Image Image Image


Glossary of Key Terms
  • 4-field - four different beams comprise a complete treatment. . See also: AP/PA
  • AP/PA - a 2-field treatment with two parallel opposed beams, front to back. . See also: 4-field
  • Atom - the smallest component of an element, consisting of a nucleus containing neutrons and protons and one or more electrons.
  • attenuation - the process by which the energy of the radiation beam is reduced by passing through tissue or other material.
  • beam weighting - is a way to assign how much dose can be delivered by a particular beam.
  • bolus - is tissue-equivalent material that is placed on the patient's skin to manipulate the dose distribution.
  • bremsstrahlung - From the German words Bremsen (to brake) and Strahlung (radiation). Means breaking or decelerating radiation occuring when a charged particle passes near the nucleus of an atom. The moving particle loses kinetic energy which is converted to a photon. Bremsstrahlung is the process through which therapeutic and diagnostic x-rays are made..
  • C2-WB - a whole brain plan that extends inferiorly to include the C1 and C2 vertebral bodies.
  • Calculation Point - a reference point inside the PTV (at the intersection of the beam axes if possible) where the prescription dose is calculated. The point should be clinically relevant, and placed in a region of uniform dose.
  • D-max (also written Dmax) - the point at which the maximum dose is deposited along a beamlet. The point at which the energy of the electrons coming to rest equals the energy of electrons being set into motion by new interactions.
  • Dose Tolerance - the amount of radiation that can be received by an organ before causing damage to that organ.
  • DVH (Dose Volume Histogram) - A DVH, Dose Volume Histogram, is the industry standard for treatment planning evaluation. It graphically summarizes 3D dose distributions of target and critical structures in a graphical 2D format which is useful in evaluating treatment plans. It is also a good way to compare similar plans..
  • Fif (Field-n-field) - a technique that uses multiple fields to deliver a more homogeneous dose to the target.
  • Flash - any portion of the radiation field that extends beyond the patient's skin surface in the Beam's Eye View.
  • GTV (Gross Tumor Volume) - gross demonstrable extent and location of tumor. Consists of primary tumor, metastatic lymphadenopathy, or other metastases.
  • Hot Spot - any dose higher than the prescription dose (100%).
  • IM (Internal Margin) - margin that is added to the CTV to compensate for internal physiological movements and change in size, shape, and position of the CTV.
  • ICRU 50 & 62 - the International Committee on Radiation Units and Measurements. Provides recommended volumes to guide radiation treatment, as well as where reference points should be calculated.
  • isocentric - pertaining to the Isocenter, the point of intersection of the collimator axis and the axis of rotation of the gantry, in other words, the point where the three setup laser planes intersect.
  • isodose line - represents a percentage of the prescribed radiation dose.
  • Lateral Tangent - the posterior oblique field that is used to treat the lateral breast tissue.
  • LAO - Left Anterior Oblique or Left Medial Tangent.
  • LPO - Left Posterior Oblique or Left Lateral Tangent.
  • Medial Tangent - The Anterior Oblique field used to treat the breast tissue that is midline.
  • OAR (Organ at Risk) - normal tissue that is in or close to the treatment field and may be affected by the treatment plan.
  • penumbra - the region at the edge of the beam, where the dose changes rapidly.
  • Photons - high energy rays composed of massless particles of energy.
  • physical wedge - a beam modifying device that is used to manipulate isodose curves. There are four individual angles: 15°, 30°, 45°, 60°.
  • Practical Range (also written Rp) - the useful range for electrons. The interaction between the steep part of the depth dose curve and the line tangent to the bremsstrahlung.
  • RAO - Right Anterior Oblique or Right Medial Tangent.
  • RPO - Right Posterior Oblique or Right Lateral Tangent.
  • Rx - prescription.
  • SAD - Source to Axis Distance.
  • Spine - vertebral column separated into 5 sections:
  • Cervical (C-Spine) - 7 vertebral bodies
  • Thoracic (T-Spine) - 12 vertebral bodies
  • Lumbar (L-Spine) - 5 vertebral bodies
  • Sacral (fused tg)
  • Coccyx
  • SSD - Source to Skin Distance.
  • supraclavicular field - may be needed to treat the lymph nodes that lie superior to the breast tissue. The inferior border matches with the superior breast Tangent border. The superior border extends to cover the top of the first rib.
  • Surface Dose - the amount of radiation the skin is receiving.
  • TV (Treated Volume) - the volume enclosed by the isodose surface that covers the PTV (defined by the 50% isodose line).
  • V20 - [need definition].