GAF Film Radiation Experiments
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Transcript of GAF Film Radiation Experiments
GAF Film Radiation Experiments
CancerCare of MaineChris Burroughs-Heineman
June 1, 2012
Purpose
• Testing the viability of GAF film for measuring dose to defibrillator/pacemaker patients
• OneDose discontinued previous detectors
Scattering Setup
• MD Anderson phantom in custom Styrofoam holder in direct beam path
• Film squares on highest point of holder, 20 cm from edge of beam field
Scattering Setup - Several Experiments
• GAF film taped to aluminum foil
• GAF film taped to brass sheet
• GAF film placed vertically into holder
• GAF film laid horizontally on top of holder
Radiation Dosage
Experiment Amount of Radiation (rad or MU)
Aluminum 1000
Brass 1000
Vertical Scattering 0.5, 1, 1.5, 2, 3, 5, 10
Horizontal Scattering 0.5, 1, 1.5, 2, 3, 5, 10
Obtaining Mean Current• Film squares scanned
into photocopier as JPEGs
• Scans uploaded into RIT, viewed under red filter (highest sensitivity provided)
• Region of interest selected from scan, mean current available under information
Scattering Current Results• Brass provided slightly
lower mean current than aluminum
• Both brass, aluminum currents less than that of non-metal film square
• Dose density not sufficient to routinely use metal in irradiation
Scattering Current ResultsVertical Increasing Radiation
y = -1.56855x + 245.04305R2 = 0.96548
y = -1.76470x + 246.41978R2 = 0.98528
y = -1.72320x + 246.06924R2 = 0.98062
y = -1.68586x + 244.70893R2 = 0.95279
225
230
235
240
245
250
0 2 4 6 8 10 12
Dose (Rad)
Mea
n C
urre
nt
Radiation vs. Current, May 21, 4 PM
Radiation vs. Current, May 22, 8 AM
Radiation vs. Current, May 22, noon
Radiation vs. Current, May 23, 8 AM
Linear (Radiation vs. Current, May 21, 4 PM)
Linear (Radiation vs. Current, May 22, 8 AM)
Linear (Radiation vs. Current, May 22, noon)
Linear (Radiation vs. Current, May 23, 8 AM)
Scattering Current ResultsHorizontal Film Placement
y = 0.0144x2 - 1.8707x + 246.4R2 = 0.9673
225
230
235
240
245
250
0 2 4 6 8 10 12
Dose (Rad)
Mea
n C
urre
nt
Mean Current (May 23, 4:30 PM)
Mean Current (May 24, 8 AM)
Mean Current (May 24, 11:30 AM)
Mean Current (May 24, 4 PM)
Linear (Mean Current (May 23, 4:30 PM))
Linear (Mean Current (May 24, 8 AM))
Linear (Mean Current (May 24, 11:30 AM))
Linear (Mean Current (May 24, 4 PM))
Poly. (Mean Current (May 24, 8 AM))
Primary Beam GAF Radiation
• GAF squares between blocks of solid water, in center of beam field
• Radiation increased (2, 5, 10, 25, 50, 100, 200 rad), depth constant (Dmax for 6 MV)
Primary Beam GAF RadiationSolid Water Increasing Dose
y = 0.0326x2 - 15.829x + 1927.6R2 = 0.9939
y = -0.0003x3 + 0.2129x2 - 50.944x + 4171.6R2 = 0.9976
y = 0.0302x2 - 14.725x + 1800.9R2 = 0.9927
y = -0.0003x3 + 0.1981x2 - 47.213x + 3861R2 = 0.9965
-50
0
50
100
150
200
250
300
350
100 120 140 160 180 200 220 240 260
Mean Current
Dos
e (R
ad) Dose
29-MayPoly. (Dose)Poly. (Dose)Poly. (29-May)Poly. (29-May)
Percent Depth Dose• Determining the viability
of GAF film in characterizing percent depth dose curve for 6x
• Film squares placed between solid water blocks at selected depths (1.5, 3, 5, 8, 10, 15, 20 cm)
• Mean current increased with depth; consistent with percent depth dose curve
Percent Depth Dose
• Thin film strip between solid water blocks• Gantry placed at 90 degrees• Ruler scanned with film; currents obtained for
several distances from beam (1.5 cm, 2 cm, every centimeter up to 20 cm)
Percent Depth Dose
• Mean currents entered into spreadsheet, likely dose calculated from coefficients from quadratic best fit line of primary beam data
• Dose compared with previously measured value
• Graphs had same shape; GAF film dose values higher (4-13%)
Percent Depth Dose
0
20
40
60
80
100
120
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0
Depth (cm)
Dos
e (r
ad)
Measured
GAF