def add_volume(volume)
      raise ArgumentError, "Invalid argument 'volume'. Expected DoseVolume, got #{volume.class}." unless volume.is_a?(DoseVolume)
      @volumes << volume unless @associated_volumes[volume.uid]
      @associated_volumes[volume.uid] = volume
    end
def add_volume(volume)
      raise ArgumentError, "Invalid argument 'volume'. Expected DoseVolume, got #{volume.class}." unless volume.is_a?(DoseVolume)
      @volumes << volume unless @associated_volumes[volume.uid]
      @associated_volumes[volume.uid] = volume
    end
Adds a DoseVolume instance to this RTDose series.

 @param [DoseVolume] volume a dose volume instance to be associated with this RTDose