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.

Table 6.1. The MLC QA Plugin test types and test parameters; additional details provided in Chapter 6, myQA
Machines Reference Guide

*Previously named Moving Window/Segmental IMRT in myQA versions earlier than myQA 2025-001
**Previously named Leaf Position Accuracy in myQA versions earlier than myQA 2025-001

The 4 gantry angles mentioned above are 0°, 90°, 180° and 270°, which are the only ones allowed in this test. If the DICOM tag includes an angle different, within ±1°, from these cardinal angles, then 0° is set as default.

If individual tolerance levels per gantry angle combination needs to be set, instead of using either PF Static/Dynamic vs Gantry or Stripe Position vs Gantry test types, an independent test for each angle combination should be created.

Example: A test type Combined for each valid gantry angle combination could be defined in the Test Setup by setting the individual tolerances. During the Test Run, since the reference and measured gantry angles may vary for some of the cases, a message indicating this will pop-up and should be accepted and the process continued. A warning symbol next to the gantry angle value will appear if this differs from the one used at the baseline, but the analysis and test can be continued and finished.

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

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 Distal MLC and Halcyon Proximal MLC

For these MLCs, the leaves for each bank (a group of leaves with the same width) are defined in terms of the number of leaves forming that bank and the width. During the test setup, these parameters can be modified, or new MLC models can be created.

An example on creating new MLC models can be found below (Creating MLC models for Halcyon LINACs).

MLC Test Requirements

Please be aware of the following requirements when setting up and running MLC Tests.

• 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.

• The distance between two consecutive stripes must be larger than 10 mm.
• To compute the interstrip ratio, a minimum of two stripes are required.
• Test Setup (baseline or reference) and Test Run images should be identical (i.e., they should have the same number of stripes, stripes’ width, distance between consecutive stripes).

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)

For detailed information on the myQA – Imaging QA – Test Setup/TestRun MLC window, see Section 6.1,
myQA Machines Reference Guide.

Note: The minimum distance between the stripes should be at least 10 mm, as well as the distance of the outermost stripes to the borders of the image. Otherwise, the stripes cannot be correctly recognized by the software.

Creating a Test Protocol for MLC QA

The MLC QA protocol can be created in the Test Setup by selecting an MLC Result Type. The protocol
includes the measurement settings 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 MLC: PF Static / Dynamic vs Gantry, MLC: Picket Fence, or MLC: Stripe Position vs Gantry for an individual test or MLC: Combined for all test results. See Section 6.1.

  • Click OK

    

    Define the test baselines:
    The 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 (1), import the reference image.

    There are three modes to import the data:

    Import file: click it, browse, and select the file (*.dcm/*.tiff/*.opg) and then click Open.

    Import Listener and Import Query (for DICOM files only): See 4.1.1, myQA Machines Reference Guide.

    The image is loaded into the Images section (2) and the SID, SAD, and gantry angle from the DICOM file are displayed in the Equipment setup section (3).

    

  myQA – Imaging QA – TestSetup MLC window (before process)

  Note: In the Tools panel, the user can change the Color Palette of the displayed image. See Section 6.1.3. myQA Machines Reference Guide for detailed information.

  Isocenter position:

  • For DICOM and OPG formats, the isocenter is taken from the tags (defined in the data file)
  • For TIFF, 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 positions are also displayed.

• Once the isocenter position is correctly defined, check the tolerances. Tolerances are set in Overall results tab (4) for the general parameters and in Detailed leaves results tab for the stripe-leaf parameters.

  Inspect the tolerances (in the Warn and Fail columns) and edit them if necessary.

  Note: The predefined expected values and tolerances are examples coming from test images, protocols or best practice.

  

  myQA – Imaging QA – TestSetup MLC window – Overall values / Detailed leaves results and Deviation
  histogram sections (after process)

• Start the calculation by clicking the Process button in the Overall values section. The expected values will be determined.

• 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 each needed 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
  The baseline is calculated from the average of the values (from the overall results). For more information on calculation of overall results, see Table 6.1 in myQA Machines Reference Guide.

Creating MLC models for Halcyon LINACs

Performing Picket Fence Analysis for Halcyon plan using both the Proximal and Distal MLC Banks:

• Using either one of the predefined MLC QA tasks in the TG-142 + Plugin Template provided with myQA, or create an MLC QA Task as described in Section 6.2.1.
• Select the task and click New in the ribbon to create tests:

• Enter the necessary information and click Open module.

  

• Click MLC Model and Edit.

  It is advised to use the Proximal Model as Varian provides a picket fence plan for either Distal or the combination of the two MLC leaf banks.

  

• Click in the Leaves window and enter the appropriate number of leaves and width.

  The number of leaves is 57 and the width is 5.0 mm (a combination of overlapping 29 pairs and 28 pairs of the proximal and distal banks which each bank having a 10 mm width).

  

• Double-click on your model to rename it.

  

• Load in the necessary file (*.dcm/*.tiff/*.opg) and perform the analysis.

  If the analysis fails, the image may need to be cropped. Please edit the image in a third-party software
  and run the analysis again.

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 Stripe Position vs Gantry 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 reference image.

  There are three modes to import the data:

  Import file: Click the , browse, and select the file (*.dcm/*.tiff/*.opg) and then click Open.

  Import Listener and Import Query(for DICOM files only): 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)

• Check that the isocenter is correctly placed. As in Test Setup (Section 6.2.1), 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 (1) 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 Supplementary data (2) (previously named Detailed results) to see more result information.

  Note: This data is only available during the test; it is not saved after the Test Run is finished and is not available in Test Repository nor Report. Copy and paste the information to save it externally.

  

  myQA – Imaging QA – TestRun MLC window (after process).

• Click OK to close the myQA – Imagine QA – TestRun MLC window.
• Repeat the above procedure if other tests are needed. Click Finish.
• If the Share results button is selected, once the Stripe Position vs Gantry test for all four angles are executed, the results are also shared by the other two tests. Click Finish for the PF Static/Dynamic vs Gantry 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 Stripe Position vs Gantry 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.