8781
After obtaining the patients ' informed consent, biopsies were performed before treatment and at doses of 4, 10, and 20 Gy of radiotherapy , and the specimens were preserved in liquid nitrogen for further examination.
 None
Locate the role in the text that participated in the event based on the event type and return it in the event list. 
 Option: Event type: RNA,cell type,protein,cell line,DNA, Arguments type: . 
Text: {0} 
Answer:
 None