Mechanical integrity

All of the attachments of the machine should be checked to make sure that fittings have not come loose, etc. It has to be checked that the free play in the couch, collimator rotation, etc. is not significant and brakes should also be checked. These are parts of the manufacturer’s maintenance schedule.

3.1. Couch deflection under load

 
The couch deflection under load must be checked. The IEC standard (IEC 2007, IEC 2008) determines that this should be carried out by placing a 30 kg weight on the couch at the isocentre above its support and distributed over 1 m when the couch is totally retracted. The height of the couch must be noted. Then the couch should be fully pushed out and a 135 kg load (2 m length) spread out symmetrically to the isocentre to represent a patient. The difference in the height of the couch at the isocentre in both cases must be less than 5 mm. The angle of roll of the table top should also be measured during it is being moved laterally from the centre to one side. It must be less than 0.5°.

3.2. Electrical safety

 
The linear accelerator has several high voltage circuits and these can be more accessible than in conventional machine and they probably contain some charge storage devices as well. Checks for electrical safety must be carried out regularly. Special attention should be payed to the integrity of the earth circuits and of the provision for discharge of high voltages. It must be checked that all covers are in place and that appropriate warning signs are posted.