2. Single photon emission computed tomography (SPECT) using lodine-123 is widely used for the study of thyroid diseases. The physical half-life if I-123 is approximately 13.2 hours, ideal for the 24- hour iodine uptake test, where measurement of thyroid uptake is performed approximately 24 hours after the radiopharmaceutical is administered orally. Assume an administered dose of 10 MBq and accumulates mostly in the thyroid gland where it emits gamma rays with a predominant energy of 159 keV. (a) Assuming that only 25% of the emitted photons are actually absorbed in the thyroid gland, calculate the absorbed dose rate in the thyroid immediately after the radiopharmaceutical is administered. Assume that the thyroid gland weighs 20 grams in adult males, although this varies significantly with various factors. (b) If we ignore the decay of the source, what would be the total absorbed dose during the 24- hour uptake period leading up to the SPECT scan? (c) Using the result from (b) and assuming that the absorbed dose is solely due to gamma radiation, calculate the equivalent dose deposited in the thyroid gland. (d) Based on the tissue weighting factor for the thyroid gland of 0.14, calculate the effective dose received by a patient.

2. Single photon emission computed tomography (SPECT) using lodine-123 is widely used for the study of thyroid diseases. The physical half-life if I-123 is approximately 13.2 hours, ideal for the 24- hour iodine uptake test, where measurement of thyroid uptake is performed approximately 24 hours after the radiopharmaceutical is administered orally. Assume an administered dose of 10 MBq and accumulates mostly in the thyroid gland where it emits gamma rays with a predominant energy of 159 keV. (a) Assuming that only 25% of the emitted photons are actually absorbed in the thyroid gland, calculate the absorbed dose rate in the thyroid immediately after the radiopharmaceutical is administered. Assume that the thyroid gland weighs 20 grams in adult males, although this varies significantly with various factors. (b) If we ignore the decay of the source, what would be the total absorbed dose during the 24- hour uptake period leading up to the SPECT scan? (c) Using the result from (b) and assuming that the absorbed dose is solely due to gamma radiation, calculate the equivalent dose deposited in the thyroid gland. (d) Based on the tissue weighting factor for the thyroid gland of 0.14, calculate the effective dose received by a patient.