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ESTRO 36 2017
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target volume with the 100% isodose. The generated plans
were evaluated in terms of dose distribution of
PTV(D95,D98,D
max
), doses of total lungs (V20,V10,V5),
heart(V30,V20 and mean dose).
Results
The mean dose values for target volume and critic organs
were displayed in Table-2. The average treatment time
and monitor unit were 6.85min, 5868MU respectively.
Conclusion
Bilateral breast treatment is complex and difficult due to
the field junction problem with the standard techniques.
However, based on the results of this study, HT plans have
shown high homogeneity and coverage indexes of target
volumes while reducing the lung and heart doses. We
expect the increase of low dose region due to helical
irradiation. However, by using complete blocking, we
provide that the values remained at the tolerance limits.
EP-1575 Automated VMAT planning for whole brain
irradiation with hippocampus sparing
J. Krayenbuehl
1
, M. Di Martino
1
, M. Guckenberger
1
, N.
Andratschke
1
1
University Hospital Zürich, Department of Radiation
Oncology, Zurich, Switzerland
Purpose or Objective
Whole-brain radiation therapy (WBRT) has been the
standard treatment for patient with multiple brain
metastases for decades. However, with broader
application of stereotactic radiotherapy the use of WBRT
has decreased in the past years to avoid possible adverse
neurocognitive effects. With the advent of
neuroprotective strategies such as hippocampus sparing
(HS) the interest in WBRT has been revived. The gold
standard constraints for HS WBRT were published by the
RTOG 0933 in 2011. In this project, we an automated
treatment planning (aTP) approach aiming especially at
reduced hot spots in the normal brain.
Material and Methods
Fourteen consecutive patients treated with HS WBRT were
enrolled in this study. The planning target volume (PTV)
was defined as the whole-brain excluding the hippocampal
avoidance regions defined as the hippocampal expanded
by 5mm in three-dimensions. 10 x 3 Gy was prescribed to
92% of the target volume. All patients were planned with
VMAT technique using four arcs and two couch kicks (300°
and 60°). The plans were optimized for a Trilogy linac
(Varian Medical System) with 5mm leaf width (Millennium
MLC). Plan were optimized using Auto-Planning (AP)
(Philips Radiation Oncology Systems) and using one single
AP template. Plan results were compared to published
dose volume histogram (DVH) parameters for HS WBRT.
Dose to 2% (D2%) and 98% (D98%) of the target volume and
homogeneity index (HI) were evaluated. The hippocampus
dose was evaluated based on the minimal dose (D100%)
and the maximal dose (Dmax). In addition to DVH
parameters evaluation, the effective planning time
defined as the working time required between the
volumes definition and the end of the plan optimization
was evaluated.
Results
Target and hippocampus DVH parameters are shown in
Table 1. The D2% to the brain was reduced on average by
> 3Gy [MG1] (34 Gy vs. RTOG 37.5Gy) and the maximum
hippocampus dose was reduced by > 1Gy. All the other
parameters were similar to published data. The effective
planning was kept below 10’ for each patient.
Conclusion
Automated TP for HS WBRT with VMAT achieved
significantly decreased maximal brain dose and maximal
hippocampus dose while fulfilling all other RTOG 0933
constraints. With this approach, hot spots > 115% could be
significantly reduced in contrast to a maximal allowance
of 130% in the RTOG protocol.
EP-1576 Tomotherapy WBRT with SIB planning for
patients with brain metastases
D. Synchuk
1
, S. Odarchenko
1
, N. Seryogina
1
, O.
Zinvaliuk
1
, M. Gumeniuk
1
, K. Gumeniuk
1
1
Ukrainian center of Tomotherapy, RT department,
Kirovograd, Ukraine
Purpose or Objective
Whole brain radiation therapy (WBRT) is usually the
primary treatment option for patients with multiple brain
metastases extending median survival time and improving
the quality of life. The aim of this study is to develop at
our institution the technique for tomotherapy planning of
WBRT with simultaneous integrated boost (SIB) for
metastases.
Material and Methods
The target/OAR volume delineation was performed using
MIM software. The PTV1 for SIB included GTV for
metastases which was defined as the contrast-enhancing
lesions on T1-weighted MRI plus 3 mm uniform margin. The
PTV2 for WBRT included the whole brain plus 3 mm margin
excluding PTV1. The aim of planning was to deliver the
40/30 Gy dose in 10 fractions to SIB/WBRT respectively.
Prescription was made to the median dose, also D
99%
should
be ≥ 95% D
presc
and D
1%
≤ 107% D
presc
.
Results
The development of the standartised planning procedure
began after treatment of 8 patients and gaining some
experience. For planning purposes an automated workflow
to produce additional contours was created: 2 consecutive
5 mm rings around the PTV1 to form the dose falloff; PRV
structures as 3 mm outer ring contours for optic nerves,
chiasm and brainstem; the structures that overlapped PTV
were subdivided into “PTV OAR” and “PTV OAR PRV”, the
subvolumes created for overlapping regions, and “OAR
Plan” and “OAR PRV Plan” for non-overlapping; a special
logical volume PTV2_nR was created by extracting
previously made rings from PTV2 for more clear DVH and
statistical analysis.