MR-XRT at 1.5T, the UMC Utrecht hybrid MRI linac
Present indications Radiotherapy
Will the future of Radiotherapy be MRI guided Interventional Radiology
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
• TCP models
• clinical experience
0,6
TCP
Based on:
0,4
0,2
0
0
2
55 Gy
Present indications Radiotherapy
Chemo
RT
Surgery
4
6
tumour radius
60 Gy
65 Gy
8
10
70 Gy
Development MRI guided RT
distant CTV GTV
++
+
++
-/+
--/+
+
New MRI linac:
distant CTV GTV
Chemo
++
+
RT
++
++
Surgery
--/+
+
Best treatment
combination
GTV, alfa = 0.35, 10e7 cell/cm3
1
Introduction MRI linac
0,8
• TCP models
• clinical experience
0,6
TCP
Based on:
0,4
0,2
0
0
2
55 Gy
4
6
tumour radius
60 Gy
65 Gy
8
10
70 Gy
1
Development MRI guided RT
Treatment combinations
New MRI linac:
distant CTV GTV
Chemo
++
+
RT
++
++
Surgery
--/+
+
Present day:
distant CTV GTV
Chemo
++
+
RT
++
-/+
Surgery
--/+
+
Introduction MRI linac
T2 weighted MRI sequence cervix
GTV primary tumor
New MRI linac:
distant CTV GTV
Chemo
++
+
RT
++
++
Surgery
--/+
+
percentage of primary
radiotherapy patients
0%
100%
Cine MRI 1.5 T
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)
Planning study: ablative dose feasible (evt. supported by breath-hold)
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
+++
Site
Amount of gain
-
Prostate
++
-
Cervix
+++
-
Head and Neck
Lung
++
+
-
Rectum
Esophagus
Brain
Bladder
++
+
++
+
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
Preferred paradigm Radiotherapy 2010 - …
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
• 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
*Earlier considered “radio-resistant”
3
Integrating a Philips MRI scanner with an Elekta
radiotherapy accelerator
Concept of integrated MR/Linac system
Accelerator
- Cylindrical 1.5T closed-bore MRI
MLC
- 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
beam
and MR system
Radiotherapy accelerator
1.5 T or 3 T MRI system
MRI linac required specifications
Dose distributions in magnetic field
Develop the ultimate targeting system:
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
•
•
•
•
•
•
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
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
Dose distributions in magnetic field
Kirkby et al. Med Phys 2008
IMRT dose distribution oropharynx comparison
(B = 0 T and B = 1.5 T)
100
80
Submand Left
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
Submand Right
60
40
Parotis Left
20
Brain
Parotis Right
Myelum
0
0
10
20
30
40
50
60
70
Dose (Gy)
Raaijmakers et al. Phys. Med. Biol. 52 (2007) p. 7045-54
5
Principle of active B field shielding
Concept of integrated MR/Linac system
Accelerator
B0out=Bpout-Bcout=0
- Cylindrical 1.5T closed-bore MRI
MLC
- Linac in z=0 plane outside magnet
0 T area
Bcout
Bpout
- MR parts transparent to beam
- Field-sensitive Linac components to
be located in low-field zone
- Proper RF shield between Linac
+
beam
=
B0=Bpin-Bcin
and MR system
0 T area
cross section through magnet
Modifications to magnet: zero field zone
Modifications to magnet: beam windows
Gun
Zero-field zone on outside
of magnet (position of
Linac gun)
Achieved by shift and
change in #turns of
shielding coils
150 mm
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
MRI
Coil ID 700 mm
Faraday cage
Central gap width 200 mm,
field size 240 mm
Gradient strength 30 mT/m
No electrical or cooling
interconnections between
halves
Prototype gradient coil
Magnet part of shield
(Futura, Heerhugowaard, NL)
Linac outside shield
Shielded cable duct
System on site at Utrecht University
Prototype magnet
Linac at midplane magnet
Magnet in its final position
(Magnex Scientific, Oxford, UK)
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:
OK
Operation of Linac with MR magnet on:
OK
(magnetometer)
Gamma beam reaches Field of View:
OK
Magnet does not quench:
OK
(zero boil-off)
Scanner makes images without
radiation:
OK
(as expected)
(gafchromic film)
400 mm phantom xy plane
Coronal stomach/liver/kidney imaging
Test results
-
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
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
HIFU
Images of healthy steak
With radiation
No differences seen!
Project team MRI linac
HDR robotic brachytherapy
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
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