Innovations conference 2014 dr shalini vinod dedicated magnetic resonance imaging for radiotherapy

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


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


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


MRI Simulator

• MRI simulator (3T) installed June 2013 at Liverpool Hospital

• Dedicated MRI physicist

• Dedicated MRI radiographer

• Trained radiation therapists

• 0.2 FTE radiologist


MRI Simulator

• Flat bed

• Laser lights

• Wide bore

• RT specific coils/supports


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


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)


Potential problems with MRI

• Patient set-up

• Distortion

– Geometric

– Patient

• Longer scan times

– Patient motion

– Organ motion

• Claustrophobia

• Contraindications – pacemakers, implants etc


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


Head & Neck Cancer – Patient position


Rectal Cancer – Patient position

PRONE

SUPINE



• 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


Prostate Cancer – CT vs MRI



• 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


Head & Neck Cancer MRI simulation


Results – Functional imaging

• Functional sequences

– Diffusion weighted imaging

– Dynamic contrast-enhanced imaging

– Perfusion imaging


Cervix Cancer – Functional Images

T2 TSE

RESOLVE

DWI

T2 HASTE

ADC MAP


MRI simulation by tumour site

0

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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


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

Innovations conference 2014 dr shalini vinod dedicated magnetic resonance imaging for radiotherapy

Healthcare

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