Calculation with fixed Mus is not possible

Developer
Oct 10, 2014 at 2:45 PM
Hi, I'm using esapi v13 to calculate dose for a rapid arc plan. I'm getting an exception: "Calculation with fixed MUs is not possible." Wondering what's missing here. Thanks.
Coordinator
Oct 10, 2014 at 4:42 PM
With a VMAT plan you should use the normal CalculateDose method. CalculateDoseWithPresetValues is only supported with an IMRT plan that has DMLCs but no optimal fluences. (e.g. an imported plan)
Developer
Oct 10, 2014 at 6:34 PM
Works well, thanks!
Developer
Oct 13, 2014 at 7:11 PM
I do have another issue related to this: when I use CalculateDoseWithPresetValues, I can make sure the MUs are correct since I modified the plan before calculation (refer to my previous post about dose calculation). However, it is not possible(?) using CalculateDose, and it seems like all MUs are default to 200. Is there a way to calculate the dose on a modified plan?
Coordinator
Oct 17, 2014 at 5:48 PM
You can adjust field weights of VMAT fields directly:
      BeamParameters param = beam.GetEditableParameters();
      param.WeightFactor = 2;
      beam.ApplyParameters(param);
This modifies the field MUs accordingly.
Developer
Oct 21, 2014 at 1:00 PM
Awesome, thanks!
Developer
Apr 1, 2015 at 1:43 PM
I just had another question: the default MU for some plans are not 200, e.g., 180. Is there a place in API that holds this piece of information? Thanks.
Developer
Apr 17, 2015 at 6:17 PM
I'm still struggling on the above question, any suggestions will be appreciated.
Coordinator
Apr 17, 2015 at 7:03 PM
I'm no expert on Eclipse dose normalization area, but I believe that in dose calculation algorithm versions 10.0 and newer, the MUCoeff is always 100 MU/Gy. If your prescribed percentage is 100 and Dose / fraction 2Gy, you will always get 200MU for VMAT fields when field weight is 1.0. VMAT optimization modifies the MUs by adjusting the field weight. And you would get 180MU if the dose / fraction is 1.8Gy.
Developer
Apr 17, 2015 at 7:39 PM
Thanks again. Looks it's working this way in my current application.