The document discusses the verification of radiotherapy with a focus on minimizing systematic positioning errors through portal control and image comparison. It highlights the significance of both random and systematic errors in patient positioning, emphasizing protocols for correcting setup errors. Additionally, it elaborates on the importance of data collection and systematic monitoring in radiotherapy quality management.

1. IGRT2
How to use image information?
Paweł Kukołowicz

2. Verification of radiotherapy
 In space of dose
 Comparison of prescribed and delivered dose
(dose distribution)
 Eg. In-vivo dosimetry
 In space of location
 Portal control
 image based
2/42

3. Portal control
 To minimize the set-up error
 There are systematic and random errors
in patient positioning
 systematic errors deteriorate the dose delivery
much more than random errors (3x)
 The aim of portal control is to minimize the systematic
error!
3/42

4. Veryfication of geometry
 Geometry
 Comparison of
 reference image and
 treatment field image
Field edges
Center of the beam
4/42

5. Reference image
 Simultor image
5/42

6. Reference image
 Simultor image
6/42

7. Reference image
Digitally Reconstructed Image
 
4
4
1
1 3
3
2
2
(
0
d
d
d
d
e
I
I 








 



7/42

8. DRR
digitally reconstructed radiograph
8/42

9. Quality of DRR
 Depends on
 slice separation
 it is recommended to use 3 mm slice separation
 but
 3 mm slice separation makes contouring very
tedious
 interpolation tools
 these tools must be checked !
9/42

10. Portal images
EPID
Courtesy of B.Heijmen

11. Edges
zero of the second derivative of intensity
11/42

12. Matching of reference and portal images
X
Y
P

12/42

13. Structures to be matched
brain
13/42
AP
lateral

14. Structures to be matched H&N
14/42
AP
lateral

15. Structures to be matched
pelvis
15/42
AP
lateral

16. Correction strategies

17. 0
-10
-5
5
10
0 5 10 15 20 25
Fraction
Systematic and random errors
Single patient, one direction
Mean value = systematic error
Standard deviation = random error
AP direction
Cortesy of B.Heijmen

18. -10
-5
0
5
10
0 5 10 15 20 25
Fraction
patient 2
patient 1
patient 3
Systematic and random errors
For a few patients
mm
Cortesy of B.Heijmen

19. Systematic and random errors – 2D
head
left
Cortesy of B.Heijmen

20. Mean group error
Mx: <mi,x>  0
My: <mi,y>  0
Distribution of systematic errors
x: SD(mi,x)
y: SD(mi,y)
Random group error



i
2
x
,
i
x
N
1



i
2
y
,
i
y
N
1
m1
m3
m2
m4
A few patients
head
left
Systemic and random errors
Group of „similar” patients
Cortesy of B.Heijmen

21. 600 prostate patients
Distribution of errors
AP
0
250
500
750
-10 -5 0 5 10
Random AP error (mm)
N
AP
0
20
40
60
-10 -5 0 5 10
Systematic AP error (mm)
N
Cortesy of B.Heijmen
(De Boer and Heijmen, IJROBP, 2001)

22. On-line protocols
- measure and correct in the same fraction
Off-line protocols
- measure during first few fractions
correct if needed
•
•SAL Shrinking Action Level (Amsterdam)
• NAL No Action Level (Rotterdam)
• eNAL extended NAL
Strategies
22/42

23. 10
-5
0
5
10
15
0 5 15 20 25 30 35
AP displacements (mm)
Prostate cancer patient
Fraction
On-line correction
A few MU
image
Remainder MU
most dose delivered with very small errors:
correction of both systematic
and random errors
23/42

24. Data for on- off-line corrections
 2D
 EPID
 3D
 2 orthogonal iamges
 CT type control
 kV cone beam CT
 MV cone beam CT
 CT on rails
24/42

25. NAL (de Boer and Heijmen, IJROBP, 2001)
 Fraction 1,2, and 3
 set-up a patient according to protocol
 portal control, (mix,miy,miz), i =1 ,2,3
 before 4th fraction
 calculate the systematic error
(mx,mean,my,mean,mz,mean)
 from 4th fraction on
 set-up a patient according to prtocol
 shift couch with –(mx,mean,my,mean,mz,mean)
 irradiate
de Boer and Heijmen, Med. Phys. 2002

26. 10
-5
0
5
10
15
0 5 15 20 25 30 35
Fraction
: initial error after set-up
Residual error
No NAL
No Action Level
The random error remains the same!
: error after correction
Residual error estimate
res  /N

27. (De Boer and Heijmen, IJROBP, 2001)
600 prostate patients
0
20
40
60
-10 -5 0 5 10
Systematic AP error (mm)
N
With no correction
in
0
20
40
60
80
100
-10 -5 0 5 10
Systematic AP error (mm)
N
With NAL
res
NAL results

28. (1) De Boer et al. 2002
(2) Kaatee et al. 2002
(3) De Boer et al. 2003
(4) De Boer et al. 2004
How precise may be radiotherapy?
Residual (after NAL) bony anatomy
displacements [mm]:
Prostate
(1)
Cervix
(2)
LR CC AP
 1.7 1.5 1.6
res 1.1 1.1 1.1
 2.6 2.9 2.7
res 1.2 1.7 1.6
Lung
(3)  2.0 2.4 2.4
res 1.3 0.6 1.2
head & neck
(4)  1.6 1.4
res 1.1 1.2
1.6
1.0
28/42

29. Why on-line verification is not
recommended?
 Because
 It is time consuming.
 Systemtic error influence on the margin three
times more than random error.
 However,
 It might be resonble if
 random error is large
 very high accuracy is needed.
29/42

30. Set Up Margin
Internal Margin
Margins
 Set-up margin
 to compensate set-up errors
 errors measured with
respect to external
coordinate system (laser
system)
 Internal margin
 to compensate movement of
the target caused by
physiology (eg. breathing)
 errors measured with
respect to internal anatomy
coordinate system
( eg. pubis symphisis)
30/42

31.    2
int
2
ernal
up
set
tot 



 
   2
int
2
ernal
up
set
tot 

 
 
How to add margins?
 If set-up and internal errors may be treated
as not correlated, than we add errors in
quadrature
systematic
random
31/42

32. tot
tot
M 




 7
,
0
2
Margins
 Two formulas
tot
tot
M 




 7
,
0
5
,
2
To cover the CTV for 90% of the
patients with the 95%
isodose (analytical solution).
Herk Red, 47: 1121 - 1135, 2000
Margin size which ensures at least
95% dose is delivered to (on
average) 99% of the CTV.
Stroom, Red, 43: 905-919,1999
32/42

33. Implementation of geometry
control
 The most important task in radiotherapy
department
 „Lens of quality”
 This can’t be an incidental action
 This must be a program for the systematic
monitoring and evaluation of the various aspects
of radiotherapy quality
33/42

34. Data
 Must be collected and regurarly analysed
 feed back is a must
 in our department ones a year all results are presented
to doctors, radiation technologiests and physicists
 big errors must be analysed as quickly as possible
 conclusions must be drawn
 group systematic errors (mean of means) play
an important role in general evaluation of
the quality of work and quality of equipment
 group systematic error should not be different from zero
34/42

35. Breathing and related problems
35/42

36. CT for planning
 Artefacts
36/42
without breathing control with breathing control

37. Changes of GTV position
37/42
In relations to bronchial tree

38. CT for planning
 With breathing control
38/42
RPM system

39. Pattern of breathing
39/42
Patient A
Patient B

40. Deep-inspiration breath hold technique
 DIBH
 for patients with left breast cancer
 for some of tchem (they have to inhale and keep inhale
for some time 10 – 15 sec)
40/42

41. DIBH - advantages
41/42

42. Thank you for your attention!
p.kukolowicz@zfm.coi.pl