def add(dcm)
      raise ArgumentError, "Invalid argument 'dcm'. Expected DObject, got #{dcm.class}." unless dcm.is_a?(DICOM::DObject)
      ProjectionImage.load(dcm, self)
    end
def add(dcm)
      raise ArgumentError, "Invalid argument 'dcm'. Expected DObject, got #{dcm.class}." unless dcm.is_a?(DICOM::DObject)
      ProjectionImage.load(dcm, self)
    end
Registers a DICOM Object to the RTImage series, and processes it to
 create (and reference) a ProjectionImage instance linked to this RTImage
 series.

 @param [DICOM::DObject] dcm an RTIMAGE DICOM object