target organ, 1. an organ intended to receive a therapeutic dose of irradiation, such as the kidney when high-energy x-rays or gamma rays are beamed to the renal area for the treatment of a tumor. 2. an organ intended to receive the greatest concentration of a diagnostic radioactive tracer, such as the liver, which accumulates 99Tc sulfur colloid when it is injected intravenously to detect hepatic lesions. 3. an organ most affected by a specific hormone, such as the thyroid gland, which is the target organ of thyroid stimulating hormone secreted by the anterior pituitary gland.
