Unfortunately the dicom standard doesn’t allow floating point data in any of the standard modality types. You need to use a parametric map for that if you really need floating point. Not many systems support parametric maps though, so even if that is technically correct it’s not very interoperable.
If you goal is to have dicom files that display in other systems then you are better off casting to 16 bit (or 12) and if needed using the RescaleSlope and RescaleIntercept to provide a linear mapping back to the original floating point values.