540 ISOTOPIC TRACERS AND NUCLEAR RADIATIONS [Chap. 29 



29.4. Radiosodium. The distribution of sodium primarily as an extra- 

 cellular cation has permitted the application of ionic Na 24 as a substitute for 

 total irradiation in leukemia and allied diseases [Na58,81]. Patients so 

 treated have shown symptomatic improvement and a fall in the blood count. 

 It may prove as valuable as P 32 and in some cases more advantageous in 

 view of the greater ease with which dosage may be regulated because of the 

 shorter half-life and more rapid excretion. Its use has yet to be thoroughly 

 tested clinically. 



The usefulness of radiosodium as a diagnostic tool is evident from a recent 

 review [Na69] in which it is reported that in a number of circulatory diseases 

 (arteriosclerosis, Raynaud's disease, etc.) and injuries (trench foot and 

 immersion foot, frostbite, etc.) of the extremities Na 24 has proved of con- 

 siderable value in determining the status of the circulation. Since it can be 

 measured by applying a counter to the surface of the skin and thus detecting 

 its penetrating gamma rays, its distribution in the blood and extracellular- 

 tissue fluids can be followed. With this technique of measuring tissue 

 vascularity it has been possible to determine in a number of cases whether 

 surgery is indicated and, if so, at what point the amputation should be per- 

 formed. Similar possibilities exist with the use of radioactive inert gases. 

 It has also been possible to measure blood-circulation time with Na 24 [Na69]. 



29.5. Radiocolloids. A number of radioactive colloids have been used in 

 preliminary therapeutic studies or suggested as therapeutically promising. 

 These include, as already mentioned, anhydrous chromic phosphate [P228], 

 which localizes almost entirely in the liver and spleen; colloidal manganese 

 dioxide protected by gelatin [Mn7,10]; zinc suspended in a suitably prepared 

 solution of pectin [Zn2-4]; colloidal sols of gold [Au2-4]; and colloids of 

 several elements, radioisotopes of which occur as fission products [Gen38]. 



The fission colloids may, depending upon the method of preparation, con- 

 centrate upon intravenous administration almost exclusively in the liver and 

 spleen or go in equal concentration into the bone marrow [Zr3]. Because of 

 the relative abundance of yttrium, zirconium, and columbium in fission, 

 there is a potentially rich source of their radioactive species for such investiga- 

 tions and for possible widespread clinical application. The criteria of Hahn 

 and Sheppard [Gen66a], however, may rule out these fission elements as 

 important radiotherapeutic agents, although shorter lived species such as 

 Y 90 (60-hr half-life) should prove very useful. 



Investigations with radiomanganese as labeled colloidal manganese 

 dioxide in an aqueous medium with gelatin as a protective colloid have 

 recently been reported [Mn7,10,ll]. These suggest the possibility that 

 manganese dioxide may be localized upon intravenous injection in the 

 lymphoid reticuloendothelium. 



In addition to the intravascular administration of these colloids there are 



