some question about the lateral distance in the kernal

[Little-Stars520]

In the "ppbkc_generateBaseData.mat" file, the TPR is scaled for different SSD to match the center bixel.

but, at this time, the reference point should no longer be in the isocenter plane(such as SSD:80cm,d:5cm). Why is the lateral distance of the isocenter plane still used in the subsequent kernel convolution?

Could you please explain the explanation of this part in Thomas Bortfeld's article?

[wahln]

Currently I don't really have time to go through this in detail again, but if I remember correctly the reason for this is that the kernel is defined in the fan-line-system (fig 1 in the paper and the transformations below), where the x/y coordinates (x/z in matRad) are equivalent to the coordinates in the isocenter plane.

[Little-Stars520]

hello， @mingersming @wahln
My confusion is that when SSD + d is not equal to SAD, the scaledTpr obtained is referenced to the plane of SSD + d instead of the SAD plane, even though your BaseData actually measure the TPR when SSD is 95 and d is 5 cm. Then why can the kernel obtained from scaledTpr still use the lateral distance of the SAD plane?

Secondly, when you use scaledTpr to obtain Wr, why does it correspond to tprFieldSizes? In fact, for scaledTpr, each depth corresponds to a different field size, which is different from the measured TPR (each depth corresponds to the same field size).

I've been thinking about this for several days and I'm really confused. Would you be able to provide some explanations?

[wahln]

I will convert this to a discussion, because currently I do not identify it as an issue with matRad