10-144-220 Me. Code R. § X-2
As used in this Part the following definitions apply.
Absorbed dose rate means absorbed dose per unit time, for machines with timers, or dose monitor unit per unit time for linear accelerators.
Accessible surface means surface of equipment or of an equipment part that can be easily or accidentally touched by persons without the use of a tool.
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).
Authorized medical physicist means an individual as defined in G.2 and in compliance with the applicable provisions of Part G of this rule .
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.
Bent beam linear accelerator means a linear accelerator geometry in which the accelerated electron beam must change direction by passing through a bending magnet.
Contact therapy system means a therapeutic radiation machine with a short target to skin distance (TSD), usually less than 5 centimeters.
Dose monitor unit(DMU) means a unit response from the beam monitoring system from which the absorbed dose can be calculated.
External beam radiation therapy means therapeutic irradiation in which the source of radiation is at a distance from the body.
Field flattening filter means a filter used to homogenize the absorbed dose rate over the radiation field.
Filter means material placed in the useful beam to change beam quality in therapeutic radiation machines subject to Subpart X.6.
Gantry means that part of a radiation therapy system supporting and allowing movements of the radiation head about a center of rotation.
Interruption of irradiation means the stopping of irradiation with the possibility of continuing irradiation without resetting of operating conditions at the control panel.
Isocenter means the center of the sphere through which the useful beam axis passes while the gantry moves through its full range of motions.
Leakage radiation means radiation emanating from the radiation therapy system except for the useful beam.
Light field means the area illuminated by light, simulating the radiation field.
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.
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.
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.
Periodic quality assurance check means a procedure, which is performed to ensure that a previous calibration continues to be valid.
Practical range of electrons corresponds to classical electron range where the only remaining contribution to dose is from bremsstrahlung x-rays.
Primary dose monitoring system means a 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.
Radiation field (See Useful beam.)
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.
Secondary protective barrier (SeeProtective barrier.)
Shadow tray means a device attached to the radiation head to support auxiliary beam blocking material.
Simulator (radiation therapy simulation system) means any x-ray system intended for localizing the volume to be exposed during radiation therapy and reproducing the position and size of the therapeutic irradiation field.
Source skin distance (SSD) (See Target skin distance.)
Stationary beam radiation therapy means radiation therapy without displacement of one or more mechanical axes relative to the patient during irradiation.
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.
Target skin distance (TSD) means the distance measured along the beam axis from the center of the front surface of the x-ray target and/or electron virtual source to the surface of the irradiated object or patient.
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.
Therapeutic radiation machine means x-ray or electron producing equipment designed and used for external beam radiation therapy.
10-144 C.M.R. ch. 220, § X-2