The phosphate ion is a normal constituent of the blood. In many kinds of
tumors, phosphates seem to be present in the cancerous tissue in a
concentration several times that of the surrounding healthy tissue. This
offers a way of using phosphorus-32 to distinguish between cancer cells
and their neighbors. Due to the fact that ³²P gives off beta rays but no
gammas, the counter must be placed very close to the suspected tissue,
since beta particles have very little penetrating power. This fact
limits the use of the test to skin cancers or to cancers exposed by
surgery.
Some kinds of brain tumors, for instance, are difficult to distinguish
visually from the healthy brain tissue. In such cases, the patient may
be given ³²P labeled phosphate intravenously some hours before surgery.
A tiny beta-sensitive probe counter then can be moved about within the
operative site to indicate to the surgeon the limits of the cancerous
area.