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
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 None