ESTRO 36 Abstract Book

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S438 ESTRO 36
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Results
Anatomical robust optimization resulted in adequate CTV
doses if at least three artificial CTs were included next to
the planning CT. Online plan adaptation also resulted in
adequate CTV irradiation, whereas this could not be
achieved using the SFUD approach, even with a PTV margin
of 5 mm (Figure 2). Anatomical robust optimization
provided considerable OAR sparing compared with the
SFUD approach (5 mm margin), with an average reduction
in max-dose and mean-dose parameters of 6.0 Gy (17%)
and 5.8 Gy (24%), respectively. The use of online plan
adaptation resulted in further OAR sparing compared with
anatomical robust optimization, reducing max-dose and
mean-dose parameters on average by 3.8 Gy (13%) and 3.4
Gy (23%), respectively.
Conclusion
We have developed an anatomical robust optimization
method that effectively dealt with the variation in nasal
cavity filling, providing substantially improved CTV
coverage and OAR sparing compared with the conventional
SFUD approach. Online plan adaptation allowed for further
OAR dose reduction and we therefore recommend this
planning strategy to be pursued for future application in
these patients.
PO-0818 Improving plan quality and efficiency by
automated rectum VMAT treatment planning
G. Wortel1, J. Trinks1, D. Eekhout1, P. De Ruiter1, R. De
Graaf1, L. Dewit1, E. Damen1
1 Netherlands Cancer Institute Antoni van Leeuwenhoek
Hospital, Department of Radiation Oncology,
Amsterdam, The Netherlands
Purpose or Objective
To develop, evaluate, and implement fully automated
VMAT plan generation for rectum patients that receive
either palliative 39 Gy (13×3 Gy), or curative 45 Gy (25×1.8
Gy, postoperative), 50 Gy (25×2 Gy, preoperative)
treatment.
Material and Methods
The automatic rectum VMAT plan generation is performed
by a combination of our in-house developed automation
framework FAST and the Pinnacle3 Auto-Planner. The
automatic planning starts after the physician has
delineated the rectum target volume(s). FAST starts our
TPS Pinnacle3, creates a patient record, and imports the
CT. The patient’s skin and bladder are auto-segmented by
Pinnacle3’s module SPICE. In addition, the small bowel is
delineated using a custom-made FAST module. The
bladder and small bowel are merged to a structure that is
used as the single OAR. Next, a density override of 0.5
g/cm 3 is performed on any air pockets in the PTV that are
identified using a density threshold. A dual arc VMAT plan
is set up and the dose distribution is optimized using the
Pinnacle3 Auto-Planner. After the generation of the Auto-
Plan, which takes about 45 minutes, it is presented to the
dosimetrist for approval.
The Pinnacle 3 Auto-Planner creates plans based on a set of
dose optimization goals and a number of advanced settings
called the “treatment technique”, which allows (indirect)
control over the resulting plan. The main challenge is to
develop a single treatment technique that leads to
optimal plans, which meet our precise and high clinical
demands, for a large patient population.
After having optimized the treatment technique using a
test set of 30 patients, we evaluated the Auto-Plans by
performing a blind test where 4 physicians and 4 planning
dosimetrists were asked to compare manual clinical plans
with Auto-Plans for 10 new patients.
Results
The optimized treatment technique is shown in Table 1.
On average, the mean dose to the small bowel + bladder
is 2.5 Gy lower for the Auto-Plans compared with manual
plans, at the expense of having a slightly increased dose
in the lateral direction. An example of a manual plan and
an Auto-Plan is shown in Figure 1. The result of the blind
test was a unanimous preference for the Auto-Plans (20-
0), based on a better PTV coverage and a lower OAR dose.
The slightly higher lateral dose was considered
acceptable.
Conclusion
We have successfully developed automatic rectum VMAT
treatment planning using our automation framework FAST
in combination with the Pinnacle3 Auto-Planner. The Auto-
Plans systematically differ from the manual clinical plans
(with an average OAR mean dose reduction of 2.5 Gy) and
are unanimously preferred by physicians and dosimetrists.
This clearly demonstrates how the implementation of an
Auto-Planner system, combined with the accompanying
reconsideration of plan style and clinical trade-offs, can
lead to improved treatment plans. As a result, automatic
rectum VMAT planning has been introduced in our clinic as
of July 2016.
PO-0819 Robustness evaluation of single- and multifield
optimized proton plans for unilateral head and neck
M. Cubillos Mesías1, E.G.C. Troost1,2,3,4,5, S. Appold2, M.
Krause 1,2,3,4,5, C. Richter1,2,3,4, K. Stützer1,4, M. Baumann1
1OncoRay – National Center for Radiation Research in
Oncology- Medical Faculty and University Hospital Carl