Earl W. Phelan

“ Cancer may be described as the runaway growth of cells. The secretions of the pituitary gland serve to stimulate cell reproduction, so it was reasoned that destruction of this gland might well slow down growth of a tumor elsewhere in the body. ”

“ Alpha particles, remember, have very little penetrating power, so all the energy of the alpha radioactivity is expended within the individual tumor cells. This is an ideal situation, for it makes possible destruction of tumor cells with virtually no harm to normal cells, even when the two kinds are closely intermingled.
Slow neutrons pass through the human body with very little damage, so a fairly strong dose of them can be safely applied to the head. Many of them will be absorbed by the boron-10, and maximum destruction of the cancer will occur, along with minimum hazard to the patient. ”

“ Radioisotopes in Medicine The Understanding the Atom Series
Nuclear energy is playing a vital role in the life of every man, woman, and child in the United States today. In the years ahead it will affect increasingly all the peoples of the earth. It is essential that all Americans gain an understanding of this vital force if they are to discharge thoughtfully their responsibilities as citizens and if they are to realize fully the myriad benefits that nuclear energy offers them.
The United States Atomic Energy Commission provides this booklet to help you achieve such understanding. ”

“ Proper production of thyroxin is essential to the proper utilization of nutrients. Lowered metabolism means increased body weight. Lowered thyroid activity may mean expansion of the gland, causing one form of goiter.
Iodine-131 behaves in the body just as the natural non-radioactive isotope, iodine-127, does, but the radioactivity permits observation from outside the body with some form of radiation counter. Iodine can exist in the body in many different chemical compounds, and the counter can tell where it is but not in what form. ”

“ The measurement of radioactivity must be accomplished indirectly, so use is made of the physical, chemical, and electrical effects of radiation on materials. One commonly used effect is that of ionization. Alpha and beta particles ionize gases through which they pass, thereby making the gases electrically conductive. A family of counters uses this principle: the ionization chamber, the proportional counter, and the Geiger-Müller counter.
Certain crystals, sodium iodide being an excellent example, emit flashes of visible light when struck by ionizing radiation. ”

“ Since a curie is the amount of radioactivity in a gram of radium that is in equilibrium with its decay products, a 1000-curie source is comparable to 2 pounds of pure radium. Neglecting for the moment the scarcity and enormous cost of that much radium (millions of dollars) , we 42 have to consider that it would be large in volume and consequently difficult to apply. Radiation from such a quantity cannot be focussed; consequently, either much of it will fall upon healthy tissue surrounding the cancer or much of it will be wasted if a narrow passage through the shield is aimed at the tumor. ”

“ When gamma rays emitted by a tracer isotope in the patient’s body struck the scanner, a flashing light produced a dot on photographic film. The intensity of the light varied with the counting rate and thus diseased tissues that differed little from normal tissue except in their uptake of an isotope could be discerned.
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With one conspicuous exception, it is impossible for a chemist to distinguish any one atom of an element from another. ”

“ Because chromium, in the molecule sodium chromate, attaches itself to red blood cells, it is useful in several kinds of tests. The procedures are slightly complicated, but yield useful information. In one, a sample of the patient’s blood is withdrawn, stabilized with heparin (to prevent clotting) and incubated with a tracer of radioactive sodium chromate. Excess chromate that is not taken up by the cells is reduced and washed away. Then the radioactivity of the cells is measured, just before injection into the patient. ”

“ Because of its unique connection with the thyroid gland, iodine-131 is most valuable in measurements connected with that organ. Thyroxin, an iodine compound, is manufactured in the thyroid gland, and transferred by the blood stream to the body tissues. The thyroxin helps to govern the oxygen consumption of the body and therefore helps control its metabolism. ”

“ The iodine concentrates in the thyroid gland where it is converted to the hormone thyroxin. Other radioactive, or “tagged”, atoms can be routed to bone marrow, red blood cells, the liver, the kidneys, or made to remain in the blood stream, where they are measured using suitable instruments. [6]
Of the three types of radiation, alpha particles (helium nuclei) are of such low penetrating power that they cannot be used for measurement from outside the body. ”

“ For several years, iodine-131 has been used as a tracer in determining cardiac output, which is the rate of blood flow from the heart. It has appeared recently that red blood cells tagged with 51Cr are more satisfactory for this measurement than iodine-labeled albumin in the blood serum. It is obvious that the blood-flow rate is an extremely important physiological quantity, and a doctor must know it to treat either heart ailments or circulatory disturbances. ”

“ Boron-10 has been used experimentally in the treatment of inoperable brain tumors. Glioblastoma multiforme, a particularly malignant form of cancer, is an invariably fatal disease in which the patient has a probable life expectancy of only 1 year. The tumor extends roots into normal tissues to such an extent that it is virtually impossible for the surgeon to remove all malignant tissue even if he removes enough normal brain to affect the functioning of the patient seriously. With or without operation the patient dies within months. ”

“ Cancer cells are self-reproducing cells, but do so in an uncontrolled manner. Hence cancer cells are particularly vulnerable to radiation. This treatment requires potent sources and correspondingly increases the hazards of use. ”

“ The difficulty is that most boron compounds themselves are poisonous to human tissues, and only small concentrations can be tolerated in the blood. Efforts have been made, with some success, to synthesize new boron compounds that have the greatest possible degree of selective absorption by the tumors. Both organic and inorganic compounds have been tried, and the degree of selectivity has been shown to be much greater for some than for others. ”

“ Therapeutic doses—those given for medical treatment—by contrast, are given to patients with a disease that is in need of control, that is, the physician desires to destroy selectively cells or tissues that are abnormal. In these cases, therefore, the skill and experience of the attending physician must be applied to limit the effects to the desired benefits, without damage to healthy organs. ”

“ By carrying out studies in the whole body counter room, the administered dose can be greatly reduced. The photographs illustrate a technique of measuring radioiodine uptake in the thyroid gland with extremely small amounts of a mixture of iodine-131 and iodine-125. A shows a small television set that is mounted above the crystal in such a way that good viewing requires that the head be kept in the desired position. This helps solve the problem of keeping small children still during a 15-minute counting period. B shows a child in position for a thyroid uptake study. ”

“ Human serum albumin labeled with 131I is sometimes used for location of brain tumors. It appears that tumors 23 alter a normal “barrier” between the brain and blood in such a manner that the labeled albumin can penetrate tumorous tissues although it would be excluded from healthy brain tissue.
The brain behaves almost uniquely among body tissues in that a “blood-brain barrier” exists, so that substances injected into the blood stream will not pass into brain cells although they will pass readily into muscular tissue. This blood-brain barrier does not exist in brain tumors. ”

“ Atoms for Health (1956) outlines two methods of diagnosis and treatment possible with radiation: a diagnostic test of the liver, and cancer therapy with a radioactive cobalt device. Case histories are presented step-by-step.
Radiation: Silent Servant of Mankind (1956) depicts four uses of controlled radiation that can benefit mankind: bombardment of plants from a radioactive cobalt source to induce genetic changes for study and crop improvement; irradiation of deep-seated tumors with a beam from a particle accelerator; therapy of thyroid cancer with radioactive iodine ”

“ Beta particles (electrons) have a moderate penetrating power, therefore they produce useful therapeutic results in the vicinity of their release, and they can be detected by sensitive counting devices. Gamma rays are highly energetic, and they can be readily detected by counters—radiation measurement devices—used outside the body. ”

“ This multi-detector positron scanner is used to locate tumors. A radioisotope-labeled substance is injected into the body and subsequently concentrates in the tumor tissue. The radioisotope emits positrons that immediately decay and produce two gamma rays that travel in opposite directions. These rays are detected simultaneously on a pair of opposing detection crystals and a line is established along which the tumor is located. This method is one of many ways doctors use radioisotopes to combat disease. ”

“ A large number of different radioisotopes have been used for measurement of disease conditions in the human body. They may measure liquid volumes, rates of flow or rates of transfer through organs or membranes; they may show the behavior of internal organs; they may differentiate between normal and malignant tissues. Hundreds of hospitals are now making thousands of these tests annually.
This does not mean that all the diagnostic problems have been solved. Much of the work is on an experimental rather than a routine basis. ”

“ This multiple-port scintillation counter is used for iron-kinetic studies. The tracer dose of iron-59 is administered into the arm vein and then the activities in the bone marrow, liver, and spleen are recorded simultaneously with counters positioned over these areas, and show distribution of iron-59 as a function of time. When the data are analyzed in conjunction with iron-59 content in blood, information can be obtained about sites of red blood cell production and destruction. ”

“ Usually the patient is given a very small dose of radioactive sodium iodide solution to drink, and two hours later the amount of iodine in the gland is determined by measuring the radiation coming from the neck area. In 20 hyperthyroidism, or high thyroid gland activity, the gland removes iodide ions from the blood stream more rapidly than normal.
Screening test for Hyperthyroidism
It is especially important in isotope studies on infants and small children that the radiation exposure be low. ”

“ The rate of radioactive decay appears to be affected only by the structure of the unstable (decaying) nucleus. Each radioisotope has its own half-life, which is the time it takes for one half the number of atoms present to decay. These half-lives vary from fractions of a second to millions of years, depending only upon the atom. We shall see that the half-life is one factor considered in choosing a particular isotope for certain uses.
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HALF-LIFE PATTERN OF STRONTIUM-90
Most artificially made radioisotopes have relatively short half-lives. ”

“ One of the results of all this is that every month new uses of radioisotopes are developed.
More persons are trained every year in methods of radioisotope use and more manufacturers are producing and packaging radioactive materials. This booklet tells some of the successes achieved with these materials for medical purposes.
What Is Radiation?
Radiation is the propagation of radiant energy in the form of waves or particles. It includes electromagnetic radiation ranging from radio waves, infrared heat waves, visible light, ultraviolet light, and X rays to gamma rays. ”

“ This procedure was useful but it was hard to make an accurate analysis of low concentrations of heavy water.
More recently, however, tritium (3H) (radioactive hydrogen) has been produced in abundance. Its oxide, tritiated water (3H2O) , is chemically almost the same as ordinary water, but physically it may be distinguished by the beta rays given off by the tritium. This very soft (low-energy) beta ray requires the use of special counting equipment, either a windowless flow-gas counter or a liquid scintillator, but with the proper techniques accurate measurement is possible. ”

“ There 37 may be a small increase in the number of cases of leukemia among those treated with 32P compared with the general population. The controversy arises over whether the 32P treatment caused the leukemia, or whether it merely prolonged the lives of the patients until leukemia appeared as it would have in these persons even without treatment. This is probably quibbling, and many doctors believe that the slight unproven risk is worth taking to produce the admitted lengthy freedom from symptoms. ”

“ Units carrying sources with intensities of more than a thousand curies are common.
The cobalt-60 unit at the M. D. Anderson Hospital and Tumor Institute in Houston, Texas, employs a 3000-curie source. This unit has a mechanism that allows for rotation therapy about a stationary patient. Many different treatment positions are possible. This patient, shown in position for therapy, has above her chest an auxiliary diaphragm that consists of an expanded metal tray on which blocks of either tungsten or lead are placed to absorb gamma rays and thus shape the field of treatment. ”

“ Such damaged cells are selectively removed by the spleen. A is a normal spleen. B shows an abscess in the spleen. Note dark ring of radioactivity surrounding the lighter area of decreased activity at the central portion of spleen.
In certain types of anemia the patient’s red blood cells die before completing the usual red-cell lifetime of about 120 days. To diagnose this, red cells are tagged with chromium-51 (51Cr) in the manner just described. Then 16 some of them are injected back into the patient and an identical sample is injected into a compatible normal individual. ”

“ 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. ”