AAPM CBCT Xing2010 · @01-258_via99-011_hepatoma_onscreen Infrared reflective markers Infrared Radiation Therapy Chain Process Real-time information of tumor position Simultaneous

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@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

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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,


Measurement-based scatter correction, PWLS noise suppression, (Wang et al., 2006)


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

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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


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.

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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

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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

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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

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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

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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

Documents

AAPM CBCT Xing2010 · @01-258_via99-011_hepatoma_onscreen Infrared reflective markers Infrared Radiation Therapy Chain Process Real-time information of tumor position Simultaneous