Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:The occurrence of soft tissue tumors in such field of low-dose irradiation (LDRI) has also been emphasized by other authors [50, 52, 53] reporting the development of tumors of the skull bone and neck after exposure to full-mouth diagnostic dental X-ray film [3] and to irradiation for enlarged tonsils [54] and thymus [55].
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