The NCRP-recommended annual dose limit for the thyroid is

The NCRP-recommended annual dose limit for the thyroid is

• A. 5 mSv
• B. 50 mSv
• C. 150 mSv
• D. 500 mSv

Answer: (D)

Focusing on how exposure is limited for specific organs helps you see why 500 mSv per year is the thyroid limit. NCRP sets organ-specific annual dose limits to protect radiosensitive tissues while recognizing the realities of medical imaging where scattered radiation can reach the thyroid. For the thyroid, the approved annual equivalent dose limit is 0.5 Sv (500 mSv). Since this uses equivalent dose and the radiation type involved is X- or gamma-rays (weighting factor = 1), the organ dose is directly reflected in mSv. In practice, shielding and good technique are used to keep thyroid exposure under this cap, balancing protection with necessary work. Other numbers refer to limits for different tissues or to the whole body, not the thyroid, so the thyroid-specific annual limit remains 500 mSv.

Focusing on how exposure is limited for specific organs helps you see why 500 mSv per year is the thyroid limit. NCRP sets organ-specific annual dose limits to protect radiosensitive tissues while recognizing the realities of medical imaging where scattered radiation can reach the thyroid. For the thyroid, the approved annual equivalent dose limit is 0.5 Sv (500 mSv). Since this uses equivalent dose and the radiation type involved is X- or gamma-rays (weighting factor = 1), the organ dose is directly reflected in mSv. In practice, shielding and good technique are used to keep thyroid exposure under this cap, balancing protection with necessary work. Other numbers refer to limits for different tissues or to the whole body, not the thyroid, so the thyroid-specific annual limit remains 500 mSv.