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5-year relative survival rate : The likelihood that a patient will not die from causes associated with his or her cancer for at last 5 years after diagnosis. This is the standard many professionals use when determining someone a 'survivor' of cancer.

adjuvant chemotherapy : Chemotherapy treatment that is given as an 'add-on' to a primary cancer treatment such as surgery or radiation therapy.

antibody : Any of various substances produced in the body (by lymphocytes and other special cells), which help to defend the body against infections due to viruses, bacteria, and other foreign organisms.

antigen : Any of various substances capable of stimulating a specific immune response (i.e., production of a specific antibody). Antigens include foreign substances, toxins, bacteria, etc.

arc : One partial revolution of the radiation source in an external beam radiation therapy treatment. An arc is defined by its starting and ending points, plane of rotation, etc.

arc therapy : A form of external beam radiation therapy in which the radiation source revolves about the patient as it delivers radiation.

arc treatment session : A treatment session in which several parallel arcs are used to treat a target volume that is too large to be treated with a single arc.

benign : Not cancerous.

biological therapy : Cancer treatment that uses natural substances or substances made in a laboratory to stimulate or restore the ability of the body's immune system to fight disease. Interferon and interleukin-2 therapies are examples. Therapies such as these are often used in conjunction with other treatments. Also called immunotherapy.

biopsy : The surgical removal of a small piece of tissue for microscopic examination. Often used to determine if cells or a tumor are cancerous.

bone marrow : The spongy material that fills the inner spaces of the bones. It is the place where many blood elements, such as red blood cells, are produced. High doses of radiation can destroy bone marrow during cancer treatment.

brachytherapy : A type of radiation therapy in which radioactive materials are placed close to or inside the patient's body.

cancer : A generic term for more than 100 different diseases that are characterized by the uncontrolled, abnormal growth of cells. Cancer cells usually invade and destroy normal tissue. Cancer cells can travel through the bloodstream and lymphatic system to reach other parts of the body.

carcinoma : A cancerous tumor originating in epithelial cells (the surface cells of tissues). Carcinomas tend to spread into surrounding tissues and to metastasize to other parts of the body.

chemotherapy : Treatment with toxic chemicals (e.g., anticancer drugs).

clinical trial : Scientific research conducted with patients, usually to evaluate a new treatment. Each trial is designed to answer specific questions and to find better ways to treat individuals with a specific disease. Many times cancer patients can receive new, experimental treatments by participating in a clinical trial.

computed tomography (CT) : A form of x-ray imaging in which 2-dimensional sections of patient anatomy are reconstructed from x-rays projected through the body from many different angles. CT images display sharp contrast based upon tissue density and exhibit high spatial accuracy.

conformal radiation therapy : External beam radiation therapy in which the shape of each radiation field closely conforms to the 2-D outline of the target volume. The goals of conformal therapy are a) to achieve higher cure rates by increasing the radiation dose that may be delivered to the patient; b) to achieve lower complication rates by reducing the radiation dose delivered to normal tissues during treatment.

dynamic IMRT : An intensity modulated radiation treatment in which the vanes of a multileaf collimator are allowed to move while the beam is on. Dynamic IMRT treatments can take less time to deliver than static IMRT treatments, but not all types of multileaf collimators are equipped to deliver them.

external beam radiation therapy : Any type of radiation therapy in which the radiation source is located at a distance from the patient's body (see also brachytherapy ).

fiducial point : A reference point defined either by patient anatomy or by an artificial marker attached to a patient fixation device.

fixation (immobilization) device : An apparatus used to immobilize a patient during imaging and treatment. These devices often incorporate localization (fiducial) markers for accurately locating patient tissue in three dimensions.

fraction : The portion of a fractionated radiation treatment that is delivered in a single session.

fractionation : A method of delivering radiation therapy in which the total radiation dose is delivered in multiple, small fractions instead of all at one time. Fractionation is effective because normal tissue is usually able to recover from radiation damage in the interval between fractions while cancerous tissue usually takes loner to recover.

gamma rays : A kind of deeply penetrating radiation that is emitted by radioactive materials. Gamma rays are used in nuclear medicine , in brachytherapy , and in external beam radiation therapy. Gamma rays are equivalent to high energy x-rays.

Gray (Gy) : The SI (System International) unit of absorbed radiation dose.

hematology/hematologist : The branch of medicine that studies and treats the blood and blood tissues.

hemorrhage : Bleeding.

Hodgkin's disease : A malignant disorder of the lymph tissue (a lymphoma ) that occurs most often in males, ad most often in individuals between the ages of 15 and 35. It is characterized by progressive, painless enlargement of the lymph nodes, spleen, and general lymph tissue. When detected early, it has a high cure rate.

imaging : To acquire an image or an image series of a patient's anatomy (e.g., with a CT scanner or an MRI scanner).

immune system : The system, made up of many different organs and cells, that defends the body against infection, disease, and foreign substances. The immune system is often stimulated in specific ways to fight cancer cells.

immunocompetence : The body's ability to develop an immune response to infection or disease. Immunocompetence is measured to see how well the body can fight off certain disease. Many cancer patients become immunocompromised, where their immune system is not as strong as a healthy person's.

immunosuppression : The prevention or suppression of the immune response. Immunosuppression leaves people unable to fight off disease or infection as well as a healthy person. Immunosuppression can be caused by certain drugs, by irradiation, and by other agents.

intensity modulated radiation therapy (IMRT) : A type of conformal radiation therapy which produces highly uniform dose distributions within target volumes , and distinct dose gradient at the edges of target volumes. In an IMRT treatment, each radiation field is divided into finite size pencil beams of differing intensities.

inverse planning : Treatment planning for radiation therapy in which treatment fields are designed by a computer in order to achieve the dose distribution prescribed by a physician. The NOMOS^® CORVUS^® treatment planning system is an inverse planning system for intensity modulated radiation therapy.

laparoscopy : A surgical technique in which a tiny scope is inserted into the abdomen through a small incision. It is used in a variety of procedures (e.g., to diagnose disease of the fallopian tubes and pelvic cavity).

laser : A medical instrument that produces a powerful beam of light and can produce intense heat when focused at close range. Lasers are often used in surgery to cut out or destroy diseased tissue.

leukemia : A progressive, malignant disease of the blood and blood-forming organs, characterized by over-proliferation and development of leukocytes (a type of white blood cell). There are many different forms of leukemia.

LINAC : An abbreviation for linear accelerator.

linear accelerator : A type of high energy x-ray machine that generates radiation fields for external beam radiation therapy. A linear accelerator is typically mounted with a collimator and/or a multileaf collimator on a gantry that revolves vertically around a treatment couch.

lymph nodes : Small, bean-shaped organs that supply lymphocytes (a type of white blood cell) to the bloodstream and filter out bacteria and foreign substances from the lymphatic system. Also called lymph glands, these organs are located throughout the body.

lymphangiogram : An x-ray of the lymphatic system using dye injected to highlight lymph nodes and other vessels.

lymphatic system : The tissue and organs (including the bone marrow, spleen, thymus, and lymph nodes) that produce and store the white blood cells used to fight infection.

lymphocytes : A type of white blood cell that fights disease and infection.

lymphoma : A general term for any disease of the lymphatic tissue characterized by abnormal, uncontrolled cell growth. Hodgkin's disease is a type of lymphoma.

magnetic resonance imaging (MRI) : A technique used to image internal structures of the body. MRI images display better contrast in soft tissues than computed tomography (CT) images, but they do not contain information about tissue density, and they are more susceptible to geometric distortion.

malignant : Cancerous

malignancy : A cancerous tumor or cancerous tissue.

mammogram : An x-ray of the breast. Mammograms are used to detect abnormalities in breast tissue, specifically breast cancer.

melanoma : Cancer that begins in the melanocytes and spreads to other skin cells. Melanoma appears on the skin and looks like a new or changing mole.

metastases : Cancer that started from cancer cells from another part of the body. For example, cancer that starts in the breast can spread to the lymph nodes and then be spread throughout the body.

metastasis : The spread of cancer from one part of the body to another.

MIMiC^® : A multileaf collimator manufactured by NOMOS^®. The MIMiC^® is designed especially for delivering intensity modulated treatments. It can be mounted on a variety of linear accelerators including some older, analog models for which other multileaf collimators are not available.

MLC : An abbreviation for multileaf collimator.

modality : A specific method of treatment or imaging (e.g., CT scans, MRI scans, and ultrasonography are different imaging modalities).

monoclonal antibody : An antibody produced in the laboratory that can target specific antigens (substances that provoke in immune response). They can be made in large quantities and are being tested for their use in cancer diagnosis and treatment.

MRI : Magnetic resonance imaging.

MU (monitor unit) : A setting used with linear accelerators to describe a relative quantity of radiation to be generated. The calibration that relates monitor units to absorbed dose is unique for each individual accelerator.

multileaf collimator (MLC) : A type of collimator which can define irregularly shaped radiation fields. A MLC has two rows of narrow metal blocks (leaves) that can be independently driven in or out of the radiation beam from opposite sides under computer control.

multiple myeloma : A cancer of the white blood cells found in the bone marrow.

mycosis fungoides : A rare type of non-Hodgkin's lymphoma that first appears on the skin, then later spreads to the lymph nodes and organs. Also called cutaneous T-cell lymphoma.

natural killer cell : A type of white blood cell that attacks tumor cells and infected body cells by binding to them and releasing lethal chemicals. Natural killer cells are thought to play a key role in cancer prevention by killing abnormal cells before they multiply and grow.

neuroblastoma : A sarcoma (a specific type of cancerous cell structure) that originates in the nervous system and usually affects infants and children under the age of 10.

nevi : A cluster of melanocytes. Nevi on the skin are commonly called moles.

non-Hodgkin's lymphoma : Any kind of cancer of the lymph tissue (lymphoma ) other than Hodgkin's disease. Also called lymphosarcoma.

nuclear medicine : The branch of medicine pertaining to diagnostic, therapeutic, and investigative use of radioactive chemical elements.

oncology/oncologist : The branch of medicine concerned with the treatment of cancer.

pathology/pathologist : The branch of medicine concerned with disease, especially its structure and its functional effects on the body.

plasma cells : White blood cells.

platelets : A blood component that is instrumental in clot formation, which stops bleeding in injured areas and prevents hemorrhage.

polyp : A protruding growth from a mucous membrane, commonly found in the nose, uterus, and rectum. Certain polyps, such as those found in the color, can become cancerous. Surgical removal of these types of polyps is sometimes recommended.

prognosis : The predicted outcome of a disease.

prostate gland : A gland in the male that surrounds the neck of the bladder and urethra. The prostate contributes to the seminal fluid.

prostate specific antigen (PSA) test : A simple blood test used to detect prostate cancer in men. The test measures a specific antigen normally secreted by the prostate. If cancer is developing, the prostate secretes more PSA than normal. A PSA test is recommended for men with an enlarged prostate and an increased risk of prostate cancer.

radiation therapy : Medical treatment using radiation from x-ray machines or from radioactive materials. The goal of most radiation therapies is to destroy unwanted (e.g., cancerous) tissue.

radiosurgery : Radiation therapy in which a large radiation dose is delivered to a target volume in a single treatment rather than in small fractions. The target volume may or may not be cancerous tissue. Radiosurgical treatments rely on tight localization of the radiation dose to minimize damage to non-target tissue.

red blood cells : A blood component. Red cells carry oxygen to organs and tissues throughout the body.

relapse : The return of signs and symptoms of a disease after a period of improvement.

remission : The decrease or disappearance of the symptoms of cancer.

resection : Surgical removal of an area of tissue or of an entire organ.

sarcoma : A cancerous growth of the soft tissues, usually appearing first as a painless swelling.

scan : To examine a patient's anatomy piece by piece and build up a detailed image or image series. (For example, using a computed tomography (CT) scanner, or a magnetic resonance imaging (MRI) scanner.) Also, an image or an image series acquired by scanning.

sensitive structure : A region in the patient's anatomy (e.g., the spinal cord or the optic nerve) where it is especially important to minimize complications.

sigmoidoscopy : A procedure in which an endoscope is used to view the patient's sigmoid flexure (a part of the colon).

simulated annealing : An optimization method used to solve many-dimensional problems in which there is no direct path to a solution. The method is slower than other optimization methods, but is capable of finding optimal solutions where other methods fail. CORVUS^® uses simulated annealing to choose optimal intensities for the finite size pencil beams that comprise an intensity modulated radiation treatment.

squamous cells : Flat cells found in the outer layer of the skin.

static IMRT : An intensity modulated radiation treatment in which the vanes of a multileaf collimator are stationary whenever the radiation beam is on and move when the beam is off. Intensity modulation is achieved by delivering a sequence of fields of differing shape and intensity.

stem cell : A 'generalized' cell whose division results in specialized cells. Its descendants have the potential to develop into several different types of mature cells.

step and shoot : Another name for static IMRT.

stereotactic radiation therapy : Radiation therapy in which the tissues being treated are located in 3-dimensional space with a high degree of accuracy. Stereotactic treatments require that the geometry of the patient during imaging be accurately reproduced in the treatment room.

surgical oncology : Treatment of cancer using surgery, usually to remove cancerous tumors and tissue.

target volume : A region in the patient's anatomy (e.g., a tumor) for which a high radiation dose is prescribed.

therapeutic ratio : A measure of the ratio between the damage done to cancerous tissue by a radiation treatment and the damage done to normal tissue.

thermoluminescent dosimeter (TLD) : A device that directly measures absorbed dosage. TLDs are sometimes used to verify the accuracy of radiation treatments.

treatment : A complete treatment plan, consisting of multiple arc treatment sessions.

treatment machine : The combination of a specific linear accelerator and a specific multileaf collimator for which a treatment plan is designed.

treatment session : A segment of a treatment plan delivered without moving the patient off the couch.

T-cell : A small lymphocyte, made in the thymus, that circulates through the bloodstream. T-cells play a role in the body's immune system.

tumor : An abnormal mass of tissue. Tumors can be benign (non cancerous) or malignant (cancerous).

tumor-infiltrating lymphocytes : Special cancer-fighting cells of the immune system which concentrate in tumors. In a type of experimental therapy, scientists harvest these cells from the tumor, grow them in a laboratory, and then return them to the patient with the hope of the cells destroying the tumor.

tumor marker : A substance in the body that usually indicates the presence of cancer. These markers are usually specific to certain types of cancer, and are usually found in the blood or other tissue samples.

ultrasonography : The use of sound waves to image the deep structures of the body. Often used during pregnancy and for the diagnosis of many diseases, including cancer. Also called sonography or ultrasound imaging.

ultraviolet (UV) radiation : A kind of non-penetrating radiation that is a component of sunlight. Short-term overexposure to ultraviolet rays can cause a sun burn. Long-term exposure repeated over many years may be a factor in some kinds of skin cancer.

X-rays : A kind of deeply penetrating radiation that is generated by an x-ray tube or by a linear accelerator. Low energy x-rays are used in diagnostic imaging, while high energy x-rays are used in external beam radiation therapy. The x-rays used in radiation therapy are effectively similar to gamma rays.

References:

Altman, R., and Michael J. Sarg, MD. The Cancer Dictionary. New York: Facts on File, Inc., 1992.

Dorland's Illustrated Medical Dictionary. Philadelphia: W.B. Saunders Company, 1985.

Mosby's Medical Encyclopedia.

US Department of Health & Human Services, National Cancer Institute