1 MAYO CLINIC Optimization of Internal Margin to Account for Respiratory Motion YILDIRIM D. MUTAF, PhD DEBRA H. BRINKMANN, PhD July 2007 Minneapolis, AAPM 2007 MAYO CLINIC Y. D. Mutaf, PhD SM – Internal Target Volume (ITV) = CTV + IM Introduction • Respiratory motion is a source of dosimetric uncertainty • ICRU 62 recommends use of Internal Margin (IM) – …to compensate for expected physiological movements, variations in shape, size and position of the CTV during therapy… • The aim of this study is to find – Optimum Internal Margin ITV PTV IM IM SM – Planning Target Volume (PTV) = ITV + SM July 2007 Minneapolis, AAPM 2007 MAYO CLINIC Y. D. Mutaf, PhD Motion Imaging • 4DCT or Fluoroscopy – Enables identification of the target motion – Ensures only the geometric coverage i.e. where target IS – Doesn’t provide direct information on the dosimetric effects due to motion i.e. what dose target GETS • Determining IM from imaging studies alone could be overly-conservative – Are smaller margins sufficient? Possible implications regarding dose escalation July 2007 Minneapolis, AAPM 2007 MAYO CLINIC Y. D. Mutaf, PhD Part I – Phantom Study • Phantom Simulation – Rectangular body with 3.0cm radius target (TV) • Treatment Plans – 4 coplanar, orthogonal fields treat TV – Conformal in the coronal plane plane of motion – Plans with different IM and SM added linearly Coronal View
4
Embed
MAYOCLINIC I ntr oduc i · MAYOCLINIC Y. D. Mutaf, PhD SM – Internal Target Volume (ITV) = CTV + IM I ntr oduc i • Respiratory motion is a source of dosimetric uncertainty •
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1
MAYO CLINIC
Optimi zatio nof Int ernal Margin
t o Account for Respi rat ory Motion
YIL DI RIM D. MUTAF, PhDDEBRA H. BRINKMANN, PhD
July 2007 Minneapolis, AAPM 2007
MAYO CLINIC
Y. D. Mutaf, PhD
SM
– Internal Target Volume (ITV) = CTV + IM
I ntrod uc tion
• Respiratory motion is a source of dosimetric uncertainty
• ICRU 62 recommends use of Internal Margin (IM)– …to compensate for expected
physiological movements, variations in shape, size and position of the CTV during therapy…
• The aim of this study is to find – Optimum Internal Margin
ITV
PTV
IM
IM
SM
– Planning Target Volume (PTV) = ITV + SM
July 2007 Minneapolis, AAPM 2007
MAYO CLINIC
Y. D. Mutaf, PhD
Motion I magin g
• 4DCT or Fluoroscopy – Enables identification of the target motion– Ensures only the geometric coverage
� i.e. where target IS
– Doesn’t provide direct information on the dosimetric effects due to motion� i.e. what dose target GETS
• Determining IM from imaging studies alone could be overly-conservative– Are smaller margins sufficient?
�Possible implications regarding dose escalation
July 2007 Minneapolis, AAPM 2007
MAYO CLINIC
Y. D. Mutaf, PhD
Part I – Phantom Study
• Phantom Simulation– Rectangular body with
3.0cm radius target (TV)
• Treatment Plans– 4 coplanar, orthogonal
fields treat TV – Conformal in the coronal
plane�plane of motion
– Plans with different IM and SM added linearly
Coronal View
2
July 2007 Minneapolis, AAPM 2007
MAYO CLINIC
Y. D. Mutaf, PhD
Sim ul ation Method
• Extract dose from the coronal plane at center of the target
• Where location of target change due to – Setup Uncertainties
through 100 fractions– Respiration motion in
each fraction
2)/(cos)( 04
0 ATtAtA −= π)/(cos)( 4
0 TtAtA π=Lujan et.al., MedPhys 99
Coronal Plane
Head
Foot
Asy
mm
etri
c(c
m) S
ymm
etric(cm
)
July 2007 Minneapolis, AAPM 2007
MAYO CLINIC
Y. D. Mutaf, PhD
Setup Uncertainti es and Resp iration
Appropriate setup margins are applied
MSM σ⋅= 7.0van Herk et.al., IJROBP 2000
July 2007 Minneapolis, AAPM 2007
MAYO CLINIC
Y. D. Mutaf, PhD
Comparison of Plans
• REFERENCE (or STATIC) Plan– No respiration motion (without IM) – With setup uncertainties (added SM)
� σM = 2, 4 and 6 mm• MOTION Plan
– With respiration motion (added IM)
� 5, 10, 15, 20 mm p2p motion– With setup uncertainties (added SM)
No Respiration (Reference)
R = 30 mm
10mm p2p Amp IM = 0 mm
R = 30 mm
July 2007 Minneapolis, AAPM 2007
MAYO CLINIC
Y. D. Mutaf, PhD
Compariso n of Plans
( )2
1%100
%95
21
−= ∫ dVDD
NF static
imotioni
DVH Based Cost Function
a
i
aiiDvgEUD
1
= ∑
Ratio of gEUDs
A. Niemierko Med. Phys. 97
3
July 2007 Minneapolis, AAPM 2007
MAYO CLINIC
Y. D. Mutaf, PhD
Optimu m Inter nal Margin
• Optimum dosimetric coverage is obtained with IM smaller than full motion amplitude– Symmetric margins
• Asymmetric margins – Using the end of exhale
images for treatment planning
– Larger but one sided margins• Observed to be independent of
the random setup uncertainties – Effect of systematic
uncertainties is not yet investigated
July 2007 Minneapolis, AAPM 2007
MAYO CLINIC
Y. D. Mutaf, PhD
Part II – Patient Study
Fluence simulation requires constant external contour along the motion direction
July 2007 Minneapolis, AAPM 2007
MAYO CLINIC
Y. D. Mutaf, PhD
Patien t Cohor t
• 12 total patients – 10 lung, 2 pancreas– TV range 7 to 210cc
• Treatment plan characteristics
– 3 to 6 beams� All coplanar beams� 6 or 10 MV
– Conformal in the direction of motion
• Setup Uncertainties are not simulated– No setup margins (SM)
• Only 10mm p2p symmetric motion studied
1 2 3 4
5 6 7 8
9 10 11 12
Note: Drawings not to scale.Targets are indexed in the order of increasing volume.
July 2007 Minneapolis, AAPM 2007
MAYO CLINIC
Y. D. Mutaf, PhD
Compariso n of Plans
Patien t #610 mm Mot ion
TV = 51.3 cc
( )2
1%100
%95
21
−= ∫ dVDD
NF static
imotioni
DVH Based Cost Function
Patient #610 mm Motion
TV = 51.3 cc
Ratio of gEUDs
a
i
aiiDvgEUD
1
= ∑A. Niemierko Med. Phys. 97
4
July 2007 Minneapolis, AAPM 2007
MAYO CLINIC
Y. D. Mutaf, PhD
Optimu m Inter nal Margin
Target Coverage (avg of 12 patients)– Minimum dose is 0.2% colder
� TV receiving colder dose is 0.2%– TV receiving 100% dose (V100) is
0.8% larger– Relative gEUD is always ≥ 100%
Target Conformity (~ Normal Tissue Sparing)
– 17% less irradiated volume receiving 100% dose
– 10% less irradiated volume receiving 50% dose
Distribution of OptimumInternal Margins
50% and 100%RTOG Conformit y Indices (CI)Relative CI ≡ CImotion / CIstatic
July 2007 Minneapolis, AAPM 2007
MAYO CLINIC
Y. D. Mutaf, PhD
Concl usions
• Optimum Internal Margin (IM) was always smaller than full motion amplitude – Example: ±1.5mm IM for 10mm p2p motion
• Standard practice of target expansion based on imaging alone (e.g. 4DCT) is overly conservative– “Where Target IS” vs “What Target GETS”
• As compared to full motion amplitude, optimum internal margin provided– Similar target coverage– Improved target conformity