def METHOD_NAME(self, dicom_file):
    """adds referenced images to series """
    if "ReferencedFrameOfReferenceSequence" in dicom_file:
        ref_frame = dicom_file.ReferencedFrameOfReferenceSequence
        if "RTReferencedStudySequence" in ref_frame[0]:
            ref_study = ref_frame[0].RTReferencedStudySequence[0]
            if "RTReferencedSeriesSequence" in ref_study:
                if "SeriesInstanceUID" in \
                        ref_study.RTReferencedSeriesSequence[0]:
                    ref_series = ref_study.RTReferencedSeriesSequence[0]
                    self.ref_image_series_uid = \
                        ref_series.SeriesInstanceUID
    else:
        self.ref_image_series_uid = ''