4D-MRI for Radiotherapy of moving Tumours:Latest developments, comparison to 4D-CT
J. Biederer Vancouver, August 2, 2011
J. Biederer Indications for Radiotherapy of Lung CancerO
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- stage III
- Pancoast tumour + stages I-II if surgery not possible
before surgery
- Pancoast tumour
after surgery
- pN2
- after incomplete resection (R1, R2)
J. Biederer
Improvements in LC radiotherapy
Increased demand of
appropriate multi-modality diagnostic imaging
Improvements in Lung Cancer Radiotherapy
J. Biederer
static CT
plan underassumption of
tu. displacement
4D-CT
detectionof
tu. displacement
plan inknowledge of
tu. displacement
4D-CT 4D-CT
Beam ON
gatingfor
tu. position
LC RT Planning: Motion Adapted RT
J. Biederer
ex.
in.
LC RT Planning: Motion Adapted RT
PTV2 w/ motion compensation
PTV1 w/ ideal motion adaption
PTV2 - PTV1= IPPT
individual potential to preserve tissue
J. Biederer
step-by-step cine CT
Capturing respiratory Motion with CT
slow helical CT
prospective
techniques
retrospective
techniqueslow pitch helical CT
external signal(belt)
integratingiGTV over time
external signal(belt)
insp./exp. CTbreathing commandor external trigger
J. Biederer Capturing RM with CT: insp./exp. ScanningH
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, Ex
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2010
, Ki
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standard CT
static breathing
Flash-CT Flash-CT
(trigger ex.)
Flash-CT
(trigger in.)breathing
J. Biederer
ZZ
Detector widthDetector widthExp InspExp Insp
Step-by-Step (e.g. GE)Step-by-Step (e.g. GE)
Capturing RM with CT: Step by step Cine CT
J. Biederer
Advantages
robust against changes of respiration frequency
no overranging at z-limits
respiration triggering easy
Disadvantages
Z-coverage incomplete w. changes of respiration depth
every single position waists 180° rotation
Capturing RM with CT: Step by step Cine CT
J. Biederer
ZZ
Low Pitch helical CT (e.g. Siemens, Toshiba)Low Pitch helical CT (e.g. Siemens, Toshiba)
Exp InspExp Insp
Capturing RM w/ CT: Low Pitch helical 4D-CT
J. Biederer
Advantages
more effective use of projections
changes in respiration frequency better tolerated
Disadvantages
Z-coverage incomplete with changes of respiration depth
(use lowest pitch – cave dose and imaging time)
overranging at z-limits
Capturing RM w/ CT: Low Pitch helical 4D-CT
J. Biederer 4D MRI as an Alternative?
- if soft tissue contrast in CT is poor (e.g. liver)
- if minimizing radiation dose is important
- if multiple respiratory cycles have to be covered
J. Biederer
fast/ultrafasttime resolved displayof respiratory motion
2D + t
3D + t = 4D
slow acquisition integratingiGTV over time
triggeredacquisition
prospective
techniques
by external signal
MIP reconstruction
Capturing respiratory Motion with MRI
by internal signal(“self-navigated“)
retrospective
techniques
reassorting/binningoversampled data
“navigator“ technique
external signal (belt)
J. Biederer Capturing RM with MRI: Integrating iGTV/t
- acquisition of 2D-SS-GRE (TrueFISP) at 3/s
- MIP of non-assorted images (“slice stacking“)
- volume/area agree with step-by-step 4D-CT
Adamson et al., Med Phys 2010;37:5914–5920
J. Biederer
Hypothesis: Robustness against respiratory motion …
… is achieved with the same technology that would produce
4D image data correlated with respiratory motion!
Capturing respiratory Motion with MRI
J. Biederer
A hybrid breathhold/Navigator-triggered approach
Hintze C, … Biederer J, … et al. RöFo 2010;182: 45-52
Dynamic CE MRI: Navigator Motion Correction
J. Biederer
3D-flash (GRE) retrospective(G. Remmert, DKFZ)
Capturing RM with MRI: Retrospective Binning
Remmert et al., Phys Med Biol 2007;18:N401-N405
J. Biederer
“Evolution“ of self-navigated MRI
Respiration belt
Navigator technique
self-navigated MRI: 3D flash
self-navigated MRI: Radial/KWIC
The Future: self navigated 4D-MRI
J. Biederer
1) 3D flash free breathing
2) quasi-random k-space ordering
3) non-spatially encoded DC signals from k-space center
> determination of respiratory cycle
4) grouping of acquisitions for respiratory phase
> expiration or multiple phases
(S. Weick et al., Würzburg)
Capturing RM: Self-navigated 3D flash MRIW
eick
S, P
roc.
17t
hSc
. M
eeti
ng,
ISM
RM,
2009
J. Biederer
1) radial data acquisition
2) signal from k-space center
> determination of respiratory cycle
3) grouping of views for respiratory phase
> expiration or multiple phases
4) further improvements of image quality
– autofocusing
- 3D image correlation
- K-space-weighted image contrast (KWIC)
- principal component analysis
Lin
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., M
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Capturing RM: Self-navigated radial MRI
J. Biederer
Biederer J et al. (2007), RSNA 2007, ISMRM 2007Biederer J et al., Int J Radiat Oncol Biol Phys. 2009;73: 919-926
LC RT: Comparison 4D-CT/4D-MRI/4D-CBCT
- 4D-MRI and CBCT overestimate lesion size
- 4D-MRI and CBCT underestimate displacement
- 4D-MRI and CBCT with less reproducibility
4D-MRI4D-CT 4D-Cone beam CT