THERAPEUTIC X-RAY SYSTEMS WITH ENERGIES
LESS THAN 1 MEV
§ 221.71. Equipment requirements.
(a) When the tube is operated at its leakage technique factors, the leakage radiation may not exceed:
(1) One hundred milliroentgens (25.8µC/kg) per hour at 5 centimeters from the surface of the tube housing assembly for contact therapy systems.
(2) One roentgen (.258 mC/kg) per hour at 1 meter from the source for 0-150 kVp systems manufactured or installed prior to December 19, 1987.
(3) One hundred milliroentgens (25.8µC/kg) per hour at 1 meter from the source for 0-150 kVp systems manufactured on or after December 19, 1987.
(4) One roentgen (.258 mC/kg) per hour at 1 meter from the source for 151 to 500 kVp systems.
(5) One-tenth percent of the exposure rate of the useful beam 1 meter from the source for 501 to 999 kVp systems at 1 meter from the source.
(b) Fixed diaphragms or cones used for limiting the useful beam must provide at least the same protection as required by the tube housing assembly.
(c) Beam limiting devices may, for the portion of the useful beam blocked by these devices, transmit not more than 5% of the original X-ray beam intensity at the maximum voltage and maximum treatment filter. This requirement does not apply to auxiliary blocks or materials placed in the useful beam to shape the useful beam to the individual patient.
(d) The filter system shall be designed so that:
(1) Filters cannot be accidentally displaced from the useful beam at any possible tube orientation.
(2) The radiation at 5 centimeters from the filter insertion slot opening does not exceed 30 roentgens (7.74 mC/kg) per hour under operating conditions.
(3) A filter is marked as to its material of construction and its thickness. For wedge filters, the wedge factor and wedge angle shall appear on the wedge or wedge tray.
(4) On equipment purchased after January 1, 1971, a filter indication system shall be used on therapy machines using changeable filters. The system must indicate from the control panel the presence or absence of a filter and be designed to permit easy recognition of an added filter in place.
(5) An X-ray system equipped with a beryllium or other low-filtration window shall be clearly labeled as such upon the tube housing assembly and at the control panel.
(e) The tube housing assembly shall be immobilized during stationary treatments.
(f) The tube housing assembly shall be so marked that it is possible to determine the location of the focal spot to within 5 millimeters, and the marking shall be readily accessible for use during calibration procedures.
(g) Contact therapy tube housing assemblies shall have a removable shield of at least .5 millimeter lead equivalency at 100 kVp that can be positioned over the entire useful beam exit port during periods when the beam is not in use.
(h) Systems of greater than 150 kVp manufactured after December 19, 1987, must have a beam monitor system which meets the following requirements:
(1) Not allow irradiation until a preselected value of exposure has been made at the treatment control panel.
(2) Independently terminate irradiation when the preselected exposure has been reached.
(3) Be designed so that, in the event of a system malfunction or electrical power failure or other interruption, the dose administered to a patient prior to the interruption can be accurately determined.
(4) Have a control panel display which maintains the reading until intentionally reset to zero.
(5) Have a control panel display which does not have scale multiplying factors and utilizes a design so that increasing dose is displayed by increasing numbers.
(i) The following apply to timers on the equipment:
(1) A timer shall be provided which has a display at the control panel. The timer must be graduated in minutes and fractions of minutes. The timer must have a preset time selector and an elapsed time indicator.
(2) The timer must be a cumulative timer which activates with the radiation and retains its reading after irradiation is interrupted or terminated. After irradiation is terminated and before irradiation can be reinitiated, it shall be necessary to reset the timer to zero.
(3) The timer must terminate irradiation when a preselected time has elapsed if a dose monitoring system present has not previously terminated irradiation.
(4) The timer must permit accurate presetting and determination of exposure time as short as 1 second.
(5) The timer may not permit an exposure if set at zero.
(6) The timer may not activate until the shutter is opened when patient irradiation is controlled by a shutter mechanism.
(j) The control panel, in addition to the displays required in this section, must have:
(1) An indication of power status.
(2) An indication of X-ray production.
(3) The means of indicating X-ray tube current and voltage.
(4) The means of terminating an exposure.
(k) When a control panel may energize more than one X-ray tube, the following requirements shall be met:
(1) It must be possible to activate only one X-ray tube at one time.
(2) There must be an indication at the control panel identifying which X-ray tube is energized.
(3) There must be an indication at the tube housing assembly when that tube is energized.
(l) There must be a means of determining the SSD to within 5 millimeters.
(m) Unless it is possible to bring the X-ray output to the prescribed exposure parameters within 5 seconds, the entire useful beam shall be automatically attenuated by a shutter having a lead equivalency not less than that of the tube housing assembly.
(1) After the unit is at operating parameters, the shutter shall be controlled electrically by the operator from the control panel.
(2) An indication of shutter position must appear at the control panel.
(n) Electronic brachytherapy devices are exempt from the requirements in subsections (k)—(m).
Authority The provisions of this § 221.71 issued and amended under sections 301 and 302 of the Radiation Protection Act (35 P.S. § § 7110.301 and 7110.302); and section 1920-A of The Administrative Code of 1929 (71 P.S. § 510-20); and the Radon Certification Act (63 P.S. § § 2001—2014).
Source The provisions of this § 221.71 adopted December 18, 1987, effective December 19, 1987, 17 Pa.B. 5235; amended May 16, 2008, effective May 17, 2008, 38 Pa.B. 2243; amended October 26, 2018, effective January 24, 2019, 48 Pa.B. 6791. Immediately preceding text appears at serial pages (333944) to (333946).
Cross References This section cited in 25 Pa. Code § 216.1 (relating to purpose and scope); and 25 Pa. Code § 216.3 (relating to exemptions).
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