ESTRO 36 Abstract Book

S154

ESTRO 36

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expected from a new anti-cancer treatment. The ESMO-

MCBS is an important first step to the critical public policy

issue of value in cancer care, helping to frame the

appropriate use of limited public and personal resources

to deliver cost-effective and affordable cancer care. The

ESMO-MCBS is a dynamic tool and its criteria will be

revised on a regular basis. The next version will include

also an approach to grade the clinical benefit data derived

from the registration trials of medications approved on the

basis of these single arm studies. Currently the grading of

newly registered drugs is included in ESMO-guidelines.

A similar approach to develop a scale can potentially be

used for other treatment or diagnostic areas in oncology

including radiotherapy. For a scale grading radiotherapy,

there will likely be a number of similarities and

differences versus a scale for drug treatment. Factors

taken into account for the radiotherapy scale might well

include the adjuvant and curative outcomes: overall

survival, disease free survival, local recurrence free

survival, pathological complete response and non-

curative/palliative outcomes such as: single symptom

relief (complete response, partial response, relief

duration of response), control of hemorrhage, relief of

obstruction, effects on skeletal events (pain, fracture) and

neurological function. We anticipate methodological

challenges in the relative weighting and scoring of

palliative outcomes form localized radiotherapy as

distinct from systemic therapies.

Debate: This house believes that proton guided photons

(online MR guided therapy) will be superior to photon

guided protons (CBCT proton therapy)

SP-0298 For the motion

B. Raaymakers

UMC Utrecht, Department of Radiation Oncology,

Utrecht, The Netherlands

The common ground for proton and photon guidance, that

is MRI and CBCT guidance, is the desire to localize the

target and the surrounding structures in order to improve

the spatial accuracy of dose delivery. This is especially

important to better target and to minimize the high dose

volumes which are leading to the most acute toxicity and

are often dose limiting.

With modern accelerators, both proton- and photon

therapy can generate a conformal high dose volume, while

image guidance is the most important parameter on

delivering this high dose volume to the correct position

and with that minimize this high dose volume. Doing

so, also hypo-fractionated treatments for more and more

tumor sites can become feasible.

MRI guidance is superior because:

1) Soft-tissue guidance of MRI will out-perform CBCT

based set-up

2) MRI provides dynamic imaging to track breathing and

peristalsis without the need for retrospective binning

3) MRI enables daily full re-planning

4) MRI provides intra-fraction (volumetric) imaging for

dose reconstruction and plan adaptation

5) Integrated MRI provides functional response assessment

during the course of radiotherapy

CBCT has greatly improved radiotherapy by offering 3D

imaging just prior to radiation delivery, these images can

be used for improved patient set up and assessment of the

breathing pattern. These data, even though they have

limited soft-tissue contrast, are acquired just prior to

treatment. Using these instead of relying on pre-

treatment images of days (if not weeks) old, provides

much more representative information on the target and

surrounding structures and will improve patient set-up.

With MRI integrated in the radiotherapy system, all the

aims from CBCT guidance can be brought to the next level.

MRI offers soft-tissue contrast, so one can much better

distinguish tumor from surrounding tissues. Also dynamic

MRI can provide 4D anatomical data with high temporal

resolution (e.g. 3Hz) to detect breathing and peristaltic

irregularities. The limitation of CBCT for needing bony

landmarks, surrogates, the need for large tissue density

differences or the retrospective binning to assess motion

data will be solved when using MRI. So MRI is at the very

least a much better CBCT in the sense that it provides

direct visualization of target and surrounding structures.

CBCT guided proton therapy is lagging behind on the much

needed image guidance offered by MRI and hybrid MRI

radiotherapy systems will improve position verification.

On-line MRI will also enable on-line re-planning strategies

that are not, or only for some sites, feasible with CBCT as

an input. This on-line re-planning fits seamlessly into the

large research interest of the radiotherapy community to

adapt the dose more to the actual anatomy and deliver

more conformal dose distributions, currently being

implemented via library of plans or off-line re-planning

strategies.

Moreover, integrated MRI allows imaging during radiation

delivery. This way, assumptions on anatomical stability or

motion as determined on pre-treatment data can be

verified. Also, the intra-fraction volumetric imaging

provides the input for dose reconstruction, so even if the

pre-treatment assumptions are failing and the anatomy is

moving/deforming unexpectedly, one can reconstruct

exactly what the dose delivered is. This can be used for

off-line re-optimization for remaining fractions.

Additionally, as this dose reconstruction can be done in

near real-time, one can also built adaptation triggers on it

such as gating and ultimately intra-fraction re-planning

strategies. The latter would be truly interventional

radiosurgery where the dose distribution is continuously

adapted to the mobile anatomy.

Another advantage of integrated MRI radiotherapy systems

is the capability to assess functional parameters such as

perfusion or water diffusion, from the patient in

treatment position. This can provide great insight in

treatment response and temporal behavior during the

course of radiotherapy.

In summary

, there is a clear desire from the image guided

radiotherapy community to use more and better imaging

prior and during radiation delivery. MRI guided photon

therapy can fulfill this desire and will contribute to more

precise radiation delivery and to a more hypo-fractionated

approach. With that hybrid MRI radiotherapy systems will

become the first choice for radiotherapy and CBCT guided

proton therapy is mainly indicated in case the integral

dose is treatment limiting, e.g. for pediatrics.

SP-0299 Against the motion

A. Lomax

Paul Scherrer Institute PSI, CPT, Villigen PSI, Switzerland

Abstract not received

Proffered Papers: Intra-fraction motion management

OC-0300 Proof of tumor position during SBRT delivery

using (limited-arc) CBCT imaging

C. Hazelaar

, M. Dahele

, B. Slotman

, W. Verbakel

VU University Medical Center, Radiotherapy,

Amsterdam, The Netherlands

Purpose or Objective

SBRT requires accurate patient positioning and robust

positional verification during irradiation itself is desirable.

We investigated if CBCT scans reconstructed from

(collimated) fluoroscopic kV images acquired during

irradiation, including over a limited arc length, can