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S189
ESTRO 36
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During a course of radiotherapy for head and neck (H&N)
cancer, non-rigid anatomical changes can occur. For
example, changes in volume of the target, changes in neck
diameter (contour) due to edema or weight loss, shifts of
hyoid or thyroid bone or other localized soft tissue
deformations. These anatomical changes cannot be
corrected for by a couch shift, but they can be observed
on daily Cone Beam CT (CBCT) and are scored digitally by
RTTs according to a traffic light protocol (TLP)(green: no
action, orange: evaluation of dose consequences before
the next fraction, red: immediate evaluation of dose
consequences). Orange and red scores can lead to a new
radiation plan, either on the original planning CT scans (O-
pCT) with local adjustment of target volumes or on a new
pCT scans (N-pCT) with complete re-delineation. In this
work, we evaluated how often re-planning was done for
non-rigid anatomical changes and which anatomical
changes lead to which new plan actions during the 7 weeks
of treatment.
Material and Methods
A consecutive series of H&N cancer patients (416) treated
from January 2015 until September 2016 were
retrospectively selected using the digital log of CBCT scans
(10862 H&N logs). These digital logs were analysed for the
number of new treatment plans on an O-pCT or a N-pCT.
Reasons for re-planning were categorized into: target
volume increase, target volume decrease, contour
decrease, contour increase and shift of target volume. To
evaluate the timing of re-planning, the week in which
delivery of the new plan started was scored as well.
Results
In 9% (37/416) of the H&N patients included in this
analyses, the treatment plan was adapted due to
anatomical changes detected during radiation treatment
on CBCT. Re-planning on a N-pCT with complete re-
delineation was done 22 times. In fifteen cases a new plan
was created after adjustment of contours on the O-pCT.
For 4 patients, two actions were taken, first a new plan
on the O-pCT and secondly (further in the treatment) a
new plan on a N-pCT. Figure 1 shows the anatomical
changes observed at the time of re-planning, as well as
the time of occurrence during treatment. In the early
weeks of treatment, the most observed reason for re-
planning was a target volume increase, both on a N-pCT as
well as on the O-pCT. In the last part of treatment, re-
planning on a N-pCT was mainly done because of contour
decrease, while re-planning on the O-pCT was chosen in
the event of local shifts of target volume. The majority of
adaptive treatment plans were made in the second, third
and fourth week of treatment for relatively 10, 9 and 10
re-plans.
Conclusion
Visual detection of anatomical changes on CBCT during
treatment of head and neck cancer, without pre-defined
adaptive radiotherapy protocol, results in re-planning in 1
out of 11 patients.
OC-0356 Adaptive strategy for rectal cancer:
evaluation of plan selection of the first 20 clinical
patients
R. De Jong
1
, N. Van Wieringen
1
, J. Visser
1
, J. Wiersma
1
,
K. Crama
1
, D. Geijsen
1
, L. Lutkenhaus
1
, A. Bel
1
1
Academic Medical Center, Department of radiation
oncology, Amsterdam, The Netherlands
Purpose or Objective
For rectal cancer, sparing the organs at risk with the use
of state-of-the-art planning techniques (IMRT/VMAT) is
compromised by the large margins that are necessary to
compensate for daily shape changes. In our clinic we
implemented a plan selection strategy with multiple plans
made prior to treatment. For each fraction, the best
fitting plan is selected based on daily cone beam CT
(CBCT) scans. The aim of this study is to assess the plan
selection strategy for the first 20 clinical patients with
respect to available plans, selected plans and safety.
Material and Methods
Multiple plans for plan selection were created for each
patient based on a single CT scan. For 20 patients, 3 PTVs
were created with different anterior margins for the upper
mesorectum. Margins could be either 25 mm, 15 mm, 0
mm, or -15 mm, with choice of margins based on the
anatomy as captured on the CT scan (fig. 1). Patients were
treated with either a long or short treatment schedule
(25x2 Gy, and 5x5 Gy, respectively). All plans were
delivered with VMAT. Plan selection was based on daily
CBCT. Selection was performed by 1 trained radiotherapist
(RTT), a physician and a physicist for all fractions of the
first week, and from the second week onwards by 2 RTTs,
one of whom trained in plan selection. Once a week a
post-treatment CBCT scan was acquired to assess the
validation of the selected plan at the end of treatment.
An expert IGRT RTT performed a weekly review,
inspecting all plan selections retrospectively, as well as
consistency between selected plans in the imaging system