Download The Role of MRI in Radiation Treatment Planning

MAGNETIC RESONANCE
IMAGING IN RADIATION
TREATMENT
ABBAS ADESINA ABDUS-SALAM

Radiation therapy is a localized treatment like surgery

It involves the use of ionizing radiation to eliminate tumour
cells “in situ” without apparent removal of tissue

Results of radiation treatment in terms of disease control is
sometimes broadly similar to surgical intervention

Surgery has the advantage of complete control over the
excision margin

Radiotherapy has the advantage of reaching places and
levels where surgical knives can not reach or not
desirable

The aim of modern radiation treatment practice is to
combine the precise control of the surgical knives and
the reach of radiation
 Achievement
of this lofty objective is built
on 2 important fulcrums
 Precision in tumour localization
 Precision in dose delivery
 These were important barriers to effective
radiation treatment in the past
 Imprecise tumour localization meant more
guesswork with resultant bigger field sizes
and more side effects






Radiodiagnosis has repeatedly come to the aid of its sister in
resolving these problem and helping to strengthen these 2 pivots
Plain X-ray helped introduced what is later to be know as 2D
treatment planning
With 2D planning, bony landmarks became important guides in
tumour localization and treatment volume delineation
But bony landmarks are at better approximation of the disease
volume
Using bony landmarks in Cervical Cancer for example will mean
that the entire pelvic brim should be involved in external beam
treatment in an effort to include all the pelvic nodes even when
there is no evidence of nodal involvements
The limitation of plain x-ray for tumour localization and treatment
quickly became obvious

Ultrasound scan improved detection of extent of disease, presence or
absence and extent of metastases, most especially the lymph nodes

Combined with sentinel node identification, USS can greatly improve the
determination of disease extent

It however found no use in radiation treatment planning

Improvement in this area had to await the introduction of the CT Scan

CT scan gave birth to the era of 3D conformal treatment planning

With CT, radiation oncologist could start dreaming of the precision of the
surgical knives

Our radiation fields do not have to be square, circle, oval, rectangle or
triangle anymore

It can follow the precise shapes of the tumours, follow them round tight
curves in the human anatomy and spare unaffected organs or in fact
parts of organs
 CT-aided
radiotherapy is the
current gold
standard
 Most radiation
treatment centres
across the world
have dedicated
CT for treatement
planning
 Planning CT are
basically like a
regular CT
 The
use of MRI is beginning to attract
attention and commentaries from
practitioners
 MRI
has better image resolution
compared to CT
 This
better is imaging resolution is most
pronounced for soft tissue
 Less
radio-diagnosis competence is
required
 Additional
benefits of MRI over CT planning
 MRI
does not use ionizing radiation, making its
repeated use possible both in children and adults
where there is a need to keep a firm grip on the total
radiation dose
 MRI
images do not have to be acquired with transaxial slices. The slices can be sagittal, coronal or using
any plane desired for the relevant anatomy or
proposed treatment fields
 MRI
is also better suited to assess intra-treatment
variations in tumour/treatment volume positions
 Modification
to MR techniques can also improve
the quality of output
 Such
 MR
include the use of contrasts
Angiography
 Dynamic
 Blood
Oxygen Level Dependent MR
 Diffusion
 MR
Contrast-Enhanced MR
Imaging
Spectroscopy

So, why has MRI not replaced CT as the imaging of choice in radiation
treatment planning?

Years of research and technological development have gone into CTtreatment planning

Radiation treatment planning system is designed to use CT images

Electron density, which many modern treatment planning depends on is
not easily or accurately measured using MRI

MRI geometric image distortion is also a serious problem that will need to
be significantly resolved

System, Patient and presence of metal artifacts

Problem with compatibility between radiotherapy treatment positions
and MRI acquisition positions

Integration of MRI and RT equipment is also creating technical
challenges that are currently being worked on

In concluding

MRI is poised to play increasingly important role in radiation
treatment planning,

It’s superior image clarity in tumour localization and
treatment delivery is enticing to the radiation oncologists

However, the current technical challenges has limited the
use of MRI in radiation oncology to mainly “offline”
diagnosis. Integration with live treatment system is still
experimental

It is safe to predict however that once some of these
technological hurdles are crossed, MRI will take its rightful as
a superior technology in radiation treatment planning and
dose delivery

Important Resources

Maria A Schmidt and Geoffrey S Payne; Radiotherapy planning using
MRI, IOP Science 2015

Yue Cao and Lili Chen; Mri in radiation treatment planningand
assessment,
https://www.aapm.org/meetings/06ss/documents/MRI_Cao2006.pdf

Mary Koshy, Michael Pentaleri, Shyam Paryani; The Role of MRI in
Radiation Therapy Planning;
https://www.healthcare.siemens.com/siemens_hwemhwem_ssxa_websites-contextroot/wcm/idc/groups/public/@global/@imaging/@mri/documents/d
ownload/mdaw/mtc1/~edisp/the_role_of_mri_in_radiation_therapy_
planning-00016933.pdf