Topics covered in this article include:

• Introduction
• Measurement Summary
• Instructions
• Available Tests
• Naming Convention
• Image Acquisition Suggestions
• Detailed Discussion of Measurements

Introduction

Halcyon Dose Rate/Gantry Speed and Leaf Speed Tests are tests of the VMAT (Volume Modulated Arc Therapy) system’s ability to deposit a constant dose while varying parameters such as dose rate, rotational velocity, and leaf speed.

They are based on the Ling et al. paper (Commissioning and Quality Assurance of RapidArc Radiotherapy Delivery System, Ling, C. Clifton et al.,International Journal of Radiation Oncology • Biology • Physics , Volume 72 , Issue 2 , 575 - 581)

• Halcyon Dose Rate/Gantry Speed test demonstrates the ability to vary dose rate and gantry speed during RapidArc delivery.
• Halcyon Leaf Speed test demonstrates the ability to accurately vary leaf speed during RapidArc delivery.

For both, an open field with a uniform dose is delivered to the EPID and captured as an image. Then strips with varying parameters are delivered to the EPID. The strip image’s dose should closely match the dose on the open-field image in the central portion of each strip thus demonstrating the system’s ability to successfully deliver the desired dose under the full range of the RapidArc’s capabilities.

Measurement Summary

• Dose Rate Corrected Readings
• Dose Rate Reading Deviations
• Dose Rate Input Images
• Dose Rate Reading Deviation Plot
• Gantry Speed Corrected Readings
• Gantry Speed Reading Deviations
• Gantry Speed Input Images
• Gantry Speed Reading Deviation Plot
• MLC Corrected Readings
• MLC Reading Deviationss
• MLC Leaf Input Images
• MLC Reading Deviation Plot

Instructions

Each test requires two images; one of which is an open field. The open field and strip image must be from the same plan set. If more than two image are uploaded at once, each set must have matching Series Instance UIDs (tag 0020,000E). VMAT test images must be DICOM files. It is necessary to use the file naming convention or to select proper test in the Type field in the upload widget to identify the image set. Below is an example of selecting the image type in the upload widget:

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

There are varying tests available across the Halcyon population. Selection of the proper test in the template will depend upon matching the Varian test.

Combined Dose Rate and Gantry Speed

Individual Dose Rate

Individual Gantry Speed

MLC Leaf Speed (7 strip)

MLC Leaf Speed (5 strip)

Naming Convention

If the test Type is not assigned in the upload widget, it is required that the filename tag be included somewhere in the filename. The tag is not case sensitive.

Image Acquisition Suggestions

Images must be acquired using the appropriate plan files provided by Varian.

Detailed Discussion of Measurements

The analysis is done by obtaining a10 cm H x 0.5cm W ROI in the center of each strip centered around isocenter in the Y direction.

The same ROI's are obtained from the open field image.

The mean values pixel for each ROI on the strip image and the open field image are measured and used in the equations below.

Calculate the Corrected Reading for each strip:

Calculate the average corrected reading from the individual strips:

Calculate the Reading Deviation for each strip from Mcorr

Below is an example of the report generated from the tests: