What effect does radiation therapy have on FDG uptake in bone marrow?

Radiation therapy is known to have a significant impact on the metabolic activity of tissues, including bone marrow. Following radiation treatment, the bone marrow typically exhibits a decrease in glucose metabolism, which is measured by the uptake of fluorodeoxyglucose (FDG). This decreased uptake can be attributed to the effects of radiation on the cellular environment and the activity of bone marrow hematopoietic cells.

Radiation causes damage to the bone marrow's microenvironment, which ultimately results in a reduction of active hematopoiesis and affects the overall metabolic rate of the tissue. FDG is taken up by metabolically active cells; thus, when the level of activity in the bone marrow decreases due to radiation therapy, so too does the FDG uptake. This results in lower observed levels of FDG on PET scans, reflecting reduced metabolic activity in the irradiated areas of bone marrow.

In summary, radiation therapy leads to a decrease in FDG uptake in bone marrow because it reduces the metabolic activity of hematopoietic cells, resulting in lower FDG retention during imaging.