In treatment of papillary carcinoma thyroid, radioiodine destroys the neoplastic cells predominantly by
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.
X-rays
Beta rays
Gamma rays
Alpha particles