In Beam Configuration, open the machine and energy, right-click on the Portal Dose Prediction Model (PDIP8114 in the screen shots) and choose "New Beam Data ..."
Enter a name and "Start with empty data".
Right-click on the Beam data, and select "New Add On ...". Choose "Open Field".
In PDIP Parameters, check "Calibration MU". This has to correspond to the MU the imager is calibrated with (the 10x10 field). Here it is 100 MU.
In Portal Image Parameters, enter "Number of Portal Images" = 2. Copy the images to a location with a short path name (e.g. C:\Temp) and enter their path (the field does not support copy/paste). Rotation is usually 90°, acquisition MU in our case is 175 MU for 6 MV and 157 MU for 15 MV. These are the MU that were delivered when treating the test pattern.

Right-click on "Open Field" and import "Output Factors ..." from file (our data for comparison: 6 MV, 15 MV)).
Interpolate the missing values. "Calibrate dose rates ..." is only necessary if the table is still uncalibrated.

Right-click on "Open Field" and insert "New Intensity Profile". Save. Select a configured Pencil Beam Model, e.g., Photon8114, with the same energy. Navigate to "Open Field" and click on the Intensity Profile icon. In the lower left corner, click on the profile with the shallowest depth (remembering the depth value) and select "Copy Curve" in the "Sedit" menu of Beam Configuration. Navigate back to the PDIP model, reight-click on the empty Intensity Profile and choose "Paste Curve". The profile appears in the lower left area. In the Parameter field on the right side, enter the distance of the profile from focus (e.g. 1014 mm, if the profile was measured in the water phantom with SPD = 100 cm and 14 mm depth). Also enter the depth in phantom (e.g., 14 mm) in the PDIP Parameters ("Import Intensity Profile At Depth (Optional) [mm]") although it says "optional".

In the File menu, select "Import > Actual Fluence from Database ...". In the Patient Explorer that opens, choose the test patient that holds the images with the test pattern. Select the plan (take care to select the plan with the correct energy). The Actual Fluence cannot be displayed.

Select "Calculate Beam Data". A few seconds later, two more items are added by the software. The "Kernel Shape" is the interesting one.

"Approve Data" and you are ready to go.