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MR-XRT at 1.5T, the UMC Utrecht hybrid MRI linac

Will the future of Radiotherapy be MRI guided Interventional Radiology

Present indications Radiotherapy

Jan Lagendijk and Bas Raaymakers: Radiotherapy UMC Utrecht Johan Overweg: Philips, Kevin Brown: Elekta

Chemo RT Surgery

distant CTV GTV ++ + ++ -/+ --/+ +

GTV, alfa = 0.35, 10e7 cell/cm3

1 0,8

Based on:

· TCP models · clinical experience

TCP

0,6 0,4 0,2 0 0 2 55 Gy 4 6 tumour radius 60 Gy 65 Gy 8 70 Gy 10

Present indications Radiotherapy

Development MRI guided RT New MRI linac: distant CTV GTV Chemo ++ + RT ++ ++ Surgery --/+ +

Chemo RT Surgery

distant CTV GTV ++ + ++ -/+ --/+ +

1 0,8

Best treatment combination

GTV, alfa = 0.35, 10e7 cell/cm3

Introduction MRI linac

Based on:

· TCP models · clinical experience

TCP

0,6 0,4 0,2 0 0 2 55 Gy 4 6 tumour radius 60 Gy 65 Gy 8 70 Gy 10

1

Development MRI guided RT New MRI linac: distant CTV GTV Chemo ++ + RT ++ ++ Surgery --/+ +

Treatment combinations Present day: distant CTV GTV Chemo ++ + RT ++ -/+ Surgery --/+ + New MRI linac: distant CTV GTV Chemo ++ + RT ++ ++ Surgery --/+ +

Introduction MRI linac

percentage of primary radiotherapy patients

0%

100%

T2 weighted MRI sequence cervix

Cine MRI 1.5 T

GTV primary tumor

bladder

CTVnodes (path.lymph nodes) GTV pathological lymph nodes (left) rectum CTVprimary (cervix, corpus uteri)

GTV pathological lymph nodes (right)

irregular breathing von Hippel Lindau kidney tumour

T2-weighted

2

MRI-linac for renal cancer

MRI-linac potential (RT sites)

·

Renal cancers are not treated with radiotherapy: ­ Kidney movements, large PTV ­ Kidney is very sensitive for radiation damage ­ Normal tissue is in close proximity (bowel, liver)

Site Prostate Cervix

Amount of gain ++ +++ ++ + ++ + ++ +

Reason Dose GTV, intra-fraction control, deformation Dose GTV, shrinkage, deformation, inter-/intra-fraction Dose GTV, spare normal tissue Dose lung tissue, compensate for breathing Dose GTV, (+ chemo) omit surgery Dose GTV, (+ chemo) omit surgery Dose GTV, visualize CTV, normal tissue Dose GTV, intra-fraction control

Planning study: ablative dose feasible (evt. supported by breath-hold)

Head and Neck Lung Rectum Esophagus Brain Bladder

MRI-linac new possibilities

Site Amount of gain - Kidney* +++ - Liver metastasis* +++ - Pancreas* +++ - Mesothelioma* +++ - Ovary cancer* ++ - Retroperitoneal sarcoma* ++ - Colon ++ - Lymph node metastasis +++ - Stomach + - Gall bladder + - Pyelum / ureter + - Thymoma ++ - Breast +++ *Earlier considered "radio-resistant" Approach GTV ablation GTV ablation GTV ablation GTV ablation GTV ablation GTV ablation Dose GTV, fractionated GTV ablation Dose GTV, fractionated Dose GTV, fractionated Dose GTV, fractionated GTV ablation GTV ablation

Preferred paradigm Radiotherapy 2010 - ...

· The GTV's are sterilized · Fractionation is used to kill the tumour infiltrations (CTV) and spare the surrounding normal tissue

· Stereotactic schemes will be extended to more and more body applications · Radiotherapy goes in competition with surgery

3

Integrating a Philips MRI scanner with an Elekta radiotherapy accelerator

Concept of integrated MR/Linac system

Accelerator - Cylindrical 1.5T closed-bore MRI - Linac in z=0 plane outside magnet - MR parts transparent to beam - Field-sensitive Linac components to be located in low-field zone - Proper RF shield between Linac and MR system beam MLC

Radiotherapy accelerator

1.5 T or 3 T MRI system

MRI linac required specifications

Dose distributions in magnetic field

Develop the ultimate targeting system:

· · · · · · · · · Diagnostic quality MRI Targeting accuracy 0.5 mm On line/Intrafraction/breathing Tracking organs movements/shape changes Therapy plan update continuously Treatment response assessment High dose rate Small focal spot Fast MLC

ERE effect is real but can be dealt with ­ Multiple opposing beams ­ Multiple beams (worst case ERE is roughly 30% of the single beam intensity) ­ IMRT

4

Dose distributions in magnetic field

Dose distributions in magnetic field

ERE effect is real but can be dealt with ­ Multiple opposing beams ­ Multiple beams (worst case ERE is roughly 30% of the single beam intensity) ­ IMRT Raaymakers AJ et al. PMB 2007, 2008

ERE effect is real but can be dealt with ­ Multiple opposing beams ­ Multiple beams (worst case ERE is about 30% of the single beam intensity) Intensity is 20-40% + 25% ­ IMRT

is 45-65% of target dose

Dose distribution, no B field

In a smart multiple beam set up, hot spots can be kept well below the target dose.

Subtraction image 1.5T Kirkby et al. Med Phys 2008

Dose distributions in magnetic field

IMRT dose distribution oropharynx comparison (B = 0 T and B = 1.5 T)

100

Volume (%)

ERE effect is real but can be dealt with ­ Multiple opposing beams ­ Multiple beams (worst case ERE is roughly 30% of the single beam intensity) ­ IMRT

80

Submand Left Submand Right

60

40

Parotis Left Parotis Right

20

Brain

Myelum

0

0 10 20 30 40 50 60 70

Dose (Gy)

Raaijmakers et al. Phys. Med. Biol. 52 (2007) p. 7045-54

5

Concept of integrated MR/Linac system

Accelerator

Principle of active B field shielding

B0out=Bpout-Bcout=0

- Cylindrical 1.5T closed-bore MRI - Linac in z=0 plane outside magnet - MR parts transparent to beam - Field-sensitive Linac components to be located in low-field zone - Proper RF shield between Linac and MR system

MLC Bpout Bcout

0 T area

beam

+

=

B0=Bpin-Bcin

0 T area

cross section through magnet

Modifications to magnet: zero field zone

Gun

Modifications to magnet: beam windows

150 mm

Zero-field zone on outside of magnet (position of Linac gun) Achieved by shift and change in #turns of shielding coils

Gap between central coils increased to ~ 15 cm Possible without compromising homogeneity (7 ppm, 40-30 cm ellipsoid) Cryostat with reduced and uniform attenuation "Standard" MR/RT design

6

Split gradient coil

Present experimental RF shielding

Accelerator

Actively shielded coil system Coil ID 700 mm Central gap width 200 mm, field size 240 mm Gradient strength 30 mT/m No electrical or cooling interconnections between halves

MRI

Faraday cage

Prototype gradient coil

(Futura, Heerhugowaard, NL)

Magnet part of shield Linac outside shield Shielded cable duct

System on site at Utrecht University

Linac at midplane magnet

Prototype magnet

(Magnex Scientific, Oxford, UK)

Magnet in its final position

7

Philips Achieva 1.5 T electronics

First test results

Standard · quadrature body coil · RF coils · sequence library

Zero field zone at Linac gun position: Operation of Linac with MR magnet on: Gamma beam reaches Field of View: Magnet does not quench: Scanner makes images without radiation:

OK OK OK OK OK

(magnetometer)

(gafchromic film) (zero boil-off) (as expected)

400 mm phantom xy plane

Test results

Coronal stomach/liver/kidney imaging

-

2D, B-SSFP, 2.0 x 2.16 x 7.0, sense 1.5 Dynamic scan time 0.41s

Images of healthy volunteers No radiation

8

MRI of brain

Test results ­ MRI with Linac operation

Without radiation T1 weighted T2 weighted Images of healthy steak

With radiation No differences seen!

Institute for Image Guided Oncological Interventions at the UMC Utrecht

Treatment equipment: · 3x 1.5T MRI accelerator · 1x 1.5T MRI HDR Brachytherapy · 1x 3T MRIgHIFU · 1x CT · 1x 3T MRI/PET combination · MRI guided Holmium Radioembolisation

Project team MRI linac

HDR robotic brachytherapy

HIFU

Holmium

MRI linac

http://umcutrecht.turnpages.nl/uniek/2009-03/pdf/compleet.pdf http://www.umcutrecht.nl/NR/rdonlyres/C5DB185D-E7BA-4637-A0E5-3BB0F187324B/11365/UMS_150dpi.pdf

9

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