Topics covered in this article include:
- Measurement Summary
- Available Tests
- Detailed Discussion of Measurements
- Example File
The QC-3 is a common phantom designed to be used weekly and/or monthly to provide an ongoing check of imaging performance, particularly those aspects which are most liable to deterioration. After an initial grey-scale check, image quality is measured simply by counting the number of details detected and the number of bar patterns resolved in the image. Two images are required for comparison for all tests to complete. An ongoing record of these numbers will reveal any trend towards deterioration in imaging performance.
Task Group 142 (TG-142) of the American Association of Physicists in Medicine (AAPM) recommends that Planar MV Imaging should be checked during monthly Quality Assurance (QA) in Table VI: Imaging.
The analysis provides the following results:
- Modulation Transfer Function (MTF)
- Spatial Resolution
- Uniformity and Noise
The measurements are completely automated, requiring the user only to drag and drop the image set into the web-based software interface. A detailed report is created.
The test requires two images of the same resolution and they must be DICOM files. If more than two image are uploaded at once, each set must have matching Series Instance UIDs (tag 0020,000E). In some cases, it may be necessary to assist the automatic image recognition with manual naming conventions. If your images are not recognized automatically for the following types please try adding "qcmv" somewhere in the file name. Alternatively, limited capabilities to manually identify planar images using DICOM tag values have been added to the image processing system. This is an extension of the existing naming convention system. The PatientID, StudyID, and SeriesDescription DICOM tags are checked and if the text "qcmv" (case insensitive) is found the image set will be processed as MV Planar Imaging test series. For more details see Manual Identification of RT Planar Images and Individual Catphan Slices through DICOM tags.
When imaging QA tests are added to templates an upload control will appear in the scheduled QA's data entry screen allowing the user to upload images for automated analysis.
To add files to the upload queue simply drag them from a Windows Explorer folder to the drag and drop folder and release them. Alternatively, by clicking on the Add Files button to the lower right of the control a windows file selection dialog will open and files can be selected for upload. Under either method, multiple files may be selected for upload at once.
If the automatically upload checkbox is checked (the default) then file uploading will start immediately as files are added.
If the automatically upload button is turned to off the file upload process must be started manually clicking the Start upload button on the lower right of the control. To clear the upload queue click the Clear button.
Once file series have been uploaded they will be displayed below the upload control. To remove a series from the queue click the Cancel button beside the series. To start processing click the Start Processing button. A description for the image series can be added at this point. Click the Edit button next to the series. Type a description for the series into the text box that appears below Description and either click Save or press the enter key. The description can also be edited after the images have been processed. Descriptions will appear in the report with the analysis of the series.
While files are being processed users may perform other tasks such as data entry.
The following tables show the tests to select in the template builder corresponding to the supported analyses.
|Planar MV Imaging||Monthly Imaging QA [TG142 Table VI]||Planar MV Imaging (EPID)|
Image Acquisition Suggestions
Below are the recommended steps to acquire the images:
- Set the jaws or MLC so that the field size is 20x20 cm.
- Position the phantom in the light field at a 45 degree angle with the area marked 1 at the top of the image.
- Acquire the image.
- Repeat for the second image.
Detailed Discussion of Measurements
Below is an example of the report generated from the asymmetric field test:
Below are example files for use in testing: