180 NAC 20-002. DEFINITIONS

002. DEFINITIONS. The following definitions apply to this chapter. 002.01 ABSORBED DOSE RATE. Absorbed dose rate is the absorbed dose per unit time, for machines with timers, or dose monitor unit per unit time for linear accelerators. 002.02 AIR KERMA (K). Air kerma (K) is the kinetic energy released in air by ionizing radiation. Kerma is determined as the quotient of dE, where dE is the sum of the initial kinetic energies of all ionizing particles liberated by uncharged ionizing particles in air of mass dM. The International System of Units (SI) unit of air kerma is joule per kilogram and the special name for the unit of kerma is the gray (Gy). 002.03 BARRIER. Barrier has the same meaning as stated in protective barrier. 002.04 BEAM AXIS. Beam axis is the axis of rotation of the beam limiting device. 002.05 BEAM-LIMITING DEVICE. Beam-limiting device is a field defining collimator, integral to the therapeutic radiation machine, which provides a means to restrict the dimension of the useful beam. 002.06 BEAM MONITORING SYSTEM. Beam monitoring system is a system designed and installed in the radiation head to detect and measure the radiation present in the useful beam. 002.07 BEAM SCATTERING FOIL. Beam scattering foil is a thin piece of material, usually metallic, placed in the beam to scatter a beam of electrons in order to provide a more uniform electron distribution in the useful beam. 002.08 BENT BEAM LINEAR ACCELERATOR. Bent beam linear accelerator is a linear accelerator geometry in which the accelerated electron beam must change direction by passing through a bending magnet. 002.09 CHANGEABLE FILTERS. Changeable filters are any filter, exclusive of inherent filtration, which can be removed from the useful beam through any electronic, mechanical, or physical process. 002.10 CONTACT THERAPY SYSTEM. Contact therapy system is a therapeutic machine with a short target to skin distance (TSD), usually less than 5 centimeters. 002.11 CONVENTIONAL SIMULATOR. Conventional simulator is any x-ray system designed to reproduce the geometric conditions of the radiation therapy equipment. 002.12 DETECTOR. Detector has the same meaning as radiation detector. 002.13 DOSE MONITOR UNIT (DMU). Dose monitor unit (DMU) means the unit response from the beam monitoring system from which the absorbed dose can be calculated. 002.14 ELECTRONIC BRACHYTHERAPY. Electronic brachytherapy is the method of radiation therapy where an electrically generated source of ionizing radiation is placed in or near the tumor or target tissue to deliver therapeutic radiation dosage. 002.15 ELECTRONIC BRACHYTHERAPY DEVICE. Electronic brachytherapy device is a system used to produce and deliver therapeutic radiation including the x-ray tube, the control mechanism, the cooling system, and the power source. 002.16 ELECTRONIC BRACHYTHERAPY SOURCE. Electronic brachytherapy source is an x-ray tube component used in an electronic brachytherapy device. 002.17 EXTERNAL BEAM RADIATION THERAPY. External beam radiation therapy is a therapeutic irradiation in which the source of radiation is at a distance from the body. 002.18 FIELD-FLATTENING FILTER. Field-flattening filter is a filter used to homogenize the absorbed dose rate over the radiation field. 002.19 FILTER. Filter is material placed in the useful beam to change beam quality in therapeutic radiation machines subject to 180 NAC 20-006. 002.20 GANTRY. Gantry is part of a radiation therapy system supporting and allowing movements of the radiation head about a center of rotation. 002.21 HALF-VALUE LAYER (HVL). Half-value layer (HVL) is the thickness of a specified material which attenuates x-radiation or gamma radiation to an extent such that the air kerma rate, exposure rate or absorbed dose rate is reduced to one-half of the value measured without the material at the same point. 002.22 INTERLOCK. Interlock is a device preventing the start or continued operation of equipment unless certain predetermined conditions prevail. 002.23 INTERRUPTION OF IRRADIATION. Interruption of irradiation is the stopping of irradiation with the possibility of continuing irradiation without resetting of operating conditions at the control panel. 002.24 IRRADIATION. Irradiation is the exposure of a living being or matter to ionizing radiation. 002.25 ISOCENTER. Isocenter is the center of the sphere through which the useful beam axis passes while the gantry moves through its full range of motions. 002.26 KILOVOLT (kV) OR KILOELECTRON VOLT (keV). Kilovolt (kV) or kiloelectron volt (keV) is the energy equal to that acquired by a particle with one electron charge in passing through a potential difference of one thousand volts in a vacuum. The current convention is to use kilovolts (kV) for photons and kiloelectron volt (keV) for electrons. 002.27 LEAD EQUIVALENT. Lead equivalent is the thickness of the material in question affording the same attenuation, under specified conditions, as lead. 002.28 LEAKAGE RADIATION. Leakage radiation is radiation emanating from the radiation therapy system except for the useful beam. 002.29 LIGHT FIELD. Light field is the area illuminated by light, simulating the radiation field. 002.30 MA. The term mA is milliampere (mA). 002.31 MEGAVOLT (MV) OR MEGAELECTRON VOLT (MEV). Megavolt (MV) or megaelectron volt (MeV) is the energy equal to that acquired by a particle with one electron charge in passing through a potential difference of one million volts in a vacuum. The current convention is to use megavolt (MV) for photons and megaelectron volt (MeV) for electrons. 002.32 MISADMINISTRATION. Misadministration is an event that meets the criteria in 180 NAC 20-005.02. 002.33 MOBILE ELECTRONIC BRACHYTHERAPY SERVICE. Mobile electronic brachytherapy service is the transportation of an electronic brachytherapy device to provide electronic brachytherapy at an address that is not the address of record. 002.34 MONITOR UNIT (MU). Monitor unit (MU) has the same meaning as dose monitor unit. 002.35 MOVING BEAM RADIATION THERAPY. Moving beam radiation therapy is radiation therapy with any planned displacement of radiation field or patient relative to each other, or with any planned change of absorbed dose distribution. Includes arc, skip, conformal, intensity modulation, and rotational therapy. 002.36 NOMINAL TREATMENT DISTANCE. Nominal treatment distance is: (A) For electron irradiation, the distance from the scattering foil, virtual source, or exit window of the electron beam to the entrance surface of the irradiated object along the central axis of the useful beam; or(B) For x-ray irradiation, the virtual source or target to isocenter distance along the central axis of the useful beam. For non-isocentric equipment, this distance must be that specified by the manufacturer. 002.37 PATIENT. Patient is an individual subjected to machine produced external beam radiation for the purposes of medical therapy. 002.38 PEAK TUBE POTENTIAL. Peak tube potential is the maximum value of the potential difference across the x-ray tube during an exposure. 002.39 PERIODIC QUALITY ASSURANCE CHECK. Periodic quality assurance check is a procedure which is performed to ensure that a previous calibration continues to be valid. 002.40 PHANTOM. Phantom is an object behaving in essentially the same manner as tissue, with respect to the absorption or scattering of the ionizing radiation in question. 002.41 PRESCRIBED DOSE. Prescribed dose is the total dose and dose per fraction as documented in the written directive. The prescribed dose is an estimation from measured data from a specified therapeutic machine using assumptions that are clinically acceptable for that treatment technique and historically consistent with the clinical calculations previously used for patients treated with the same clinical technique. 002.42 PRIMARY DOSE MONITORING SYSTEM. Primary dose monitoring system is the system which will monitor the useful beam during irradiation and which will terminate irradiation when a pre-selected number of dose monitor units have been delivered. 002.43 PROTECTIVE BARRIER. Protective barrier is a barrier of radiation absorbing material or materials used to reduce radiation exposure. The types of protective barriers are as follows: 002.43(A) PRIMARY PROTECTIVE BARRIER. Primary protective barrier is the material, excluding filters, placed in the useful beam. 002.43(B) SECONDARY PROTECTIVE BARRIER. Secondary protective barrier is the material which attenuates stray radiation. 002.44 RADIATION DETECTOR. Radiation detector is a device which, in the presence of radiation provides, by either direct or indirect means, a signal or other indication suitable for use in measuring one or more quantities of incident radiation. 002.45 RADIATION FIELD. Radiation field has the same meaning as stated in useful beam. 002.46 RADIATION HEAD. Radiation head is the structure from which the useful beam emerges. 002.47 RADIOLOGICAL MEDICAL PHYSICIST. Radiological medical physicist is an individual qualified according to 180 NAC 15-004.01. 002.48 REDUNDANT BEAM MONITORING SYSTEM. Redundant beam monitoring system is a combination of two independent dose monitoring systems in which each system is designed to terminate irradiation according to a pre-selected number of dose monitor units. 002.49 SCATTERED RADIATION. Scattered radiation is an ionizing radiation emitted by interaction of ionizing radiation with matter, the interaction being accompanied by a change in direction of the radiation. Scattered primary radiation means that scattered radiation which has been deviated in direction only by materials irradiated by the useful beam. 002.50 SECONDARY DOSE MONITORING SYSTEM. Secondary dose monitoring system is a system which will terminate irradiation in the event of failure of the primary dose monitoring system. 002.51 SHADOW TRAY. Shadow tray is a device attached to the radiation head to support auxiliary beam blocking material. 002.52 SHUTTER. Shutter is a device attached to the tube housing assembly which can totally intercept the useful beam and which has a lead equivalency not less than that of the tube housing assembly. 002.53 SIMULATOR OR RADIATION THERAPY SIMULATION SYSTEM. Simulator or radiation therapy simulation system is any x-ray system intended for localizing the volume to be exposed during radiation therapy and establishing the position and size of the therapeutic irradiation field. See conventional simulator and virtual simulator. 002.54 SOURCE. Source is the region or material from which the radiation emanates. 002.55 SOURCE SKIN DISTANCE (SSD). The source skin distance (SSD) has the same meaning as target skin distance. 002.56 STATIONARY BEAM RADIATION THERAPY. Stationary beam radiation therapy is radiation therapy without displacement of one or more mechanical axes relative to the patient during irradiation. 002.57 STRAY RADIATION. Stray radiation equals the sum of leakage and scattered radiation. 002.58 TARGET. Target is that part of an x-ray tube or accelerator onto which a beam of accelerated particles is directed to produce ionizing radiation or other particles. 002.59 TARGET SKIN DISTANCE (TSD). Target skin distance (TSD) is the distance measured along the beam axis from the center of the front surface of the x-ray target or electron virtual source to the surface of the irradiated object or patient. 002.60 TENTH VALUE LAYER (TVL). Tenth value layer (TVL) is the thickness of a specified material which attenuates x-radiation or gamma radiation to an extent such that the air kerma rate, exposure rate, or absorbed dose rate is reduced to one tenth of the value measured without the material at the same point. 002.61 TERMINATION OF IRRADIATION. Termination of radiation is the stopping of irradiation in a fashion which will not permit continuance of irradiation without the resetting of operating conditions at the control panel. 002.62 THERAPEUTIC RADIATION MACHINE. Therapeutic radiation machine is an x-ray or electron producing equipment designed and used for external beam radiation therapy. For the purpose of these regulations, therapeutic radiation machine includes, but is not limited to devices used to administer used to administer electronic brachytherapy. 002.63 TUBE. Tube is an x-ray tube, unless otherwise specified. 002.64 TUBE HOUSING ASSEMBLY. Tube housing assembly is the tube housing with tube installed. It includes high voltage or filament transformers and other appropriate elements when such are contained within the tube housing. 002.65 USEFUL BEAM. Useful beam is radiation emanating from the tube housing port or the radiation head and passing through the aperture of the beam limiting device when the exposure controls are in a mode to cause the therapeutic radiation machine to produce radiation. 002.66 VIRTUAL SIMULATOR. Virtual simulator is a computed tomography (CT) unit used in conjunction with relevant software which recreates the treatment machine; and that allows import, manipulation, display, and storage of images from computed tomography (CT) or other imaging modalities. 002.67 VIRTUAL SOURCE. Virtual source is a point from which radiation appears to originate. 002.68 WEDGE FILTER. Wedge filter is a filter which effects continuous change in transmission over all or a part of the useful beam. 002.69 WRITTEN DIRECTIVE. Written directive is an order in writing for the administration of radiation to a specific patient or human research subject, as specified in 180 NAC 20-005.01(A). 002.70 X-RAY TUBE. X-ray tube is any electron tube which is designed to be used primarily for the production of x-rays.