Irradiation of the bone marrow is most likely to cause which of the following effects?

• A. Hematological depression
• B. Cataracts
• C. Neurological depression
• D. Melanoma

Answer: (A)

Bone marrow is highly radiosensitive because its cells divide rapidly. When irradiated, these progenitor cells can be damaged or killed, and the marrow’s capacity to produce blood cells drops. This leads to hematological depression: lower counts of red cells, white cells, and platelets, which manifests as anemia, increased infection risk, and easy bleeding or bruising. The other effects involve different tissues or exposure contexts—cataracts affect the eye’s lens from radiation to the eye, neurological depression relates to brain or nerve tissue exposure, and melanoma is a cancer risk from skin or other irradiated tissues. In the context of bone marrow irradiation, the dominant and most likely outcome is suppression of the blood-forming system.