Question
When using the myQA Machines VMAT Plugin, how can I generate ROIs for analysis of the Varian RapidArc Dynamic QA test?
Answer
Varian proposes for the TrueBeam, TrueBeam STx, and Edge Radiosurgery System a dynamic test which involves collimator rotation and an adaptation of the applied dose rate. Details can be found in the Varian document P1071511-001-A RapidArc Dynamic QA Test Procedures for TrueBeam. The vendor provides the corresponding RTPlans for the Millenium MLC 120 or the HD120 High Definition MLC. Data are recorded by the imaging panel and saved as DICOM RT images.
Figure 1 shows an image acquired for the RapidArc Dynamic QA test. Each of the sectors (1-5) represents a different combination of collimator rotation speed and dose rate. As the same number of MU is irradiated for each segment, the registered intensity should be equal in each segment.
The steps to analyze these data in the myQA Machines VMAT plugin are given below:
Create a Test:
- In Test setup of myQA Machines create a new test of type MLC: VMAT/Dynamic MLC.
Create an ROI model:
- After clicking on Open module, the VMAT plugin opens.
- Click on Edit, then Add to create a new ROI model. Give the model a name, e.g. Varian RapidArc. Close the window by clicking Ok.
Define the ROIs:
- Select Region of interest and click on Edit. A new window opens and ROIs can be created by clicking on Add.
- For the ROI name, the irradiation parameters (in terms of collimator rotation speed and dose rate) can be given.
The Coordinates define the corners of a square. They are given in mm as distances to the center of the image. The coordinates shown here correspond to a square in sector 1 (Figure 1). Coordinates for all 5 ROIs will be given below.
Figure 4: Creation of ROIs The Varian document P1071511-001-A RapidArc Dynamic QA Test Procedures for TrueBeam proposes to use quadratic ROIs with sizes of 20 mm x 20 mm . The coordinates given here correspond to ROIs where the centers are on a circle with a radius of 65 mm.
| ROI Nr. | Name | X | Y |
| 1 | [15 deg/s 600 MU/min] | 46.30 | -22.50 |
| 66.30 | -22.50 | ||
| 66.30 | -42.50 | ||
| 46.30 | -42.50 |
| ROI Nr. | Name | X | Y |
| 2 | [2.5 deg/s 100 MU/min] | 46.30 | 42.50 |
| 66.30 | 42.50 | ||
| 66.30 | 22.50 | ||
| 46.30 | 22.50 |
| ROI Nr. | Name | X | Y |
| 3 | [10 deg/s 400 MU/min] | -10.00 | 75.00 |
| 10.00 | 75.00 | ||
| 10.00 | 55.00 | ||
| -10.00 | 55.00 |
| ROI Nr. | Name | X | Y |
| 4 | [5 deg/s 200 MU/min] | -66.30 | 42.50 |
| -46.30 | 42.50 | ||
| -46.30 | 22.50 | ||
| -66.30 | 22.50 |
| ROI Nr. | Name | X | Y |
| 5 | [3.75 deg/s 150 MU/min] | -66.30 | -22.50 |
| -46.30 | -22.50 | ||
| -46.30 | -42.50 | ||
| -66.30 | -42.50 |
ROI Check:
- After importing the Open field and the VMAT field, the positions of the ROIs can be verified.
- If required, the ROIs can either be moved directly with the mouse, or the coordinates of the corners can be altered manually.
- When the positioning of the ROIs is correct, Process and Show detailed results can be clicked.