Quality assurance is a very important aspect of radiotherapy delivery. There are many facets of quality assurance but a basic concept is to ensure the radiation is delivered to the correct target area. At the start of a course of radiotherapy treatment the standard at the Cross Cancer Institute is to confirm the correct area is being treated. This is done by taking an x-ray on the treatment unit with the patient in the treatment position (portal image or verification film). This portal image is examined by the treating oncologist and compared to the simulation film or a digitally reconstructed radiograph that was generated when the patient was simulated (set up) for radiotherapy treatment. Some alterations may be suggested by the oncologist but once a portal film is deemed to reflect the original set-up - no more routine verifications are performed. It is assumed that the treatment set-up will be accurate for the remainder or the treatments.