Definitions

As used in this chapter, the following definitions apply: 1. "Absorbed dose (D)" means the mean energy imparted by ionizing radiation to matter. Absorbed dose is determined as the quotient of dE by dM, where dE is the mean energy imparted by ionizing radiation to matter of mass dM. The SI unit of absorbed dose is joule per kilogram and the special name of the unit of absorbed dose is the gray (Gy). The previously used special unit of absorbed dose (rad) is being replaced by the gray. 2. "Absorbed dose rate" means absorbed dose per unit time, for machines with timers, or dose monitor unit per unit time for linear accelerators. 3. "Accelerator-produced material" means any material made radioactive by exposing it in a particle accelerator. 4. "Accessible surface" means surface of equipment or of an equipment part that can be touched by persons without the use of a tool. 5. "Activity" means the rate of disintegration or transformation or decay of radioactive material. The units of activity are the becquerel (Bq) and the curie (Ci). 6. "Added filtration" means any filtration which is in addition to the inherent filtration. 7. "Air kerma (K)" means the kinetic energy released in air by ionizing radiation. Kerma is determined as the quotient of dE by dM, where dE is the sum of the initial kinetic energies of all the charged ionizing particles liberated by uncharged ionizing particles in air of mass dM. The SI unit of air kerma is joule per kilogram and the special name for the unit of kerma is the gray (Gy). 8. "Barrier" (see "protective barrier"). 9. "Beam axis" means the axis of rotation of the beam-limiting device from the source through the centers of the x-ray field. 10. "Beam-limiting device" means a device which provides a means to restrict the dimensions of the useful beam. 11. "Beam-monitoring system" means a system designed and installed in the radiation head to detect and measure the radiation present in the useful beam. 12. "Beam-scattering foil" means 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. 13. "Bent-beam linear accelerator" means a linear accelerator geometry in which the accelerated electron beam must change direction by passing through a bending magnet. 14. "Brachytherapy" means a method of radiation therapy in which sealed sources are utilized to deliver a radiation dose at a distance of up to a few centimeters, by surface, intracavitary, or interstitial application. 15. "Calibration" means the determination of: a. The response or reading of an instrument relative to a series of known radiation values over the range of the instrument; or b. The strength of a source of radiation relative to a standard. 16. "CFR" means the Code of Federal Regulations. 17. "Changeable filters" means any filter, exclusive of inherent filtration, which can be removed from the useful beam through any electronic, mechanical, or physical process. 18. "Contact therapy system" means an x-ray system used for therapy with the x-ray tube port placed in contact with or within five centimeters of the surface being treated. 19. "Department" means the department of environmental quality. 20. "Detector" (see "radiation detector"). 21. "Dose" is a generic term that means absorbed dose, dose equivalent, effective dose equivalent, committed dose equivalent, committed effective dose equivalent, total organ dose equivalent, or total effective dose equivalent. For purposes of these rules, "radiation dose" is an equivalent term. 22. "Dose equivalent HT" means the product of the absorbed dose in tissue, quality factor, and all other necessary modifying factors at the location of interest. The units of dose equivalent are the sievert (Sv) and rem. 23. "Dose monitor unit (DMU)" means a unit response from the beam-monitoring system from which the absorbed dose can be calculated. 24. "Electron applicator" means any accessory device utilized during electron therapy which determines the extent of the treatment area at a given distance from the source. 25. "Entrance" means any opening through which an individual or extremity of an individual could gain access to radiation areas or to licensed or registered radioactive materials. This includes entry or exit portals of sufficient size to permit human entry, irrespective of their intended use. 26. "Exposure" means being exposed to ionizing radiation or to radioactive material. 27. "External beam radiation therapy" means therapeutic irradiation in which the source of radiation is at a distance from the body. 28. "Field-flattening filter" means a filter used to homogenize the absorbed dose rate over the radiation field. 29. "Filter" means material placed in the useful beam to absorb preferentially selected radiations. 30. "Gantry" means that part of a radiation therapy system supporting and allowing movements of the radiation head about a center of rotation. 31. "Gray (Gy)" means the SI unit of absorbed dose, kerma, and specific energy imparted equal to one joule per kilogram. The previous unit of absorbed dose (rad) is being replaced by the gray. [1 Gy = 100 rad]. 32. "Half-value layer (HVL)" means 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. 33. "Healing arts" means diagnostic or healing treatment of human and animal maladies, including the following which are duly licensed by the state of North Dakota for the lawful practice of: medicine and its associated specialties, dentistry, veterinary medicine, osteopathy, chiropractic, and podiatry. 34. "Individual" means any human being. 35. "Inspection" means an official examination or observation, including tests, surveys, and monitoring to determine compliance with rules, regulations, orders, requirements, and conditions of the department. 36. "Interlock" means a device preventing the start or continued operation of equipment unless certain predetermined conditions prevail. 37. "Interruption of irradiation" means the stopping of irradiation with the possibility of continuing irradiation without resetting of operating conditions at the control panel. 38. "Irradiation" means the exposure of a living being or matter to ionizing radiation. 39. "Isocenter" means the center of the sphere through which the useful beam axis passes while the gantry moves through its full range of motions. 40. "Kilovolt (kV) [kilo electron volt (keV)]" means 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. [Note: Current convention is to use kV for photons and keV for electrons.] 41. "Lead equivalent" means the thickness of lead affording the same attenuation, under specified conditions, as the material in question. 42. "Leakage radiation" means radiation emanating from the diagnostic or therapeutic source assembly except for: a. The useful beam; and b. Radiation produced when the exposure switch or timer is not activated. 43. "Light field" means the area illuminated by light, simulating the radiation field. 44. "mA" means milliampere. 45. "Medical use" means the intentional internal or external administration of radiation or radioactive material or the radiation therefrom to patients or human research subjects under the supervision of an authorized user as defined in chapter 33.1-10-07.2-01 [10 CFR 35.2]. 46. "Megavolt (MV) [megaelectron volt (MeV)]" means 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. [Note: Current convention is to use MV for photons and MeV for electrons.] 47. "Monitor unit (MU)" (see "dose monitor unit"). 48. "Monitoring" means the measurement of radiation and the use of the results of these measurements to evaluate potential exposures and doses. For purposes of these rules, "radiation monitoring" and "radiation protection monitoring" are equivalent terms. 49. "Moving beam radiation therapy" means radiation therapy with any planned displacement of radiation field or patient relative to each other, or with any planned change of absorbed dose distribution. It includes arc, skip, conformal, intensity modulation, and rotational therapy. 50. "Nominal treatment distance" means: 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. 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 shall be that specified by the manufacturer. 51. "Patient" means an individual or animal subjected to radiation for the purposes of diagnosis or treatment. 52. "Peak tube potential" means the maximum value of the potential difference across the x-ray tube during an exposure. 53. "Periodic quality assurance check" means a procedure which is performed to ensure that a previous calibration continues to be valid. 54. "Person" means any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, agency, political subdivision of this state, any other state or political subdivision or agency thereof, and any legal successor, representative, agent, or agency of the foregoing, other than the commission, or any successor thereto and other than federal government agencies licensed by the commission or any successor thereto. 55. "Phantom" means a volume of material behaving in a manner similar to tissue with respect to absorption and scattering of the ionizing radiation in question. 56. "Physician" means a medical doctor or doctor of osteopathy licensed by a state or territory of the United States, the District of Columbia, or the Commonwealth of Puerto Rico to prescribe drugs in the practice of medicine. 57. "Practical range of electrons" corresponds to classical electron range where the only remaining contribution to dose is from bremsstrahlung x-rays. A further explanation may be found in "clinical electron beam dosimetry: report of AAPM radiation therapy committee task group 25" [Medical Physics 18(1): 73-109, Jan./Feb. 1991] and ICRU report 35, "radiation dosimetry: electron beams with energies between 1 and 50 MeV", international commission on radiation units and measurements, September 15, 1984. 58. "Primary dose monitoring system" means a system which will monitor the useful beam during irradiation and which will terminate irradiation when a preselected number of dose monitor units have been delivered. 59. "Primary protective barrier" (see "protective barrier"). 60. "Protective barrier" means a barrier of radiation absorbing materials used to reduce radiation exposure. The types of protective barriers are as follows: a. "Primary protective barrier" means the material, excluding filters, placed in the useful beam. b. "Secondary protective barrier" means the material which attenuates stray radiation. 61. "Qualified expert" means an individual having the knowledge, training, and experience to measure ionizing radiation, to evaluate safety techniques, and to advise regarding radiation protection needs, for example, individuals certified in the appropriate field by the American board of medical physics, or those having equivalent qualifications. With reference to the calibration of radiation therapy equipment, "qualified expert" means an individual having, in addition to the above qualifications, training and experience in the clinical applications of radiation physics to radiation therapy, for example, individuals certified in therapeutic radiological physics or x-ray and radium physics by the American board of radiology, or those having equivalent qualifications. 62. "Rad" means the special unit of absorbed dose. One rad is equal to an absorbed dose of one hundred erg per gram or one one-hundredth joule per kilogram (0.01 gray). 63. "Radiation" means alpha particles, beta particles, gamma rays, x-rays, neutrons, high-speed electrons, high-speed protons, and other particles capable of producing ions. For purposes of these rules, ionizing radiation is an equivalent term. Radiation, as used in these rules, does not include nonionizing radiation, such as radiowaves or microwaves, visible, infrared, or ultraviolet light. 64. "Radiation detector" means a device which in the presence of radiation provides a signal or other indication suitable for use in measuring one or more quantities of incident radiation. 65. "Radiation exposure" means the quotient of dQ by dm where "dQ" is the absolute value of the total charge of the ions of one sign produced in air when all the electrons (negatrons and positrons) liberated by photons in a volume element of air having mass "dm" are completely stopped in air. The SI unit of radiation exposure is the coulomb per kilogram (C/kg). (See section 33.1-10-01-14 units of exposure, dose, and activity for the special unit equivalent "roentgen" (R).) 66. "Radiation exposure rate" means the radiation exposure per unit of time, such as R/min, mR/h, etc. 67. "Radiation field" (see "useful beam"). 68. "Radiation head" means the structure from which the useful beam emerges. 69. "Radiation machine" means any device capable of producing radiation except those devices with radioactive material as the only source of radiation. 70. "Radiation therapy physicist" means an individual qualified in accordance with subsection 4 of section 33.1-10-15-03. 71. "Radiation therapy simulation system" means a radiographic or fluoroscopic x-ray system intended for localizing the volume to be exposed during radiation therapy and confirming the position and size of the therapeutic irradiation field. 72. "Redundant beam-monitoring system" means a combination of two dose monitoring systems in which each system is designed to terminate irradiation in accordance with a preselected number of dose monitor units. 73. "Registrant" means any person who is registered with the department and is legally obligated to register with the department pursuant to this article and North Dakota Century Code chapter 23.1-03. 74. "Registration" means the notification of the department of possession of a source of radiation and the furnishing of information with respect thereto, in accordance with North Dakota Century Code chapter 23.1-02. 75. "Rem" (see "sievert"). 76. "Restricted area" means an area, access to which is limited by the licensee or registrant for the purpose of protecting individuals against undue risks from exposure to sources of radiation or radioactive material. "Restricted area" does not include areas used as residential quarters, but separate rooms in a residential building may be set apart as a restricted area. 77. "Scattered radiation" means radiation that, during passage through matter, has been deviated in direction. 78. "Secondary dose-monitoring system" means a system which will terminate irradiation in the event of failure of the primary dose-monitoring system. 79. "Secondary protective barrier" (see "protective barrier"). 80. "Shadow tray" means a device attached to the radiation head to support auxiliary beam-blocking material. 81. "Shutter" means a device attached to the tube housing assembly which can intercept the entire cross-sectional area of the useful beam and which has a lead equivalency not less than that of the tube housing assembly. 82. "Sievert (Sv)" means the SI unit of dose equivalent. The unit of dose equivalent is the joule per kilogram. The previous unit of dose equivalent (rem) is being replaced by the sievert. [1 Sv = 100 rem]. 83. "Source" means the region or material, or both, from which the radiation emanates. 84. "Source-skin distance (SSD)" (see "target-skin distance"). 85. "Stationary beam radiation therapy" means radiation therapy without displacement of one or more mechanical axis relative to the patient during irradiation. 86. "Stray radiation" means the sum of leakage and scattered radiation. 87. "Target" means 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. 88. "Target-skin distance (TSD)" means the distance measured along the beam axis from the center of the front surface of the x-ray target or electron virtual source, or both, to the surface of the irradiated object or patient. 89. "Tenth-value layer (TVL)" means 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. 90. "Termination of irradiation" means the stopping of irradiation in a fashion which will not permit continuance of irradiation without the resetting of operating conditions at the control panel. 91. "Test" means a method for determining the characteristics or condition of sources of radiation or components thereof. "Test" may also mean the process of verifying compliance with this article. 92. "Therapeutic radiation machine" means x-ray or electron-producing equipment designed and used for external beam radiation therapy. 93. "Tube" means an x-ray tube, unless otherwise specified. 94. "Tube housing assembly" means the tube housing with tube installed. It includes high-voltage or filament transformers, or both, and other appropriate elements when such are contained within the tube housing. 95. "Unrestricted area" means an area, access to which is neither limited nor controlled by the licensee or registrant. 96. "Useful beam" means the 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 system to produce radiation. 97. "Virtual source" means a point from which radiation appears to originate. 98. "Wedge filter" means an added filter effecting continuous progressive attenuation on all or a part of the useful beam. 99. "X-ray tube" means any electron tube which is designed for conversion of electrical energy into x-ray energy.