ESTRO 36 Abstract Book

S209

ESTRO 36 2017

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which combines a 1.5 Tesla MRI with a high-end linear

accelerator. The MR linac will provide real-time high-

quality MRI guidance, not only before, but also during

treatment.

With the introduction of the MR linac, radiotherapy will

enter a new era of high precision treatment with a wide

range of opportunities. MRI guidance will improve tumor

targeting accuracy, allow for smaller PTV margins and thus

result in a reduction of normal tissue exposure.

Consequently, highly accurate tumor targeting with small

PTV margins will enable hypofractionation and dose

escalation up to ablative dose levels, potentially omitting

the necessity of surgery to control the macroscopic tumor.

In addition, daily and even intrafraction plan adaptation

and dose painting based on anatomical changes, tumor

regression and functional MR imaging will further refine

dose escalation and might provide an organ-sparing

treatment strategy for a growing number of indications.

The excellent soft tissue contrast in combination with

advanced online motion-compensation of the MR linac will

also broaden the potential indications for radiotherapy.

Besides its numerous opportunities, the MR linac also

brings challenges. Its clinical implementation requires

thorough revision of workflows and clinical

protocols, training of personnel , adaptation of QA

procedures, etc. In addition, a standard assessment

methodology for the evaluation of innovations in

radiotherapy such as the MR linac is required.

In conclusion, the MR linac has the potential to provide a

high-precision, high-dose, adaptive, non-invasive therapy,

with improved local control, less toxicity and the

possibility of omitting surgery in an extended field of

radiotherapy indications.

SP-0394 MR guided brachytherapy - successes and

potential future developments

P. Hoskin

Mount Vernon Hospital, Northwood Middlesex, United

Kingdom

Brachytherapy has led the way in the development of MR

guided radiotherapy. The technical requirements in

brachytherapy differ from external beam planning in that

the source being placed within the CTV means that the

problems of tissue inhomogeneity and beam entry and exit

profiles do not need consideration. The main challenge in

brachytherapy is to design applicators which can be

readily visualised on MR so that accurate definition of

applicator geometry within the CTV is achieved. In the

two most common indications for brachytherapy,

gynaecological cancers and prostate cancer MR guided

techniques are well established and considered standard

practice. The development of MR guided gynaecological

brachytherapy demonstrates well the advantages of the

superior anatomical information obtained from MR and the

ability to accurately delineate tumours defining the CTV.

The evolution can be traced from conventional point A

based dosimetry using orthogonal x-rays to 3-D image

guided brachytherapy using MR which has been estimated

to account for a 13% increase in survival with modern

treatment techniques. Similarly in prostate cancer, whilst

ultrasound-based implantation is the standard for

definition of the CTV registration with MR provides

additional information. As the practice of focal therapy

and dose painting using functional MR information evolves

then MR based planning is seen to have significant

advantages which will again translate into patient benefit.

For the future refinement of MR compatible applicator

design, access to MR guided implant techniques and MR

based planning algorithms will further enhance the role of

MR in brachytherapy.

SP-0395 Challenges associated with MR guided

radiotherapy

D. Jaffray

Princess Margaret Cancer Centre University Health

Network, Toronto, Canada

The sensitivity and definition of magnetic resonance (MR)

imaging makes it a compelling technology to guide the

delivery of highly conformal radiotherapy (RT).

Technological advances have now made this concept a

reality in a variety of forms ranging from its use in the

design of the treatment plan to enabling on-line planning

and/or real-time verification of plan delivery. While the

paradigm of MR-guided radiotherapy already is operating

in various forms, including dedicated machines that

combine MR imaging and delivery, there are numerous

challenges that prevent the full exploitation of this

technology to maximize the therapeutic ratio for today’s

cancer patient. These challenges can be broadly grouped

as biological, physics / computational, operations /

procedural, and cost / value. While the implementation

of MR-guided RT is advancing, clinical, research, and

industry teams are exploring the radiobiological effects,

addressing computation of dose and deformation,

developing adaptive workflows, and seeking evidence of

the value of these new processes will bring to the patient

and health system as a whole. In this presentation, the full

scope of these challenges will be presented to provide the

audience with an understanding of their interplay and to

allow them to identify areas of priority.

SP-0396 Can we perform RCTs evaluating MR guided

radiotherapy?

V. Valentini

Università Cattolica del Sacro Cuore - Policlinico A.

Gemelli, Gemelli ART, Rome, Italy

Image guided radiotherapy (IGRT) has offered in the last

years great opportunities to reduce treatment related

uncertainties and errors and to develop new dose

escalation protocols with local control improvement and

toxicity reduction. The recent technological introduction

of MRI in RT treatment rooms, offer new IGRT paradigms,

which will allow an adaptive therapy, approach through

the analysis of organ motion 3D and 4D features and

volume changes. To define the metric to evaluate the

assumed benefit is of utmost importance in order to

achieve the best clinical outcomes in the daily

management of radiotherapy (RT) treatments delivery.

The issue to apply the RCT methodology to measure the

assumed clinical benefit of this new technology is

challenging the appropriateness of this approach, as any

time that an innovative technology has to be evaluated,

and the cost and time needed to get a reliable

evaluation. On the other side the cost effectiveness

benefit of this new technology needed to have a proper

metric to allow a full understanding of its role. The

possibility to manage RCT, in term of aim, feasibility and

expected outcome, and to use a similarity large data base

approach will be addressed.

Symposium with Proffered Papers: Novel approaches in

head and neck tumour control

SP-0397 State of the art in head and neck tumour

radiobiology

B. O'Sullivan

Princess Margaret Cancer Centre University Health

Network, Toronto, Canada

Much contemporary knowledge and application of

radiobiology to cancer treatment derives from experience

and management of head and neck cancers (HNCs). In

part, this relates to the more accessible nature of these

lesion compared to other cancers for observation and

tissue access, and because radiotherapy (RT) has provided