Workshop #5: MBDCA Commissioning Elekta ACE algorithm · ACE Commissioning Guide - Workshop #5, AAPM Summer School 2017 2 Overview In this workshop you will perform the key steps

ACE Commissioning Guide - Workshop #5, AAPM Summer School 2017

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Workshop #5: MBDCA Commissioning

Elekta ACE algorithm

Ron Sloboda

Matt Kass

10 June 2017


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Overview

In this workshop you will perform the key steps involved in ACE algorithm commissioning for

Test Case 3, whose geometry is summarized in Table 1. The virtual phantom consists of a

(201 mm)3 water cube placed concentrically within a (511 mm)

3 air cube, and is located at the

origin of the Oncentra® Brachy coordinate system at (0, 0, 0) mm. A single Ir-192 source dwell

position is located off-center at (70, 0, 0) mm.

Table 1: Test Case 3 geometry for ACE algorithm testing during AAPM Summer School 2017

Test

Case

Inner cube material

‘Cube’

Outer cube material

‘BgBOX’

Ir-192 source

center location

Ir-192 source

orientation Applicator

3 H2O air (70, 0, 0) mm +y none

The commissioning process involves the following steps:

1. Access the Registry of MBDCA data (already done for you to save time)

2. Download a Test Case treatment plan and the corresponding Monte Carlo reference

dose distribution (already done for you to save time)

3. Import the Test Case plan and reference dose distribution into Oncentra Brachy

4. Calculate dose locally for the Test Case plan using ACE

5. Compare the ACE and reference dose distributions

In this workshop you will pick up the commissioning process at step 3. At home, you can

follow the User Guide available on the Registry at

http://irochouston.mdanderson.org/RPC/pagerequest.htm?page=BrachySeeds/Model_calculations.htm

to perform the downloads in step 2. and carry out a more in-depth dose comparison in step 5.


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Step 3. Import treatment planning and reference dose data

a. Importing ACE Images, Plan, Structure Set & Dose Data

• Open Oncentra Brachy and click on the ‘Import’ button at the lower left of the Select

Case window.

• Click the ‘Browse...’ button and select the desktop folder

‘Model-Based Dose Calcs\Elekta Database\Case-3-OCB\Case-3-OCB\’

• The system will display a list of CT data, RTPlan, RTSTRUCT and RTDOSE files.

• If checked, uncheck the ‘Image fix enable’ box at the bottom. Then click the ‘Import’

button; the system will read and validate the data ready for import.

• When the import window appears (this takes some time), select the ‘New Patient’

button at the bottom. The Patient Information will automatically populate the fields (as

shown on the following page).


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• Click the ‘OK’ button to import the new patient data.

• A ‘Successful Import’ message will appear when the import is complete. Uncheck the

‘Open Case’ box and click ‘OK’.

b. Importing MCNP6 Plan & Dose Data

• Click the ‘Browse..’ button again and select the desktop folder

‘Model-Based Dose Calcs\Reference Data\Case3-OCB-MCNP6\Case3-OCB-MCNP6\’

• The system will display all available DICOM objects. Select only the ‘RP_Case-3-

MCNP6.dcm’ and ‘RD_Case-3-MCNP6.dcm’ files (top 2 files in the list) by highlighting

both of them (use ‘<ctrl> click’ for the RD file) as shown in the figure below.


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• Click the ‘Import’ button; the system will read and validate the data ready for import.

• Click the ‘OK’ button to start the import of the MCNP6 data.

• A message will appear ‘The Case already has a RT Structure Set and it will be used.’ Click

the ‘OK’ button to continue.

• A ‘Successful Import’ message will appear when the import is complete. Click ‘OK’ to

continue.

• Click ‘Close’ on the Import Activity window.

The data for Test Case 3 has now been imported.


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Step 4. Calculate the dose distribution locally

a. Selecting the Plan & Setting the Virtual Source

• Select the Brachy Planning activity from the vertical menu at left, then select plan

‘ACE(H):WG-F’ by highlighting it, and finally click the ‘Start activity’ button.

• A warning message will appear stating the treatment unit associated with the Test Case

does not appear in the local physics database. Click the ‘Modify Plan’ button.

• Select ‘MBDC-WG-F’ from the list of available treatment units.

• Click ‘OK’ to continue; the Test Case will load.

• Open the flashing ‘!Notification’ tab and click OK. Then open the ‘Prescription’ tab and

confirm that the treatment date/time is 01 Apr 2016 10:00:00 and that the Air Kerma

Strength is 36260.00 cGy cm2/h ( Apparent Source Activity 10.000 Ci).

• Also confirm that the prescription dose is set to 100 cGy.

b. Setting the Source Dwell Time

• Using the Case Explorer confirm the active source dwell position is offset from the

centre of the cube at (70.0, 0.0, 0.0) mm.

• Open the ‘Optimization’ tab and select the ‘Manual dwell weight/time’ option.

• Change the active dwell position dwell time to 10 seconds by double clicking the

‘Time [s]’ cell in the Case Explorer and editing the time value.


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c. Setting the Dose Calculation Accuracy & Performing the Calculation

You will now perform a local model based dose calculation for Test Case 3, overwriting any

previous dose contained in the ‘ACE(H):WG-F’ plan.

• To perform an ACE dose calculation, click the ‘186’ button .

• The Collapsed Cone dose calculation window will appear. (Un-tick the ‘Auto start/stop’

option and tick the ‘Algorithm settings’ option).

• Set the ‘Accuracy level’ to ‘High’ and click ‘Start’ to begin the ACE calculation. (Note: It

may be several minutes before movement is seen on the progress bar)

Some time after the calculation starts, the number of First and Residual scatter transport

directions will be displayed along with the ‘Margin’ and ‘Voxel’ parameters. For the High

Accuracy level, the calculation is expected to take about 5 min.

• When the dose calculation is complete click the ‘Close’ button. The display will be

updated with isodoses for the ACE calculation.

• The display will also specify the calculation algorithm .

d. Creating a 3D Dose Distribution

A dose grid must be created in order to perform a comparison with the reference dose data.

• Click the ‘3D dose grid setting’ button.

• Select the ‘Cube size and position’ option and click the ‘More…’ button to set the cube

size to be 200x200x200 mm centered at (0, 0, 0).


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• Click ‘OK’ when done.

• Click the ‘Calculate 3D dose grid’ button to create the dose grid with the specified

parameters. This step must be done after every TG43 or TG186 dose re-calculation in

order to create a 3D dose distribution for use later in the ‘Plan Analysis’ window.

• Save the plan by clicking menu item ‘File � Save’.

• Close the Brachy Planning Activity by clicking menu item ‘File� Close Case’.

The Test Case 3 dose distribution calculated locally using ACE is now ready for comparison with

the reference dose distribution previously downloaded from the Registry.


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Step 5. Compare ACE and reference dose distributions

A. 2D Dose Maps

To set up a side-by-side display of a locally calculated and a reference dose distribution:

• Click ‘Open case’ , and in the ‘Select Case’ window click the ‘Plan Analysis’ activity ,

then select patient ‘WGDCAB_3_IIC’ and case ‘1 : Phantom Study’, and click ‘OK’.

• When the ‘Plan Analysis’ activity opens click the ‘Individual Plans’ icon at the top of

the Case Explorer window, navigate to the locally calculated and reference plans in the

Case Explorer, and select both plans for comparison by checking the box for each.


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• Select ‘Plan � Edit Isolines’ from the main menu, and apply the “test_case” isoline set

by selecting it from the ‘Stored definitions’ drop-down box in the Isolines window and

clicking ‘Apply’ followed by ‘OK’.

• Create a 1 row x 2 column display grid using the grid definition tool in the toolbar.

• If the plan ‘ACE(H):WG-F’ is not displayed in the left panel of the display grid, click the

‘Next object’ button at the top of the Case Explorer window.

• Click in the left panel of the display grid to activate the axial dose image. For greater

clarity in viewing, turn off the reconstructed points display by clicking the ‘Show-hide

reconstructed points’ button if need be. Close the thumbnail palette window at the

right by clicking the ‘x’ in that window to create a larger display area.

• Using the mouse wheel, scroll to axial slice 256/511 located at 0.0 mm. Then right-click

the image to access the supplementary menu. ‘Zoom’ the image so the inner cube of

the Test Case 3 phantom nearly fills the display panel, then right-click and ‘Stop zoom’.


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• Create a side-by-side display of corresponding 2D doses for the locally calculated and

reference plans by selecting ‘Tools � Create object sequence’ from the main menu.

• Scroll through the now corresponding slices to visually compare 2D dose distributions

throughout the inner water cube of the Test Case 3 phantom.

B. 2D Dose Map Differences

To display differences between the locally calculated and reference dose distributions:

• First decouple the object sequence created for the side-by-side dose display by selecting

‘Tools � Decouple sequence’ from the main menu.

• Click the ‘Summed Plans’ icon in the Case Explorer window and check the box for

each plan if unchecked. Set the ‘Display factor’ for the ‘MCNP6:WG-F’ plan to -1; this

yields the difference in the ACE dose distribution relative to the reference distribution.

• Select ‘Plan � Edit Isolines’ from the main menu, and apply the “cold-hot” isoline set by

selecting it from the ‘Stored definitions’ drop-down box in the Isolines window and

clicking ‘Apply’ followed by ‘OK’.


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• Restore the thumbnail palette by selecting ‘View � New Thumbnail palette’ from the

main menu, and click on the ‘Reconstructed images’ button. Load a sagittal

reconstructed image into the right display panel by dragging it from the palette.

• Zoom the sagittal image and close the thumbnail palette window. Scroll through the

slices to inspect 2D dose differences throughout the phantom. Right-click and select

‘Live dose’ to view the dose difference at the location pointed to by the mouse.


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C. Doses at Specified Points

Two sets of 6 dose points are available for quantitative comparisons. The points are centered

on the 6 faces of virtual cubes of sides 20 mm and 100 mm, centered on the Ir-192 source. For

the larger cube, the dose point at (x, y, z) = (120, 0, 0) mm has been moved to (x, y, z) =

(100, 0, 0) mm to keep it within the water-filled inner cube of the Test Case 3 phantom.

To import the dose point sets into the Case Explorer in OcB:

• Open plan ‘ACE(H):WG-F’ in the ‘Brachy Planning’ activity.

• Click the ‘Add new point set’ button, select point set Type ‘Patient points’ from

the drop-down menu in the dialogue box, and click ‘OK’. Expand the left-hand pane

of the Case Explorer window and navigate to ‘Plans\ACE(H):WG-F\Points\Patient’.

• Go to the desktop and open the text file ‘Model-Based Dose Calcs\

Elekta Database\Case-3-OCB\Case-3-OCB\DP_source_displaced.txt’

• Highlight all 6 dose points in set #1 in their entirety such that the cursor lies at the

beginning of the line after the 6th

dose point (if all columns are not selected, OcB will

report “Invalid Format” when you paste the data into Case Explorer; if the carriage

return in the line containing the 6th

point is not included, that point will not be

included). Right-click the selection and select ‘Copy’ from the drop-down menu.

• Right-click in the right-hand pane of Case Explorer and select ‘Paste’ from the drop-

down menu to import point set #1 into OcB and see the doses there.

• Repeat the preceding two steps for point set #2 to import it into OcB.

The Case Explorer window now displays the point dose values obtained from the 3D dose

matrix calculated by ACE. For comparison, point dose values obtained from the MCNP6

reference dose distribution are reproduced on the next page.


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Finally, click the ‘43’ button. The Case Explorer window now displays the point dose

values obtained from the 3D dose matrix calculated using the TG-43 formalism.

Compare ACE and TG-43 calculated doses for point DP_d1.2 located at (80, 0, 0) mm and point

DP_d2.2 at (100, 0, 0) mm. The difference is < 0.5 % at DP_d1.2, but ~5% at DP_d2.2. Why?

Thanks for participating in Workshop #5!

Ron & Matt

Documents

Workshop #5: MBDCA Commissioning Elekta ACE algorithm · ACE Commissioning Guide - Workshop #5, AAPM Summer School 2017 2 Overview In this workshop you will perform the key steps