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observed on W2-CT. The degradations for D95 are 10.6%
and 11.8% for W2-CT and BS-W1-CT, respectively.
Similarly, the D90 degradations are 3.2% and 4%.
Conclusion
Our model was validated by comparing the WET and
dosimetric deviations between a simulated scenario and
the real data set. As a future work, we will use our model
to automatically generate uncertainty scenarios to feed a
TPS for robustness evaluation and optimization of proton
therapy plans. For instance, the new 4D robust optimizer
of the RayStation can easily consider multiple 4D-CT series
during the
optimization
process.
EP-1644 Deep inspiration breath hold respiratory
gated 3DRT for left breast cancer:Our clinical
experience.
M. Pinto Monedero
1
, M. Castanedo Álvarez
1
, J. Martínez
Ortega
1
, N. Gómez González
1
1
Hospital Universitario Puerta de Hierro Majadahonda,
Medical Physics, Madrid, Spain
Purpose or Objective
The purpose of this work is to describe Deep Inspiration
Breath Hold (DIBH) Respiratory Gated 3D Radiotherapy
Treatments (RT) in left breast cancer patients in our clinic
and to compare the results to free breathing (FB)
treatments.
Material and Methods
Patients were trained prior to simulation to evaluate
suitability for DIBH technique. Varian Real Time Position
Management (RPM) System (Varian Medical Systems, USA)
was used to monitor the patients’ respiratory motion.
They were asked to take a deep breath and hold it
repeatedly. A deep breath amplitude was set as a
reference level for the treatment sessions. For those
patients eligible to this technique, two CT scans were
acquired, under FB and DIBH conditions using a Toshiba
Aquilion LB CT (Toshiba Medical Systems, Japan).
Two treatment plans prescribed to 50 Gy in 25 fractions
were computed for each patient: one in FB and one in DIBH
conditions with XiO 5.02 treatment planning system
(Elekta AB, Sweden). Average dose and V20 for heart and
left lung as well as V95 for PTV were evaluated with the
physician to decide the treatment technique.
Patients were treated in a Varian Clinac-21 EX (Varian
Medical Systems, USA) with analogous Varian RPM System.
Patient position was verified through AP and lateral planar
images in DIBH conditions. The same amplitude which was
set as reference level at the simulation must be reached.
Results
25 patients underwent this procedure since the technique
was introduced at our clinic. Only one patient was found
not eligible. 20 of them were finally treated under DIBH
conditions, whereas 5 of them were treated in free
breathing conditions. Table I summarize average V20 for
heart and left lung as well as V95 for PTV. A significant
heart dose sparing was achieved in every patient, as V20
was reduced by 77.4%. Moreover, the left lung benefits of
a 24% reduction in V20.
Table I: Main Dose volume histogram results: average PTV
V95, V20 Left Lung, V20 Heart.
V95 PTV V20 Left Lung V20 Heart
DIBH 90,0% 21,65%
2,98%
FB 89,0% 28,47%
13,17%
Figure1: Axial and coronal CT slices of FB (on the left side)
and DIBH (on the right side) dose distributions for the same
patient.