Topics covered in this article include:

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

Introduction

Task Group 142 (TG-142) of the American Association of Physicists in Medicine (AAPM) recommends verifying MLC transmission (average of leaf and interleaf transmission) annually in Table V. Multileaf collimation.

The static leaf transmissions are calculated from comparisons between open and closed fields in both the A and B leaf banks. For the dosimetric leaf gap calculation a series of increasing leaf gaps is swept across a 10x10 cm field. The EPID readings for each gap are then corrected and regressed to calculate the leaf gap.

Below is an example test image:

Measurement Summary

The analysis displays the following test results:

• A and B Leaf Bank MLC Transmission Percentage
• Dosimetric leaf gap

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

This analysis requires certain files to run depending on which tests are desired.

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 by  clicking the Start upload button on the lower right of the control. To clear the upload queue click the Clear button.

The type "MLC Transmission and DLG" must be selected or the files must contain "mlctrans" 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 "mlctrans" (case insensitive) is found the image set will be processed as an asymmetric field test series. For more details see Manual Identification of RT Planar Images and Individual Catphan Slices through DICOM tags.

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.

Detailed Discussion of Measurements

MLC Transmission

Transmission is determined by dividing the mean pixel value for the central 8x8 cm of the field area in the in the transmission A or B image and dividing by the mean pixel value for the central 8x8 cm of the field area in the open field image and multiplying by 100. 

R_T,A  = mean pixel value transmission bank A / mean pixel value open field *100

R_T,B  = mean pixel value transmission bank B / mean pixel value open field *100

The average transmission percent is calculated as:

Dosimetric Leaf Gap Plot

The dosimetric leaf gap plot displays corrected gap readings along with a linear fit line. 

Dosimetric Leaf Gap

Dosimetric gap value, corresponds to the y-axis intersection in the Dosimetric Leaf Gap plot. This is also displayed in the dosimetric leaf gap plot as a green mark.

Dosimetric Leaf Gap Readings

The dosimetric leaf gap readings table displays the filename, gap in millimeters, and the reading.

The dosimetric leaf gap readings are corrected readings with the contribution of transmission to the overall gap reading factored out. The contribution of transmission to gap reading, R_gT, is calculated as:

Where g is the the gap size in millimeters.

The corrected gap reading, R_g', for each gap is calculated as:

R_g' = R_g - R_gT

Example Report

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

Example Files

Below are example DICOM files for use in testing: