Radiation Therapy - deciphering common Radiation Therapy terms


The world of cancer care is often surrounded by terms and
acronyms unfamiliar to most of us. In this blog we offer a glossary of common terms related to radiation therapy:
 APBI Accelerated Partial Breast Irradiation (APBI) used after a lumpectomy, APBI differs from WBEBRT in two ways. First, it reduces the treatment area from the entire breast to the area of the breast immediately around the lumpectomy site. This is the part of the breast where most cancers are likely to recur. Second, it shortens the treatment time from 5-7 weeks to 4-5 days.  Since the duration of treatment is shorter, radiation is delivered in fewer fractions at larger doses per fraction.
Brachytherapy Sometimes referred to as internal therapy, brachytherapy means short distance therapy. The advantage of brachytherapy is the ability to deliver a high dose of radiation to a small area and is useful in situations that require a high dose of radiation or a dose that would be more than normal tissue could tolerate if given by external beam. There are several types of internal radiation therapy:
  • interstitial - the radiation source is placed in the affected tissue in small pellets, wires, tubes, or containers.
  • intracavitary - a sealed container of radioactive material is placed in a body cavity a short distance from the affected area.
  • high dose rate (HDR) brachytherapy, uses needles containing radioactive material. The radioactive source travels through the needles to the tumor.
Breast Conservation Therapy
Also known as a lumpectomy, this involves surgery to remove a breast cancer tumor and a small area of normal tissue around the cancer but preserving most of the breast. It is almost always combined with axillary lymph node removal and is usually followed by radiation therapy. This method may also be called segmental excision, limited breast surgery, or tylectomy.
Cobalt-60 Nonradioactive cobalt occurs naturally in various minerals. The radioisotope, cobalt-60, is produced for commercial use in linear accelerators.  Prior to the widespread availability of linear accelerators, cobalt-60 was used as a radiation source to treat cancer.
Ductal Carcinoma In Situ
Early stage cancer that that starts in the milk passages (ducts) but has not penetrated the duct walls into the surrounding tissue. This is a highly curable form of breast cancer that is treated with surgery, or surgery plus radiation therapy.
Electronic Brachytherapy

A relatively new technology designed to deliver non-radioactive, isotope-free radiation treatment directly to cancer sites. Using disposable micro-miniature X-ray radiation sources to deliver treatment, this localized approach is designed to minimize exposure of healthy tissue. Because the system does not require a shielded environment, it can be used in virtually any clinical setting under the supervision of a radiation oncologist.

Unlike radioisotope sources, the non-radioactive X-ray source can be turned on and off at will during treatment and may be operated at variable voltage rates to change the penetration properties. The amount of x-ray radiation generated can be completely controlled by the amount of current operating through the device.  Through carefully controlled physical, material and geometric parameters, radiation is generated and transmitted in a consistent three-dimensional pattern.

External Beam Radiation Therapy External radiation therapy delivers a beam of high-energy X-rays to the location of the patient's tumor. The beam is generated outside the patient, usually by a linear accelerator – no radioactive sources are placed inside the patient's body. These x-rays can destroy the cancer cells and careful treatment planning reduces exposure to surrounding normal tissues. Typically, patients receive treatment once a day, five days a week for five to seven weeks.
Fractions Radiation therapy regimens are broken into smaller doses in order to allow healthy tissue time to repair itself from incidental radiation exposure.

Term used for the measurement of radiation absorbed by the body.   One Gray is equal to 100 RADS.

Intensity Modulated Radiation Therapy

IMRT is a computerized form of external radiation therapy that utilizes computer-controlled x-ray accelerators to deliver precise radiation doses to a malignant tumor. The radiation dose is designed to conform to the 3-D shape of the tumor by modulating—or controlling—the intensity of the radiation beam to focus a higher radiation dose to the tumor while minimizing radiation exposure to surrounding normal tissues.
Internal Radiation Therapy
Please see Brachytherapy
Ioninizing Radiation Used to treat cancer, ionizing radiation (usually X-rays or gamma rays) can be generated from the decay of radioactive elements or through devices such as x-ray sources or linear accelerators.
Ions Atoms that have acquired an electric charge through the addition or loss of an electron.
Iridium/192 Radioactive isotope used in traditional brachytherapy treatments.
Isotope Also known as a radioisotope.  An element that gives off radiation as it decays.  Can be used for diagnosis as well as for treatment of cancer.
LINAC  Short for Linear Accelerator.  In the 1950s, linear accelerators represented a generational advance in radiation therapy from cobalt-60.  LINACS use microwave technology (similar to that used for radar) to accelerate electrons and then allows these electrons to collide with a heavy metal target. As a result of the collisions, high-energy X-rays are scattered from the target. A portion of these X-rays is collected and then shaped to form a beam that matches the patient's tumor.
Mastectomy Surgery to remove all or part of the breast and sometimes other tissue. Modified radical mastectomy removes the breast, skin, nipple, areola, and most of the axillary lymph nodes on the same side, leaving the chest muscles intact. Partial, or segmental, mastectomy removes less than the whole breast, taking only part of the breast in which the cancer occurs and a margin of healthy breast tissue surrounding the tumor.
Metastasis The spread of cancer cells from the original tumor to distant parts of the body via the lymph system and the blood stream.
Mitosis Rapid cell growth and division.  In this stage of the cell cycle, the cell splits into two new cells identical to the original cell.
Radiation Energy that can be used to alter the genetic code of a cell, which controls how a cell grows and divides in the body.
Radiation Therapy Used to treat cancer for more than 100 years, radiation therapy is administered after breast-sparing surgery to kill any stray cancer cells that might remain in the breast and is proven to reduce the rate of local recurrences and improve long-term survival.   Data from several randomized controlled clinical studies has demonstrated that radiation therapy is an essential component of treatment for breast cancer when the patient wishes to conserve her breast with lumpectomy surgery as opposed to undergoing a full mastectomy.
Radiation vs. Radioactivity Radiation is the energy that is released as particles or rays, during during radioactive decay. Radioactivity is the property of an atom that describes spontaneous changes in its nucleus that create a different element.
  • Non-ionizing radiation - Radiation that has enough energy to move atoms in a molecule around or cause them to vibrate, but not enough to remove electrons, is referred to as "non-ionizing radiation." Examples of this kind of radiation are sound waves, visible light, and microwaves.
  • Ionizing radiation - Radiation that has enough energy to remove tightly bound electrons from atoms, thus creating ions. This is the type of radiation that most usually think of as “radiation"
Radiation Oncologist A physician that specializes in the use of radiation therapy to treat cancer.
Radiologist A physician trained in the diagnostic use of X-rays and other medical imaging tools, such as MRI, CT, and ultrasound. 
Radiosensitivity Refers to how vulnerable a cell is to radiation damage.  Radiation therapy is usually most effective on fast growing cells, or cells undergoing mitosis, but also can affect normal cells, which can result in side effects.
Radiation Absorbed Data
A radiation dose measurement.  One Gray is equal to 100 RADS.
Total Dose The cumulative amount of radiation absorbed during radiation therapy.  To allow healthy tissue time to repair itself from incidental radiation exposure, therapy is broken into smaller doses known as fractions. 
Treatment Plan A radiation oncologist’s prescription describing detailing the dose, fractions and length of time a patient is to be treated with radiation therapy. The radiation oncology team, including the physicist, reviews the plan and checks formulas and protocols to maximize radiation is delivered to the tumor while sparing as much healthy tissue as possible.
Tumor An abnormal lump or mass of tissue. Tumors are either benign (noncancerous) or malignant (cancerous).
Whole Breast External Beam Radiation Therapy
Whole breast radiation therapy is usually given after a lumpectomy to kill any stray cancer cells. Studies have shown that the treatment can reduce the rate of local recurrences and improve long-term survival. Therapy is given five days a week for 5-7 weeks.
X-ray  High-energy radiation.
In low doses, x-rays are used to diagnose diseases. In high doses, x-rays are used to treat cancer


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