5. myQA Machines - MLC QA Plugin

Introduction

The MLC QA Plugin is intended to find MLC positioning errors by determining if any of the strips are offcentered and check the ratio between the exposed and non-exposed areas.

For positioning tests, very fine spatial accuracy and high-resolution images are mandatory, i.e., images
acquired with EPID, and the MLC images shall be irradiated with multiple thin strips produced by narrow MLC openings (picket fence).

The resulting lines can be analyzed in the MLC Plugin. Note that the algorithm for MLC analysis Requires
that the images have equally distributed strips

MLC QA Plugin tests

MLC QA Plugin tests provides test result are listed in the table below:

Table 6.1. The MLC QA Plugin test types and test parameters

The test procedures of these three test types are similar. However, the Picket Fence requires analysis for only one gantry angle position; whereas the other two test types require analysis for four gantry angle positions: 0°, 90°, 180°, and 270°.

The VMAT QA Plugin provides individual tests for each test type and a combined test for all test result types.

Supported MLC modules

The application supports the following MLC models:

• Elekta Agility, Beam Modulator, and MLCi2
• Novalis 52mMLC
• Siemens 58, 82, and 160
• Varian HD-120, Millennium 52, Millennium 80, Millennium 120, Halcyon

For these MLCs, the leaves for bank are defined in terms of numbers and widths. During the test setup, these parameters can be modified, or new MLC models can be created.

MLC QA Workflows

Pre-conditions

• The MLC QA image is measured.
• Following DICOM tags are mandatory:
  
  • Rows (0028,0010)
  • Columns (0028,0011)
  • Bits allocated (0028,0100)
  • High Bit (0028,0102)
  • Photometric interpretation (0028, 0004)
  • Image Plane Pixel Spacing (3002,0011)

Note: The minimum distance between the stripes around the isocenter should be at least 10 mm; otherwise,            the stripes cannot be correctly recognized by the software.

Note: For detailed information on the myQA - Imaging QA – TestSetup/TestRun MLC window, see Section               6.1, myQA Machines Reference Guide.

Creating a Test Protocol for MLC QA

The MLC QA protocol can be created in the Test Setup by selecting Result Type as MLC: Picket Fence / Leaf Position Accuracy / Moving Window / Segmental IMRT. The protocol includes the measurement sittings and baselines.

• Click Edit in the Test Setup ribbon to enter the Edit mode.
• Select the desired machine in the Machines & Templates panel.
• In the Protocol Tree panel, click New in the ribbon to create a Task.
• With the task selected, click New in the ribbon to create tests:
• In the New Test Definition window, enter the required information:
  Name: name of the test
  Description: a description of the test (optional)
  Category: Select MLC (for information display only)
  Result Type: Depending on the test, select Result Type: MLC: Picket Fence / Leaf Position Accuracy / Moving Window / Segmental IMRT for an indiviual test or MLC: Combined for all test results
• Click OKNew Test Definition window

Define the test baselines. Baseline for a test is defined once in the Test Setup and will be used in every
execution of the test.

• In the Test Definition panel, click the Open Module button. The myQA – Imaging QA – TestSetup MLC window opens.
• In the MLC image combo box, import the reference image.
  There are three modes to import the DOCOM data:
  Import file: click it, browse, and select the *dcm file and then click Open.
  Import Listener and Import Query: See 4.1.1, myQA Machines Reference Guide.
  The image is loaded into the Images section and the SID, SAD, and gantry angle from the DICOM file are displayed in the Equipment setup section.myQA – Imaging QA – TestSetup MLC window (before process)

By default, the isocenter (indicated with a red cross) is placed in the center of the original EPID image
(before the automatic preprocessing steps are applied). The isocenter position can be modified:

• To select the isocenter, place the mouse cursor on it and then press and hold the mouse.
• Drag-and-drop the isocenter to the desired position.The Images section is displayed in full view and further enlarged. The coordinates and intensity of the cursor position is also displayed.
• Once the isocenter position is correctly defined, start the calculation by clicking the Process button in the Baseline values section. The expected values will be determined.
• Inspect the tolerances (in the Warn and Fail columns) provided in the software. Edit them if necessary.
  Note: The predefined expected values and tolerances are example values coming from test
  images, protocols or best practice and users should inspect these values.myQA – Imaging QA – TestSetup MLC window – Baseline values and Deviation histogram sections
  (after process)
• Click OK. The reference image and configuration files will be listed. The current reference image and configuration files can be deleted by clicking Reset configuration.
• Repeat the above steps until the baselines for other MLC QA tests are created.
• Click Set Active in the ribbon if the protocol is not yet set as an active protocol.
• Click Save in the ribbon.
  Note: In this step, you can also create a test template first, and then copy the template into the                     machine protocol.IMPORTANT NOTICE: BASELINE CALCULATION
  Starting from myQA v2.13, 2020-001, the baseline is calculated from the average of all calculated values and not the maximum value as implemented in myQA 2.11, 2019-001 and v2.12, 2019-002. Therefore, the existing users should re-do the baseline measurements in the Test setup.

Executing MLC QA Test

• Click Test Run in the myQA Navigation panel.
• Select the corresponding protocol and task in the Agenda panel.
• In the Task View panel, select the machine, task, and test, then click Start, the myQA – Imagine QA – TestRun MLC window opens.Test Run workspace – an MLC QA task is selected (before tests are executed)
  Note that for the Leaf Position Accuracy test, it requires analysis for four gantry angle positions: 0°, 90°, 180°, and 270°. Click the corresponding Start button to execute the test for each gantry angle.
• In the Equipment setup section, the parameters, reference image, and the baseline that was set in the Test Setup are displayed.
• In the MLC image combo box, import the test image.
  There are 3 modes to import the DOCOM data:Import file: click it, browse, and select the *dcm file and then click Open.
  Import Listener and Import Query: See 4.1.1, myQA Machines Reference Guide..
  The image is loaded into the Images section and the SID, SAD, and gantry angle from the DICOM file are displayed in the Equipment setup section.myQA – Imagine QA – TestRun MLC window (before process)
• Since the default isocenter position is the center of the image, check whether it is correct. As in Test
  Setup, the isocenter position can be changed by drag-and-drop with the mouse.myQA – Imaging QA – TestRun MLC window - the Images section is displayed in full view and the test
  image is further enlarged. The coordinates and intensity of the cursor position is displayed.
• Once the isocenter position is correctly defined, start the calculation by pressing the Process button in the Baseline values section. The Actual values are calculated and compared to the specified Expected values. The test results (pass, fail, warning) are displayed with designated tolerance icons. If interested, click Show detailed results to see more result information.
• myQA – Imaging QA – TestRun MLC window (after process).
• Click OK to close the myQA – Imagine QA – TestRun MLC window.
• Repeat the above procedure to perform the test for other gantry angles. Click Finish.
• If the Share results button is selected, once the Leaf Position Accuracy test for all four angles are
  executed, the results are also shared by the other two tests. Click Finish for the Moving Window / Segmental IMRT test.
• Click Finish in the Test Run ribbon and then Finish in the Finish Task dialog.
  Afterwards, the test results will appear in myQA Cockpit and a report can be created in the Test Repository page.
• Test Repository page with executed test list

Sharing results

Since the three MLC QA test types use the same images, the analysis results for one test can be propagated to the other MLC QA tests in the test list by selecting the Share results box. This box is available as long as there are more than one of the similar tests in one task.

Please note that results are only shared among the same type of tests that either have a matching baseline configuration or no baseline configuration.

Since the images of Leaf Position Accuracy and Picket Fence tests are gantry angle dependent, the results
can be shared only for the tests with the same gantry angle. For the image of the Picket Fence test, the gantry angle from Test Setup is taken.