Because the radiation passes through normal tissue to reach the effected area the side effects must be limited. To ensure this a CT scan is done which is then transferred to a dedicated Treatment Planning System (TPS). On the TPS a 3D image of the treatment area is created using the CT slices. The oncologist delineates the area of interest (tumor) on this 3D image. MRI images where soft tissue tumours are better shown can also be used in conjunction with CT images. The 3D image is used to plan the treatment with multiple field combinations with different angles and energies, to ensure that the dose to the normal tissue and sensitive organs is limited while an optimal dose to the tumor is achieved. The combined dose of the fields where they intersect give the optimal dose required. The different tissue densities, the beam is traveling through, is also taken into account since they have different absorption properties.
To limit the dose to critical organs and normal tissue in the beam path, shielding is used to shape the radiation beam. Modern technology allows for this to be done easily with multi leaf collimators (MLC) instead of lead shielding blocks which are time consuming and labour intensive. To achieve optimum treatment planning, highly skilled and experienced planning radiographers, physicists and a specialized TPS is essential.
To ensure that the treatment is being given correctly, recording and verification systems are essential. This will prevent treatment being given unless all parameters are set-up correctly. The system also records treatment data for future reference. Anatomical verification is also required to ensure that the correct treatment position is used. This is done with a portal imager or the use of verification films.
The area to be irradiated is determined by means of a localising scan or X-rays, and then marked. This is called a simulation.
PLEASE BRING ALONG ANY PREVIOUS X-RAYS OR SCANS that may be of use. Sometimes the treatment area is decreased during the course of the treatments. This is called a booster.
It is very important that the marks that have been made on your body remain there.
YOU MAY BATH OR SHOWER, but you must make sure that these marks are not washed off. A quick bath or shower is preferable. If you do take a bath, do not soak in the water. Use a gentle soap for example Dove soap.
Irradiation is not painful and patients are not radioactive after irradiation, therefore you pose no threat to other people.
During irradiation you will be alone in the treatment room, but you will be monitored on a television screen. There is also an intercom system.
It is extremely important that you keep very still, but you may breathe normally.