972 / 1082
S956
ESTRO 36 2017
_______________________________________________________________________________________________
Results
This method was tested on 7 linacs of different makes and
models (Elekta Synergy Platform, Elekta Versa HD, Varian
Unique, Novalis Tx) in the authors' radiotherapy centres.
The average distance by which the isocentre moves
between both gantry positions was found to be 1.04 mm
(SD 0.30 mm), with the whole range covered by the [0.53,
1.48] interval. The two lowest values were achieved on
the two single energy Varian Unique linacs. It was found
out that the longitudinal isocentre shift is largely
independent of the gantry isocentre wobble determined
by the star-shot test. We also tested the alignment of the
collimator 0° setting with the gantry rotation plane. The
average deviation was found to be 0.16° (SD 0.10°), range
[0.04°, 0.31°].
Conclusion
The results appear consistent, but it would be helpful to
test the method on a wider pool of treatment machines
over a longer period of time. The longitudinal isocentre
shift during gantry rotation is a non-negligible parameter
which needs to be incorporated into the uncertainty
budget which is the basis for the CTV-PTV margin.
EP-1761 Workflow development for the clinical
implementation of an MR-guided linear accelerator
T. Stanescu
1
, A. Berlin
2
, L. Dawson
2
, J. Abed
2
, A.
Simeonov
2
, T. Craig
2
, D. Letourneau
2
, D. Jaffray
2
1
Stanescu Teodor, Radiation Physics- PMH, Toronto,
Canada
2
Princess Margaret Cancer Centre, RMP, Toronto, Canada
Purpose or Objective
Development of clinical workflows for the implementation
of a new external beam radiation therapy environment
which relies on hybrid MR-CBCT in-room imaging guidance.
Material and Methods
A standard radiation therapy 6X linac (TrueBeam, Varian
Medical System, Palo Alto, CA) was integrated with a 1.5
T diagnostic MR scanner (IMRIS, Minnetonka, MN). The MR
can move on rails and was tuned up to perform optimal
imaging inside the treatment room in the proximity of the
linac. The patient load is transferred directly between the
MR diagnostic table and the linac IGRT couch via a
hovercraft system (Zephyr XL, Diacor, Salt Lake City, UT).
No special MR safety requirements were employed
regarding the curation of the linac room – the linac/couch
can be freely operated mechanically when the MR magnet
is present - only typical MR room screening for
ferromagnetic content was implemented. Comprehensive
testing was completed to confirm negligible magnetic
field coupling between the MR and the TrueBeam system
(linac and patient table). Since the linac retains its default
features and an MR imager is available in the linac vault a
combined MR-kV approach can be employed for the
patient setup verification and treatment delivery. A new
software tool was developed in collaboration with Varian
to provide the computation and implementation of
treatment couch shifts based on soft-tissue information,
i.e. image matching between plan MR and guidance MR. In
this study, clinical workflows for liver and prostate were
developed and tested. Each site posed challenges from
patient image data planning and acquisition to RT planning
and in-room guidance. The approach was to integrate the
capabilities offered by the new technology in existing
processes.
Results
MR imaging protocols for planning and guidance were
established. The guidance scans were optimized to
minimize session time with negligible penalty on the
accuracy of the image matching process (planned vs. on
demand). MR acquisition was also designed to allow for
collection of data needed for CT+MR as well MR-only (or
synthetic CT) workflows. This is expected to facilitate
access to the in-house adaptive RT implementation in
RayStation (RaySearch, Stockholm, Sweden). All MR image
data was validated for RT use by means of comprehensive
testing for global image quality and correction of spatial
distortions. In particular for liver, the management of
motion was adapted for the MR environment in the case of
potential subjects undergoing either breathhold or
abdominal compression (AC). Breathhold was evaluated
using Medspira (Minneapolis, MN) whereas AC was
implemented using pneumatic pressure belts. Staff
requirements and safety for in-room operations was
evaluated via simulations and dry runs.
Conclusion
Workflows for MR guidance in prostate and liver were
designed and preliminary tested. The next step is to
enable imaging-only clinical trials in patients. Based on
feedback the workflows will be refined to allow for the
full implementation of MR-guidance studies.
EP-1762 A Comparative Study of 4D and 3D
CTSimulation in Esophageal Carcinoma
J. Li
1
, G. Lai
1
1
Fujian Cancer Hospital, radiation oncology, Fuzhou-
Fujian, China
Purpose or Objective
To compare the internal gross target volume (IGTV) and
its displacement of primary esophageal carcinoma (EPC)
on the base offour-dimensionaland three-dimensional
computed tomography (4D-CT and 3D-CT) simulation
technology.
Material and Methods
Twenty-two esophageal cancerpatients with pathological
proved diagnosiswererecruited in this prospectively study.
Every patient sequentially received contrast enhancement
free-breathing 3D-CT and respiration-synchronized4D-CT
simulationchest.Then the target volume and the
displacement on three orthogonal directionsof three
different
IGTV
planningmethods
(including
IGTV
4D,
IGTV
4D'
and IGTV
3D
. The dice similarity coefficient
(DSC) and overlap index (OI) between IGTV
4D
and IGTV
4D'
,
between IGTV
4D
and IGTV
3D
for different segments of
esophagus were calculated. Statistical analysis included
theFriedman test, analysis of variance on the base of
repeated measurement data and paired-samples student t
test and the
P
<0.05 was set as statistically significant.
Results
There were statistical significance of displacement at left-
right, anterior-posterior, and superior-inferior directions
of primary esophageal tumor GTV of the ten phases
originated from medium-thoractic segments and medium-
lower-thoractic segments (
P
= 0.005 and
P
= 0.001). There
presented a significant differences of primary tumor
volume where appeared IGTV
3D
> IGTV
4D
> IGTV
4D'
(
P
<0.05).In
other words, the implementation of GTV by means of
extending position error from based of 3D-CT wouldlead
to unnecessary radiation of the surrounding normal tissues
(about 9~24%); However, the application of GTV only by
means of integrating end-inhalation and end-exhalation
phases would result in uncover target area (about
10~34%).
Conclusion
4D-CT simulation technology is superior to 3D-CT
simulation technologyfor IMRT in esophageal cancer.
EP-1763 Acute toxicity and in-vivo dosimetry of a two
week hypofractionated schedule within the HYPORT
study
A. Saha
1
, G. Goswami
2
, S. Mandal
2
, A. Mahata
2
, D.
Midha
3
, R. Ahmed
4
, S. Agarwal
4
, S. Ray
5
, J. Das
5
, S.S.
Datta
6
, S. Sinha
7
, S. Chatterjee
2
1
Tata medical center, Radiotherapy, Kolkata, India
2
Tata medical center, Radiation Oncology, Kolkata, India
3
Tata medical center, Oncopathology, Kolkata, India
4
Tata medical center, Breast Surgery, Kolkata, India
5
Tata medical center, Nuclear Medicine, Kolkata, India