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).
[Illustration: Showing:]
1 Patient drinks ³²P in water solution
2 ³²P selectively absorbed
Blood cell production in bone marrow
[Illustration: _Survival of_ polycythemia vera _patients after ³²P
therapy_.]
No. cases 201
Average age 52
Median survival 13.2
Survival for
5 years 91.5%
10 years 70.0%
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.