Section 35.642 - Periodic spot-checks for teletherapy units(a) A licensee authorized to use teletherapy units for medical use shall perform output spot-checks on each teletherapy unit once in each calendar month that include determination of-(1) Timer accuracy, and timer linearity over the range of use;(3) The coincidence of the radiation field and the field indicated by the light beam localizing device;(4) The accuracy of all distance measuring and localization devices used for medical use;(5) The output for one typical set of operating conditions measured with the dosimetry system described in § 35.630(b) ; and(6) The difference between the measurement made in paragraph (a)(5) of this section and the anticipated output, expressed as a percentage of the anticipated output (i.e., the value obtained at last full calibration corrected mathematically for physical decay).(b) A licensee shall perform measurements required by paragraph (a) of this section in accordance with written procedures established by the authorized medical physicist. That individual need not actually perform the spot-check measurements.(c) A licensee shall have the authorized medical physicist review the results of each spot-check within 15 days. The authorized medical physicist shall notify the licensee as soon as possible in writing of the results of each spot-check.(d) A licensee authorized to use a teletherapy unit for medical use shall perform safety spot-checks of each teletherapy facility once in each calendar month and after each source installation to assure proper operation of-(1) Electrical interlocks at each teletherapy room entrance;(2) Electrical or mechanical stops installed for the purpose of limiting use of the primary beam of radiation (restriction of source housing angulation or elevation, carriage or stand travel and operation of the beam on-off mechanism);(3) Source exposure indicator lights on the teletherapy unit, on the control console, and in the facility;(4) Viewing and intercom systems;(5) Treatment room doors from inside and outside the treatment room; and(6) Electrically assisted treatment room doors with the teletherapy unit electrical power turned off.(e) If the results of the checks required in paragraph (d) of this section indicate the malfunction of any system, a licensee shall lock the control console in the off position and not use the unit except as may be necessary to repair, replace, or check the malfunctioning system.(f) A licensee shall retain a record of each spot-check required by paragraphs (a) and (d) of this section, and a copy of the procedures required by paragraph (b), in accordance with § 35.2642 .