Comparison of film sensitivity with epid for different doses.

Presented by- Jyoti Bisht

Pushpanjali Crosslay Hospital Galaxy
Cancer Institute

 Staff & Facilities available in the hospital :
 Two Linacs : Varian 600C (6MV)and
Varian IX(6 &15 MV)
 Treatment Planing System : Eclipse (AAA)
 HDR Brachytherapy :Nucletron
MicroSelectron
 Treatment Planing System : Oncentra
 Imaging Modelities : MRI,CT

Pushpanjali Crosslay Hospital
Galaxy Cancer Institute

 AIM- Comparison of Film Sensitivity With
EPID For Different Doses.
 What we are doing?
 We have taken four patient’s plan of small and irregular target in
Head & Neck area(Highly modulated).
 For all of four plans we are delivering 200 cGy and 800 cGy.

 Study:
 Effect on the GAFCROMATIC film sensitivity with increasing
dose(MU)and comparing it with portal image fluence getting
from EPID.
 Film orientation, MU dependency.


 Material needed for this purpose:
Test plan :Four plans generated From
TPS(complicated & highly
modulated plans)
GAFCROMIC EBT2 :1cGy -1000cGy
Phantom :RW3 slab phantom
Point ion chamber :0.125cc
Electrometer :UNIDOS E
Varian LINAC :Varian 600C EPID of
( 0.768*0.384)
 Scanner :Microtek ScanMarker
1000XL (0.34to 0.042ps)


For this measurement we are using GAFCHROMIC EBT
film. Why GAFCROMATIC EBT2 film ???
 It has the Zeff =6.84 and when
compared to water ,Zeff=7.3
provides a comparatively good
match.
 Its Energy dependence is less
than 10% over 60kvp to 6MV.
 Having high spatial resolution
(100um).
 Active layer incorporate yellow
Marker dye.
 Real time development.

 Response OF GAFCROMATIC EBT2 film
depends:
 The film response in lower MU is non-linear.
 Energy spectrum of the LINAC.
 Characteristics of scanner or densitometer.
 Elapsed time between exposure and measurement.


 Electronic Portal Imaging Device (EPID):
 Used for patient’s position
verification in IMRT/IGRT
cases.
 Mounted on gantry head.
aSi-500 portal imager has
following parts-
 Image detection unit.
 Image acquisition system.

 A Portal Vision Workstation.

Sensitive area of panel : 512*384
Active area of EPID :22cm*20cm

Pixel size Crosslay Hospital Galaxy 0.384
:0.768* EPID Portal Dosimeter
Pushpanjali
Cancer Institute

 EPID calibration :

Dark Image :from
aSi 500 without
any exposure

Flood Image: By
exposing whole imaging
cassette to an open field

CI=[RI-DF]/FF*kff

 EPID Characteristics:
 Linearity :EPID response is linear over a large range .
 Dose rate dependency in EPID is very less (2% for
300MU/min).
 For smaller fields EPID response is linear .


 Film Calibration(Absolute Dose Measurement ):
Chamber :0.125cc point
chamber
Ref point :on central axis at
of Cham the center of
cavity
Phantom :RW3 slab phan
SCD : 95cm
Dose rate :320 MU/min
Temperature :20.7C
Pressure :976 mbar
Energy : 6MV
Electrometer :UNIDOS E

Cancer Institute

 Set Up: For Film Calibration
Set up :SAD
Phantom :RW3 slab
phantom
EBT2 film :3cm*3cm
Backscatter :19.5cm
C SSD :100cm
V
SFD :95cm
Field Size :10cm*10cm
Dose Rate :320 MU/min


 Film Calibration :
 Set the 0.125cc chamber at 95cm in RW3 slab
phantom.
 Expose with the same MU are for which we are
exposing the film for calibration.
 Note down the readings in terms of dose.
 This point measurement will help us to know the
central point dose in the film.
 Now expose the films with the same MU given to the
chamber.
 All films should be scanned after 24 hours.


 Film Calibration Curve :
Delivered MU Dose
25 0.2376
50 0.4725
75 0.7071
100 0.942
200 1.883
300 2.824
400 3.768
500 4.711
600 5.652
700 6.595
800 7.535
900 8.478
1000 9.420
Pushpanjali Crosslay Hospital OD vs Dose graph

Patient -1(IMRT QA)
Machine-600C Case:Head &Neck Chamber :0.125cc SFD :100cm

SSD :95cm SCD:100cm kcorr :0.995 Phantom :RW3 Slab Phantom

Gamma>1 in(%)
Meas Cal
Fields % Dev DTA DTA Film Response
dose(Gy) Dose(Gy)
:3mm :4mm
F1 0.264 0.267 3.105 1.197
Delivered dose 2Gy Delivered dose 8Gy
F2 0.322 0.334 2.493 1.073
F3 0.319 0.325 4.156 0.749 Total Total
13761.00 11938.00
F4 0.335 0.342 1.249 0.600 Points Points

F5 0.308 0.309 1.641 0.219 Passing Passing
13312.00 11902.00
Points Points
F6 0.497 0.508 1.897 0.798

Passing % 96.740 Passing % 99.700
SUM 2.046 2.085 -1.871

 X and Y profiles in EPID Gamma Evaluation:

Field1 DTA:3mm DTA:4mm
DD:3% DD:4%
Passing Criteria 95.844 99.251

 For patient -1 (2Gy)

DTA 4mm
DD 4%
Total Points 13761

Passing 13312
Points
Passing % 96.74

 For patient -1 (8Gy)

DTA 4mm
DD 4%
Total Points 11938

Passing 11902
Points
Passing % 99.7
Cancer Institute

Patient -2(IMRT QA)
Machine-600C Case:Head &Neck Chamber :0.125cc kcorr :0.995

SSD :95cm SCD:100cm SFD :100cm Phantom :RW3 Slab Phantom

Gamma>1
Meas Cal in(%)
Fields % Dev Film Response
dose(Gy) Dose(Gy) DTA DTA
:3mm :4mm
F1 0.383 0.390 1.454 0.250 Delivered dose
Delivered dose 2Gy
F2 0.470 0.475 3.511 0.427 8Gy
F3 0.576 0.582 1.214 0.467 Total Total
16503.00 18574.00
F4 0.304 0.312 1.472 0.682 Points Points

F5 0.5181 0.523 0.435 0.111 Passing 15866.00
Passing
18019.00
Points Points
SUM 2.251 2.281 1.31 Passing Passing 97.010
95.480
Galaxy Cancer Institute % %


DD:3% DD:4%

For patient -2 (2Gy)

DTA 5mm
DD 5%
Total Points 16503

Passing 15866
Points
Passing % 95.48

For patient-2 (8Gy)

DTA 5mm
DD 5%
Total Points 18574

Passing Points 18019

Passing % 97.01
Cancer Institute

Patient -3(IMRT QA)
Machine-600C Case:Head &Neck Chamber :0.125cc SFD :100cm
SSD :95cm SCD:100cm kcorr :0.995 Phantom :RW3 Slab Phantom
Gamma>1 in(%)
Field Meas Cal
% Dev DTA :3mm DTA :4mm Film Response
s dose(Gy) Dose(Gy)
DD:3% DD :4%
F1 0.123 0.131 12.260 4.154
Delivered dose 2Gy Delivered dose 8Gy
F2 0.210 0.215 3.919 1.187
F3 0.083 0.086 3.168 1.590
Total Total
F4 0.065 0.066 7.710 2.310 26182.00 22698.00
Points Points
F5 0.358 0.381 0.356 0.071
F6 0.031 0.033 4.715 2.802
Passing Passing
F7 0.323 0.346 0.470 0.022 24999.00 18749.00
Points Points
F8 0.085 0.077 0.374 0.000
F9 0.201 0.208 2.445 0.178
Passing
F10 0.375 0.397 0.461 0.076 95.480 Passing % 82.600
%
SUM 1.854 Cancer Institute
Galaxy 1.940 -4.448


DD:3% DD:4%

 For Patient-3 (2Gy)

TG profile

DTA 5mm
DD 5%
Total Points 26182

Passing 24999
Points
Passing % 95.52
Cancer Institute

 For Patient-3 (8Gy)

DTA 5mm
DD 5%
Total Points 22698

Passing 18749
Points
Passing % 82.6

 Analysis :

 Film is commercially a good tool for IMRT QA cross
check with respect to EPID.
 Film sensitivity is good in high dose region(>200MU).
 If we change the orientation of the film then drastic
change in the measured values because of the
construction of the film and the readout orientation
while calibration of the film.
 In EPID due to saturation in high dose we can’t get
good response.


 Conclusion :
 In film due to high spatial resolution we are getting
reliable results.
 Getting good results in high dose region(>200MU).
 In routine measurements EPID is convenient in
comparison to the Film.
 Film set-up is easy but evaluation takes time and
requires very much alertness.
 Film is direction dependent and should be careful while
handling, cutting and scanning.
 In low dose region film response is not linear.


 Special thanks to:
 Dr. Sandeep Agrawal : Head of Galaxy Cancer
Institute
 Mr. Venketeshan K. : Head Medical Physicist
 Mr. Bala subhramanaym : Medical Physicist
 Mr. Swaminathan T. : Medical Physicist

Cancer Institute

Thank you

Comparison of film sensitivity with epid for different doses.

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