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heterogeneous, and the EBRT dose distribution may also
include significant dose gradients in the vicinity of the
brachytherapy high dose region, e.g. in case of lymph node
boosts. Organ motion between fractions as well as change
in anatomy between brachytherapy and EBRT constitute
specific challenges for dose summation. Deformable
image registration (DIR) aims to match each tissue voxel
irradiated by each fraction of external-beam radiation
with the corresponding voxel irradiated by each fraction
of brachytherapy. However, DIR is related with specific
uncertainties and does not necessarily provide added
value for dose accumulation. The alternative of
accumulating dose through DIR is to perform direct
addition of DVH parameters as recommended in the ICRU
report 89. Direct addition assumes inherently that hot
spots and cold spots remain in the same spatial region
across suceeding fractions and is therefore also related
with uncertainties or even not appropriate for certain
scenarios. DIR can be carried out with deformation models
based on image intensity, biomechanical models, or
combinations of these. Biomechanical models take into
account organ shapes and potentially biomechanical
properties of organs or organ walls/surfaces, such as
elasticity. Biomechanical models based on contours need
to have these defined in both source and target images,
and the correspondence of contours becomes part of the
objective function which drives the optimisation. DIR
models based entirely on image intensity do not take into
account contours, and the objective function is based on
correspondence in image intensity. The major questions
with regard to DIR and dose accumulation in
brachytherapy are: 1) Is it problematic to accumulate dose
without DIR? I.e. what is the accuracy and limitations of
dose accumulation with DVH addition? 2) Can DIR solve the
problem? I.e. what is the accuracy of DIR-based dose
accumulation? For summation of EBRT and brachytherapy,
direct DVH addition is accurate if the EBRT dose
distribution is homogenous in the region where the BT
boost is going to be delivered. In case of a homogeneous
EBRT dose, the EBRT dose contribution to the primary
target D
90%
and D
98%
as well as D
2cm3
for organs at risk will
be equal to the prescribed EBRT dose. Dose distributions
from four-field -box techniques are normally
homogeneous . Furthermore, it is also possible to control
the homogeneity of IMRT and VMAT in the region the the
BT boost through dose optimisation, e.g. by introducing
help structures in the region of the primary target/GTV
with specific constraints on homogeneity. However, in the
case of lymph node boosts which are in close relation to
the primary target and the BT boosted region, direct
addition of EBRT and BT DVH parameters may not reflect
the true accumulated dose. DIR has not been investigated
for this purpose, but may provide an added value. For
summation of dose from succeeding BT fractions, there
are indications that DVH addition has an accuracy better
than 5% for organs such as bladder and rectum, as hotspots
are quite stable across brachytherapy fractions. For target
structures, there have not been any systematic
evaluations, but often cold spots are located in the same
region of the target, and DVH addition is assumed to work
well. For highly mobile organs such as sigmoid colon or
bowel loops, it is well know that hotspots may end up in
very different parts of the loops and DVH addition is
expected to significantly overestimate the hotspot dose.
DIR algorithms which are based on contours and
biomechanical models have been demonstrated to work
well for bladderand improves dose assessment although
the improvement with DIR as compared to direct DVH
addition is normally less than 5%. However, some DIR
algorithms based on image intensities can be related with
significant uncertainties and may provide dose
assessments which are less accurate than with DVH
addition, and DIR should therefore be used with great
caution. Sigmoid and bowel are highly deformable organs
and represent a significant challenge for DIR. There are
currently not any deformable registration algorithms
which have shown performance in sigmoid and bowel
which is sufficent for dose accumulation. In conclusion,
DVH addition is currently recommended by the ICRU 89
report for dose summation in brachytherapy, and provides
in most scenarios a good accuracy for assessment of total
dose in targets and in organs such as bladder and rectum.
Dose summation in highly mobile organs such as sigmoid
and bowel is currently related with significant
uncertainties, and there could be potential to improve this
with appropriate DIR algorithms.
SP-0312 Imaging and fusion techniques for focal
brachytherapy
L. Beaulieu
1
1
Laval University - Faculty of Science and Engineering,
Université laval Cancer Research Centre, Québec City,
Canada
Over the last decade, numerous technological
developments have made brachytherapy one of the most
precise needle-based procedures on the market. The
cornerstone of interstitial brachytherapy for many years
now has clearly been real-time ultrasound (US) image-
guidance and more recently real-time 3DUS image-
guidance. From whole gland prostate cancer treatments
to focal boosts and now focal therapy, brachytherapy is
head of the curve of any other prostate focal therapy
modality at this time in terms of precision and accuracy.
However, current standard US-guidance is not sufficient
for focal therapy; our real-time image-guidance technique
needs to be supplemented with more information. This
presentation will look at the role of multi-parametric MRI
in prostate focal therapy as well as US-augmented with
MRI for real-time guidance. This brings the notion of
augmented reality as well as the challenge of image fusion
among two very different imaging modalities and image
sets also taken under very different conditions. We will
also discuss the topic of merging tissue information (e.g.
biopsy) with imaging data to provide a complete cancer
burden maps for targeting purposes. Finally, we will
provide a forward-looking view of real-time multi-
parametric 3DUS guidance and targeting for such
procedures.
Proffered Papers: Breast and gynaecology
OC-0313 What is the effect of axillary treatment on
patient reported outcomes in breast cancer patients?
M.L. Gregorowitsch
1
, H.M. Verkooijen
1
, N. Fuhler
1
, D.A.
Young Afat
1
, A.N.T. Kotte
1
, M. Vulpen van
1
, C.H. Gils
van
2
, D.H. Bongard van den
1
1
University Medical Center, Radiation Oncology, Utrecht,
The Netherlands
2
Julius Center for Health Sciences and Primary Care-
University Medical Center, Epidemiology, Utrecht, The
Netherlands
Purpose or Objective
In breast cancer patients with limited (sentinel) lymph
node involvement, axillary lymph node dissection (ALND)
is increasingly being replaced by axillary radiotherapy.
Since ALND is associated with a high risk of upper-body
morbidity, axillary radiotherapy might be favorable in
patients with limited lymph node involvement. However
radiation-induced morbidity can also influence quality of
life, the extent of which may depend on the irradiated
volumes. We compared patient reported outcome
measures (PROMs) of breast cancer patients at the start
adjuvant radiotherapy, during and after radiotherapy
according to the extent of axillary treatment.