This document summarizes the work completed during a medical physics rotation focused on imaging for treatment planning and verification. Key tasks included: - Performing quality assurance tests on the electronic portal imaging device (EPID) including measurements of image uniformity, signal-to-noise ratio, and modulation transfer function at varying imaging parameters. - Analyzing contrast-to-noise ratio, signal-to-noise ratio, and dose dependence using phantoms imaged with the EPID. - Validating calculations of the EPID's modulation transfer function. - Ensuring proper alignment of the EPID with the radiation isocenter using reticule alignment tests at different gantry angles. - Observing clinical treatments for sites

1. Imaging
for
Planning
and
Treatment
Verifica4on
(Rota&on
7)
Mentor:
Ryan
Flynn,
Ph.D.
(12/16/09
–
01/15/10)
By
Vibha
Chaswal,
Ph.D.
2/24/14
1

2. Syllabus
PHEW!!!!!!!
2/24/14
2

3. EPID
QA
• Uniformity
versus
thickness
(across
flat-­‐field
images)
• SNR
versus
thickness
of
solid
water
• MTF
• CNR
• SNR
• EPID’s
alignment
with
gantry
isocenter
2/24/14
3

4. Addi4onal
•
•
•
•
•
CNR
vs
Thickness
vs
Dose
Effect
of
filtraRon
on
images
MTF
calculaRon
validaRon
Contrast
calculaRons
for
Air
&
Bone
in
water
DidacRc
2/24/14
4

5. EPID
QA:
Image
Uniformity
vs
Thickness
2/24/14
5

6. 1
3
5
4
2
Uniformity
(Normalized
mean
PV
in
an
ROI)
Image
Uniformity
vs
Solid
Water
Thickness
1.010
0.980
0.950
ROI_1
(top)
ROI_2
(boaom)
ROI_3
(right)
ROI_4
(leb)
ROI_5
(center)
0.920
0.890
0.860
0.830
0.800
0
2/24/14
5
10
15
20
Solid
Water
Thickness
(cm)
25
30
35
6

7. EPID
QA:
Signal-­‐to-­‐Noise
raRo
vs
Thickness
2/24/14
7

8. 2/24/14
8

9. Signal-­‐to-­‐Noise
Ra4o
vs
Thickness
of
SW
slab
300
250
SNR
200
150
100
50
0
0
5
10
15
20
25
30
35
Sold
Water
Thickness
(cm)
2/24/14
9

10. EPID
QA:
Imaging
Parameters
(SNR,
CNR,
MTF,
Dose
dependence)
2/24/14
10

11. Material
Physical
density
(g/cm3)
PVC
1.00
Al
2.6
Pb
11.34
0.23 lp/mm
5 mm lead
15 mm PVC
QC - 3V Phantom s/n 104
0.43 lp/mm
15 mm Al
11 mm Pb
0.76 lp/mm
0.2 lp/mm
0.1 lp/mm
7.5 mm Pb
2/24/14
11

12. MTF Calculation
Validation
2/24/14
Droege R.T, Morin R. L, ‘A practical method to measure MTF of scanners’, Med. Phys. 9(5), 1982
12

13. EPID spatial resolution: MTF Calculation
lp/mm
0.1
663.45
0.2
1342.163
0.23
2066.66
0.43
MTF
measured
using
QC-­‐3V
phantom
Std
Dev
2315.17
0.76
2825.81
1.20
1.00
MTF
0.80
0.60
0.40
0.20
0.00
0
2/24/14
0.1
0.2
0.3
0.4
0.5
line-­‐pairs/mm
(lp/mm)
0.6
0.7
0.8
13

14. Imaging
Parameters:
SNR
Region
Physical
density
(g/
cm3)
Depth
(cm)
Radiological
Path-­‐
length
(g/cm2)
1
(Pb)
11.34
0.75
8.505
2
(PVC)
1
1.5
1.5
3
(Pb)
11.34
0.5
5.67
4
(Al)
2.6
1.5
3.9
5
(Pb)
11.34
1.1
12.474
6
(Pb)
11.34
0.75
8.505
SNR
versus
Radiological
Path-­‐length
SNR
(standard
devia4on)
140
120
100
80
60
40
20
0
0
2/24/14
2
4
6
8
10
Radiological
pathlength
(g/cm2)
12
14
14

15. SNR
analysis
ROIs
1
&
6
ROI 1
2/24/14
ROI 6
15

16. EPID
QA:
CNR
vs
Thickness
vs
Dose
10-QC-10 1MU
2MU
3MU
(QC-3V as tumor
inside varying solid
water thickness
patients)
10 cm
20-QC-10 1MU
2MU
3MU
30-QC-10 1MU
2MU
3MU
20 cm
30 cm
2/24/14
16

17. CNR
of
QC-­‐3
phantom
vs
Radiological
Thickness
(for
different
doses
and
solid
water
thicknesses)
60.00
Contrast-­‐to-­‐Noise
Ra4o
w.r.t.
15mm
PVC
1 MU
2 MU
50.00
10 cm
3 MU
40.00
30.00
20 cm
20.00
30
cm
10.00
-­‐
0
2
4
6
8
10
12
14
Radiological
Thickness
(g/cm2)
2/24/14
17

18. EDPI QA:
EPID
Alignment
(Oncor A)
Gantry 0 degree
Gantry 90 degree
2/24/14
18
Gantry 270 degree,
Gantry 180 degree

19. Fig 4(c): Gantry 180 degree, distance measurements
between x-retic and e-retic.
2/24/14
Fig 4(d): Gantry 180 degree, distance measurements
between x-retic and e-retic at the central ISIS sphere
region that coincides with radiation isocenter; note that
distance between x-retic and e-retic is 2.3mm,
which is more than the tolerance value of 2mm.
Hence, EPID is not aligned within specifications at
19
Gantry angle 180-degrees.

20. Fig 4(e): Gantry 180 degree, distance measurements
between x-retic and center of pinhole of ISIS.
Fig 4(f): Gantry 180 degree, distance measurements
between e-retic and center of pinhole of ISIS.
2/24/14
20

21. Clinical
ObservaRon
•
•
•
•
•
•
Whole
brain
x
1
Head
and
neck
x
2
(MVCBCT)
Pelvis
x
1
(portal)
x
3
(MVCBCT)
Thoracic
x
1
(portal)
x
2
(MVCBCT)
Extra-­‐cranial
lung
x
1
(MVCBCT)
Supine
Breast
x
1
(portal)
2/24/14
21

22. Treatment Verification: MVCBCT
Extra-Cranial Lung
Head & Neck
2/24/14
Pelvic
22

23. Treatment Verification: Portal Imaging
Reference DRR Right Lat
Treatment day Right lat portal image
Whole Brain DRR
Registered DRR and portal image
Pelvic DRR
Reference Planning PA DRR
2/24/14
Treatment day PA portal image
Registered PA images
23

24. Thoracic
DRR
Reference Planning AP setup DRR
Reference Planning Left Anterior Oblique field DRR at
Gantry 45-deg
Reference Planning field DRR Left Lat Gantry 90-deg
Reference Planning Right Anterior Oblique field DRR
2/24/14
at Gantry 344.9-deg
Treatment day AP double exposure portal image
Treatment day Left Anterior Oblique field portal
image at Gantry 45-deg
Registered AP DRR and portal images
Registered Left Anterior Oblique DRR and portal
images
Treatment day Left Lat field portal image at Gantry 90- Registered Left Lat DRR and portal images
deg
Treatment day Right Anterior Oblique field
portal image at Gantry 344.9-deg
Registered Right Anterior Oblique DRR and portal
24
images

25. THANK
YOU!!!!!
2/24/14
25