innovations conference 2014 prof peter metcalfe moving towards mri along radiation therapy...

Peter Metcalfe*, Amy Walker, Gary Liney, Lois Holloway

Centre for Medical Radiation Physics, University of WollongongLiverpool and Macarthur Cancer Therapy Centres and Ingham Institute

Moving towards MRI alone radiation therapy

treatment planning:

What is the impact of MRI distortion?

* Acknowledge support from Cancer Institute NSW Clinical Leaders Program

1. Current MRI/CT in Radiotherapy Planning (RTP)

2. Challenges to MRI alone RTP

3. Quantifying MRI distortion

4. Impact of MRI distortion on RTP

5. Current X-ray Image Guided Radiation Therapy

6. MRI for Image Guided Radiation Therapy?

Content

CT

CT MR

MRI

1. Current MRI/CT in RTP

MRI better soft tissue contrast

Process - CT scan + MRI scan

Register MR contours to CT (rigid/deformable)

Transfer MR contours onto CT data set

CT MR

1. Current MRI/CT in RTP

Courtesy Google Images

Why do we plan using CT data?

CT number to electron density

Geometric certainty of CT

Technology in Cancer Research & Treatment 2013 April 24. Epub ahead of print

MRI in Radiation-therapy Treatment Planning 5

Site-specific Use of MRI in Radiotherapy

Treatment Planning

This section reviews clinical trials of sites for which vari-

ous MRI sequences and analysis methods have been useful

in cancer management. The sites selected for review cover

brain, head and neck, breast, lung, prostate and cervix, and

are not intended to be exhaustive.

Brain

Owing to its small size and central location within the mag-

net, the brain is one of the easiest organs to image well.

MRI is well established as the superior imaging modality

for diagnostic purposes when assessing the brain. In the

brain, MRI often provides better visualization of tumor

and normal tissue than CT, and hence the target volume for

high-precision intracranial radiotherapy is commonly delin-

eated directly on MRI studies (Figure 2). It can be imaged

in standard diagnostic RF coils usually in the treatment

position, and its registration to CT is trivial even with dif-

ferences in position.

The brain was the first site where MRI was routinely used

in treatment planning. Routine clinical use of MRI in the

treatment-planning process of fractionated radiotherapy (RT),

Figure 2: CT (left) co-registered with a T1-3D-SPGR MRI image set (right). The difference in tumor visualization can be clearly appreciated.

Figure 1: 3He polarization image showing polarized MR helium 3 diffusion scan (right) fused on a proton-density-weighted MR scan (left). These active

zones would be the regions of conformal avoidance, defined as low-dose objectives during the radiotherapy treatment planning process.

CT MR

2. Challenges to MRI alone RTP

B field inhomogeneity

Non linear gradients

from RF excitation

Displacement of signal

from actual location

Apparent signal

location

Real signal location


Sunrise Phantom

Poly-ethylene

+5830 Vitamin E Capsules

length 513 mm

diameter 500 mm

height 350mm

Amy Walker

PhD student


MRI moving couch MRI static couch


Moving couch MRI Static couch MRI

Centre

Slice

Extreme

slice # 2

(~216 mm

from

phantom

centre)

S

Experimental Method:

Measure MRI distortion on phantom

Apply distortion map to CT on

patient images

RTP plan on ‘distorted’ CT dataset

Plan copied onto ‘undistorted” CT

Assess dosimetric impact (e.g. DVH)


* CTV Breast

* Cont. Breast

* Lungs

* Heart

Superior

Inferior mm

MILXView

Coronal

Acknowledge Jason Dowling CSIRO


http://aehrc.com/research/biomedical-imaging/software-solutions/milxview

Dosimetric variations:

15 breast tangent IMRT treatment plans

Plans optimised on distorted data met dose

criteria when reviewed on original CT

Less than 3% variation in PTV coverage

OAR dose variations low


Literature

Metcalfe P, Liney G, Holloway L, Walker A, Barton M, Delaney G,

Vinod S, Tome W (2013)

”The potential for an enhanced role

for MRI in radiation-therapy treatment planning”

Technology in Cancer Research and Treatment

Review Article

12(5) 429-446

Speculative

Walker A, Liney G, Metcalfe P,

Holloway L (2014)

"MRI distortion: considerations for

MRI based radiotherapy

treatment planning”

Australasian Physical &

Engineering Sciences in

Medicine.

37 (1), 103-113.

Philips 1.5 T 60 cm bore scanner-T2 turbo spin echo

AAPM 2D phantom

Literature

Fiducial markers

Surrogate for soft-tissue

alignment

Then make couch shift

Courtesy: http://c431376.r76.cf2.

rackcdn.com/37184/fonc-02-00172-HTML

/image_m/fonc-02-00172-g003.jpg

Gold Marker and needle

Reference Wikipedia images

5. Current X-ray Image Guided Radiation

Therapy?

17

Australian MRI-Linac Program

U Alberta- Rotating Magnet

Viewray-MRIdian MRI-Cobalt

U Utrecht-Philips Elekta

http://www.viewray.com


MR-IGRT

Prototype at Liverpool Hospital - Ingham (Sydney)

CT MR

http://inghaminstitute.org/Mri-linac.html

NHMRC Grant Principal Investigators: Paul Keall, Michael Barton and Stuart Crozier


Orientation Questions?

Inline

Electron Focus Effect

(EFE)

Transverse

Electron Return Effect

(ERE)


Dosimetry Questions?

MP512 – Diode Array – 2mm pitchCourtesy Maegan Gargett

PhD student CMRP


3T MRI of MP512

Rapid MR Imaging

Real-time Position

Estimation

Slide adapted from images

courtesy of Paul Keall, U Sydney


Goal

Real-time adaptive radiation therapy

Accounting for anatomic soft tissue

Questions?

Peter Metcalfe email: [email protected]

http://inghaminstitute.org/Mri-linac.htmlSiemens 3T MRI at Liverpool Cancer Care, Sydney

innovations conference 2014 prof peter metcalfe moving towards mri along radiation therapy...

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