimetry Green channel dosimetry Position, x0.34 mm Red channel dosimetry Triple channel dosimetry Position, x 0.34 mm

54 Dealing with Newton s Rings Presence is not predictable Replace film on scanner Film is not perfectly flat place the concave side towards glass Anti-Newton Glass Glass microspheres, cornstarch Polyester base with silica treatment

Penetration, mm EBT2 is Water Resistant Penetration of Water into EBT2 Film 8 7 6 5 4 3 2 GAFCHROMIC EBT-2

55 Penetration, mm EBT2 is Water Resistant Penetration of Water into EBT2 Film GAFCHROMIC EBT-2 GAFCHROMIC EBT Time, hours Profile Magnification Water front at position 365 Edge of film at position 388

56 EBT2 is Usable in Water Phantoms

57 Controlling Interscan Variability EBT Control Strip EBT2 Control Strip Red channel Green channel Blue channel

58 Normalized Response Value Scan-to-scan Variability Interscan Consistency: Epson 10000XL Red channel Green channel Blue channel Scan #

59 Normalized response value Interscan Correction with Control Strip Interscan Consistency: With interscan correction Red channel Green channel Blue channel Scan #

60 Normalized response - red/blue Benefit of Interscan Correction Interscan Consistency: Red response/blue response Without Interscan Correction With Interscan Correction Scan #

61 Temperature Effects on Scanning

62 Dose, cgy Relative thickness Use Triple Channel Dosimetry Removes the effects of small (½-1%) thickness differences!!! Triple channel 200 Red channel Position, mm

63 Thank you

GafChromic EBT2 and EBT3 Films for Ball Cube II Phantom

GafChromic EBT2 and EBT3 Films for Ball Cube II Phantom Introduction: These EBT2/EBT3 films, shown in Figure 1a-c, are specially sized and formatted to uniquely fit the Accuray Ball Cube II Phantom. Each