ABSTRACT

When a patient is treated, it is just as important that the radiation should be delivered to

the correct anatomical site as it is that the correct dose should be delivered. With the advent of

conformal radiotherapy, the requirements for positional accuracy are increased. Traditionally,

quality assurance of patient positioning has been achieved using industrial x-ray film, but film

needs to be processed, and the information is only available some time after the treatment

fraction has been delivered. In order to provide an instantaneous verification of the patient

setup, electronic portal imaging devices (EPIDs) have been developed that are attached to the

gantry of the linear accelerator.