Which organ receives the highest radiation dose from Tc HDP and Tc MDP?

• A. Liver
• B. Bone marrow
• C. Bladder
• D. Kidneys

Answer: (C)

The bladder receives the highest radiation dose from technetium-99m labeled compounds such as Tc HDP (Hydroxymethylene diphosphonate) and Tc MDP (Methylene diphosphonate) primarily because of the way these radiopharmaceuticals are excreted and their distribution in the body. After intravenous administration, these compounds are rapidly cleared from the blood and accumulate in the bone by binding to hydroxyapatite in areas of increased osteoblastic activity, which makes them valuable for imaging bone metabolism in conditions such as metastatic disease and osteoporosis.

However, the majority of the administered dose is eventually excreted through the urinary system. The kidneys play a role in filtration and urinary excretion, but as urine accumulates in the bladder, the concentration of the radiopharmaceutical increases significantly. This localized concentration leads to a higher radiation dose to the bladder compared to other organs. The risk of radiation exposure is compounded by the presence of urine, which affects the dosimetry calculations for the bladder wall.

The other organs, such as the liver, bone marrow, and kidneys, do receive radiation from Tc HDP and Tc MDP, but the effective dose to the bladder from the concentrated radiopharmaceutical in the urine is greater