innovations conference 2014 dr shalini vinod dedicated magnetic resonance imaging for radiotherapy
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Dr Shalini Vinod - Dedicated Magnetic Resonance Imaging for RadiotherapyTRANSCRIPT
Liverpool & Macarthur Cancer Therapy Centres
Dedicated Magnetic Resonance Imaging for Radiotherapy Planning
SK Vinod, LC Holloway, E Juresic, R Rai, L
Cassapi, A Xing, G Goozee, D Moses, GP Liney
Liverpool & Macarthur Cancer Therapy Centres
Background
• MRI is increasingly being used for volume definition in radiotherapy
– Superior soft tissue contrast compared to CT
– Can also provide functional imaging
• Diagnostic MRI not ideal
– Different patient positioning
– Time interval between diagnostic imaging and radiotherapy planning
– Cost & access issues
Liverpool & Macarthur Cancer Therapy Centres
Aims
• To describe the implementation of MRI simulation for common tumour sites treated with radiotherapy:
– Head & Neck cancer
– Cervix cancer
– Prostate cancer
– Rectal cancer
– Brain cancer
Liverpool & Macarthur Cancer Therapy Centres
MRI Simulator
• MRI simulator (3T) installed June 2013 at Liverpool Hospital
• Dedicated MRI physicist
• Dedicated MRI radiographer
• Trained radiation therapists
• 0.2 FTE radiologist
Liverpool & Macarthur Cancer Therapy Centres
MRI Simulator
• Flat bed
• Laser lights
• Wide bore
• RT specific coils/supports
Liverpool & Macarthur Cancer Therapy Centres
Methods
• Basic requirements for MRI simulation developed by the MRI Sim Group
• Diagnostic protocols for MRI acquisition used as starting point for scans
• Site-specific tumour groups consulted about requirements from MRI scans
– Tumour vs Lymph node vs Normal tissue visualisation
• Protocols refined with site-specific input
Liverpool & Macarthur Cancer Therapy Centres
Methods
• Healthy volunteers scanned to optimise images before clinical scan acquisition
• Volunteers scanned in supine and prone position with and without bellyboard to optimise imaging for rectal cancer
• Standard bladder and bowel protocols for pelvic imaging (as per CT sim)
Liverpool & Macarthur Cancer Therapy Centres
Potential problems with MRI
• Patient set-up
• Distortion
– Geometric
– Patient
• Longer scan times
– Patient motion
– Organ motion
• Claustrophobia
• Contraindications – pacemakers, implants etc
Liverpool & Macarthur Cancer Therapy Centres
Results – Basic requirements
• Patient set-up
– Identical patient positioning to CT simulation and treatment
– Flat bed couch with 32 channel integrated spine coil
– Use of MRI compatible immobilisation devices
– MRI bore size may preclude use of some immobilisation devices
– Placement of RF coils must not alter patient anatomy
Liverpool & Macarthur Cancer Therapy Centres
Head & Neck Cancer – Patient position
Liverpool & Macarthur Cancer Therapy Centres
Rectal Cancer – Patient position
PRONE
SUPINE
Liverpool & Macarthur Cancer Therapy Centres
Results – Basic requirements
• Field of View < 30cm
– To minimise geometric distortion
– To adequately image required anatomy for fusion
• Slice thickness 2mm
– To enable detailed visualisation of anatomy
– To optimise fusion to simulation CT and better interpolation in RTP
Liverpool & Macarthur Cancer Therapy Centres
Prostate Cancer – CT vs MRI
Liverpool & Macarthur Cancer Therapy Centres
Results – Basic requirements
• Bandwidth ≥ 440 Hz
– To minimise patient distortion from susceptibility artefact and chemical shift
• Scan acquisition in one concatenation & use of parallel imaging
– To minimise scan time
• Patient motion
• Patient tolerability
Liverpool & Macarthur Cancer Therapy Centres
Head & Neck Cancer MRI simulation
Liverpool & Macarthur Cancer Therapy Centres
Results – Functional imaging
• Functional sequences
– Diffusion weighted imaging
– Dynamic contrast-enhanced imaging
– Perfusion imaging
Liverpool & Macarthur Cancer Therapy Centres
Cervix Cancer – Functional Images
T2 TSE
RESOLVE
DWI
T2 HASTE
ADC MAP
Liverpool & Macarthur Cancer Therapy Centres
MRI simulation by tumour site
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Aug-13 Sep-13 Oct-13 Nov-13 Dec-13 Jan-14 Feb-14 Mar-14 Apr-14 May-14 Jun-14
No
of
pat
ien
ts
H&N MRI Gynae MRI Prostate MRI Rectum MRI Brain MRI
Liverpool & Macarthur Cancer Therapy Centres
Conclusions
• Presence of MRI simulator allows improved patient access for radiotherapy planning
• Specific requirements for MRI for radiotherapy planning which are different to diagnostic requirements
• Balance between acquiring adequate images vs length of scan (patient tolerability & motion)
• Multidisciplinary input required between RO, ROMP, RT, MRI radiographers and radiologist for successfulimplementation of MRI simulation