- For Patients

Glossary of terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z All 

Also known as radiation absorbed dose.
The scientific unit of measurement for the amount of radiant energy absorbed in a certain amount of tissue. See the Radiation Dose in X-ray and CT Exam page for additional information.

Radiant energy from waves or subatomic particles.

radiation dermatosis
Skin changes at the site of ionizing radiation, particularly redness of the skin due to capillary dilatation in the acute stage, temporary or permanent loss of hair, and chronic changes in the epidermis and dermis resembling a premalignant wart-like lesion.

radiation oncologist
Doctors who oversee the care of each cancer patient undergoing radiation treatment. They develop and prescribe each cancer patient's treatment plan, they make sure that every treatment is accurately given, and they monitor the patient's progress and adjust treatment to make sure patients get quality care throughout treatment. Radiation oncologists also help identify and treat any side effects of radiation therapy and work closely with all members of the radiation oncology team. Radiation oncologists have completed four years of college, four years of medical school, one year of general medical internship, then four years of residency (specialty training in radiation oncology). They have extensive training in the safe use of radiation to treat disease. If they pass a special examination, they are certified by the American Board of Radiology. Patients should ask if their doctor is board certified.

radiation oncology
Also known as radiation therapy.
The study and use of x-rays or radionuclides to treat abnormal tissue growths (malignant or nonmalignant).

radiation oncology nurses
Nurses work with the radiation team to care for patients during the course of treatment. They help evaluate the patient before treatment begins and talk to the patient about their treatment, the potential side effects and their management. During the course of radiation treatments patients may be evaluated weekly, or more frequently by the nurse to assess problems and concerns. Radiation oncology nurses are registered nurses. Most nurses in radiation therapy have additional accreditation in the specialty of oncology nursing. Advanced practice nurses in oncology, which include clinical nurse specialists and nurse practitioners, have completed a master's degree program.

radiation pneumonitis
Inflammation of lung tissue caused by exposure to radiation therapy.

radiation therapist
Radiation therapists work with radiation oncologists. They administer the daily radiation treatment under the doctor's prescription and supervision, maintain daily records and regularly check the treatment machines to make sure they are working properly. Radiation therapists go through a two-to-four year educational program following high school or college, then take a special examination and must be certified by the American Registry of Radiologic Technologists. In addition, many states require that radiation therapists be licensed.

radiation therapy
Also known as radiotherapy.
The study and use of x-rays or radionuclides to treat abnormal tissue growths (malignant or nonmalignant).

Radiation Units
There are a number of units to measure radiation dose and exposure:

  • rad or radiation absorbed dose
    The amount of radiant energy absorbed in a certain amount of tissue.
  • gray (Gy)
    A unit of absorbed radiation equal to the dose of one joule of energy absorbed per kilogram of matter, or 100 rad. The unit is named for the British physician L. Harold Gray (1905-1965), an authority on the use of radiation in the treatment of cancer.
  • milligray (mGy)
    A unit of absorbed radiation equal to one thousandth of a gray, or 0.1 rad.
  • rem or roentgen-equivalent-man
    A unit of measurement that takes into account different biological responses to different kinds of radiation. The radiation quantity measured by the rem is called equivalent dose.
  • millirem
    One thousandth of a rem, the unit for measuring equivalent dose.
  • roentgen (R, r) (rent-gen, rent-chen)
    The international unit of exposure dose for x-rays or gamma rays. Roentgens are named after Professor Wilhelm Konrad Roentgen, the man who discovered x-rays in 1895.
  • sievert (Sv) (see-vert)
    The unit for measuring ionizing radiation effective dose, which accounts for relative sensitivities of different tissues and organs exposed to radiation. The radiation quantity measured by the sievert is called effective dose.
  • millisievert (mSv) (mill-i-see-vert)
    One thousandth of a sievert, the unit for measuring effective dose.

radical trachelectomy
Surgical removal of the cervix.

Giving off radiation.

radioactive disintegration
The decrease in the amount of any radioactive material with the passage of time due to the spontaneous emission of radiation from an atomic nucleus.

radioactive iodine I-131
Also called radioiodine I-131.
A radioactive isotope created from iodine to emit radiation for medical use. See also radioactive iodine therapy.

radioactive iodine I-131 therapy
radioactive iodine I-131 therapy. The use of radioactive iodine I-131 to treat an overactive thyroid, a condition called hyperthyroidism. When a small amount of I-131 is swallowed, it is absorbed into the bloodstream in the gastrointestinal (GI) tract and concentrated from the blood by the thyroid gland, where it begins destroying the gland’s cells.

radioactive iodine uptake test (RAIU)
See thyroid uptake.

radioactive material
Also called radioactive substance.
As used in the brachytherapy treatment of cancer, a radioactive material is sealed inside a seed or pellet and placed inside the body, in or near a tumor. The radiation material used in brachytherapy comes from radioactive iodine 125, strontium 89, phosphorous, palladium, cesium, iridium, phosphate, or cobalt.

radioactive substance
See radioactive material.

radiodense markers
Small pieces of radiodense, or radiopaque, material placed inside the body near a tumor to help the treatment team direct radiation beams at the cancerous cells. Radiodense markers are made from materials that cannot be penetrated by x-rays or any other form of radiation.

radiofrequency ablation
A treatment technique that uses high-frequency alternating electrical current to destroy tissue cells by heating them.

radiofrequency electrodes
A type of electrode (a fine wire through which electrical current may flow when attached to a power source) that carries high frequency electromagnetic waves that create heat to ablate or destroy tissue (called radiofrequency ablation) or to seal blood vessels.

Referring to the examination of any part of the body for diagnostic purposes by means of x-rays.

Examination of any part of the body for diagnostic purposes by means of x-rays with the findings usually recorded digitally or on film.

A combination of radiation therapy and immunotherapy that delivers a high dose of radiation directly to a tumor.

radioiodine I-131
See radioactive iodine I-131.

An isotope that changes to a more stable state by emitting radiation.

radioisotope bone scan
A nuclear imaging examination that produces pictures of bones to help detect abnormalities caused by disease or injury. During a bone scan, a small amount of radioactive material is injected into the body and collects in the bones.

A physician trained in the diagnostic and/or therapeutic use of x-rays and radionuclides, radiation physics, and biology; a diagnostic radiologist may also be trained in diagnostic ultrasound and magnetic resonance imaging and applicable physics.


  1. The science of high energy radiation and of the sources and the chemical, physical, and biologic effects of such radiation; the term usually refers to the diagnosis and treatment of disease.
  2. The scientific discipline of medical imaging using ionizing radiation, radionuclides, nuclear magnetic resonance, and ultrasound.

Radiology Information System (RIS)
A special case of a hospital information system (HIS) tailored to radiological imaging, containing information such as imaging examination orders, schedules on imaging modalities, imaging device parameters, billing codes and information.

Almost completely transparent to x-rays.

An isotope of artificial or natural origin that exhibits radioactivity.

Radionuclides serve as agents in nuclear medicine and genetic engineering, play a role in computer imaging for diagnosis and experiment, and account for a percentage of background radiation to which humans are exposed. In cancer therapy, radionuclides are used to destroy tumors.

Impenetrable by x-rays or any other form of radiation.

radiopaque dye
See contrast material.

A drug that emits radioactivity. Also called a radiotracer.

Drugs that enhance the effect of radiation on cancer cells.

One who practices radiotherapy or is versed in radiotherapeutics.

The medical specialty concerned with the use of electromagnetic or particulate radiation in the treatment of disease.

See radiopharmaceutical.

A radioactive gas without odor, taste or color that occurs naturally with the decay of uranium and thorium, metallic chemicals found in rocks and soil. Radon ingestion or inhalation can cause health problems (e.g., lung cancer).

A scan pattern in which an area is scanned in a rectangular pattern from side-to-side in lines from top to bottom to create an image that is projected on a cathode-ray tube and displayed on a screen.

reactive airway disease
An asthma-like syndrome due to muscle spasms in the airways. It can cause wheezing, chest tightness, coughing and difficulty breathing. This includes patients with asthma.

rectal prolapse
A medical condition found most often in young children and the elderly where part of the rectum wall falls out of and protrudes from the anus.

The lower part of the large intestine where water is absorbed from the gut and where stool is formed.

red blood cells

Also known as erythrocytes.
Cells found in the blood that contain hemoglobin and carry oxygen to and carbon dioxide from body tissues.

Reed-Sternberg cell
A cell that distinguishes diseased tissue as Hodgkin lymphoma.

referring physician
Usually a non-radiologist physician who sends a patient to a specialist for more information or treatment.

regional anesthesia
The injection of a local anesthetic, a medication that produce a temporary loss of sensation, near a specific group of nerves in order to block sensation in a larger, but still limited, area of the body supplied by those nerves.

regional enteritis (Crohn's disease)
See Crohn's disease.

The backward flow of undigested food from the esophagus to the mouth.

renal artery
The major artery supplying the kidney.

renal hypertension
High blood pressure caused by a narrowing of the kidney arteries

Relating to the system of organs and parts used in reproduction. In the male, this consists of the testes, penis, seminal vesicles, prostate, and urethra. In the female, this consists of the ovaries, fallopian tubes, uterus, vagina, and vulva.

Surgical removal of part or all of an organ or an area of diseased tissue.

Related to the process of moving air into and out of the lungs, exchanging oxygen and carbon dioxide within the body's tissues.

respiratory therapy
Treatment to preserve or improve lung function.

The gradual re-closing of an artery after it has been widened through a procedure such as angioplasty.

A tumor of the retina, occurring in children.

rheumatoid arthritis
A chronic autoimmune disease that occurs when the immune system attacks the lining, cartilage, bones, and supporting structures of multiple joints.

A monoclonal antibody used in the immunotherapy treatment of non-Hodgkin lymphoma; it binds to a protein found on the surface of normal and abnormal B cells.

roentgen (R, r)
The international unit of exposure dose for x-rays or gamma rays; that quantity of radiation that will produce in 1 cc of air at standard temperature pressure, or 0.001293 g of air, 2.08 ×109 positive and negative ions , each totaling 1 electrostatic unit (e.s.u.) of charge; in the MKS system this is 2.58 ×10-4 coulombs per kg of air.

rotator cuff
A group of muscles around the shoulder joint that help stabilize and move the upper arm.