Question
How do I perform a User Uniformity Correction (UUC or UCT) for myQA SRS?
Answer
The uniformity correction for myQA SRS can be performed with all types of LINAC, including standard and LINACs with FFF.
If the defect or drifting pixels reach to a certain level, the wizard will give warning messages containing suggestions for actions to be taken (see the table below).
Failed pixel type | Criteria | Actions to be taken | Warning shown in |
Defect | Overall defect pixels ≥ 3% | Contact IBA Dosimetry Service | Steps 2+3 |
Defect | Central defect pixels ≥ 30 % | Contact IBA Dosimetry Service | Steps 2+3 |
Drifting | 1% ≤ central drifting pixels < 30% | Advise to perform UUC | Step 3 |
Drifting | Overall drifting pixels ≥ 3% | Require to perform UUC | Step 3 |
Drifting | 1% ≤ central drifting pixels < 30% | Advise to perform UUC | Step 3 |
Drifting | Central drifting pixels ≥ 30% | Require to perform UUC | Step 3 |
The tolerances for identifying defect and drifting pixels can be edited in the Settings dialog.
Preparation
Go to myQA Platform and then Equipment Setup. Choose the SRS device and then click Edit in the Calibrations section.
Step 1: Device Position
- In the myQA SRS Editor dialog, click the Connect and then New User Uniformity Correction button. The User Uniformity Correction Wizard window opens.
- Check whether the devices are set up according to the instruction displayed in the wizard. If so, click Next to go to the next step.
Step 2: Background - Checking Defect Pixels
During the background measurement, the defect pixels are being detected. The background measurement time is 20 second by default and can be edited. Upon clicking the Next button in the Step 1, the wizard takes the latest measurement (if it is available) and displays the defect pixels with designated color graphically (heat map) and defect pixel numbers in the Summary box. If the background measurement is not available, a red dot appears in the Measure Background button.
- Make sure the beam is off during background measurements. If the background measurement is not yet available or you want to run the background measurement, click the Measure Background button to start the measurement.
- By starting the measurement, the previous saved background is removed. Stopping the measurement before the measurement time, no background is available, indicating with a red dot in the Measure Background button.
- Check the detected defect pixels. If the detector can be used for measurement, click Next to go to the next step.
Step 3: Measurement - Checking Drifting Pixels
During the measurement, the drifting pixels are identified. In this step, the defect pixels displayed are the defect pixels detected in the background measurement (Step 2).
- Follow the instruction to set up the beam.
- To start the measurement, click the Measure button and then start the beam. When all planned MUs are delivered, click the Stop button. The results will be displayed.
- If the results are satisfied, click Next to go to the calculation of the uniformity correction factors step.
- By clicking the Export Failing Pixels button, a *.json file containing the defect pixel coordinates determined during the background measurement will be saved at the same location as the log files.
Step 4: Uniformity Correction - Calculating the User Uniformity Correction Factors
Except for the defect pixels, the User uniformity correction factor is calculated for each pixel. The reference data must not have any defect pixels. After it is loaded into the wizard, it is checked against any defect pixels. If it is valid, both the reference and measured dose maps are displayed. The uniformity correction factor is calculated for each good or drifting pixel detected in Step 2 and 3.
- Import the OPG file by clicking the Select OPG file button. The wizard validates the file. If it is valid, both imported file and the measured data in Step 3 will be displayed. If not, an error message will be shown.
- Verify that the energy and field size used for the measurement corresponds to the energy and field size of the imported RTPlan.
- Click the Calculate button, the message, and wait until the calculation completed message appears.
Step 5: Finish – Saving the Correction Matrix and Closing the Wizard Window
- Enter the name for the user uniformity correction factors (1).
- Optionally enter comments, if desired, to be able to save the user uniformity correction factors for myQA (2).
- By clicking the Finish button (3), the correction factor matrix and the list if defect pixels will be saved in myQA and stored in the device and the wizard window will be closed.
By clicking the Close button (4), if there are unsafe defect pixels, a message pops up:
Done.
For additional details, please see the myQA Platform User's Guide.