Mississippi Administrative Code › Title 15 - Mississippi Department of Health › Part 21 - Division of Radiological Health › Subpart 78 - Radiological Health › Chapter 1 - REGULATIONS FOR CONTROL OF RADIATION IN MISSISSIPPI › Subchapter 15 - Therapeutic Radiation Machines › Rule 15-21-78-1.15.2 - Definitions

Current through June 25, 2024
As used in this section, the following definitions
						apply:
1. "Absorbed dose" is the energy imparted to matter by
						ionizing radiation per unit mass of irradiated material at the place of
						interest. The special unit of absorbed dose is the rad (see "Rad").
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. "Accessible surface" means the external surface of the
						enclosure or housing provided by the manufacturer.
4. "Added filtration" means any filtration which is in
						addition to the inherent filtration.
5. "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. Kerma is
						measured in the same unit as absorbed dose.
6. "Barrier" (See "Protective barrier").
7. "Beam axis" means the central ray of the useful
						radiation beam that passes through the isocenter and the source of
						radiation.
8. "Beam-limiting device" means a field defining
						collimator which provides a means to restrict the dimensions of the useful
						beam.
9. "Beam monitoring system" means a system designed and
						installed in the radiation head to detect and measure the radiation present in
						the useful beam.
10. "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.
11. "Bent beam linear accelerator" means a linear
						accelerator geometry in which the accelerated electron beam must change
						direction by passing through a bending magnet.
12. "Changeable filters" means any filter, exclusive of
						inherent filtration, which can be removed from the useful beam through any
						electronic, mechanical, or physical process.
13. "Contact therapy system" means a therapeutic
						radiation machine with a short source to skin distance (SSD), usually less than
						5 centimeters.
14. "Detector" (See "Radiation detector").
15. "Dose monitor unit (DMU)" means a unit response from
						the beam monitoring system from which the absorbed dose can be
						calculated.
16. "External beam radiation therapy" means therapeutic
						irradiation in which the source of radiation is at a distance from the
						body.
17. "Field-flattening filter" means a filter used to
						homogenize the absorbed dose rate over the radiation field.
18. "Filter" means material placed in the useful beam to
						change beam quality in therapeutic radiation machines subject to1.15.6.
19. "Gantry" means that part of a system supporting and
						allowing movements of the radiation head about a center of rotation.
20. "Gray (Gy)" means the special name for the SI unit of
						absorbed dose, kerma, and specific energy imparted equal to 1 joule per
						kilogram. The previous unit of absorbed dose (rad) is being replaced by the
						gray. [1 Gy=100 rad].
21. "Half-value layer (HVL)" means the thickness of a
						specified material which attenuates under narrow beam conditions, 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.
22. "Interlock" means a device preventing the start or
						continued operation of equipment unless certain predetermined conditions
						prevail.
23. "Interruption of irradiation" means the stopping of
						irradiation with the possibility of continuing irradiation without resetting of
						operating conditions at the control panel.
24. "Irradiation" means the exposure of a living being or
						matter to ionizing radiation.
25. "Isocenter" means the center of the smallest sphere
						through which the useful beam axis passes.
26. "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.]
27. "Lead equivalent" means the thickness of the material
						in question affording the same attenuation, under specified conditions, as
						lead.
28. "Leakage radiation" means radiation emanating from
						the therapeutic source assembly except for the useful beam.
29. "Light field" means the area illuminated by light,
						being the locus of points at which the illumination exceeds a specific or
						specified level, simulating the radiation field.
30. "mA" means milliampere.
31. "Megavolt (MV) [mega electron 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.]
32. "Monitor unit (MU)" (See "Dose monitor unit").
33. "Moving beam radiation therapy" means radiation
						therapy with continuous displacement of the radiation source relative to the
						patient during irradiation. It includes arc therapy, skip therapy, conformal
						therapy and rotational therapy.
34. "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.
35. "Patient" means an individual subjected to machine
						produced external beam radiation for the purposes of medical therapy.
36. "Peak tube potential" means the maximum value of the
						potential difference across the x-ray tube during an exposure.
37. "Periodic quality assurance check" means a procedure
						which is performed to ensure that a previous calibration continues to be
						valid.
38. "Phantom" means an object behaving in essentially the
						same manner as tissue, with respect to absorption or scattering of the ionizing
						radiation in question.
39. "Practical range of electrons" corresponds to
						classical electron range where the only contribution to dose is from
						bremsstrahlung x-rays. Precise definition 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.
40. "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
						acquired.
41. "Primary protective barrier" (See "Protective
						barrier").
42. "Protective barrier" means a barrier of radiation
						absorbing material(s) 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, to protect anyone other than the
						patient from radiation exposure.
b. "Secondary protective barrier" means a barrier
						sufficient to attenuate the stray radiation to the required degree.
43. "Radiation detector" means 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.
44. "Radiation head" means the structure from which the
						useful beam emerges.
45. "Radiation Therapy Physicist" means an individual
						qualified in accordance with 1.15.3(4).
46. "Redundant dose monitoring combination" means a
						combination of two dose monitoring systems in which both systems are arranged
						to terminate irradiation in accordance with a preselected number of dose
						monitor units.
47. "Response time" means the time required for an
						instrument system to reach 90 percent of its final reading when the
						radiation-sensitive volume of the instrument system is exposed to a step change
						in radiation flux from zero sufficient to provide a steady state midscale
						reading.
48. "Scattered radiation" means 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.
49. "Secondary dose monitoring system" means a system
						which will terminate irradiation in the event of failure of the primary dose
						monitoring system.
50. "Secondary protective barrier" (See "Protective
						barrier").
51. "Shadow tray" means a device attached to the
						radiation head to support auxiliary beam blocking material.
52. "Shutter" means 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.
53. "Sievert (Sv)" means the special name for 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].
54. "Simulator (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.
55. "Source" means the region and/or material from which
						the radiation emanates.
56. "Source-skin distance (SSD)" means the distance
						measured along the central ray from the center of the front surface of the
						radiation source to the surface of the irradiated object or patient. [See also
						Target-skin distance]
57. "Stationary beam radiation therapy" means radiation
						therapy without displacement of the radiation source relative to the patient
						during irradiation.
58. "Stray radiation" means the sum of leakage and
						scattered radiation.
59. "Target" means that part of an x-ray tube or particle
						accelerator onto which is directed a beam of accelerated particles to produce
						ionizing radiation or other particles.
60. "Target-skin distance (TSD)" means the distance
						measured along the central ray from the center of the front surface of the
						x-ray target to the surface of the irradiated object or patient. [See also
						Source-skin distance]
61. "Tenth-value layer (TVL)" means the thickness of a
						specified material which attenuates under broad beam conditions, 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.
62. "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.
63. "Therapeutic radiation machine" means x-ray or
						electron-producing equipment designed and used for external beam radiation
						therapy.
64. "Tube" means an x-ray tube, unless otherwise
						specified.
65. "Tube housing assembly" means the tube housing with
						tube installed. It includes high-voltage and/or filament transformers and other
						appropriate elements when such are contained within the tube housing.
66. "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
						therapeutic radiation machine to produce radiation.
67. "Virtual source" means a point from which radiation
						appears to originate.
68. "Wedge filter" means a filter which effects
						continuous change in transmission over all or a part of the radiation
						field.
69. "X-ray tube" means any electron tube which is
						designed to be used primarily for the production of x-rays.
Miss. Code Ann.
						§
												45-14-11