Circulating Blood Cells
These all fall into 'early effects' but seemed to fit here nicely.
Following total body exposure, there is a rapid fall in lymphocyte numbers in the circulating blood (over 1 day). This is due to most cells undergoing apoptosis. Lymphocyte numbers recover slowly over several weeks if an ablative dose is not given. Unlike the other immune cells, lymphocytes have a long life expectancy, but die during interphase through apoptosis. This is in contrast to the other circulating immune cells, which die of natural causes after a set period of time.
The granulocyte family of cells includes monocytes/macrophages, neutrophils and eosinophils. Neutrophils are the most numerous member within the bloodstream, with a lifespan of several days. Following doses of 4 - 6 Gy to the whole body, there is an initial surge in numbers due to release from a reserve pool of neutrophils. Numbers then fall over 1 week, reaching levels about 10% of normal. This is maintained for approximately one week before recovery takes place (if recovery takes place). During the neutropenic period patients are susceptible to opportunistic infections.
Platelets have a lifespan of several weeks, intermediate between the granulocytes and the erythrocytes. Platelets may also increase in number shortly after radiation, but then fall over a period of weeks. This may be asymptomatic until levels fall below 20; spontaneous bleeding may then occur.
Erythrocytes have a lifespan of 2 - 3 months and changes in their numbers are not observable for several weeks following radiation. Long term anaemia may result from depletion of this compartment; however anaemia is relatively mild compared to the other cells as (if the patient has survived) regeneration of the bone marrow is already taking place.
Late Effects in the Bone Marrow
The bone marrow is formed by the haemotopoietic cells (stem cells and their progeny) and a network of supportive cells. The