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25 Pa. Code § 228.2. Definitions.

§ 228.2. Definitions.

 The following words and terms, when used in this chapter, have the following meanings, unless the context clearly indicates otherwise:

   Accelerator or particle accelerator—A radiation-producing machine capable of accelerating electrons, protons, deuterons, or other charged particles in a vacuum and of discharging the resultant particulate or other radiation into a medium at energies usually in excess of 1 megaelectron volt (MeV).

   Applicator—A structure which determines the extent of the treatment field at a given distance from the virtual source.

   Beam-limiting device—A device providing a means to restrict the dimensions of the X-ray field.

   Beam scattering filter—A filter used to scatter a beam of electrons.

   Central axis of the beam—A line passing through the virtual source and the center of the plane figure formed by the edge of the first beam limiting device.

   Dose monitoring system—A system of devices for the detection, measurement and display of quantities of radiation.

   Dose monitor unit—A unit response from the dose monitoring system from which the absorbed dose can be calculated.

   Existing equipment—Systems manufactured on or before October 3, 1998.

   Field flattening filter—A filter used to provide dose uniformity over the area of a useful beam of X-rays at a specified depth.

   Field size—The configuration of the radiation field along the major axes of an area in a plane perpendicular to the specified direction of the beam of incident radiation at the normal treatment distance and defined by the intersection of the major axes and the 50% isodose line.

   Filter—Material placed in the useful beam to modify the spectral energy distribution and flux of the transmitted radiation and remove radiation that does not contribute to the efficacy of the useful beam.

   Isocenter—A fixed point in space located at the center of the smallest sphere through which the central axes of the beams pass.

   Leakage radiation—Radiation emanating from the source assembly except for the following:

     (i)   The useful beam.

     (ii)   Radiation produced when the exposure switch or timer is not activated.

   Moving beam therapy—Radiation therapy with relative displacement of the useful beam and the patient during irradiation.

   New equipment—Systems manufactured after January 1, 1985.

   Normal treatment distance

     (i)   For isocentric equipment, the isocenter.

     (ii)   For nonisocentric equipment, the target to patient skin distance along the central axis as specified by the manufacturer.

   Particle accelerator—See the definition of ‘‘accelerator.’’

   Phantom—A volume of material behaving in a manner similar to tissue with respect to the attenuation and scattering of radiation.

   Primary dose monitoring system—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 attained.

   Radiation detector—A device which provides a signal or other indication suitable for measuring one or more quantities of incident radiation.

   Radiation head—The structure from which the useful beam emerges.

   Secondary dose monitoring system—A system which will terminate irradiation in the event of failure of the primary dose monitoring system.

   Shadow tray—A device attached to the radiation head to support auxiliary beam limiting material.

   Spot check—A procedure to assure that a previous calibration continues to be valid.

   Stationary beam therapy—Radiation therapy without relative displacement of the useful beam and the patient during irradiation.

   Subsystem—A combination of two or more components of an accelerator.

   Target—The part of a radiation source which intercepts a beam of accelerated particles with subsequent emission of other radiation.

   Tube housing assembly—The term includes high-voltage or filament transformers, or both, and other appropriate elements when contained within the tube housing.

   Useful beam—The radiation which passes through the tube housing port and the aperture of the beam-limiting device when the exposure switch or timer is activated.

   Virtual source—The nominal location of either the first scattering foil (for equipment providing electrons only) or the photon focal spot (for equipment capable of delivering both photons and electrons).

   Wedge filter—An added filter effecting continuous progressive attenuation on all or part of the useful beam.


   The provisions of this §  228.2 amended October 2, 1998, effective October 3, 1998, 28 Pa.B. 4894; amended July 16, 2004, effective July 17, 2004, 34 Pa.B. 3823; amended August 11, 2023, effective 90 days after publication, 53 Pa.B. 4977. Immediately preceding text appears at serial pages (304573) to (304574) and (394153).

Cross References

   This section cited in 25 Pa. Code §  216.1 (relating to purpose and scope).

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