Topics covered in this article include:

• Introduction
• Measurement Summary
• Instructions
• Available Tests
• Image Acquisition Suggestions
• Detailed Discussion of Measurements
• Example File

Introduction

The radiation light/field coincidence (aka Rad/Light) routine automatically analyzes the Standard Imaging FC-2 phantom with the center marker to provide accurate measurements for field size, shape and geometric coincidence of radiation and optical fields. The routine automatically detects the nominal field size and recognizes radiation fields as formed by the MLC or jaws.

Task Group 142 (TG-142) of the American Association of Physicists in Medicine (AAPM) recommends that the radiation light/field coincidence should be checked during monthly Quality Assurance (QA) in the Mechanical subsection of Table II.

Measurement Summary

The analysis provides the following results:

• Radiation-Light Field Displacement and Magnitude
• Radiation-Crosshair Displacement and Magnitude
• Measured Field Size and Area
• Jaw Position Indicators (Left, Right, Top, Bottom)
• MLC Position (Left, Right, Top, Bottom)
• Maximum deviation of measured jaw locations from expected
• Maximum deviation of measured jaw locations from expected

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.

Instructions

Radiation light/field coincidence images must be DICOM files. In some cases, it may be necessary to assist the automatic image recognition with manual naming conventions. If the images are not recognized automatically please try adding radlight 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 "radlight" (case insensitive) is found the image set will be processed as a asymmetric field 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.

Available Tests

Image Acquisition Suggestions

Below are the recommended steps to acquire the radiation/light field coincidence images:

1. Move the couch to 100 cm SSD.
2. Rotate the collimator to 0 degrees.
3. Set the jaws or MLC so that the field size is 10x10 cm.
4. Place the phantom on the couch and align the light field to the engraved squares on the phantom, adjusting the jaws or MLC as needed to align with the phantom.
5. Add the center marker plate if crosshair results are desired.
6. Acquire the first image.
7. Set the jaws or MLC so that the field size is 15x15 cm.
8. Place the phantom on the couch and align the light field to the engraved squares on the phantom, adjusting the jaws or MLC as needed to align with the phantom.
9. Add the center marker plate if crosshair results are desired.
10. Acquire the second image.

Detailed Discussion of Measurements

To determine whether Radiation/Lightfield type is mlc or jaws, the analysis looks at the 'bumpiness' of the left and right edges of the field. If the edges are bumpy we assume they are leaves, while smoother edges tend to be jaws. The analysis expects the collimator to be at 0, if it is not then the analysis might mislabel the type.

Below is an example of the report generated from the asymmetric field test both with and without a center marker. Note that the "Setting vs. radiation field for two patterns (non-IMRT)" test requires a center marker and will only display images with a center marker. The other tests do not require the center marker; any results based on the center marker will be left blank if a center marker is not present.

Example Files

Below are example files for an asymmetric field test series for use in testing: