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Still another common m e a s u r e m e n t using C r - l a b e l e d r e d blood cells is the determination of the amount and location of bleeding from the gastrointestinal tract (the stomach and bowels). The amount is found by simple m e a s u r e m e n t of chromium in the blood that appears in the stools. To find the location is slightly m o r e complicated. The intestinal contents a r e sampled at different levels through an inserted tube, and the radiation of the samples d e t e r mined separately. Finally, gastrointestinal loss of protein can be measured with the aid of ^'Cr-labeled blood s e r u m . The s e r u m is treated with CrClg and then injected into a vein. In s e v e r a l very serious ailments there is serious loss of blood p r o tein through the intestines. In these conditions the ^'Cr level in the intestinal excretions is high, and this a l e r t s the doctor to apply remedial m e a s u r e s .
Cobalt-60 Vitamin B12 is a cobalt compound. Normally the few milligrams of B12 in the body a r e stored in the liver and released to the blood s t r e a m as needed. In pernicious anemia, a potentially fatal but curable disease, the B12 content of the blood falls from the usual level of 3 0 0 - 9 0 0 m i c r o m i c r o g r a m s per milliliter (ml) to 0 to 100 m i c r o m i c r o g r a m s per ml. The administration of massive doses of B12 i s the only known remedy for this condition. If the B12 is labeled with radioactive cobalt, its passage into the blood s t r e a m may be observed by several different methods. The simplest is to give the B12 by mouth, and after about 8 hours study the level of cobalt radioactivity in the blood. Cobalt-60 has been used for s e v e r a l y e a r s , but recently cobalt-58 has been found more satisfactory. It has a half-life of 72 days while ^"Co has a 5.3-year halflife. This reduces greatly the amount of radiation to the patient's liver by the retained radioactivity.
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nostic skill. All radioisotope p r o c e d u r e s a r e m e r e l y tools to aid the skilled physician. As the practice of medicine has changed from an a r t to a science, radioisotopes have played a useful part.
THERAPY A Successful Case A doctor recently told this story about a cancer patient who was cured by irradiation with cobalt-60. " A 75-year-old white male patient, who had been hoarse for one month, was treated unsuccessfully with the usual medications given for a bad cold. Finally, examination of his larynx revealed an ulcerated swelling on the right vocal cord. A biopsy (microscopic examination of a tissue sample) was made, and it was found the swelling was a squamous-cell cancer. "Daily radiation treatment using a cobalt-60 device was started and continued for 31 days. This was in September 1959. The cobalt-60 unit is one that can be operated by remote control. It positions radioactive cobalt over a collimator, which determines the size of the radiation beam reaching the patient. The machine may be made to rotate around the patient or can be used at any desired angle or position.
Iodine-131 Like chromium-51, iodine is a versatile t r a c e r element. It is used to determine blood volume, cardiac output, plasma volume, liver activity, fat metabolism, thyroid
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