Respiratory gating window and internal motion margins to accommodate the fluctuation of exhalation l

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Respiratory gating window and internal motion
margins to accommodate the fluctuation of
exhalation levels during proton beam therapy for
liver tumor
Y.Asada, H.Fuji M.D., M.Numano, T.Saida
I.Kawashima, A.Toi, H.Yamashita Ph.D., E.Urakabe
Ph.D. S.Murayama M.D.
Shizuoka Cancer Center , Proton therapy division
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Respiratory gating treatment system for proton
beam therapy
Infrared range meter
Synchrotron
Inhale
Gate open signal
Abdominal wall motion signal (AWM)
Exhale
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Trading offTreatment time vs. Preciseness
Abdominal wall motion
Long treatment time
Short treatment time
Short duty cycle
Long duty cycle
Large gating window
Small gating window
Large residual motion
Small residual motion
Robust treatment
Precise treatment
Tumor motion by respiration
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Abdominal wall motion (AWM) signal
Inhale
Amplitude of abdominal wall motion
Exhale
Level of abdominal wall at the end of exhalation
(LAE)
The end of exhalation is supposed to be
appropriate for duty cycle. However, the
respiratory level at the end of exhalation is not
sufficiently reproducible.
More reproducible Less tumor motion than other
phase of respiration
Long duty cycle and less residual motion
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Objectives

• To define adequate respiratory gating windows and
  internal motion margins to accommodate the
  fluctuation of the end of exhalation during
  proton beam treatment

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Patients Characteristics
Median age
69 (51- 82)
Gender
F
15
M
4
ECOG PS
0
9
1
9
2
1
Disease
Hepatocellular carcinoma
18
1
Metastatic tumor
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Methods
Retrospective analysis of patients introduced
respiratory gating proton beam therapy for liver
tumor from November 2005 to April 2006.
Dataset abdominal wall motion from respiratory
gating system
Traces of the fiducial marker motion implanted
close to the tumor during obtaining verification
X-ray picture
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Abdominal wall motion (AWM) dataset sampling

• Whole AWM dataset during a treatment session was
  divided into 20 parts equally.
• The peak levels of peak of inhalation (LPI) and
  end of exhalation (LEE) at the beginning of each
  part were measured.
• The averages of LPI and LEE calculated.
• The averages of LPI and LEE were defined as 100
  and 0 of amplitude of AWM, respectively.

100
Average level of peak of inhalation
0
Average level of end of exhalation
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Tumor motion monitoring
The positions of fiducial marker on AP and
lateral views of X-ray picture were traced The
trace data from two images were combined to show
3-D motion of the tumor by respiration
Fiducial marker
AP view
Lateral view
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Results
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Fluctuation of LAE
LAE Fluctuation 95 Confidential Interval (CI)
Maximum LAE Fluctuation
Average 10.9 SD 6.5
Exhalation
Inhalation
()
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Tumor motions by respiration
Residual motion corresponding LAE fluctuation
95 CI
Length of tumor motion by respiration
Average 1.80mm SD 1.61mm
Average 16.7mm SD 10.2mm
(mm)
(mm)
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Summary
Mean
Minimum
Maximum
SD
LAE fluctuation CI
4.2
25.1
10.9
6.5
Length of tumor motion by respiration
16.7mm
10.24mm
5.1mm
51.5mm
Residual motion corresponding with LAE
fluctuation CI
0.47mm
6.48mm
1.80mm
1.61mm
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Conclusion

• Fluctuation of LAE (level of end of exhalation)
  varied with each patient and was as large as to
  be considered to define efficient gating windows.
• Tracks of tumor also varied each patients.
• Residual motions estimated by LAE fluctuation and
  track of tumor were required to be considered for
  internal target volume definition in respiratory
  gating treatment.
• These variations of respiratory motion parameters
  encourage us to individualize the gating windows
  and the internal target volumes with LAE
  fluctuation evaluations.