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Radiotherapy Physics - Glossary

Article Index


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Alpha Cradle: A treatment device that is custom-made from a foam substance, and is placed on the patient during a radiation treatment for the purpose of immobilising and/or positioning the patient.

Arc: refers to a radiation beam that is not stationary, that is, the beam moves around an axis is a curvedpath during the treatment. Also called a rotation.



Barium: a radiographic contrast agent used in radiation oncology during simulation to visualise specific organs (e.g., esophagus, stomach, bowel).

Bite Block: a treatment device that is placed in the patient's mouth during treatment for the purpose of positioning oral structures in the radiation beam. Also called a mouthbite or stent.

Block: a treatment device made from a lead alloy that is placed in part of the radiation beam by attaching it to the treatment unit on a plastic tray for the purpose of preventing the beam form entering a portion of the body. A block is used either to spare sensitive or uninvolved body organs.

Brachytherapy: refers to radiation therapy given form a very short distance form the radiation source,that is, radioactive needles, seeds, liquid, or tubes are placed inside a body cavity or organ or on the skin.



Cesium: an element made radioactive and used in Brachytherapy, gene rally in the form of either needles or tubes.

Cone Down Boost: An additional radiation dose delivered to a more narrowly defined port.

Conformal Radiation Therapy: Conformal therapy allows for the radiation beam to conform to the tumour's contour and size, reducing side effects and increasing cure rates.

Contrast Material: liquid or gel -type agents introduced into a body cavity for the purpose ofvisualising specific organs.

Computerised Tomography(CT): a specialised x-ray taken by a "CT" scanner that takes "slices" of abody part.



Dosimetry: the measurement of radiation dose.

Dummy: a radioactive source that is made to simulate the size and appearance of a radioactive source on a verification X-Ray. It is used to prevent radiation exposure to the healthcare workers during the planning phase for a Brachytherapy treatment.



Electron Therapy: A form of radiation therapy in which the radiation oncologist selects a specific shallow depth and treats only this area without treating structures above and below this interest point.



Field: a specific area of the body designated for treatment. Generally a field is named by the part of the body that the radiation beam enters

Fraction: Pertaining to a portion of the whole treatment course. Generally a fraction can be described as a treatment visit. Most radiation treatment courses are "fractionated" i.e., the total prescribed dose is divided into several treatment visits or fractions. e.g., A total dose of 3000 cGy may be divided into 10 treatment visits or fractions of 300 cGy each.



HDR: High dose rate. Refers to a particular method of delivering a dose for Brachytherapy in which the dose rate is much higher than in conventional Brachytherapy.

Hyperfractionation: the delivery of treatments more than once per day. In radiation oncology this term generally refers to two or three treatment visits per day with a separation of at least six hours between treatments.

Hyperthermia: the use of heat to help to intensify the effects of radiation.



Implant: refers to the placement of radioactive sources within the body.

Intra-operative: refers to radiation treatment delivered while the patient is undergoing surgery.

Interstitial: relating to the spaces within an organ or tissue. Refers to the placement of radioactive sources within the tissues of the body. i.e., breast, tongue, lip, brain prostate. In contrast to intracavitary

Intracavitary: Within a body cavity. Refers to the placement of radioactive sources within a body cavity. i.e., cervix, uterus, esophagus. In contrast to interstitial.

Iodine: an element made' radioactive and used in Brachytherapy. A non-radioactive form of this element may be used as a radiographic contrast agent during simulation to visualise specific organs.

Iridium: an element made radioactive for the use in Brachytherapy.



Linear Accelerator: a teletherapy machine that produces radiation by moving particles very rapidly(accelerating) along a straight path (linear) and then hitting a target. Linear accelerators are manufactures with the capability of having either a single energy or a dual energy. The higher the energy, the deeper the beam reaches inside the body.



Mantle: specialised radiation treatment field to the chest in which the chest and neck lymph system istreated and the other areas are spared by blocks.

MRI: Magnetic resonance image. a special diagnostic image taken by an "MRI" scanner that takes"slices" of a body part.



Photon Treatment: a form of radiation therapy in which the radiation oncologist selects a specific radiation energy appropriate for the patient's body size and depth of the tumour(the higher the energy the deeper the beam reaches inside the body. Contrary to electron treatment, photon treatment deposits a radiation dose above and below the tumour site.

Physicist: the radiation oncology health professional whose primary duty is to oversee the quality assurance aspect of a patient's treatment. Some duties may include calibration and overseeing of the radiation equipment and overseeing charting.

Port Film: a radiographic image captured on film that shows the prescribed treatment area (port). A port film is different form an X-Ray in that a port film is taken for the purpose of a record of the body site treated with radiation and is generally not used as a diagnostic tool.



Radiation Oncologist: the radiation oncology health professional who is a physician who prescribes and oversees a course of radiation therapy.

Radiographer: the radiation oncology health professional who carries out the radiation prescription by using a radiation machine. Some radiographers also perform treatment simulations and planning.

Remote Afterloading: refers to Brachytherapy delivered by loading the radioactive sources into the patient form a remote location.

Ribbons: refers to the temporary interstitial placement of radioactive elements.



Set Up: a procedure whereby the physical parameters (i.e. body position, machine angle) are defined before the treatment is given. A set up may be done on a simulator, radiation therapy treatment unit, or a diagnostic X-Ray unit.

Shield: a treatment device,that' generally is custom made which spares radiation to a specific body area.

Simulation: a radiation oncology procedure, performed prior to treatment, carried out on a dedicated"simulator", radiation therapy treatment unit, or diagnostic X-Ray unit during which the treatment parameters (patient position, field size, etc.) are defined. This procedure "simulates" the actual treatment without delivering the radiation dose.

Simulator: a treatment planning machine whose physical parameters mimics those of an actual radiation treatment unit, but without the high radiation beam energy that actually delivers a treatment.

Sources: refers to intracavitary placement or permanent interstitial placement of radioactive elements.In contrast to ribbons.

Stereotactic: refers to a method of precisely locating areas in the brain.



TBI: total body irradiation. Refers to a radiation beam that encompasses the entire body.

Treatment: specifically, the radiation beam time for each field or more generally all ports that are treated in one visit.

Treatment Plan: the process whereby the radiation oncologist provides interpretation of tests, tumour localisation, treatment time/dose determination, choice of treatment modalities, determination of number and size of treatment ports, selection of treatment devices, etc.

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