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:as D90HR CTV (the dose covering 90% of the highrisk clinical target volume) for tumors and D2cc (the minimum dose in the 2cc most irradiated tissue volume) for OAR, have been demonstrated to be predictive of the tumor control probability and occurrence of LSE for OAR [1, 2, 8].
Category: