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How can radiation therapy lower blood-cell counts?

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linear accelerator; external beam radiation therapy — radiation therapy External beam radiation therapy (also known as external beam teletherapy, or long-distance therapy) being delivered using a machine known as a linear accelerator.

Radiation therapy can lower blood-cell counts because the blood-forming cells located in the bone marrow are highly radiosensitive. These cells, known as hematopoietic stem cells, are responsible for producing red blood cells, white blood cells, and platelets.123

When these cells are exposed to radiation—either through targeted radiation therapy or whole-body irradiation—they can be damaged or destroyed. Because these cells are essential for the continuous replacement of circulating blood, their depletion impairs the body's ability to maintain normal blood-cell levels.12

If a significant portion of these cells is killed, the resulting depression in blood-cell counts can lead to serious clinical complications, including increased susceptibility to infection, anemia, and hemorrhage. While radiation therapy is typically a local treatment, side effects like lowered blood-cell counts occur when the bone marrow is included within the field of the radiation beams.132