Dose delivery is measured by treatment time as opposed to monitor units, as the time required to deliver a dose increases as the source activity decreases. An emergency shut off is required in the event of power failure. The source is rotated or slid into the treatment position when dose delivery is desired.
Typically a light field is generated when the source is in the off position which allows visualisation of the radiotherapy field prior to treatment. Some radiation leaks out of the head, which must be less than 0.02 mSv/h to comply with radiation safety standards. When not in use, the source is located in the ‘off’ position that prevents significant dose from exiting the treatment head. A machine console outside the bunker which allows therapists to operate the machine remotely.A bunker to protect staff, patients and the general public from unnecessary radiation exposure.A patient support assembly or patient couch which allows the patient to be positioned in the desired position.The gantry is typically attached to a stand which houses motors and monitoring equipment. A gantry (in isocentric machines) to allow the source to rotate around a fixed position.The source housing can also shift the source to allow gamma rays to exit the unit through the collimator aperture. Source housing, which includes the primary beam collimator to prevent unwanted radiation emission.A radioactive source, in this case 60Co, which is housed in a steel capsule.The components of a cobalt-60 machine are: Gamma ray treatment machines are known as teletherapy units. The Cobalt 60 source is usually replaced before a single half life has elapsed. The source typically has an activity of 185 – 370 MBq, giving a dose rate at 80 cm of 1 – 2 Gy/minute. This rapidly releases a gamma ray of either 1.17 or 1.33 MeV to reach a stable state. It has a half life of 5.3 years and decays by negative beta emission to metastable 60Ni. Cobalt-60Ĭobalt 60 is produced in a nuclear reactor by bombarding 59Co with neutrons. Although not used commonly in developed countries, cobalt-60 teletherapy machines were an important advancement in radiotherapy delivery and are still used throughout the world.
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