Phosphorus-32
Another disease which is peculiarly open to attack by radioisotopes is polycythemia vera. This is an insidious ailment of a chronic, slowly progressive nature, characterized by an abnormal increase in the number of red blood cells, an increase in total blood volume, enlargement of the spleen, and a tendency for bleeding to occur. There is some indication that it may be related to leukemia.
Until recent years there was no very satisfactory treatment of this malady. The ancient practice of bleeding was as useful as anything, giving temporary relief but not striking at the underlying cause. There is still no true cure, but the use of phosphorus-32 has been very effective in causing disappearance of symptoms for periods from months to years, lengthening the patient’s life considerably. The purpose of the ³²P treatment (using a sodium-radiophosphate solution) is not to destroy the excess of red cells, as had been tried with some drugs, but rather to slow down their formation and thereby get at the basic cause.
Phosphorus-32 emits pure beta rays having an average path in tissue only 2 millimeters long. Its half-life is 14.3 days. When it is given intravenously it mixes rapidly with the circulating blood and slowly accumulates in tissues that utilize phosphates in their metabolism. This brings appreciable concentration in the blood-forming tissues (about twice as much in blood cells as in general body cells).
Survival of polycythemia vera patients after ³²P therapy.
One other pertinent fact is that these rapidly dividing hematopoietic cells are extremely sensitive to radiation. (Hematopoietic cells are those that are actively forming blood cells and are therefore those that should be attacked selectively.) The dose required is of course many times that needed for diagnostic studies, and careful observation of the results is necessary to determine that exactly the desired effect has been obtained.
There exists some controversy over this course of treatment. No one denies that the lives of patients have been lengthened notably. Nevertheless since the purpose of the procedure is to reduce red cell formation, there exists the hazard of too great a reduction, and the possibility of causing leukemia (a disease of too few red cells). There may be a small increase in the number of cases of leukemia among those treated with ³²P compared with the general population. The controversy arises over whether the ³²P treatment caused the leukemia, or whether it merely prolonged the lives of the patients until leukemia appeared as it would have in these persons even without treatment. This is probably quibbling, and many doctors believe that the slight unproven risk is worth taking to produce the admitted lengthy freedom from symptoms.