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Cone Beam CT Verification PROCEDURE
OBI Advanced Imaging version 1.4
Cone Beam CT version 2.1
4D ITC version 8.2
Clinac version 7.5
Revision 2.0.0
Objective: After completing this module the student will have
performed the following tasks
using the OBI Operations Manual as a resource: Setup the patient
Perform a Cone Beam CT Acquire a Topogram Export the Images to OBI
Analyze images Shift the Exact Couch into treatment position Treat
the patient
A. Exercise Key
1. Right mouse click denoted as RMC. 2. Left mouse click denoted
as LMC. 3. Bracket () denotes additional options.
4. The > symbol denotes drill down from menus.
B. Procedure Content:
1. Load Session on 4D ITC 2. On Board Imager Graphical User
Interface 3. Acquire Images 4. Imaging and Verification Tools
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5. Review CBCT Images
C. 4D ITC
1. Check-in the patient 2. Select the patient from the treatment
queue and click OK (Figure 1).
Figure 1: 4D ITC; Treatment Queue
3. Select the CBCT Setup Field and click Mode Up (Figure 2).
Figure 2: CBCT Setup Field; Mode Up
4. Set up the patient. Make sure couch rails are removed. 5.
Insert appropriate Bow-Tie Filter. For information on Bow-Tie
Filters refer to the
System Components Procedure. 6. The OBI arms can be extended
using the hand pendant to verify clearance
while inside the treatment room.
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D. OBI workstation
1. If not already positioned, extend the arms from outside the
room by clicking Download Axes.
Press Motion Enable and Auto buttons on the OBI Console to
position the arms.
WARNING: Always verify clearance prior to extending the OBI arms
from the OBI console.
2. On OBI workstation click 3D/3D Match to start acquisition
(Figure 3). The CBCT application will open automatically. The
original planning CT will be downloaded on to the OBI for
matching.
Figure 3: 3D/3D Match Button
3. The following warning message may appear: Make sure Couch
Rails are removed if fitted.
Remove the couch rails and confirm the warning message by
clicking OK (Figure 4). This message can be disabled in CBCT
Administration.
Figure 4: Remove Couch Rails Dialog Box
4. If this is the patients first Cone Beam CT the following
options will be available.
Click Acquire New Scan (Figure 5). Quick Scan (Param. Display)
will be covered in section G of this procedure.
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Figure 5: Acquire New Scan
5. Patient Setup Wizard page appears (Figure 6).
Figure 6: Patient Set Up Page
1. The Default CBCT Mode will be selected the first time a
patient is scanned. If a different mode is selected the system will
then default to that mode for all subsequent scans. 2. If Patient
Orientation is provided with the plan this field will populate
automatically, if not it must be selected. 3. Diameter [cm] of the
scan correlates to the selected CBCT mode. 4. Acquisition Mode
correlates to the selected CBCT Mode. 5. Reconstruction Volume
defaults to 512x512. This can be changed if desired. 6. Slice
Distance [mm] defaults to 2.5mm and can be changed if desired.
Planning CT slice thickness and CBCT slice thickness do not have to
match.
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6. Select the appropriate predefined CBCT mode from the CBCT
Mode Menu and if necessary select the appropriate patient
orientation. (Figure 7)
Figure 7: CBCT Mode
Diameter and Acquisition Mode will vary based on the selected
CBCT mode.
7. Click Next. (Figure 6) 8. If a Topogram is required refer to
the Topogram Acquisition procedure for
instructions, otherwise click next. The Topogram step can be
turned off in OBI administration in which case the system will
continue to step 9.
9. The system will calculate maximum scan range based on the
CBCT mode selected, approximately 18cm for Full Fan scans and 16cm
for Half Fan scans. (Figure 8) Scan Range Definitions will be
displayed. (Figure 9)
Figure 8: Scan Range
*OBI only allows Single Scan CBCTs. 1. Width- Axial length of
the scan. 2. Center- Defines the Isocenter of the scan. Changing
the value will result in a couch shift. 3. Z-Zero Pos.- Defines the
position of the DICOM Origin for the scan.
Figure 9: Scan Range Definition
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10. Press Start Scan (Figure 10). The following message will
appear: Acquiring
Dark Field Please Wait (Figure 11). The system performs a Dark
Field to account for and eliminate background
noise.
Figure 10 Figure 11: Dark Field Message
11. Once the dark field has been acquired the gantry needs to be
moved to the start position. This will be 185 or 175 whichever is
closer to the actual gantry position. The couch may also move to a
safe position for the Cone Beam CT.
Press and hold MEB and >> on the Clinac dedicated keyboard
to move gantry and/or couch into position (Figure 12).
The following message will appear if the couch movement is
aborted. Couch Position error the couch is outside of the allowed
area (Figure 13).
Figure 12: Enable Clinac Movement Figure 13: Couch out of range
for Scan
12. At Start Position Dialog Box will appear.
Read instructions and then click OK (Figure 14).
Figure 14: Start Scan Position
13. Press and hold X-ray footswitch or the Hand Pendant. Then
press and hold the MEB and >> on the Clinacs dedicated
keyboard. This will start CT acquisition.
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Hold all three depressed until the acquisition has finished
(audio signal will stop).
Once the scan is complete release the MEB and >> first and
then release the X-ray footswitch.
14. Acquisition and reconstruction progress will be displayed on
the screen (Figure 15).
The Acquisition Progress is the data being acquired and sent
from the CBCT cache to the Reconstructor computer.
The Reconstruction Progress is the process of reconstructing the
projection data by the Reconstructor computer.
The Serialization Progress is the process of sending the data
back from the Reconstructor computer to the OBI computer.
Figure 15: Acquisition Progress
15. If the scan is interrupted due to a purposeful action (ex.
Breath-hold CBCT) or
an accident (release of dedicated keyboard or foot/handswitch)
the scan can be resumed. Select Resume Acquisition(Figure 16a). The
system will request the gantry be repositioned approximately 10
degrees prior to the interruption position (Figure 16b). The system
will then request that the acquisition be resumed(Figure 16c)
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Figure 16a: Resume Figure 16b: Reposition Gantry Figure 16c:
Resume Acquisition
16. If the couch was moved to a safe position for scanning it
will need to be returned to the original set up position prior to
beginning the match process (Figure 17).
Figure 17: Restoring Couch Positions
Press and hold MEB and >> on the Clinac dedicated keyboard
to move the couch into position (Figure 18).
The following message will appear if the couch movement is
aborted. Reminder the couch positions have been changed since
startup (Figure 19).
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Figure 18: Enable Clinac Movements Figure 19: Couch Position
17. Once the scan is complete the reconstructed images will be
displayed on the screen. Review them if needed (Figure 20).
Select Accept and Export Scan (File > Export to DICOM). If
the patient moved during the scanning process, select Decline Scan
and re-
start the process.
Figure 20: CT Image Review Page
18. Once the Accept and Export Scan button has been selected,
the CBCT image is
stored on the OBI workstation. The CBCT image will then be
imported into the 3D/3D Match workspace of OBI. The entire process
may take a few seconds to complete. Upon completion, the
Acquisition workspace closes and the OBI Analyze workspace opens
automatically.
E. OBI 3D/3D Workspace
1. At this point there are two options for matching: Automatic
Match (see step 3) and Manual Match (see step 5). They can be used
individually or in combination.
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2. To perform an Automatic Match, click on the Automatic Match
Icon (Figure 21).
OBI will perform an automatic match using the Mutual Information
Algorithm (see Appendix E for more information on the
Algorithm)
Figure 21: 3D/3D Toolbar
3. The Auto Match Control dialog box opens and the matching
process starts (Figure 22).
Figure 22: Auto Match Control Dialog Box
4. The system shifts the two superimposed images relative to
each other during the match and calculates the couch correction
values (Figure 23 and 24).
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Figure 23: Automatic Match in progress
Figure 24: Dashboard; Couch Values
Always manually verify an automatic match using the match
verification tools.
5. To perform a Manual Match, make sure the Manual Match Icon is
active. Then use the mouse or the arrow keys on the keyboard
(Figure 25).
Adjust the image using the arrow keys on the keyboard. This
allows for small adjustments in the match alignment. Make large
adjustments by clicking and dragging the image with the mouse or
hold the Alt key and press the appropriate arrow key.
Rotate the image by holding the left mouse button and then click
and drag outside of the dotted red circle or hold the Ctrl key and
use the right or left arrow keys. Rotate the image in large steps
by holding the Alt+Ctrl keys and using the right or left arrow
key.
To rotate the main viewing window between Transversal, Sagittal,
and Coronal views press Ctrl+R or this icon in the main viewing
window.
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Verify the match using the match verification tools (see Step
6).
Figure 25: Manual Match
6. Verify the match using the Match Verification Tools.
Select Window and Level . This allows manual adjustment of
brightness and contrast (Figure 26a).
Right Click on the Window and Level bar to select Range which
automatically adjusts to a specific anatomical selection and can be
used on both the CBCT and the reference CT (Figure 26b). (Can also
be used in the CBCT window (Figure 20).)
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Figure 26a: Window and Level Figure 26b: Range
From the Dynamic Window check or uncheck contours as needed
during the verification process (Figure 27a).
Contours can be turned off and on as a group using the Contour
button (Figure 27b)
Figure 27a: Dynamic Window Figure 27b: Contour button
Select Split Window . This allows for viewing of 50% Reference
CT and 50% Cone Beam CT (Figure 28).
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Figure 28: Matching; Split Window View
Select Moving Window . This allows viewing of the acquired Cone
Beam CT within the rectangle (Figure 29).
Figure 29: Matching; Moving Window View
Select Color Blending . The blend function is used to overlay
one image over another and shows the two images in complimentary
colors to assist in matching. Colors can be changed in OBI
administration (Figure 30).
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Figure 30: Matching; Color Blending
Other Tools used during the Match Verification Process
Tool Description
Page Up and Page Down Keys
You can scroll through the sagittal, coronal, and transversal
views of CBCT or CT images by pressing the Page Up/Page Down
keys.
Flicker Display To activate this tool, take the following steps:
1. Move the Blend slider to the extreme left or right. 2. Press
Ctrl+A to make the display switch between the one blend setting
(100% reference image) and the other (100% acquired image). When
you see no motion or the smallest amount of motion, then the two
images are superimposed properly.
Table 1: Other Match Verification Tools
WARNING: If the match is performed incorrectly and the images
are mismatched, corrections to the treatment setup values will be
incorrect, causing the wrong area to be irradiated during
treatment. Be sure to follow department mandatory clinical quality
assurance procedures to prevent wrong treatments. Before making any
corrections to the treatment setup values, always verify all
matches visually. To determine whether the images are properly
overlaid, use the matching verification tools.
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7. Once you have verified the match result and accepted the
couch correction
values, you can apply the couch shift. If for some reason you do
not want to send a specific shift it can be deselected by
un-checking the include box.
Reset Shift will zero out any shifts and realign the images to
there initial positions.
The Save Match button saves the match back to the database for
immediate review in Offline Review.
Click Apply Shifts to send the Target positions to the clinac
console. (Figure 31).
Figure 31: Dashboard; Apply Shift
Use the MEB and the >> key on the Clinac dedicated
keyboard to move the couch into the new position.
8. Click Done on the OBI workstation (Figure 32).
Figure 32: OBI workstation; Select Done
9. Prior to treating, retract the OBI arms to reduce damage to
the kV detector from scattered radiation.
NOTE: After acquiring a CBCT the OBI is unable to communicate
correctly with the generator causing a problem with radiographic
acquisitions. Switch the generator from radiographic to fluoro mode
and back to radiographic mode. This will reset generator
communication and solve the problem.
F. 4D ITC
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1. The 4D ITC Apply Couch Shift dialog box opens.
Select Apply for Session and then click Apply (Figure 33).
Select Apply Permanently only if its desired to apply the couch
values
permanently (Figure 34).
Figure 33: Apply Shifts; Session Figure 34: Apply Shifts;
Permanently
2. Plan, Shifted and Actual Couch parameters (Figure 35).
Figure 35: Couch Parameters
3. Select the first field to treat and click Mode Up (Figure
36).
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Figure 36: Mode Up
4. If the couch values are out of tolerance the following
message will appear asking for confirmation of table parameters
(Figure 37).
Enter User name and password and then click OK.
Figure 37: Out of Tolerance Override
5. Continue treatment as usual.
WARNING: When OBI is being used, closed circuit video and an
audio intercom must be available to the user to observe and
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communicate with the patient. The priority here is to avoid all
collision risks.
G. Quick Scan (Param. Display) 1. The Quick Scan (Param.
Display) button (Figure 38) opens up the Scan
Parameter menu for quick and easy selection of CBCT settings
(Figure 39). After selections have been made continue from step
D-10.
Figure 38: Quick Scan (Param. Display)
Reconstruction Filter: Standard: 50/50 smooth and
sharp Smooth: Best at defining soft
tissue Sharp: Emphasis on bone Ultra Sharp: Max emphasis on
bone Ring Artifact Suppression: You can control the strength of
the image correction by selecting one of the following levels of
ring artifact suppression: None: allows you to switch ring
artifact suppression off Weak: might miss some rings Medium: is
recommended Strong: might remove essential
information
Figure 39: Scan Parameters
H. Quick Scan
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1. When Quick Scan is selected the system will apply the same
parameters that were selected in the previous CBCT acquisition for
that patient. (Only settings in the parameter window are saved,
dashboard changes will not be saved.) Continue from step D-10.
I. Reconstruct Existing Scan
1. Reconstruct Existing Scan can be used in situations where
changes to the reconstruction parameters would be beneficial to the
matching process or when certain system errors occur during the
CBCT process. Clinically this would be performed immediately
following a CBCT acquisition. For example, following the CBCT
acquisition the therapist decides that the smooth filter would have
been a better option than the selected sharp filter.
2. Select Accept and Export Scan (Step D17). 3. Select Cancel in
the 3D/3D match analyze workspace (Figure 40).
Figure 40: Cancel
4. Select 3D/3D (Figure 41)
Figure 41: 3D/3D
5. The CBCT application will reopen. Select Reconstruct Existing
Scan and select the most current (just performed) scan (Figure 42a
and 42b). Click Next.
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Figure 42a: Reconstruct Existing Scan Figure 42b: Verify most
current scan.
6. Make changes to the reconstruction parameters if necessary
(Figure 43a) then click Reconstruct (Figure 43b)
Figure 43a: Parameters Figure 43b: Reconstruct
7. When reconstruction has finished select Accept and Export
Scan (Step D17) and continue with section E.
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Cone Beam CT Verification PROCEDUREOBI Advanced Imaging version
1.4Cone Beam CT version 2.14D ITC version 8.2Clinac version
7.5Revision 2.0.0