650 ADOLF F. VOIGT 



of the latter as accurately as possible. P*^ has had a number of diag- 

 nostic applications. For example, since the rate of iodine uptake is 

 greater in the case of hyperthyroidism, this condition can be diagnosed 

 by the use of P^' and an external counter. Another application of 

 I^^^ not related to the thyroid has been reported by Moore (81), 

 based on the fact that fluorescein and its derivatives are preferentially 

 taken up by tumor tissue. Diiodofiuorescein containing I'^^ was 

 injected into patients previously diagnosed as having brain tumors. 

 In the relatively few cases reported the physician was able to deter- 

 mine by an external counter the existence and location of the sus- 

 pected tumor. In all cases in which an operation was performed the 

 counter diagnosis was found correct. 



The other application of radioisotopes in medicine is, of course, 

 therapy. Radioisotope therapy requires activities several orders of 

 magnitude greater than those used in tracer work and should be car- 

 ried out only by institutions that include on their staffs radiologists 

 familiar with the literature and capable of calculating proper dosages. 

 The substitution of Co^'' or other long-lived isotope in a capsule or wire 

 for the usual radium or radon needle in the irradiation of cancer tissue 

 is not really a different technique but a modification of the old. The 

 really new technique is the use of a radioisotope that will by reason 

 of its chemical nature (or the nature of the compound of which it is 

 made a part) locate itself at the site of the malignancy. Some of the 

 principal successes of artificial tracers in this field are the use of P^^ for 

 the treatment of polycythemia vera {S, p. 353) and of I^^^ for inoper- 

 able hyperthyroidism (2, p. 377). A large fraction of the total ship- 

 ment of isotopes from Oak Ridge has gone to hospitals that make 

 such use of them. It is a field somewhat foreign to the subject of 

 this chapter since it is governed by the rules of medicine and not those 

 of health physics. In other words, in radium, radon. X-ray, or arti- 

 ficial isotope treatment of cancer or other malignant conditions, doses 

 are given to the patient that are as much as a thousand to ten thou- 

 sand times tolerance. Such doses are allowable only as the lesser of 

 two evils, the other being the death of the patient if the pathological 

 condition is not checked. 



References 



GENEKAL 



1 . Kamen, M. D., Radioactive Tracers in Biology. Academic Press, New 

 York, 1947. 



