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: Surgery
In treatment of papillary carcinoma thyroid, radioiodine destroys the neoplastic cells predominantly by 
Select and explain. 
A. X-rays, B. Beta rays, C. Gamma rays, D. Alpha particles
B: Beta rays
Answer: B: Beta rays 
Explanation: RADIOACTIVE IODINE (I131) THERAPY:

I131 is an effective agent for delivering high radiation doses to the thyroid tissue
It emits mainly beta radiation (90%), which penetrates only 0.5 mm of the tissue and thus allow therapeutic effects on the thyroid without any damage to the surrounding structures, particularly the parathyroids.

Mechanism of Action:

I131 emits beta particles and X-rays.
Beta rays are utilized for their destructive effects on thyroid cells.
X-rays are useful for tracer studies.