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Timers designed for automated measuring of the active duration of exposure to high-dose radiation (e.g., x-rays, electrons) from a radiotherapy unit, such as a cobalt unit or a linear accelerator. These timers typically consist of a detector that is placed in the beam path while radiation is delivered, an electromechanical or electronic time measuring instrument, and a display. Radiotherapy timers are usually dedicated instruments intended to detect a particular type of radiation (e.g., x-rays, electrons, gamma rays); timers that are hard-wired to the control system are frequently an integral part of the radiotherapy unit (e.g., orthovoltage, linear accelerator, stereotactic radiosurgery) and used to control the intensity, duration, and/or other parameters of the treatment. Stand-alone radiotherapy timers are used mainly for inspection, calibration, and/or quality control of radiation generators and radiotherapy systems.
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