I want to calculate the modulation factors of RA plans and the only thing left not found is the dose rate for each control point (CP). The Tag "DoseRateSet" is only present in the first CP and states the highest possible DoseRate.
Looking in the TPS you can right-click on the MLC of an arc and in properties you got the "segmented treatment table" with Gantry speed, Monitor Units, Gantry angle for each CP.
Is this information stored in some DICOM file or can I export on itself?
Hallo Claas,
did you find a solution for your problem in the mean time?
Hi Volker,
Yes and no (Jein). It seems that the dose rate is not saved within the dicom files, but is controlled by the treatment console on the fly, like the gantry speed.
My workaround was an algorithm that is recalculating the dose rate for each CP under the assumption that the gantry speed is constant at its maximum (4.8°/s for our LINAC). This can be checked easily in Eclipse.
A verification showed a match of 99.8% with the values given in eclipse as well.
Hallo Claas,
thx for your answer.
I don't really understand your approach because our TrueBeam Linacs always rotate with different speed. Maybe it's because you have a Clinac?
I need a relation to time, because I want to simulate target movement...
Hi,
In theory the gantry speed might change as needed, but the optimization algorithm includes a factor to maintain the maximum speed as long as possible, so that one is still able to treat within the promised 2 minutes for a single arc.
My workaround was tested and verified for a TrueBeam and an 2100C/S. I believe that we always obtain maximum speed, because we are only doing dual-arc treatments, giving the optimizer more freedom and "space to breathe" to keep the 4.8°/s.
All my control checks in the SMT showed this value.
Anyway I'm only considering the theoretic RT plan to calculate its modulation index. I couldn't find a way to get the "true" applied values since I was told that the dynalog files are only saving the MLC leaf positions...
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