ESTRO 36 Abstract Book

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S826 ESTRO 36
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spared by the CAA, which decreased by 0.62% from the CA0.
Minimizing the x-jaws significantly reduced the number of
split field from 61 to 37. In every field tested the
CA X optimization produced as good or superior results than
the other three techniques. For aspherical PTVs, CA X on
average reduced the number of split fields, the maximum
dose, minimized the dose to the surrounding OAR, and
reduced the MU all while achieving the same control of the
PTV.
Conclusion
For aspherical lesions larger than 100 cc, rotating the
collimator to minimize the x-jaw gap produced equal
tumor control while reducing the toxicity to the organs at
risk with lower monitor units and less split fields compared
to keeping the collimator fixed at 0º or with using
the Eclipse collimator optimization method. Compared to
the fixed collimator angle, the monitor units decreased an
average of 6% using a CAX approach, which was the lowest
of the four methods tested. The maximum dose to the
organs at risk also showed trends of decreasing, as well as
evidence to decrease the peripheral dose. The number of
split fields was highly controlled with CAX by optimizing
the parameter that determines if a field will divide. Of the
20 cases studied, the number of split fields decreased by
about 40% with the CAX from any other method used. The
CA X optimization allowed for a rotation of the collimator
between each field, which showed positive results in the
overall dose shape of the delivered quality assurance tests
on an electronic portal imaging device.
EP-1537 Iterative dataset optimization in automated
planning: implementation for breast radiotherapy
J. Fan 1, J. Wang1, Z. Zhang1, W. Hu1
1 Fudan University Cancer Hospital, Department of
radiation oncology, Shanghai, China
Purpose or Objective
To develop a novel automated treatment planning solution
for the breast radiotherapy.
Material and Methods
An automated treatment planning solution developed in
this study includes selection of the optimal training
dataset, dose volume histogram (DVH) prediction for the
organs at risk (OARs) and automatically generation of the
clinically acceptable treatment plans. The optimal
training dataset was selected by using an iterative
optimization strategy from 40 treatment plans for breast
cancer patients who received radiation therapy. Firstly,
the 2D KDE algorithm was applied to predict OAR DVH
curves, including the heart and left lung, for patients in
group A by considering the other group B as the training
dataset. New plans in group A were automatically
generated using the Pinnacle 3 Auto-Planning (AP) module
(version 9.10, Philips Medical Systems) based on the dose
constrains derived from the predicted DVHs. Next the
point-wise comparison, taking V 5, V 20 and mean value as
the criteria, between the automatic plans and original
clinical plans was performed both objectively and
subjectively. Finally the preferred plans in group A got
updated after the comparison and were used for the next
iteration by considering itself as the training dataset
instead. Above steps repeated until search and update for
new preferred plans was exhausted. After selecting the
optimal training dataset, additional 10 new breast
treatment plans were re-planned using the AP module
with the objective functions derived from the predicted
DVH curves. These automatically generated re-optimized
treatment plans were compared with the original
manually optimized plans.
Results
The proposed new iterative optimization strategy, shown
in Fig. 1, could effectively select the optimal training
dataset and improve the accuracy of the DVH prediction.
The average of mean dose of the OARs in the iterative
process for each group, group A and group B are illustrated
in Fig. 2. The dose differences, between the real and
prediction, decreased with iterations which indicated the
convergence of our proposed technique. As can be seen
from Tab. 1, the automatically AP generated treatment
plans using the dose constrains derived from the predicted
DVHs could achieve better dose sparing for some OARs
with the other comparable plan qualities.
Conclusion
The proposed novel automated treatment planning
solution can be used to efficiently evaluate and improve
the quality and consistency of the treatment plans for
modulated breast radiation therapy.
EP-1538 VMAT craniospinal radiotherapy, planning
strategy and results in twenty pediatric and adult
patients
F. Lliso1, V. Carmona1, J. Gimeno1, B. Ibañez1, J. Bautista1,
J. Bonaque1, R. Chicas1, J. Burgos1, J. Perez-Calatayud1
1Hospital Universitario La Fe, Radiotherapy Department,
Valencia, Spain
Purpose or Objective
To describe our VMAT craniospinal radiotherapy planning
strategy, to report the dosimetric results for the first 20
patients treated with RapidArc and to compare with
previously published data.
Material and Methods
Patients were treated in supine position in Varian Clinac
iX linacs (Millennium 120 MLC, OBI) and 6 MV RapidArc,
prescription doses (Dprescr ) were 23.4, 30.6 and 36 Gy.
Twelve patients were children (3-13 years, avg.: 7.2) and
nine adults (23-71 years; avg.: 38.8), the resulting PTV
avg. length was 64.8 cm (47-82 cm). The treatment
planning was performed with Eclipse® (V 13.0). Depending
on the PTV length, 2 or 3 isocenters were used with an
overlapping region of about 4cm, all coordinates being
equal except the longitudinal one. Two complete arcs
were applied in the cranial isocentre, one of them
encompassing the cranium plus the superior part of the
spinal region, and the other one intended to improve
conformity and optic sparing, only encompassing cranium.
For the spine, one full arc per isocentre was employed
except in 36 Gy cases for which a partial posterior arc was
added at lungs level. Collimator angles were set to ±5º
except for the second cranial arc (40º).
Plans were optimized using Progressive Resolution
Optimizer (PROII) and calculated with AAA algorithm, the
main were goals that at least 95% of the PTV received
D prescr and also the OAR sparing. The planning objectives
were defined at the first step of the optimization. Firstly,
optimization weights to PTV, Normal Tissue, lenses and
lungs were assigned and, once DVH values were close to
the desired ones, the rest of the surrounding OARs were
sequentially included (mean doses were employed); in
addition, for pediatric patients, homogeneous irradiation
of the vertebrae was required; finally, weights to
maximum dose to OAR located inside the brain PTV were
set to avoid hot spots. After that, the rest of the
optimization was carried out using the automatic
“Intermediate Dose Calculation” option.
Various dosimetric parameters and indices were
employed: PTV mean dose; D1cc, D2% and D98%; mean and
maximum doses for OAR; V5 and V20 for lungs; conformity
(CI=Vol95%/VolPTV) and homogeneity (HI=D1cc/Dprescr)
indices; Normal Tissue mean and V5 dose.
Results
We found avg. values for CI, 1.02 (0.98-1.09) and for HI,
1.08 (1.05-1.10) regardless of D prescr. OAR mean dose
values along with average values reported by different
authors are shown in Fig. 1. A great reduction is observed
for almost all OAR for 23.4 Gy, while for 36 Gy our results
are favorable for eyes and lenses and similar or slightly