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