Topics covered in this article include:

• Introduction
• Measurement Summary
• Instructions
• Available Tests
• Specifications to Create a Plan File
• Example Plan File Downloads
• Determination of Static versus Rapid Arc
• Detailed Discussion of Measurements
• Example Files

Introduction

Task Group 142 (TG-142) of the American Association of Physicists in Medicine (AAPM) recommends verifying the positional accuracy of the Multileaf Collimator (MLC) for the four cardinal gantry angles in Table V. Multileaf collimation. The picket fence pattern is formed by radiation fields measured on an Electronic Portal Imaging Device (EPID) as all leaves are moved across the field of view at the same speed with several stops at measured intervals. There are two versions of the picket fence test supported by the software, static and Rapid Arc. The static test is done with the gantry stationary at various gantry angles and the RapidArc is done with the gantry moving. When performing the static picket fence test it is recommended that the test be repeated at the four cardinal gantry angles to measure the effects of gravity and other mechanical factors on the MLC. Below is an example of a static picket fence test image:

Measurement Summary

The analysis displays the following test results:

• Leaf position deviation
• FWHM per leaf pair
• Max leaf position deviations
• Max FWHM per leaf pair
• Picket position deviation, summary
• FWHM of pickets, summary

The measurements are completely automated, requiring the user only to drag and drop the file into the web-based software interface. A detailed report is created.

Instructions

Picket fence 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 picketfence somewhere in the file name. Also when using an HD MLC, add hd somewhere in the file name in addition to picketfence. If your picket fence is from a Halcyon use halcyonpfs for static or halcyonpfa for rapid arc instead of picketfence. When Halcyon is specified, the algorithm is expecting 29 leaf pairs.

When using the file naming conventions, be sure to select unassigned for the type otherwise the type will override the filename convention used.

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

Specifications to Create a Plan File

Please use your manufacturers recommended plan file where available. If using an Elekta, please use the appropriate plan in the Example Plan File Downloads section.

Determination of Static versus Rapid Arc

Historically, before 40x40 cm EPID panels were common, the static pattern had to be rotated to fit on a 30x40 panel. Right now if the collimator is rotated 90 the algorithm marks the image as static. If there is no collimator rotation the algorithm marks the image as rapid arc. This behavior is under review and may change in the future.

Example Plan File Downloads

Below are known plan files that we support. If you have a plan file that is not on the list and is not working, please contact support.

Detailed Discussion of Measurements

Below is an example of the test output generated on a report:

Example Files

Below are example picket fence DICOM files for use in testing: