Combine Fields
The Combine Fields wizard, which combines two fields in the inline (Y) direction, enables performing Patient QA for large fields. For a field larger than the detector sensor area, two measurements are taken, an upper and a lower section, with a small amount of overlap to ensure full coverage. The two field sections are combined into the complete field by applying the Combine Fields wizard. The values in the overlapping area are the average values of the two measurements (1 and 2). See an example illustrated with a MatriXX below.
Note: The Combine Fields feature is available for the myQA SRS Phantom2.
Isocenter for the combine fields measurement
Note: It is located away from the center of the sensors and the electronics.
Measurement example: Area measured twice (3) = Overlapping area (4)
1st image measured at 0° 2nd image measured at 180° Combined image
+: Isocenter of the combine fields. In this example, the isocenter is aligned to the 3rd row (5) (a maker is
printed on it) of the sensors from the edge of the MatriXX Resolution detector:
Typical measurement workflow
The device setup should not only fulfill the requirements for combining the two measured fields but also
avoid the electronics being irradiated (unless using the myQA SRS with couch kicks). Here only the setup
steps specifically required for the combined fields are described.
For normal equipment setup information, please see the specific device user manuals. For measurement
procedure, see Section 2.4.
- Place the detector or the detector-phantom assembly on the treatment table.
- Align the isocenter to the isocenter for Combine Fields.
If the detector is used without a phantom:- MatriXXEvolution and MatriXX Resolution: Align to, e.g., the 3rd row (at least) from the edge.
- myQA SRS: Align to, e.g., the 10 cm × 10 cm field size marker
If the detector is inside a phantom, the combined field isocenter markers are used:
Alignment markers printed on the phantoms or detectors (1) / made by users Section 4.1.2 (2)
*This applies to both the myQA SRS Phantom, and myQA SRS Phantom2
- Perform the first measurement at 0° to acquire the first field (see the left photo below).
- Remove the parts placed on the top of the detector.
- Rotate the detector 180°, then align the device to the same isocenter as the first measurement.
- Perform the second measurement to acquire the second field (see the right photo below).
Add Alignment Markers on miniPhantom for Combine Fields Isocenter
For miniPhantom, it is recommended that the user marks the combined field isocenter on the phantom.
- Place the MatriXXEvolution – miniPhantom (without the top part) assembly under the LINAC.
- Align room lasers to, e.g., the 3rd row of the sensor from the edge of the detector.
- Place the top part of the phantom on the assembly. Using a water-proof marker and ruler, draw lines on the top and sides where the laser projections are.
Verification Workflow using a Combined Field
- In Verification compare – Project explorer, open the folder which contains the two images to be
combined. - (Option, for checking the combined image orientation) Drag the TPS dose plan to the B pane (1).
- Select the two images. Then right-click and select Combine Fields in the context meu. Note that the one which is selected first will be the lower field in the Combine Fields window.
- In the Combine Fields window, check the parameters (First row, Number of overlapping rows, etc.).IMPORTANT NOTICE: INDICATE CORRECT NUMBER OF OVERLAPPING ROWS
The number of overlapping rows indicated by the user corresponds to the rows where
the pixel signal will be represented by the average value from 2 measurements. The
number of discarded rows indicates rows which will not be included in the creation of
the combined integral from both measurements. - (Option) To check the orientation of the combined image, compare it with the TPS dose plan in the B pane. Swap or rotate the two measured images if necessary.
- Click OK.
- In the Verification compare workspace, drag the combined image to the A pane (2). Click the Align data icon (3) to align the measurement to the calculated plan.
- If desired, select to show profiles (4), move the inline / crossline cursor to check if the combined image is ok.
- In the Result pane, perform the Gamma analysis.
Field by Field Measurement Workflow
Field by field measurement workflow is dedicated to facilitating IMRT commissioning according to AAPM TG-119 guidelines. Additionally, this functionality can be used for the detailed investigation of the failing QA IMRT measurements, validation of the treatment couch model in TPS, IMRT verification when gantry angle sensor is not available or single arc validation of the complex VMAT plans (gantry angle sensor is mandatory for rotational deliveries)..
To use this function, the following requirements must be fulfilled:
- Only (!) RTPLAN and RTDOSE per beam should be imported.
- RTBEAMs have Treatment Delivery Type, “TREATMENT”.
- RTBEAMs have at least one valid gantry angle.
- RTDOSEs have Dose Summation Type, “BEAM”.
Before starting the Field by Field workflow, the following measurement settings / setup should be
accomplished:
- RTPLAN and RTDOSE are available.
- Detector and gantry angle sensor (if used) devices are set up under the LINAC. If GS+ is used, ensure that it is properly initiated (see thecorresponding device user’s guide).
- Measurement settings and configurations, such as energy, detector orientation, and user uniformity
calibration, are defined in the Measurement Configurations dialog (see Section 6.1, myQA Platform Instructions for Use). - Background has been measured.
Although the Movie mode is used normally, both Movie and Beam triggered modes can be used for
measurements.
Initiate the Field by Field Workflow
The Field by Field measurements are carried out in the Field by Field measurements window. This window
can be opened in two methods:
1: DICOM data have been imported
- In the context menu of an imported DICOM folder, select Initiate field by field workflow.
Note: DICOM data must be imported in an opened project to activate the Initiate field by field
workflow function / check box (see image below).
2: During the DICOM data import
- In the Project explorer panel, right-click the folder where the imported data will be stored, and then
select Import data > DICOM... - In the DICOM Import window, after importing RTPLAN and RTDOSE, select the Initiate field by field
workflow after import box (1). If the DICOM data does not fulfill the requirements for the workflow, this box (therefore the workflow) is not available. Message (2) is displayed instead.
Field by Field Procedure
- Check the order of the beams in the table (1, see the image of the Field by field window above). If it is different from the order of the beams for the measurement, follow the instructions (2) or the instruction below to rearrange it.
Changing the beam order
- Click and hold the mouse on the beam to be reordered, and then drag to the desired location and
release the mouse. See an example of moving Beam-153° below Beam-102°: - Reverse the beam order by clicking once on the header of the Energy column:
- Keep the Calculate integrals box (3) selected if the Movie mode is used.
- If the gantry angle correction should be applied, check the Apply gantry angle correction box (4) and select the applicable lookup table (5). (Gantry angle correction should be always applied if beams are not from 0°.)
- Click OK.
- Click the Start button in the Measurement ribbon; the beam marked with “Next” will be measured.
- Once the measurement is finished, the Repeat icon (5) appears in the next column and a green tick
replaces “Next”, and the beam below is marked with “Next” and will be measured next. - A measurement can be repeated by clicking the Repeat icon; it will be executed next.
- After all beams are measured, click OK; the measurements will be saved in the Integral folder in the
Verification compare workspace.
Messages and warning tooltips during the measurement
In the window for measurements, a warning tooltip may appear for energy or gantry angle and information may be displayed under the table according to the situation, e.g.,