Therapy Radiopharmaceuticals Practice Test

For Ra-223 dichloride, which organ receives the highest radiation dose?

Bone surface Liver Kidney Bone marrow

Correct Answer:

Bone surface

Explanation:

Ra-223 dichloride acts like calcium and localizes to bone, especially at sites of active bone formation (osteoblastic remodeling surfaces). Its emissions are alpha particles, which deposit a lot of energy over a very short distance. Because the radiopharmaceutical concentrates at the bone mineral at remodeling surfaces, the energy is deposited most intensely right at the bone surface where those cells are located. Other organs like the liver or kidney don’t accumulate Ra-223 to the same extent, and alpha particles don’t travel far enough to deliver comparable doses to deeper tissues. Some dose to nearby bone marrow can occur due to proximity, but the highest local dose remains at the bone surface where Ra-223 sits.

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