A thyroid received an absorbed dose of 0.59 Gy from an intravenously injected radionuclide. The thyroid tissue-weighting factor is 0.04 and the emitted radiation-weighting factor is 1.0. What is the effective dose (EfD)?

• A. 0.0236 sievert (Sv)
• B. 0.59 sievert (Sv)
• C. 0.59 millisievert (mSv)
• D. 14.76 sievert (Sv)

Answer: (A)

Effective dose accounts for tissue sensitivity by weighting the equivalent dose in each tissue. First find the thyroid’s equivalent dose by multiplying the absorbed dose by the radiation weighting factor: 0.59 Gy × 1.0 = 0.59 Sv. Then apply the thyroid tissue-weighting factor to obtain the EfD: 0.04 × 0.59 Sv = 0.0236 Sv. So the EfD is 0.0236 Sv (which is 23.6 mSv). The result reflects how the thyroid’s risk contribution is scaled down by its lower weighting factor compared with the raw absorbed dose.