What is the highest dose organ for Tc succimer (DMSA)?

• A. Heart and lungs
• B. Kidneys and bladder
• C. Brain and liver
• D. Spine and muscles

Answer: (B)

The correct answer identifies the kidneys and bladder as the highest dose organ for Tc succimer (DMSA) due to the distribution and excretion characteristics of this radiopharmaceutical. When Tc succimer is administered, it is specifically designed to bind to renal cortical tissue, where it accumulates during imaging studies aimed at evaluating renal function and morphology.

The kidneys receive a significant radiation dose primarily because of this accumulation, as Tc succimer preferentially concentrates in renal tissues. Furthermore, the bladder also receives a notable dose since the kidneys excrete the radiopharmaceutical into the urine, which subsequently collects in the bladder. This excretory mechanism leads to an increased exposure of bladder tissues to radiation, contributing to the overall dose received by these organs.

Understanding the radiopharmaceutical's pharmacokinetics and biodistribution helps clarify why the kidneys and bladder are subject to the highest radiation doses.