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ESTRO 36 2017
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alleviate the need for full 3D coverage at each time-point
thus allowing dose deposition mapping in both the tumor
and surrounding organs at risk. The efficacy of motion
modelling relies on the available information (input) and
the redundancy in the data (dimensionality reduction).
Optimal results are therefore only achieved when both the
acquisition strategy and motion modeling are matched.
In this talk I will go through the basic requirements of an
online MR-guided workflow and discuss the use of
respiratory motion models for 1) tumor tracking, and 2)
dose accumulation mapping. An outlook in then given, in
which the foreseen advances in imaging speed are
discussed and the role of motion models in the future.
SP-0576 Tracking: present status and what to expect
in the near future
T. Ravkilde
1
1
Aarhus University Hospital, Medical Physics- Department
of Oncology, Aarhus, Denmark
In recent years there has been a growing trend towards
hypofractionation in radiation therapy. The recent surge
of interest in stereotactic body radiation therapy is yet
another stone on this path. With these treatment schemes
large radiation doses are delivered in few fractions,
making the correct delivery of every treatment fraction
critical. Unfortunately, many sites in the thorax, abdomen
and pelvis are subject to motion, which can significantly
deteriorate the highly conformal dose distributions typical
of today’s standard of care. One way to restore dose
conformity is by adjusting the radiation delivery to the
moving anatomy on-the-fly; so-called tumour tracking.
Tumour tracking was originally proposed more than 15
years ago and has been heavily investigated since, yet is
very sparsely available in clinics worldwide. While
dedicated machines are now commercially available,
tracking on the ubiquitous standard C-arm linear
accelerators is still lacking. Despite a large body of
research publications and many convincing results in
phantom experiments at multiple institutions tumour
tracking has proven difficult to push into the clinic, with
very few clinical trials existing.
Unfortunately, tumour tracking inherently presents a
problem for existing pre-treatment plan-specific QA
regimes as parameters of the treatment machine is
continuously adjusted during beam delivery of each
treatment fraction and thus cannot be known beforehand.
This has shown to be a concern for many physicians and
physicists with regards to the clinical introduction of
tumour tracking.
This presentation will present an overview of machinery
and techniques and discuss pros, cons and opportunities.
It will make a brief review of the history of research and
development and attempt to sum up the present status of
tumour tracking while finally sharing a few thoughts on
the direction it could be headed in the near future.
Symposium: Modelling and treatment customisation
SP-0577 Developments in head and neck toxicity data,
models, and treatment optimisation
A. Van Der Schaaf
1
1
UMCG University Medical Center Groningen, Radiation
Oncology, Groningen, The Netherlands
Radiotherapy in the head and neck region plays a pivotal
role in the treatment of cancer but it is also associated
with a large spectrum of toxicities. In past years many
studies have concentrated on xerostomia and dysphagia as
the toxicities with the most detrimental effect on quality
of life, but the list of complications that are studied is
expanding. Prospective data registration programs are
increasingly used to collect large standardized data sets
of good quality. Modelling techniques become more
advanced by adopting methods from the field of
(bio)statistics and machine learning, enabling data driven
exploration of complicated dose response relationships
and a large variety of other predictive factors, including
emerging factors like genetics and image features. Also,
biological experiments are narrowing down on the
potential mechanisms, aiming to find anatomical targets,
e.g., a stem cell rich compartment in the parotid glands.
All these findings can be used to (automatically) optimise
treatment planning, or to select patients that benefit
most from advanced treatment modalities, such as
protons. For this to be effective, however, it is required
that the observed findings describe general and causal
relationships, which is checked with validation studies and
rapid learning methodologies. This talk will include
characteristic examples from literature and details from
recent developments in the Netherlands and at our
department, illustrating current processes from data
collection to toxicity reduction.
SP-0578 New NTCP data in the thoracic region:
probing 'dark toxicity'
J. Deasy
1
, M. Thor
1
, J. Oh
1
, A. Rimner
1
1
Memorial Sloan-Kettering Cancer Center, Medical
Physics, New York- NY, USA
Following the shocking results of RTOG 0617, it has
become clear that high dose radiotherapy to the thorax
can be lethal within a few months to a few years following
treatment. This previously unappreciated syndrome is
greater than any expected treatment benefit due to dose
escalation, although it goes the wrong way. Given this new
perspective, we can freshly review old and emerging data
related to irradiation of central thorax structures.
Although heart irradiation appears to be the likely cause
of this 'dark toxicity', there are many remaining questions,
such as the sensitive anatomic sub-structures. In our
search for safe 'tolerance' thresholds, we will review all
the data currently available to better understand this
unexpected lethal toxicity in lung cancer. We will also
highlight new methods of interrogating imaging data to
identify local damage. In addition, we will also review
recent data and risk modeling results for severe
esophagitis and pneumonitis.
SP-0579 New NTCP data in the pelvic area
C. Fiorino
1
1
San Raffaele Scientific Institute, Medical Physics,
Milano, Italy
The last years were very fruitful in improving our
knowledge regarding the prediction of toxicities after
pelvic radiation therapy (RT). Prostate cancer (PCa)
patients (pts) mostly contributed to the picture; on the
other hand, results came also from other fields such as
gynaecological, rectal and bladder cancer RT. Compared
to the pivotal reviews of the Quantec group, published in
2010, our knowledge dramatically increased for most
organs. Concerning rectum, the prevalently serial
behaviour when considering moderate/severe bleeding
was confirmed. In addition, several clinical parameters
were found to significantly modulate the risk, primarily
previous abdominal/pelvic surgery and cardio-vascular
disease: the existence of a relationship between acute
symptoms and late bleeding was also corroborated. Other
end-points were investigated such as faecal incontinence,
loose stools, urgency and pain: overall, robust models
were reported for faecal incontinence showing a
prevalently parallel behaviour of the rectum and/or of the
anal canal and a relevant impact of clinical factors such
as previous abdominal/pelvic surgery and pre-existing
disease of the colon. Although much has still to be
explored, bowel dose-volume effects were better
quantified in recent studies showing correlation between