Radiation and radioisotopes are extensively used medications to allow physicians and other medical professionals to image internal structures and processes in vivo (in the living body) with a minimum of invasion to the patient. Higher doses of radiation are also used as means to kill cancerous cells.
Radiation is actually a term that includes a variety of different physical phenomena. However, in essence, all these phenomena can be divided in two classes: phenomena connected with nuclear radioactive processes are one class, the so-called radioactive radiation (RR); electromagnetic radiation (EMR) may be considered as the second class.
Both classes of radiation are used in diagnoses and treatment of neurological disorders.
Devices such as x-ray machines and computed tomography (CT) medical imaging instruments are used commonly in the medical community. Any patient of a physician or other such medical professional in need of such devices for diagnosis and/or treatment would be subjected to various amounts of radiation or radioisotopes.
There are three kinds of radiation useful to medical personnel: alpha, beta, and gamma radiation. Alpha radiation is a flow of alpha particles that have been emitted by an atomic nucleus; beta radiation is a flow of electrons (or positrons) emitted by radioactive nuclei such as strontium-90; and gamma radiation is electromagnetic radiation of very high frequency (very short wavelength), otherwise called gamma rays.
Radioisotopes for medical use, containing unstable combinations of protons and neutrons, are made by neutron activation. This process involves the capture of a neutron by the nucleus of an atom, resulting in an excess of neutrons (neutron rich). Proton-rich radioisotopes are manufactured in cyclotrons. During radioactive decay, the nucleus of a radioisotope seeks energetic stability by emitting particles (alpha, beta, or positron) and photons (including gamma rays).
Radiation can damage any and all tissues in the body. The particular manifestation will depend upon the amount of radiation, the time during which it is absorbed, and the susceptibility of the particular type of tissue. However, in small doses, radiation can be helpful in the diagnosis and treatment of medical conditions. Some symptoms may occur when radiation is used on humans.
These symptoms depend on the amount of dosage used and the region of the body in which the radiation is applied. Commonly felt symptoms include skin reactions (such as redness or itchiness), tiredness, and loss of appetite. Inflammation of the tissues in and around the affected area can also occur. Such tissue inflammation depends on the particular organs affected. For instance, radiation of the colon may cause diarrhea, whereas radiation to the lungs may cause radiation pneumonitis (or inflammation of lung tissue caused by radiation), with symptoms that include difficulty breathing, chest pain, and coughing. Other signs of radiation exposure are bruising, skin burns, vomiting of blood, hair loss, mouth ulcers, and open sores. Even though undesirable and temporary symptoms often occur, they can be minimized with the use of caution and expertise by medical professionals.
The use of radiation for the diagnosis of disease or damage to the body can greatly benefit patients, but the benefit must outweigh its risk when recommending such procedures. In almost all cases the amount of radiation given in such diagnoses is generally low. For instance, a single diagnostic radiology examination of the (lateral) chest provides about 4 millirem (mrem), or 0.04 milli-Sievert (mSv), of radiation to the patient, while an exam to the abdomen gives approximately 53 mrem (0.53 mSv). As a comparison, the amount of natural background radiation that the average American receives each year is approximately 300 mrem (3 mSv). Consequently, the benefits typically outweigh the risks. Research has consistently shown that such low doses of radiation, used for diagnostic radiological examinations, do not cause any serious harm to the human body. However, the increasing use of medical radiation is a growing concern to the medical profession. In fact, a 2010 article in The Wall Street Journal stated that “Americans get the most medical radiation in the world—even more than folks in other rich countries—and the average American's dose has grown sixfold over the last couple of decades.”
The diagnosis of certain medical conditions is commonly performed with the use of nuclear radiation. Some of these methods include the use of x rays and tomography.
X RAYS. The use of x rays for examining people and animals is called diagnostic radiology. Because the density of tissues is unequal, x rays (a high frequency and energetic form of electromagnetic radiation) pass through tissues in an unequal manner. The beam passed through the body layer is recorded on special film to produce an image of internal structures. However, conventional x rays produce only a two-dimensional (2D) picture of the body structure under investigation.
TOMOGRAPHY. Tomography (from the Greek tomos, meaning “to slice”) is a method developed to allow the detailed construction of images of the target object. Initially using the x rays to scan layers of the area in question, with computer assisted tomography, a computer then analyzes data of all layers to construct a three-dimensional (3D) image of the object.
Computed tomography (also known as CT, CT scan) and computerized axial tomography (CAT) scans use x rays to produce images of anatomical structures.
Positron emission tomography (PET) scans use isotopes produced in a cyclotron. Positron-emitting radionuclides are injected and allowed to accumulate in the target tissue or organ. As the radionuclide decays, it emits a positron that collides with nearby electrons to result in the emission of two identifiable gamma photons. PET scans use rings of detectors that surround the patient to track the movements and concentrations of radioactive tracers. PET scans have attracted the interest of physicians because of their potential use in research into metabolic changes associated with mental diseases such as schizophrenia and depression. PET scans are used in the diagnosis and characterizations of certain cancers and heart disease, as well as clinical studies of the brain. PET uses radio-labeled tracers, including deoxyglucose, which is chemically similar to glucose and is used to assess metabolic rate in tissues and to image tumors, and dopa (3,4-dihydroxyphenylalanine), within the brain.
Another type of CT scan device was first tested in 2007. Using what is called super x rays, the device has the capability of directing a much more concentrated beam of x rays than any older type of technology. The new super x-ray device is called 64-slice CT because it uses 64 detectors to produce the images. It is faster and less expensive at diagnosing heart disease. One day, such advanced technology may eliminate the need for millions of cardiac catheterizations (procedures to unblock clogged arteries) performed annually in the United States. However, a much larger amount of radiation is directed into the patient, which raises considerable controversy in the medical profession. The risk for cancer when such procedures are performed is a major concern of doctors and patients alike.
In contrast to imaging produced through the emission and collection of nuclear radiation (e.g., x rays, CT scans), magnetic resonance imaging (MRI) scanners rely on the emission and detection of electromagnetic radiation.
MAGNETIC RESONANCE IMAGING. Electromagnetic radiation consists of oscillations of components of electric and magnetic fields. In the simplest cases, these oscillations occur with definite frequency; the unit of frequency measurement is 1 hertz (Hz), which is one oscillation per second. Arising in some point (under the action of the radiation source), electromagnetic radiation travels with velocity that is equal to the velocity of the light, and this velocity is equal for all frequencies. Another quantity, wavelength, is often used for the description of electromagnetic radiation (this quantity is similar to the distance between two neighboring crests of waves spreading on a water surface, which appeared after dropping a stone on the surface). Because the product of the wavelength and frequency must equal the velocity of light, the greater the wave frequency, the less its wavelength.
MRI technology was developed from nuclear magnetic resonance (NMR) technology. Groups of nuclei brought into resonance, that is, nuclei absorbing and emitting photons of similar electromagnetic radiation such as radio waves, make subtle yet distinguishable changes when the resonance is forced to change by altering the energy of impacting photons. The speed and extent of the resonance changes permit a nondestructive (because of the use of low-energy photons) determination of anatomical structures.
MRI images do not utilize potentially harmful ionizing radiation generated by three-dimensional x-ray CT scans; rather, they rely on the atomic properties (nuclear resonance) of protons in tissues when they are scanned with radio frequency radiation. The protons in the tissues, which resonate at slightly different frequencies, produce a signal that a computer uses to tell one tissue from another. MRI provides detailed three-dimensional soft tissue images.
These methods are used successfully for the treatment of medical conditions. Because higher doses of radiation are used, when compared to diagnosis procedures, the risks are much greater. Consequently, physicians seriously consider the risks and benefits of the treatments for the patient.
When radiation beams are used for the treatment of patients, the procedure is called radiotherapy. As such, radiotherapy requires the use of radioisotopes and higher doses of radiation that are used diagnostically to treat some cancers (including brain cancer) and other medical conditions that require destruction of harmful cells.
Radiation therapy is delivered via external radiation or via internal radiation therapy (the implantation/injection of radioactive substances).
Cancer, tumors, and other rapidly dividing cells are usually sensitive to damage by radiation. The goal of radiation therapy is to deliver the minimally sufficient dosage to kill cancerous cells or to keep them from dividing. Cancer cells divide and grow at rates more rapid than normal cells and so are particularly susceptible to radiation. Accordingly, radioisotope irradiation can restrict or eliminate some cancerous growths. The most common forms of external radiation therapy use gamma rays and x rays. During the last half of the twentieth century, the radioisotope cobalt-60 was the frequently used source of radiation used in such treatments. Subsequent methods of irradiation included the production of x rays from linear accelerators.
Iodine-131 and phosphorus-32 are commonly used in radiotherapy. The use of boron-10 to specifically attack tumor cells is one of several more radical uses of radioisotopes. Boron-10 concentrates in tumor cells and is then subjected to neutron beams that result in highly energetic alpha particles that are lethal to the tumor tissue.
Radiation therapy is not without risk to healthy tissue and to persons on the healthcare team, and precautions (shielding and limiting exposure) are taken to minimize exposure to other areas of the patient's body and to personnel on the treatment team.
Therapeutic radiologists, radiation oncologists, and a number of technical specialists use radiation and other methods to treat patients who have cancer or other tumors.
Care is taken in the selection of the appropriate radioactive isotope. Ideally, when the radioactive compound is used it loses its radioactive potency rapidly (this is expressed as the half-life of a compound). For example, gamma-emitting compounds used in SPECT scans can have a half-life of just a few hours. This is beneficial for the patients, as it limits the contact time with the potentially damaging radioisotope.
The use of radiation for therapy widely varies due primarily to the type of cancer being treated, the location of the cancer, the degree that the cancer has spread in the body, and the type of radiation therapy being administered to the patient. In some cases, radiation can cure the cancer, such as in the treatment for skin tumors, laryngeal cancer (of the vocal cords), and early-stage breast cancer (after a lumpectomy has been performed). In other cases, radiation does not cure the cancer but prevents the cancer from spreading and improves the patient's quality of life.
New areas of radiation therapy that may prove more effective in treating brain tumors (and other forms of cancers) include three-dimensional conformal radiation therapy (a process where multiple beams are shaped to match the contour of the tumor) and stereotactic radiosurgery (used to irradiate certain brain tumors and obstructions of the cerebral circulation). Gamma knives use focused beams (with the patient often wearing a special helmet to help focus the beams), while cyberknifes use hundreds of precise pinpoint beams emanating from a source of irradiation that moves around the patient's head.
See also Background radiation ; Radiation exposure .
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