Starshot Plugin is a mechanical test that checks the isocenter position of a LINAC using star-shot pattern images. The image is formed by thin radiation fields delivered to a radiographic film or an EPID (Electronic Portal Imaging Device) as the collimator, gantry or couch is rotated around the isocenter. A star-shot pattern image should be acquired separately for each LINAC component, i.e., each of collimator, gantry, or couch requires one independent image.
Starshot Plugin supports images in TIFF or DICOM format. Therefore, if the image is acquired on a radiographic film, it must be scanned and saved in TIFF format.
CAUTION: EMPLOY REASONABLE FILE NAMING CONVENTION
When creating the StarShot images, it is recommended to employ a reasonable and descriptive file naming convention so that they can be easily identified in the StarShot Plugin.
Prerequisites:
- Starshot pattern images (DICOM or TIFF) are available for gantry, collimator, and couch, respectively. Resolution tags for TIFF images are mandatory.
- At least 3 beam angles must be present.
- A star pattern must be formed by extending the beams to both sides of the intersection area.
- For each tested energy, an independent image must be provided.
CAUTION: ENSURE GOOD QUALITY OF THE IMAGES
To perform the StarShot test successfully, the user must assure good image quality.
Recomendations:
- Beam width: 3 – 10 mm
- Angle between two adjacent beams: ≥ 25°
This chapter provides the Starshot Plugin application workflows. More information about the Starshot Plugin workspace is available in myQA Machines Reference Guide.
Creating Starshot Test Protocol in Test Setup
Procedure:
- In Test setup, click Edit (1) in the ribbon.
- In the Machines & Templates panel, select the desired machine in the Protocol Tree panel (2).
- Click New (3) in the ribbon. In the Protocol definition panel,
- Name: Enter the test name
- Description: (optional) enter any description, e.g., "Gantry rotation isocenter test."
- While the protocol is selected, click New in the ribbon. In the Task definition panel,
- Name: Enter the task name (4)
- Recurrence area (5): Set up the test schedule
- Start date: Enter or use the calender to set up the starting date (6)
- While the task is selected, click New in the ribbon. The New Test definition dialog opens,
- Name: Enter the test name (7)
- Category: Select Mechanical (for information display only) (8)
- Result Type: Select Starshot: Mechanical Isocenter Check (9)
- Warning tolerance: Define value for the warning tolerance (10)
- Error tolerance: Define value for the error tolerance (11)
- Click OK (12)
- Click Set Active (13) in the ribbon if the protocol should be run next.
- Click Save (14) in the ribbon.
Executing Starshot Test Protocol in Test Run
- Click the Test Run button (1), and then select the machine (e.g., 2) and task (e.g., 3) to be excecuted.
- Click the Start button (4). The myQA - Imaging QA - Test Run Starshot window opens. Note that the Instruction is provided. Click the toggle icon in the lower left corner to toggle the instruction display on or off.
- In the Equipment setup section, click the Import button (9), the Image Import dialog opens.
- Click the Import dropdown button (5) and select an import method in the dropdown list (6), and then import the desired image.
The detailed information about the 3 import methods are described in Section 9.1.1, myQA Machines Reference Guide. - Edit the SID and SAD values if necessary (7). These values are taken from the DICOM tags or the machine settings in myQA.
- Select an energy and then click the Import button (8). After the image is imported, it is listed in the
Loaded image box. - Select an image in the Loaded Images box (10).
- Before processing the selected image, you may need to make the following adjustments: First, ensure that the mechanical isocenter is correctly defined, otherwise adjust it accordingly. Afterwards, you can adapt the ROI radius as needed.
- o Mechanical isocenter: It is represented by the intersection of the two axes. Place the intersection (11) or one of the axes (e.g., 12) in the image and then drag it or enter the X/Y Position values in the Parameters panel > Mechanical Isocenter (laser marker) section (13) to fit mechanical isocenter to the laser markers (e.g., 14 ) (Note that the rotation can be adjusted only here).
- ROI Radius: Radius of ROI (Region-Of-Interest) is displayed as the red circle. Place the cursor on the ROI circle (e.g, 15) and then drag it or enter the values in the Parameters panel > ROI Radius box (16). If the Find best ROI while processing box is ticked (default), the Plugin automatically finds the best ROI. If the image quality is poor or if artifacts are present close to the borders of the image, you may need to manually resize the ROI.
For a better view of the image, the image display settings may be used:
- Tick the Show zoom area box; the small region around the cursor will be magnified.
- Adjust Brightness & ContrastZoom & Pan ( 17). Changing these settings does not affect the analysis.
- Click Process image (18); the analysis results will be displayed in the lower part of the window, and the beam lines (dotted blue lines) are shown in the image.
- Inspect the results (see Section 9.1.4, myQA Machines Reference Guide, for details on results display.). To view detailed results, click the Show detailed results button. If necessary, change the parameters and then re-process the data.
For example,
- To move the mechanical center with the help of the Zoomed image display:
- To change beams, see Section 9.3
- Re-process is mandatory if any change is made
- Repeat the same procedure to process the next image in the Loaded Imges box. Only when all images are processed, the OK button is enabled.
Note that when more than one image for the same energy are loaded, only select one and the others must be deleted. Otherwise, the OK button is disabled and the test run cannot be completed. - Click the OK button to finish the processing. The results will be displayed in the Test run workspace.
- Click the Finish button in the ribbon.
Aterwards, the results are loaded in Test Repository and myQA Cockpit (if the Show in myQA Workspace and Show in myQA Cockpit options are selected in the Equipment setup).
Editing Beams
After image processing, the detected beam angles are listed in ascending order and the clockwise direction. If the angle of two adjacent beams is detected less than 2°, they are considered as duplicate beams. The change cannot be saved and a popup message will appear.
It may be necessary to edit the beams, which can be done in the Edit Beams dialog. Click the Edit button in the Parameters panel > Beam Angles section to open the Edit Beams dialog.
- Deactivated a beam from processing: Untick its selection box (1). This beam is disabled for analysis.
- Modify the beam angle: Click its editing icon ( ) and then enter the new value (2).
The Edit Beams dialog.
- Add a new beam: Click the Add new beam button (3), follow the instruction in the dialog.
- A minimum of 3 beams must be selected to continue the test; otherwise, a message is displayed, and the changes cannot be saved.
a: new beam on the image, b: new beam in the list, c: Confirm button, d: Reset button
- Delete a user-defined beam (e.g., b): Click the Delete icon of this beams (
).