Hematologic depression is noted on blood tests of a patient who has had several radiation therapy treatments. What is the most probable minimum dose that this patient received?

• A. 0.25 Gy
• B. 0.01 Gy
• C. 0.15 Gy
• D. 0.50 Gy

Answer: (A)

Hematologic depression happens when the bone marrow’s ability to produce blood cells is suppressed by ionizing radiation. Blood-forming tissues are very radiosensitive, so even relatively small exposures can start to show up as changes in blood counts on tests. In this context, a dose around 0.25 Gy is enough to produce detectable hematologic effects, making it the practical minimum at which depression would be observed.

A dose as low as 0.01 Gy is typically too small to cause noticeable changes in standard blood work, and while 0.15 Gy might begin to affect counts, it’s 0.25 Gy that’s generally recognized as the threshold associated with observable hematologic depression. A dose of 0.50 Gy would likely produce more pronounced, rapid changes, but the question asks for the minimum dose most likely to cause the effect, which is 0.25 Gy.