2. SIMULATION
•The goal of Radio therapy is to deliver a
homogeneous dose to tumor & less dose to
critical structure and normal tissue, so that we
need to locate the position of tumor in relation
to the surrounding tissue this process is known
as" SIMULATION”
3. The primary goal of simulation is
•Localize the isocentre
•The central axis of the beam
•Edge of the treatment field to optimize
coverage of target & minimize irradiation of
normal tissue
4. Conventional Simulator
• It consists of diagnostic
X-ray tube mounted on
a rotating gantry, just
mimic all the
mechanical features and
geometric field
arrangement of various
mega voltage machines
ranging from co-60 to
high energy Linac
5. In mega voltage machine radiation
fields are defined with collimator.
In conventional simulator the
rectangular and square fields are
defined with delineator wires to
enable visualization of the target
as well as of healthy tissues
adjacent to the target
6. In this it covers the fallowing process
•Tumor and adjacent normal tissue
localization
•Treatment simulation
•Treatment plan verification
•Monitoring of treatment
7. Limitations
• It may lead to more normal tissue irradiation
• Information obtained only in 2D
• Soft tissues are not visible, thus placement of field in relation
to only Bony land mark
• Conventional image receptor are unable to resolve difference
smaller than few percentage in the intensity of incident
radiation
• Large area of x-ray beam used in conventional radiation
therapy produce significant amount of scattered radiation
that interfaces with visualization of subtle difference in x-
ray transmission
8. CT-SIMULATION
• It is the process in which simulator is carried out
using software created Virtual simulator on patient
CT data set. It simulates all the parameters of the
actual treatment machine (Gantry angle, couch
position, Radiation field). The presence of patient
physically is not required, while doing treatment
simulation planning. Thus it also called as Virtual
simulation
9. CT-Simulator has 3major components
•CT-scanner
•Patient marking system
(laser-2 in lateral, one
in sagital)
•Virtual simulation
work station
10. Important features
• The patient is marked
with reference
markers by using
lasers.VSIM software
calculate the distance
of CT isocenter with
reference marker.
After the target
volume h’s been
determined, the
computer calculate the
shift of target
isocenter from the CT
isocenter with
11. •Fast scanning and
reconstruction of
transfer slices,
exceptionally useful for
visualizing anatomy in
many region of body
(crossectional, coronal &
sagital section)
12. •It should not
necessary to out line all
features on all slices,
methods of linear &
quadratic (GTV,CTV
& PTV) interpolation
are combined with
manual slices by slice
checking and editing
14. •VSIM also having the
features such as a virtual
light field,wich
illuminates the skin 3D
image of the patient,
also have an image
treatment machine
together with a gantry
and the treatment table
will move to show the
position of the beam
chosen and particularly
weather there is any
possibility of collision
15. •VSIM also provide 2D planar image that
is DRR (Digitally reconstructed radio
graph), which are ray line construction
through a 3D-volumetric CT data set,
which simulate the treatment using DRR
The planar simulation provides Beam eye
view (BEV)
16. Basic approach of DRR is
Virtual source
position
Definition of image
plane
Ray tracing from
virtual source to
image plane
17. Advantages of CT-Simulation
• Patient throughput is more
• Non coplanar simulation is possible
• 3D data set is available, resulting in better
visualization of tumor and nodal involvement, leads
to reduction in side effect
• Full 3D allowing unique verification of beam
coverage and avoidance in three dimensions
• Beams can be simulated and verified that are n’t
possible with conventional simulation
18. advantages
• The verification images,DRRs can contain more information
than conventional simulation and can be manipulated to
enhance tumor visualization.
• There is a much closer connection to diagnostic information
with CT -sim allowing integration of multimodality images
• Reduced transference accuracies by omitting conventional
simulator verification
Disadvantages of CT-simulation
• Organ motion are nt visualized
19. By using VSIM treatment simulation & planing
can be carried out by 2 ways
• The simulation based on bony land mark by using
DRR for conventional radio therapy planning
• The simulation based on the 3D target volume&
critical structures for conformal radio therapy
planning
