The Picker Cobalt-60 unit was given to the Indiana University School of Medicine in 1968 by the Indiana Lions. There are several thousand Cobalt-60 teletherapy units in use throughout the world. Even in the USA more persons are still treated for cancer with Cobalt-60 than with all other high-energy x-ray units combined.
The source of radiation from the Cobalt-60 unit is a radioactive isotope of cobalt, which gives off high-energy gamma rays. Gamma rays are essentially the same as x-rays of the same energy except they are produced in the nucleus of atoms while x-rays originate in the electron shells outside the nucleus. Cobalt-60 gamma rays have an energy 1.25 MeV. Introduction of Cobalt-60 units in the early 1950’s revolutionized radiation therapy by making available a highly reliable device that provided remarkably improved patient care; the rate of complications went down dramatically and the control rate rose.
Gamma rays from Cobalt-60 are given off continuously although the rate decreases gradually with time; the rate decreases by 50% in five and one-quarter years. Because of this change, new sources of cobalt-60 are placed in the units approximately every five years. Radiation from LINACs and other electricity is turned off. To shut off a beam of gamma rays from a Cobalt-60 unit, the “source” or container of Cobalt-60 is moved into a position where thick lead shields prevent all but a very small fraction of the gamma rays from getting out.
The Cobalt-60 unit at Indiana University medical Center is of the modern design that has been adapted in recent years to high energy medical LINACs. It can rotate 360 degrees to point its beam of gamma rays at the patient from any angle. There is also a table for the patient, which can be moved in or out, up or down, right or left, and rotated around the floor like the hands of a clock. A bright light shines out of the unit indicating exactly where the gamma rays will strike the patient, a scale is projected on the patient showing how far he is from a reference point, and laser beams from three wails project small dots and sharp lines on the patient. With these devices each patient can be carefully lined up so that the gamma ray beam is shaped and pointed to strike the correct portion of each patient.
Depending upon the age and the original strength of the Cobalt-60 source, average treatment times vary from less than a minute to several minutes. As with the LINACs, positioning the patient correctly takes much more time than the actual treatment itself so about four or five patients are treated each hour on a typical Cobalt-60 machine. Two well-trained technicians very carefully provide treatment according to the technique outline by the doctor. On an average day about 25 to 30 patients are treated on the Cobalt-60 unit at Indiana University Medical Center.
At Indiana University, most cancer of the head and neck are treated on the cobalt unit. The energy and quality of the gamma ray beams makes the cobalt unit the machine of choice for many of those cancers that arise in the nose, mouth and throat. The cost of a modern Cobalt-60 unit in 1980 was approximately $150,000.