This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
Osteoradionecrosis occurs at a dose of: 
Select and explain. 
A. > 10 Gy, B. > 70 Gy, C. > 30 Gy, D. None of the above.
B: > 70 Gy
Answer: B: > 70 Gy 
Explanation: Life-Long threat:
Hyposalivation

Radiation caries

Occurs 3 months after expose (PG1)

Trismus
Osteoradionecrosis > 70 Gy