Basic Film Dosimetry
Indra J. Das, Ph.D.
Department of Radiation Oncology
University of Pennsylvania
Philadelphia, PA
&
Chee-Wai Cheng, Ph.D.
Department of Radiation Oncology
Morristown General Hospital
Morristown, NJ
Das/Cheng/AAPM/SLC/2001
Basic Film Dosimetry
What is a film?
Why to use film ?
How to use film?
Where to use film?
Das/Cheng/AAPM/SLC/2001
Historical Perspective
1826
Joseph Niepce
First Photograph
1836
J. M. Daguerre
Concept of developer
1889
Eastman Kodak
Cellulose nitrate base for emulsion
1890
Hurter &Driffield
Defined the term optical density
1895
Roentgen
First Radiograph
1896
Carl Schlussner
First glass plate for radiography
1913
Kodak
Film on Cellulose nitrate base
1918
Kodak
Double emulsion film
1933
Dupont
X-ray film with blue base
1942
Pako
Automatic film processor
1960
Dupont
Polyester base introduced
1965
Kodak
Rapid film processing
1972
Kodak
XTL and XV film for therapy
1983
Fuji
Computed radiography system
1994
3M
Dry process laser imaging
Das/Cheng/AAPM/SLC/2001
Film Dosimetry
k Silver halides
v Radiographic film
• Available in various sizes
• Radiation range (mGy-Gy)
• Wet chemical processing
• Strong energy dependence
• Densitometer- any
k Self Developing
v Radiochromic, Gafchromic film
• Relatively smaller film (10x10 cm2)
• Radiation range (Gy-100Gy)
• No processing
• Little energy dependence
• Densitometer- Specialized (light sensitive)
Das/Cheng/AAPM/SLC/2001
Radiochromic Film
Niroomand-Rad et al, Radiochromic film
dosimetry: Recommendations of AAPM
Radiation Therapy Committee Task group
55, Med. Phys. 25(11), 2093-2115, 1998
Das/Cheng/AAPM/SLC/2001
Film
k Base (Cellulose nitrate or Polyester) (typically 200 µm)
k Emulsion (10-20 µm; 2-5 mg/cm3)
v Gelatin (derivative from bone)
Emulsion
Base
v grain (size: 0.1 -3 µm diameter)
u AgBr (cubic crystal with lattice distance of 28 nm
u AgI
u KI
• There are 109-1012 grains/cm2 in x-ray films
k Coating
v Very sensitive which may determine X & Y
direction uniformity
Das/Cheng/AAPM/SLC/2001
Photographic Process
k Silver halides (AgBr, AgCl, AgI)
are sensitive to radiation.
k Radiation event (latent image)
can be magnified by a billion fold
(109 ) with developer.
Das/Cheng/AAPM/SLC/2001
Emulsion of Film/Radiograph
The heart of film is emulsion which contains grains
(crystals of silver halides) in gelatin
Gelatin is suitable due to
v it keeps grains well dispersed
Electron micrograph of grain in gelatin
v it prevents clumping and
sedimentation of grains
v it protects the unexposed grains
from reduction by a developer
v it allows easy processing of
exposed grains
v it is neutral to the grains in
terms of fogging, loss of
sensitivity
Das/Cheng/AAPM/SLC/2001
Film Processing
k Developing [(Metol; methyl-p-aminophenol sulphate or
Phenidone; 1phenol 3pyrazolidone)]
v Converts all Ag+ atoms to Ag. The latent
image Ag + are developed much more
rapidly.
k Stop Bath
v dilute acetic acid stops all reaction and
further development
k Fixer, Hypo (Sodium Thiosulphate)
v it dissolves all undeveloped grains.
k Washing
k Drying
Das/Cheng/AAPM/SLC/2001
Latent image
k The change which causes the grains to be
rendered developable on exposure is
considered to be the formation of latent image.
k It is composed of an aggregate of a few silver
atoms (4-10).
k On average 1000 Ag atoms are formed per xray quantum absorbed in a grain.
k Gurney & Mott provided a clear picture of
latent image
Ref. Herz,
Herz, 1969
Das/Cheng/AAPM/SLC/2001
Grain
X-ray
Silver
Speck
Das/Cheng/AAPM/SLC/2001
Hurter & Driffield (1890)
Optical Density (OD)
OD= log10(Io/I)
OD=log10 (T) where T is transmittance
T=ean
a= average area/grain; n is number of exposed grains/cm2;
N is number of grains/cm2
OD = log (T) = an log10e = 0.4343 an
n/N = aΦ ; where Φ electron fluence
OD = 0.4343 a2NΦ
OD is proportional to Φ and hence dose and
square of grain area.
Das/Cheng/AAPM/SLC/2001
Characteristic curve
H&D Curve
Gradient, gamma, slope = (D2-D1)/Log(E2/E1)
Speed (sensitivity)= 1/Roentgens for OD equal to unity
Optical Density
Latitude (Contrast): range of log exposure to give
an acceptable density range
shoulder
slope
base
Log (exposure)
Das/Cheng/AAPM/SLC/2001
Characteristic curves of various film
4.0
3.5
Optical Density
3.0
Dx
2.5
Rx
2.0
1.5
1.0
0.5
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Log Relative Exposure
Haus et al 1997
Das/Cheng/AAPM/SLC/2001
Characteristics of Commercially Available Radiographic Films
Film
Optimum Dose
Gamma
Latitude
CEA TVS
60
4.4
0.35
CEA TLF
19
3.6
0.4
Agfa Ortho STG2
4.7
3.6
0.4
Agfa HTA
3.5
2.7
0.3
Agfa RP1
1.5
2.6
0.5
Agfa MR3
4.2
2.1
0.6
Du Pont Cronex
4.0
2.6
0.5
Du Pont UV
1.5
1.9
0.5
Fuji MIMA
6.3
2.8
0.5
Fuji HRG
6.2
2.8
0.5
Kodak XV
50
2.9
0.6
Kodak TL
4
2.0
0.5
Kodak XL
1.7
2.0
0.6
Kodak MinR
12.3
1.8
0.4
Kodak TMATG
2.5
2.5
0.4
Kodak Ortho
4.5
2.3
0.4
Konica MGH
5.0
2.7
0.4
Das/Cheng/AAPM/SLC/2001
3D
Tabular
Cubic
Eastman Kodak Company, 2001
Das/Cheng/AAPM/SLC/2001
Kodak, XV
CEA, TVS
Cheng & Das, Med. Phys. 23, 1225, 1996
Das/Cheng/AAPM/SLC/2001
Kodak Min-R
Kodak ECL
Unusual silver halide grain morphologies
Haus,
Haus, 2001
Das/Cheng/AAPM/SLC/2001
Developed grain showing filamentary silver
Das/Cheng/AAPM/SLC/2001
Optimum Optical Density
7.0
Range
6.0
Contrast
5.0
4.0
3.0
2.0
1.0
0
0
1.0
2.0
3.0
4.0
5.0
Optical Density
Das/Cheng/AAPM/SLC/2001
Temperature Dependence of Various Films
1.6
Dupont
Kodak MRM
Fuji
Kodak MR5
Optical Density
1.4
1.2
1.0
0.8
0.6
0.4
84
86
88
90
92
94
96
98
100
102
Developer Temperature (degree F)
Das/Cheng/AAPM/SLC/2001
Change in OD per Degree Processor Temperature
(δOD/δT)
Kodak Films
.10
OD=K0T +K1T2
.08
Min R M
.06
Ektascan HN
.04
T-Mat G/RA
.02
Ektascan IR
0.0
91
92
93
94
95
96
97
98
99
Processor Temperature (degree F)
Bogucki et al, Med.Phys., 24, 581, 1997
Das/Cheng/AAPM/SLC/2001
Change in OD per Degree Processor Temperature
(δOD/δT)
Kodak Films
.10
.08
Min R M
.06
Ektascan HN
.04
T-Mat G/RA
.02
Ektascan IR
0.0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Optical Density
Bogucki et al, Med.Phys., 24, 581, 1997
Das/Cheng/AAPM/SLC/2001
40
Speed
% change
Standard Processing Cycle
20
0
-20
3.6
3.4
Contrast
Average
Gradient
3.2
3.0
2.8
Base
+
Fog
0.22
0.20
0.18
0.16
91 F
33 C
95 F
35 C
99 F
37 C
Temperature
103 F
39 C
Das/Cheng/AAPM/SLC/2001
Log (exposure, dose)
Log (exposure)
(c)
(d)
Exposure, Dose
Optical Density
Sensitometric
(b)
Exposure, Dose
DX
Tx
Calibration
Log (Optical Density)
Optical Density
H&D
(a)
Contrast
Various types of plots for film response
Optical Density
Das/Cheng/AAPM/SLC/2001
Optical Density = OD(D, Dr, E, T, d, FS, Θ)
D = Dose
Dr = Dose rate
E = Energy
T = type of radiation (x-rays, electrons etc)
d = depth of measurement
FS= Field Size
Θ = Orientation: parallel or perpendicular
Das/Cheng/AAPM/SLC/2001
Film Dosimetry in therapy
k 1954, Granke et al; tissue dose studies with 2 MV xrays
k 1969, Dutreix et al; highlights of the problems in film
dosimetry
k 1981, Williamson et al; Provided solution to the film
dosimetry problems
k 1996, Cheng & Das; CEA film, better film for
dosimetry
k 1997, Burch et al & Yeo et al; lateral scatter filtering
Das/Cheng/AAPM/SLC/2001
Optimum properties
k Linear with dose (dose dependence)
k Linear with dose rate (dose rate
independence)
k Radiation type (independent of photon and
electron)
k Energy independent
k Uniformity in x & y (coating artifact)
k Processing condition
v
v
v
Fading
Delayed processing
Atmospheric condition, temperature, humidity
Das/Cheng/AAPM/SLC/2001
Dose Rate Dependence
6
Optical Density
5
4
62R/sec
1100R/sec
3
0.033R/sec
2
1.31R/sec
1
0
10-2
10-1
100
101
102
103
104
105
Exposure, R
Ehrlich,
.Am. 46,801, 1956
Ehrlich, J.Opt.Soc
J.Opt.Soc.Am.
Das/Cheng/AAPM/SLC/2001
Energy Dependence of Radiographic Film
28 keV 44 keV
2.5
79 keV
Net Optical Density
2.0
1.71 MeV
97 keV
1.5
142 keV
1.0
0.5
Kodak XV Film
0
0
10
20
30
40
50
60
70
80
Dose (cGy)
Muench et al, Med.
Med. Phys. 18, 769, 1991
Das/Cheng/AAPM/SLC/2001
Energy response balancing with filter
used in personnel monitoring
100
Relative response
unfiltered
10
1.0
filtered
0.1
10
R.H. Herz,
Herz, The photographic action, 1969
100
1000
Photon Energy, (keV)
Das/Cheng/AAPM/SLC/2001
Energy Dependence of CEA TVS film
5.0
Optical Density
4.0
Gamma rays
X-rays
ODγ = 0.054 Dose
3.0
ODx = 0.047 Dose
CsCs-137
CoCo-60
4 MV
6 MV
10 MV
18 MV
2.0
1.0
0.0
0
20
40
60
80
100
Dose (cGy)
Cheng & Das, Med.
Med. Phys. 23, 1225, 1996
Das/Cheng/AAPM/SLC/2001
Effect of film air gap on depth dose
0.75 mm
0.50
0.25
100
Dose (%)
0
Air gap
Film
50
0
5
Dutreix et al, Ann NY Acad Sci,
Sci, 161, 33, 1969
10
Depth (cm)
Das/Cheng/AAPM/SLC/2001
Effect of film misalignment on depth dose
100
0
2
Dose (%)
5 mm
Air gap
Film
50
0
5
Dutreix et al, Ann NY Acad Sci,
Sci, 161, 33, 1969
10
Depth (cm)
Das/Cheng/AAPM/SLC/2001
Effect of film under alignment on depth dose
100
4
7 mm
Dose (%)
0 mm
Air gap
Film
50
0
5
Dutreix et al, Ann NY Acad Sci,
Sci, 161, 33, 1969
10
Depth (cm)
Das/Cheng/AAPM/SLC/2001
Methods to eliminate problems with Film
k To eliminate air trapped inside jacket, vacuum
packing could be used (CEA film).
k To keep identical position and pressure, RMI
sells film cassettes for dosimetry.
k Use film in water as suggested by van Battum
et al, Radiother.Oncol. 34, 152, 1995
k Special phantom; Bova, Med. Dos. 15, 83, 1990
Das/Cheng/AAPM/SLC/2001
CEA Films (TLF, TVS)
Kodak TL
Optical Density
4
CEA TVS
CEA TLF
Kodak XV
3
2
1
0
0
20
40
60
80
100
120
Dose (cGy)
Cheng & Das, Med.
Med. Phys. 23, 1225, 1996
Das/Cheng/AAPM/SLC/2001
OD Vs Dose
Dose = a+b(OD) +c(OD)2
PDD = [a+b(OD) +c(OD)2]d / [a+b(OD) +c(OD)2]max
OAR=[a+b(OD) +c(OD)2]x / [a+b(OD) +c(OD)2]cax
For limited range and linear film
D = m(OD) then
D2/D1 = OD2/OD1
Das/Cheng/AAPM/SLC/2001
Williamson et al , Med. Phys. 8, 94, 1981
OD depth and field size dependent
OD(D, d) = ODs[1-10-α(d)D]
α(d) = α(dm)[1+β(d-dm)]
β = 0.0182
Co-60
β = 0.0150
4 MV
β = 0.0062
10 MV
Das/Cheng/AAPM/SLC/2001
1.4
Film Density
1.3
1.2
1.1
1.0
0.9
0.8
0
5
10
15
20
25
30
Depth (cm)
Williamson et al , Med.
Med. Phys. 8, 94, 1981
Das/Cheng/AAPM/SLC/2001
120
110
100
90
80
70
60
50
40
Ion Chamber
30
Williamson et al , Med.
Med. Phys. 8, 94, 1981
Film
Das/Cheng/AAPM/SLC/2001
100
95
90
Ion Chamber
80
Film
70
60
50
40
30
Williamson et al , Med.
Med. Phys. 8, 94, 1981
Das/Cheng/AAPM/SLC/2001
Sensitivity of film to scatter
k Depth and field size dependence of OD
k Van Battum et al, film in water
k Burch et al, lead filter
k Yeo et al , Lead filter
k Skyes et al, against filter method
v “although scatter filtering method appears to have
the desired effect it seems intuitively wrong to
introduce a high Z filter in order to make an
inadequate dosimeter, film, behave as if it is water
equivalent”
k Suchowerska et al MC simulation to prove scatter as
a problem
Das/Cheng/AAPM/SLC/2001
Optical Density (Normalized)
Effect of depth and field size on OD
108
106
30x30
104
102
20x20
100
10x10
98
4x4
96
94
0
5
10
15
20
25
Depth (cm)
Van Battum et al , Radiother Oncol,
Oncol, 34, 152, 1995
Das/Cheng/AAPM/SLC/2001
Ion Chamber
100
Relative Dose (%)
Film
80
20x20
60
4x4
10x10
40
20
0
0
2
4
6
8
10
12
14
16
18
20
Depth (cm)
Van Battum et al , Radiother Oncol,
Oncol, 34, 152, 1995
Das/Cheng/AAPM/SLC/2001
Compton Scattering
3
4
2
5
Scattered photon, hν’
6
1
Primary Photon, hν
1
6
2
5
4
3
Scattered electrons
Das/Cheng/AAPM/SLC/2001
Photon
Movable position
t= 0.15, 0.30,
.0.46, 0.76 mm
Parallel film Orientation
X, 6, 12, 19 mm
Film Lead filter
Yeo et al Med. Phys. 24, 1943, 1997
Burch et al, Med. Phys. 24, 775, 1997
Das/Cheng/AAPM/SLC/2001
MC simulation of photon spectrum at various depths
Relative Fluence (%)
10.0
1.5 cm
8.0
10 cm
6.0
30 cm
4.0
2.0
0.0
0
2
4
6
8
Energy (MeV)
Suchowerska et al, Phys. Med.
Med. Biol.
Biol. 44, 1755, 1999
Das/Cheng/AAPM/SLC/2001
200
4 MV, 25x25 cm2
180
0.76 mm Pb
X=0 mm
160
Dose (cGy)
140
120
100
80
X=6 mm
60
X=12 mm
40
Ion chamber
20
0
0
5
10
15
20
25
30
35
40
Depth (cm)
Burch et al, Med. Phys., 24, 775, 1997
Das/Cheng/AAPM/SLC/2001
Effect of Pb filter on depth dose
120
120
4 MV, 6x6
Dose ((ccGy
Gy)
100
cm2
4 MV, 25x25 cm2
100
80
80
60
60
No Pb
No Pb
40
40
Ion Chamber
Ion Chamber
20
20
Film+.46 mm Pb
Film+.46 mm Pb
0
0
0
5
10
15
20
25
Depth (cm)
30
35
40
0
5
10
15
20
25
30
35
40
Depth (cm)
Burch et al, Med. Phys., 24, 775, 1997
Das/Cheng/AAPM/SLC/2001
Sensitometric curves for 15x15 cm2 field
with perpendicular film exposure
3.0
2.5
2.0
1.5
Depth
1.0
0.5g/cm3
4 g/cm3
9 g/cm3
0.0
0
0.5
1.0
2.5
2.0
1.5
Depth
1.0
0.5g/cm3
4 g/cm3
9 g/cm3
0.0
1.5
2.0
0
Dose (Gy
(Gy))
3.0
1.0
3.0
2.5
2.0
2.0
Depth
1.5
Depth
1.0
0.5g/cm3
4 g/cm3
9 g/cm3
0.5g/cm3
g/cm3
1.0
1.5
2.0
45 MV
Kodak
2.5
1.5
0.5
Dose (Gy
(Gy))
18 MV
Kodak
6 MV
Kodak
Net Optical Density
Net Optical Density
3.0
C0-60
Kodak
4
9 g/cm3
0.0
0.0
0
0.5
1.0
1.5
Dose (Gy
(Gy))
2.0
0
0.5
1.0
1.5
2.0
Dose (Gy
(Gy))
Danciu et al, Med.
Med. Phys. 28, 972, 2001
Das/Cheng/AAPM/SLC/2001
Agfa
3.0
3.5
Co-60
Net Optical Density
Net Optical Density
3.5
Parallel
Perpendicular
2.5
2.0
1.5
Kodak
1.0
Parallel
Perpendicular
3.0
2.5
2.0
1.5
Kodak
1.0
0
2
4
6
8
10
12
14
16
0
2
4
Depth (cm)
3.5
Net Optical Density
2.5
2.0
1.5
Kodak
1.0
0
2
4
6
8
8
10
3.5
Parallel
Perpendicular
3.0
6
12
14
16
Depth (cm)
15 MV
Agfa
Net Optical Density
6 MV
Agfa
10
12
14
Depth (cm)
45 MV
3.0
Parallel
Perpendicular
2.5
2.0
Kodak
1.5
1.0
16
0
2
4
6
8
10
12
14
16
Depth (cm)
Danciu et al, Med.
Med. Phys. 28, 972, 2001
Das/Cheng/AAPM/SLC/2001
30
25
Dose (cGy)
20
15
10
6x6, 5 cm depth
25x25, 5 cm depth
6x6, 15 cm depth
25x25, 15 cm depth
5
0
0
0.2
0.4
0.6
0.8
1.0
1.2
Net Optical Density
Sykes et al, Med.Phys., 26, 329, 1999
Das/Cheng/AAPM/SLC/2001
Photons
ew
ew
( e w) n
ew
electrons
ew
ef
(ew)n+(ef)m
P
Perpendicular
ew
P
Parallel
film
# ew<< # ef
ODperpendicular < ODparallel
Das/Cheng/AAPM/SLC/2001
1.12
1.10
Kodak XV Film
Normalized Response
1.08
1.06
1.04
Spectral + air gap
1.02
1.00
.98
Spectral
.96
80
84
82
86
88
90
Gantry Angle
Suchowerska et al. Phy.
Phy. Med.
Med. Biol.
Biol. 46, 1391, 2001
Das/Cheng/AAPM/SLC/2001
Das/Cheng/AAPM/SLC/2001
Das/Cheng/AAPM/SLC/2001
Variation of cone factor, St, using film
1.06
1.04
1.02
Cone Factor (St)
1.00
0.98
0.96
0.94
0.92
V-1
V-2
V-3
V-4
V-5
CEA-1
CEA-2
0.90
0.88
0.86
0.84
0.82
10
15
20
25
30
35
40
Cone Diameter (mm)
Das et al, J. Radiosurg.
Radiosurg. 3, 177, 2000
Das/Cheng/AAPM/SLC/2001
Electron beam film & isodose
Das/Cheng/AAPM/SLC/2001
Densitometer: Device that measures
optical density
k Visual type densitometer (Dobson, Griffith &
Harrison, 1926)
k Photoelectric type
v light densitometer (wide spectrum)
• Standard: McBeth, Xrite, Nuclear Associate etc
• Vidar scanning system
v laser densitometer (single wavelength)
• Lumysis scanning system
Das/Cheng/AAPM/SLC/2001
Incident light
Film
Specular
Diffuse
Double diffuse
Transmitted light
Das/Cheng/AAPM/SLC/2001
Disadvantage of film dosimetry
k Chemical processing (except Gafchromic films)
v OD depends on:
• developer temperature
• drying conditions
k Strong energy dependence (high sensitivity to low
energy photons due to photoelectric interactions in
grains)
k Sensitivity to environments
v
high temperature and humidity crating fading
v
Storage stability
• 0.05-0.1 OD in (6-60mR) among various
films (ref Soleiman et al Med.
Med. Phy.
Phy. 22, 1691, 1995)
k Microbiological growth in gelatin
k Solarization: at extremely higher doses, OD decreases
k Absolute dosimetry is difficult
Das/Cheng/AAPM/SLC/2001
Advantage of film dosimetry
k Unrivaled spatial distribution of dose or energy
imparted.
k Repeated reading of same film: permanent
record
k Wide availability: Kodak, Agfa, Fuji, Dupont,
CEA etc.
k Large area dosimetry: Especially for electron
beam
k Linearity of dose (over a short dose range, OD
can be treated linear with dose for most films)
k Dose rate independence
Das/Cheng/AAPM/SLC/2001
Conclusions
k Film is ideal for spatial dose mapping and relative
dose measurements
k Proper storage is needed
k Proper processing is needed: QA on processor
k Use calibration factor (Sensitometric curve) from
same batch of film
k Note for energy and dose rate dependence
k Use same optical densitometer that has been used
for sensitometric curve
Das/Cheng/AAPM/SLC/2001
-Conclusions
k When exposing film; use proper methods to
eliminate air trapped in the jacket if vacuum packed
films are not available
v Use identical pressure on film (invest in
pressure gauge)
v Use 2-3 degree angle when exposing parallel
film
k Keep film orientation same
v Parallel films gives higher OD than
perpendicular orientation
Das/Cheng/AAPM/SLC/2001
-Conclusions
k Select proper film for a dosimetric application
k Be aware of differences in electron and photon OD
for same dose
k Keep identical exposure, processing and reading
conditions
Das/Cheng/AAPM/SLC/2001
-Conclusions:
Accuracy in film dosimetry
2%
On the same film
3%
Films processed simultaneously
5%
Films processed separately but
identical processing conditions
10%
On films of different batches
Das/Cheng/AAPM/SLC/2001
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