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MR-XRT at 1.5T, the UMC Utrecht hybrid MRI linacWill the future of Radiotherapy be MRI guided Interventional Radiology
Jan Lagendijk and Bas Raaymakers: Radiotherapy UMC UtrechtJohan Overweg: Philips, Kevin Brown: Elekta
Present indications Radiotherapy
distant CTV GTVChemo ++ + -RT - ++ -/+Surgery -- -/+ +
0
0,2
0,4
0,6
0,8
1
TC
P
0 2 4 6 8 10 tumour radius
55 Gy 60 Gy 65 Gy 70 Gy
GTV, alfa = 0.35, 10e7 cell/cm3
• TCP models • clinical experience
Based on:
Present indications Radiotherapy
distant CTV GTVChemo ++ + -RT - ++ -/+Surgery -- -/+ +
0
0,2
0,4
0,6
0,8
1
TC
P
0 2 4 6 8 10 tumour radius
55 Gy 60 Gy 65 Gy 70 Gy
GTV, alfa = 0.35, 10e7 cell/cm3
• TCP models • clinical experience
Based on:
Best treatment combination
Development MRI guided RT
New MRI linac:distant CTV GTV
Chemo ++ + -RT - ++ ++Surgery -- -/+ +
Introduction MRI linac
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Development MRI guided RT
New MRI linac:distant CTV GTV
Chemo ++ + -RT - ++ ++Surgery -- -/+ +
Introduction MRI linac
Treatment combinations
Present day:distant CTV GTV
Chemo ++ + -RT - ++ -/+Surgery -- -/+ +
New MRI linac:distant CTV GTV
Chemo ++ + -RT - ++ ++Surgery -- -/+ +
0% 100%
percentage of primary radiotherapy patients
T2 weighted MRI sequence cervix
GTV primary tumor
rectum
GTV pathological lymph nodes (right)
bladder
GTV pathological lymph nodes (left)
T2-weighted
CTVnodes (path.lymph nodes)
CTVprimary (cervix, corpus uteri)
Cine MRI 1.5 T
irregular breathingvon Hippel Lindaukidney tumour
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MRI-linac for renal cancer
• 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)
Planning study: ablative dose feasible (evt. supported by breath-hold)
MRI-linac potential (RT sites)
Site Amount of gain Reason
- Prostate ++ Dose GTV↑, intra-fraction control,deformation
- Cervix +++ Dose GTV↑, shrinkage, deformation, inter-/intra-fraction
- Head and Neck ++ Dose GTV↑, spare normal tissue- Lung + Dose lung tissue↓, compensate for
breathing- Rectum ++ Dose GTV↑, (+ chemo) omit surgery- Esophagus + Dose GTV↑, (+ chemo) omit surgery - Brain ++ Dose GTV↑, visualize CTV, normal tissue- Bladder + Dose GTV↑, intra-fraction control
MRI-linac new possibilities
Site Amount of gain Approach- Kidney* +++ GTV ablation- Liver metastasis* +++ GTV ablation- Pancreas* +++ GTV ablation- Mesothelioma* +++ GTV ablation- Ovary cancer* ++ GTV ablation- Retroperitoneal sarcoma* ++ GTV ablation- Colon ++ Dose GTV↑, fractionated- Lymph node metastasis +++ GTV ablation- Stomach + Dose GTV↑, fractionated- Gall bladder + Dose GTV↑, fractionated- Pyelum / ureter + Dose GTV↑, fractionated- Thymoma ++ GTV ablation- Breast +++ GTV ablation
*Earlier considered “radio-resistant”
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
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1.5 T or 3 T MRI systemRadiotherapy accelerator
Integrating a Philips MRI scanner with an Elekta radiotherapy accelerator
Concept of integrated MR/Linac system
- 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
Accelerator
MLC
beam
MRI linac required specifications
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
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
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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)
– IMRTRaaymakers AJ et al. PMB 2007, 2008
Dose distributions in magnetic field
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)
– IMRT
Kirkby et al. Med Phys 2008
Intensity is 20-40% + 25% is 45-65% of target dose
In a smart multiple beam set up, hot spots can be kept well below the target dose.
Subtraction image 1.5T
Dose distribution, no B 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
0 10 20 30 40 50 60 700
20
40
60
80
100
Dose (Gy)
Vo
lum
e (
%)
Parotis LeftParotis Right
Submand Left Submand Right
BrainMyelum
IMRT dose distribution oropharynx comparison (B = 0 T and B = 1.5 T)
Raaijmakers et al. Phys. Med. Biol. 52 (2007) p. 7045-54
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Concept of integrated MR/Linac system
- 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
Accelerator
MLC
beam
Principle of active B field shielding
B0=Bpin-Bcin
B0out=Bpout-Bcout=0
0 T area
0 T area
Bpout Bcout
+ =
cross section through magnet
Modifications to magnet: zero field zone
Zero-field zone on outside of magnet (position of Linac gun)
Achieved by shift and change in #turns of shielding coils
Gun
Modifications to magnet: beam windows
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
150 mm
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Split gradient coil
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
Prototype gradient coil(Futura, Heerhugowaard, NL)
Present experimental RF shielding
Magnet part of shield
Linac outside shield
Shielded cable duct
MRI
Faraday cage
Accelerator
Prototype magnet(Magnex Scientific, Oxford, UK)
Magnet in its final position
System on site at Utrecht University Linac at midplane magnet
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Philips Achieva 1.5 T electronics
Standard • quadrature body coil • RF coils• sequence library
First test results
Operation of Linac with MR magnet on: OK
Gamma beam reaches Field of View: OK (gafchromic film)
Magnet does not quench: OK (zero boil-off)
Scanner makes images without radiation:
OK (as expected)
400 mm phantom xy plane
Zero field zone at Linac gun position: OK (magnetometer)
Test results
Images of healthy volunteersNo radiation
Coronal stomach/liver/kidney imaging
- 2D, B-SSFP, 2.0 x 2.16 x 7.0, sense 1.5
- Dynamic scan time 0.41s
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MRI of brain
T1 weighted T2 weighted
Test results – MRI with Linac operation
Images of healthy steak
Without radiation With radiation
No differences seen!
Institute for Image Guided OncologicalInterventions 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
HIFU Holmium
HDR robotic brachytherapy
MRI linac
Project team MRI linac
http://umcutrecht.turnpages.nl/uniek/2009-03/pdf/compleet.pdfhttp://www.umcutrecht.nl/NR/rdonlyres/C5DB185D-E7BA-4637-A0E5-3BB0F187324B/11365/UMS_150dpi.pdf
