* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Dosimerty/Radiation Therapy Terms
Survey
Document related concepts
Positron emission tomography wikipedia , lookup
Medical imaging wikipedia , lookup
History of radiation therapy wikipedia , lookup
Brachytherapy wikipedia , lookup
Nuclear medicine wikipedia , lookup
Center for Radiological Research wikipedia , lookup
Backscatter X-ray wikipedia , lookup
Proton therapy wikipedia , lookup
Radiation therapy wikipedia , lookup
Neutron capture therapy of cancer wikipedia , lookup
Industrial radiography wikipedia , lookup
Radiation burn wikipedia , lookup
Transcript
Dosimerty/Radiation Therapy Terms DRR (digital reconstructed radiograph)- based on acquired CT information, these are images that render a beam’s eye view display of the treatment field anatomy and areas of treatment interest. These images resemble conventional radiographs Attenuation- removal of photons and electrons from a radiation therapy by scatter or absorption as it travels through a medium, typically tissue or tissue equivalent materials Beam hardening- increasing the average energy level of the beam by filtering out lowenergy photons CT window and leveling- the CT number setting in Hounsfield unites of the midpoint of the window width, which is the gray scaled of the image. Dmax- the depth of maximum buildup, in which 100% of the dose is deposited beneath the skin. Depth at which electronic equilibrium occurs for photon beams. This is also the depth of maximum absorbed dose and ionization, for photons, from a single treatment field. Depth of maximum ionization and maximum absorbed dose are usually not the same depth for electrons Tomotherapy- IMRT treatments using a continuously rotating gantry. Radiation is helically delivered slice by slice Effective field- blocked field size. Effective field size is the equivalent rectangular field dimensions of the open or treated area within the collimator field dimensions. Effective field is the actual area treated Equivalent square- square field that has the same percentage depth dose and output of a rectangular field. This method takes different rectangle field sizes and compares them to square fields that demonstrate the same measurable scattering and attenuation characteristics Given dose- the dose delivered at the depth of maximum equilibrium (Dmax) through a single treatment field. Aka applied dose or Dmax dose Gray- SI derived unit of absorbed dose Hinge angle- measure of the angle between central rays of two intersection treatment beams Heterogeneity correction- corrections that account for the presence of irradiated media other than water CT Simulation- computed tomography scanner equipped with software that can provide information needed to design the patient’s treatment parameters Hot Spots- volume outside the PTV which receives dose larger than 100 % of the specified PTV dose HVL- thickness of absorbing material necessary to reduce the x-ray intensity to half its original value Bolus- tissue equivalent material that is usually placed on the patient to increase the skin dose and/or even out irregular contours in the patient Isodose curve- plotted percentage depth dose at various points in the beam along the central axis and elsewhere Magnification factor- the degree of image enlargement how magnification is expressed and measured by formula: Image size/object size Minification factor- objects on a film are smaller than actual size Maximum target dose- (105%) largest dose consistent with safety Minimum target dose- (97%) smallest does that will produce an appreciable effect Output factor- ratio of the dose rate of a given field size to the dose rate of the reference field size Orthogonal films- two images taken 90 degrees apart. They are required for treatment planning purpose to define the location and relationship of various anatomic structures relative to the field’s isocenter Percentage Depth Dose- ratio, expressed as a percentage of the absorbed dose at a given depth to the absorbed dose at a fixed reference depth usually (Dmax) Penumbra- area of region at the beam’s edge where the radiation intensity falls to 0 Prescribed dose- planned treatment dose Primary radiation- radiation arriving directly from its source without interaction with matter Rad- unit of absorbed dose Scatter radiation- type of secondary radiation that occurs when the useful beam intercepts any object Skin Sparing- property of megavoltage irradiation where the maximum dose occurs at some depth beneath the skin surface SAD technique- isocentric technique, three dimensional treatment using multiple imaging modalities, including fluoroscopy,CT, MRI,PET and ultrasound planning where the isocenter is placed in or near the target volume SSD technique- non isocentric technique, based on the distance from the source of radiation to the patients skin (PDD) High Dose Rate brachytherapy (HDR)- delivery of brachytherapy on an outpatient basis using HDR brachytherapy equipment. Actual treatment delivery lasts about 5 to 10 minutes in contrast to a hospital stay that might take several days for low-dose rate brachytherapy Low Dose Rate brachytherapy (LDR)- Brachytherapy that is delivered in a conventional low dose rate regimen that lasts several days and requires a hospital stay Coplanar- geometrical principle describing two radiation fields configured in such a way that the beam edges lie in the same plane Non coplanar- beam edges don’t lie in the same plane 3-D planning- three-dimensional image visualization and treatment-planning tools are used to conform isodose distributions to only target volumes while excluding normal tissues as much as possible 4-D planning- uses three dimensional treatment planning +time =4D Absorbed dose- energy absorbed per unit mass of any material; units are the cGy or rad Activity- rate at which a radioactive isotope undergoes nuclear decay; units are the Curie or Becquerel (Bq=1 disintegration per second) 1 Ci=3.7x10^10Bq Linear attenuation coefficient- constant that describes the rate of energy loss by a photon beam. Describes the probability that each photon in the beam will interact with the medium and lose its energy per centimeter of material that the photons pass through and has units of cm^-1 Build up region- region between the skin surface and the depth of Dmax. Build up region is a characteristic of megavoltage irradiation. In this region, the dose increases with depth until it reaches a maximum at the depth of Dmax Calibration- determation of the accuracy of an instrument, usually by measurement of its variation from a standard, to ascertain necessary correction factors Decay Constant- total number of atoms that decay per unit time Dynamic wedge- use of a moving collimator jaw to produce a wedged isodose distribution Entrance dose- measure of radiation dose absorbed by the skin Gap Calculation- treatment fields overlapping at a prescribed depth in a patient. Exact length of gap must be calculated by knowing the length of each treatment field and depth at which the intersection of the fields is to be positioned [(1/2L1/SSD1)+(1/2L2/SSD2)]x match depth GM detector- highly sensitive, best for measuring contamination and other low levels of radiation Normalization- re-expressing of isodose distribution in terms of percents. All dose distribution points are re-adjusted to be specified 100% point and then the distribution of isodose lines is able to be selected in terms of percentages Heterogeneity- consisting of different frequencies, various energies or a variety of particles ICRU( international commission on Radiation Units and Measurements)international standard that determines the radiation tumor volumes Inverse square law- mathematical relationship that describes the change in beam intensity as the distance from the source changes, where intensity is inversely proportional to the distance squared DVH (dose volume histogram)- plot of target or normal structure volume as a function of dose Mass attenuation coefficient- describes the fraction of a beam of xrays or gamma rays that is absorbed or scattered per unit thickness of the absorber Monitor Unit (MU)- unit of output measure used for linear accelerators. Accelerators are calibrated so that 1 MU delivers 1 cGy for a standard, reference field size at a standard reference depth at a standard source to calibration point Multi Leaf Collimator (MLC)- distinct part of the linear accelerator that allows treatment field shaping and blocking through the use of motorized leaves in the head of the machine Monte Carlo Method- any method which solves a problem by any method which solves a problem by generating suitable random numbers and observing that fraction of the numbers obeying some property or properties. The method is useful for obtaining numerical solutions to problems which are too complicated to solve analytically. Non Conformal radiation- also known as traditional radiation. Traditional radiation is limited to between two and four ports of entry. The shape of the fields and the depth of penetration can be manipulated, but that is the limit of the ability to conform the radiation. It does not allow for any specific conformation to avoid normal structures in the area of treatment. The treatment is therefore limited by the normal structure’radiation tolerance. The treatment area can be moderated over time, but the entire plan is still delivered based on the acceptable dose limits of the normal tissues involved. Natural Background Radiation: ionizing radiation from natural sources including cosmic rays from outer space and the sun, terrestrial radiation from radioactive materials in the earth, and internal radiation from radioactive materials normally present in the body. Inverse planning- treatment planning in which the clinical objectives are specified mathematically and computer software is used to determine the best beam parameters that will lead to the desired dose distribution (IMRT). Forward planning- process of entering dose altering parameters and beam modifiers into the treatment plan by the planner (3D). Peak Scatter factor- peak scatter factor is a backscatter factor sometimes normalized to a referenced field size, usually 10X10cm, for energies of 4MV and above. Patterson-Parker method- it was developed to deliver uniform dose (+/- 10%) to a plane or volume. The system specified rules of source distribution to achieve the dose uniformity and provided dosage tables for these idealized implants. Quimby method- it is characterize by a uniform distribution of sources of equal linear activity. Planar implants: the dose stated is the dose at the center of the plane (maximum dose).Volume implants: the dose stated is the minimum dose within the volume. Corrections are the same as the Patterson-Parker system. Quality factor- the value of the quality factor for each type of radiation depends on the distribution of the absorbed energy in a mass of tissue. X-ray and gamma rays quality factor is 1. Neutrons and protons quality factor is 10 and alpha particles quality factor is 20. Scatter Air Ratio (SAR) - the difference between the TAR for a field of definite area and that for a zero area Collimator scatter (Sc) - the larger the field size, the more scatter created. The Sc is 1.0 for a 10x10 field size, less than 1.0 for fields under 10x10 and more than 1.0 for fields larger than 10x10. Phantom scatter (Sp) - amount produced in tissue. Tissue- Maximum Ratio (TMR) - ratio of the absorbed dose at a given depth in phantom to the absorbed dose at the same point at the level of dmax in phantom. Thermoluminescent dosimeter (TLD) - device for measuring dose. It uses the phenomenon that some solid materials, when irradiated, will subsequently give off light when heated. Amount of light emitted is proportional to the dose delivered to the crystal. Tissue tolerances- is the ability of the skin and it’s supporting structures to endure the effects of pressure without adverse effects. Wedge Angle- angle between the slanted isodose line and a line perpendicular to the central axis of the beam. Intensity Modulated Radiation Therapy (IMRT) - therapy that delivers non-uniform exposure across the beam’s eye view using a variety of techniques and equipment. The main advantage of using a Dynamic MLC is that the continuous leaf motion enables the delivered intensity to closely match with the optimal fluence calculated by the inverse treatment planning algorithm, accurately preserving both the spatial and intensity resolutions. On the other hand, the static MLC approach resembles a conventional multi-segmented treatment and requires approximating the intensity profile into discrete intensity levels (briefly described in the methods and materials section), resulting inlower resolution. The Static MLC IMRT may be convenient to verify and is technically less demanding than a Dynamic MLC treatment. A Dynamic MLC-based delivery requires more monitor units (MU) than the Static MLC method, as the beam is kept on throughout the delivery of radiation. Equivalent dose- is a computed average measure of the radiation absorbed by a fixed mass of biological tissue that attempts to account for the different biological damage potential of different types of ionizing radiation. Exit dose- the dose absorbed by a point that is located at the depth of DMAX at the exit of the beam. Bremsstrahlung- a German term for “braking” radiation. Fluence pattern- refers to an intensity pattern of the IMRT beam. This may be described at the sequence and the progression of dose delivered per beam, as a product of several segments. Past pointing-moving isocenter farther away from the source in order to evenly cover the intended target. Isocenter- the intersection of the axis of rotation of the gantry and the axis of rotation of the collimator for the treatment unit. Electron therapeutic range- common isodose depths are 80% and 90%. 90% is the most common=therapeutic range. Off axis ratio (OAR) - the OAR is the ratio of the dose at a point (Q) relative a point on the central axis at the same depth (P). OAR=DQ/DP. The OAR is used for calculation of dose at points away from the central axis. Backscatter- radiation that is deflected back toward the patient. The term backscatter factor (BSF) is simply the tissue-air ratio at the depth of maximum dose on central axis of the beam. BSF= TAR Backscatter Factor (BSF): the ratio of the dose rate with a scattering medium to the dose rate at the same point without a scattering medium at the level of maximum equilibrium. GTV- the tumor - this is called the GTV or Gross Tumor Volume. CTV- the tumor plus a margin for microscopic spread - this is called the CTV or Clinical Target Volume. PTV- the tumor plus a margin to account for microscopic tumor spread and plus another smaller margin to account for day to day set up variability. This is called the PTV or Planning Target volume Cone beam CT (CBCT) - based image guided systems have been integrated with medical linear accelerators to great success. With improvements in flat-panel technology, CBCT has been able to provide volumetric imaging, and allows for radiographic or fluoroscopic monitoring throughout the treatment process. Cone beam CT acquires many projections over the entire volume of interest in each projection. Stereotactic radiation therapy- SRT is fractionated and can be done on linac, the brain lab, Cyberknife, or Gammaknife. Stereotatic radiosurgery (SRS) is a single dose treatment and involves the use of a halo brace for the head. Both SRS and SRT involve a 1-3cm diameter cones (no blocks used) and the gantry moves in arcs as the dose is delivered in thin strips. IGRT- image-guided radiation therapy is a process of using various imaging technologies to locate a tumor target prior to a radiation therapy treatment. This process is aimed to improve the treatment accuracy so that the need for large target margins which have traditionally been used to compensate for errors in localization. As a result, the amount of healthy tissue exposed to radiation can be reduced, minimizing the incidence of side effects. EPID- electronic portal imaging is the process of using digital imaging, such as a CCD video camera, liquid ion chamber and amorphous silicon flat panel detectors to create a digital image with improved quality and contrast over traditional portal imaging. The benefit of the system is the ability to capture images, for review and guidance, digitally. These systems are in use throughout clinical practice CT- computerized tomography scans. Pictures of structures within the body created by a computer that takes the data from multiple X-ray images and turns them into pictures on a screen. MRI- a magnetic resonance imaging scan is a radiology technique that uses magnetism, radio waves, and a computer to produce images of body structures. The MRI scanner is a tube surrounded by a giant circular magnet. The patient is placed on a moveable bed that is inserted into the magnet. The magnet creates a strong magnetic field that aligns the protons of hydrogen atoms, which are then exposed to a beam of radio waves. This spins the various protons of the body, and they produce a faint signal that is detected by the receiver portion of the MRI scanner. The receiver information is processed by a computer, and an image is PET- positron emission tomography. A highly specialized imaging technique that uses short lived radioactive substances to produce three-dimensional colored images of those substances functioning within the body Bat- B-mode Acquisition and Targeting is an ultra sound-based targeting system used with IMRT and external beam radiation, to precisely localize targets. To accomplish great precision it uses technologies of 3-D computer imaging, a sophisticated linear accelerator alignment and delivery system, and advanced ultrasound technology. BAT is useful for prostate cancer, breast cancer, liver cancer, and bladder cancer. Mayneord- F factor- a special application of the inverse square law. Does not account for changes in scatter because of a change in beam divergence. New PDD = PDD x (SSD1 + d / SSD1 + DMAX) 2 x (SSD2 + DMAX / SSD1 + d)2