Cone Beam CT Verification

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

Varian Medical Systems rh, March 09 FOR TRAINING PURPOSES ONLY!

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Cone Beam CT Verification

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

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Cone Beam CT Verification