aapm cbct xing2010 · @01-258_via99-011_hepatoma_onscreen infrared reflective markers infrared...
TRANSCRIPT
1
@01-258_via99-011_hepatoma_onscreen
Lei Xing Ph D Professor
Department of Radiation Oncology
Stanford University School of Medicine
Lei Xing , Ph.D., Professor
Linear accelerator with onboard cone-beam CT
movies
Scatter Artifacts• Large Scatter-to-Primary Ratios (SPR) in CBCT cause severe cupping/shading artifacts.
Wide collimator, high scatter narrow collimator, low scatter
Display window: [min max]; no anti-scatter grid, no scatter correction.
Zhu L, Wang J, Xing L, Scatter correction for cone beam CT in radiation therapy, Medical Physics 36(6):, 2258-68, 2009.
ProstatePTV
Planned (IMRT)DVHs (planned vs delivered)
Use CBCT for Dose Verification
PTVProstate
To be delivered (reconstructed dose on CBCT)
Yang Y, Schreibmann E, Li T, Wang C, Xing L: Evaluation of on-board kV cone beam CT
(CBCT) based dose calculation. Physics in Medical Biology, 52: 685-705, 2007.
Work Flow
Reconstruction Rigid registration
CB
CT
Projection
“Registered” scatter estimate
Subtract
Reconstruction
Reconstruction
Scatter estimation using interpolation
Partial C
BC
T projection
Scatter estimate
Scatter corrected CT image
L. Zhu, J. Wang and L. Xing, Med. Phys. 2008
2
@01-258_via99-011_hepatoma_onscreen
Scatter noise in post-processing methods
No scatter correction, no noise suppression,
Noise in the ROI: 1.01e-6
Measurement-based scatter correction, no noise suppression,
Noise in the ROI: 1.01e-5
Measurement-based scatter correction, PWLS noise suppression, (Wang et al., 2006)
Noise in the ROI: 9.75e-7
L. Zhu, J. Wang and L. Xing, Med. Phys. 2008
Motion artifacts in fan beam CT and CBCT
Cone-Beam CT
Scatter
Cone Beam
z
CBCT using Trilogy
Tianfang Li et al, Li T, Xing L: IJROBP, 67: 1211-1219, 2007.
CBCT projections before and after phase sorting
Stanford ResearchStanford Research
Static phantom - 3D CBCT
CBCT phantom images
motion “switched on” - 3D CBCT
motion “switched on” - 4D CBCT
Li, Koong, Loo, Xing, Med. Phys., 2006
3
@01-258_via99-011_hepatoma_onscreen
4D CBCT 4D CT
Li, Koong, Loo, Xing, Med. Phys.
Ultra-low dose CBCT
210 220 230 240 2500.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
0.05510 mA80 mA10 mA PWLS
(a) (b)
10mA 10mA 80mA
J. Wang & L Xing, PMB, 2008
)()ˆˆ()ˆˆ()( 1 pRpypyp T )()ˆˆ()ˆˆ()( 1 pRpypyp T
)()ˆˆ()ˆˆ()( 1 pRpypyp T n
niin ppwpR 2)()(
)()ˆˆ()ˆˆ()( 1 pRpypyp T
PWLS (Penalized Weighted Least-Squares method):
n
niin ppwpR 2)()(
])(exp[ 2
ni
in
ppw
n
niin ppwpR 2)()(
12000
14000
16000
Linear fit of measured data
Variance = 2.7*Mean + 180.7
R = 0.996
Noise property of projection images
0 1000 2000 3000 4000 5000 60000
2000
4000
6000
8000
10000
Va
rian
ce
Mean
100
200
300
400 3
4
5
x 10
200 400 600 800 1000
500
600
7001
2
Incident X-ray intensities across the field of view with 80 mAtube current and 10 ms pulse time. Relative intensity is
mainly caused by the bow-tie filter.
n
niin ppwpR 2)()(
n
niin ppwpR 2)()(
kk )()1(2
iterative Gauss-Seidel updating strategy
i
ii
Nnini
Nn
knin
Nn
kninii
ki w
pwpwy
p2
)()1(2
)1(
1
)(21
4
@01-258_via99-011_hepatoma_onscreen
Ultra-low dose CBCT
210 220 230 240 2500.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
0.05510 mA80 mA10 mA PWLS
(a) (b)
10mA 10mA 80mA
J. Wang & L Xing, PMB, 2008
Compressed sensing for CBCT recon with sparse projections
K. Choi, L. Zhu, T. Suh, S. Boyd, L. Xing, Med. Phys., in press, 2010
Ultra-low dose fluoroscopic imaging
kV source
kV imager
(a)
xy
z
kV source
EPID
vu
Metal artifacts removal
J. Wang & L. Xing, X-ray Science & Technology, 2010
Dose Reconstruction: Closing the Loop of IMRT/RapidArc/Gated
RapidArc treatment
MLC log-file generated Fluence MapMLC log-file
MLC Workstation
• every 50 ms• leaf position & beam status
Actual leaf sequencesDeliveredfluence map
in-houseprogramTPS
leaf position & beam status
Delivered dose distribution
Lee L, Le Q, Xing L: IJROBP, 70: 634-644, 2008.
5
@01-258_via99-011_hepatoma_onscreen
Figure 2.10 (a)
Case 1: Dose Distribution
pCT
CBCT3CBCT2CBCT1
Lee L, Le Q, Xing L: IJROBP, 70: 634-644, 2008.
80
100
Case 1: DVHs
pCT
DVH comparison of the intended and delivered plans
me
(%)
0
20
40
60
0 40 80 120 160 200 240
Brainstem
PTV
CBCT3
CBCT1
CBCT2
Dose (cGy)
Rel
ativ
e vo
lum
Case 2: Dose Distribution
pCT
CBCT3CBCT2CBCT1
80
100
Case 2: DVHs
PTV pCTm
e (%
)
DVH comparison of the intended and delivered plans
0
20
40
60
0 40 80 120 160 200 240
Brainstem
CBCT3
CBCT1
CBCT2
Dose (cGy)
Rel
ativ
e vo
lu
0
20
40
60
80
100
0 50 100 150 200 250
Case 2: DVHsDVH comparison of the intended and delivered plans
Rel
ativ
e vo
lum
e (%
)
pCT
CBCT3
CBCT1CBCT2
RT Temporal lobe
0
20
40
60
80
100
0 50 100 150 200 250
pCT
CBCT3
CBCT1CBCT2
Dose (cGy)
Rel
ativ
e vo
lum
e (%
)
Dose (cGy)
LT Temporal lobe
6
@01-258_via99-011_hepatoma_onscreen
Case 2: Dosimetric comparison
220 cGy at 100%
MLC Workstation
• every 50 ms• leaf positions & gantry angle logged
Regenerated Leaf Sequence File
Treatment Planning System
DCATDose Reconstruction
in-houseprogram
Planned and Reconstructed Dose Profile Comparison
R L
A
R-L profile A-P profile
Qian J, Lee L, Liu W, Fu K, Luxton, G, Le Q, and Xing L, PMB 57, 3597–3610, 2010.
P
Dose Distribution Comparison
planreconstruction
Reconstruction
PlanPTV DVH Comparison
Positioning errors intentionally introduced
Positioning Errors and Dose Delivered to PTV
Position #1: same as the plan
Position #3: L R: 3 mm; A P: 5mm; S I: 5 mm
Position #2: L R: 0 mm; A P: -2 mm; S I: 2 mm
planreconstruction
Patient Study
100%
50%
10%
PTVPTV PTV
PTV
100% =180 cGy
pCT CBCT1 CBCT2
• CBCT1 / CBCT2: monitored the anatomic change, if any
• CBCTs’ dose distribution very close to pCT’s
7
@01-258_via99-011_hepatoma_onscreen
DVH Resultsve
Vol
ume
(%)
dose reconstructed on CBCT1, CBCT2
planned dose on pCT
PTV 54 Gy
Optic chiasm
,
• slight compromise (< 5%) on the target coverage
• dose deposited to the critical organs:
in general <10% change; worst ~20%
Rel
ativ
Relative Dose (%)
pCT
Bilateral optic
nerves
ProstatePTV
Planned (IMRT)
DVHs (planned vs delivered)
Use CBCT for Dose Verification
PTVProstate
Delivered (reconstructed dose on CBCT)
No
YesRe-optimization
Is replanningneeded?
Treatment delivery
Volumetric imaging, Image registration
& auto-contour propagation
Forward dose calculation and
assessment
Reconstruction of delivered dose New treatment session
Adaptive Radiation Therapy
• CBCT.• Deformable model.
What are needed to bring ART into clinic?
• Automated contour mapping from pCT to CBCT.
• Retrospective dose reconstruction.• Deformable registration for cumulative dose
calculation• Inverse planning for ART• Dose shaping tool.
CBCT imaging of a rectal cancer patient during a course of RT
1st wk (planning CT) 2 wk
IMMOBILIZATION DOES NOT ALWAYS WORK!
4 wkoverlay
P. Lee, K. Goodman, L. Xing, et al, 2006 ASTRO
4D Treatment Planning
Static (with 4D CT info - 3.5D RT)
Gating Tracking
Adapted from Y. Yang, UPMC
8
@01-258_via99-011_hepatoma_onscreen
Infrared reflectivemarkers
Infrared
Radiation Therapy Chain Process
Real-time information of tumor position
Simultaneous kV/MV imaging guided RT delivery
(R. Wiersma, W. Mao, &L. Xing, Med. Phys., 2008)
xd
z
dd
x
skVdkVskV
kV
yy
zd
x
dd
x
sMVdMVsMV
MV
zd
y
dd
y
sMVdMVsMV
MV
xd
y
dd
y
skVdkVskV
kV
z
y
x
z
y
x
cos0sin
010
sin0cos
9
@01-258_via99-011_hepatoma_onscreen
Results – example 1Real-time Image Guidance for Prostate VMAT/IMRT
Example 1
• The sudden drop represents repositioning.
L. Zhu, T. Li, J. Qian, R. Wiersma, W. Liu, J. Wang, K. Choi, L. Lee, B. Meng, X. Zhang, Y. Yang, A. de la Zerda, B. Armbrush,…
Clinical faculty –A. Koong, Q. Le, B. Loo, G Luxton, C. King, S.
Hancock P Maxim E Mok L Wang
ACKNOWLEDGEMENT
Hancock, P. Maxim, E. Mok, L. Wang …
Research supports from-
National Cancer InstituteNational Science FoundationVarian Medical Systems