Because radiation can affect both normal and diseased cells in the path of the radiation beam, your radiation oncologist must plan your treatments so that all the abnormal areas are included in the radiation field or port and as much normal tissue as possible is spared. This usually requires a treatment planning session using a special X-ray machine or CT-scanner called a simulator.

Additional imaging procedures, such as studies using radio-opaque dyes, computerized tomographic (CT) scans, magnetic resonance imaging (MRI) scans and positron emission tomography (PET) scans, may also be necessary to outline the affected areas and/or to spare normal tissues.

Depending on your individual requirements, the treatment planning session may last from 30 minutes to two hours. During this time your physician and therapist work together to design the treatment. A simulator is not an actual treatment machine. It is a diagnostic x-ray machine that is similar in appearance to a treatment machine only it does not contain the high energy x-rays that are necessary for treatment.

A computer system connected to the simulator records the exact parameters of each individual's treatment set-up such as, table height, gantry angle (angle which the x-ray beam enters the body), table angle and all other parameters that are generated during the time that your treatments are planned.

Following the simulation, further treatment planning and calculations are made to determine the best method of delivering the exact dose to the affected area. Additionally, special shielding devices or blocks may be custom made for use in your treatment. The treatment planning process may take up to one week to complete.

Depending on the part of the body that will be treated, an immobilization device may be required. Patients who are to receive radiation to the head and neck area, for example, will need one of these devices to prevent the head from moving during the treatment. This device will be custom made for you during the simulation. It is sometimes necessary to place wires on the skin, or to use radio-opaque contrast to help define the normal tissues.

The physician decides where the radiation beams will enter the body. The therapist will take x-rays and measurements of your body, and place marks on your skin. The marks are first made with a marker; they can be removed with soap. However, just prior to completing the simulation the therapist will make a few pinpoint marks on the skin that are permanent. These marks are made with a drop of ink and a pinprick, and are called tattoos. The therapists will refer to them daily during the course of your treatment. In addition, since radiation to a specific part of the body is often given only once during one's lifetime, the tattoos serve as a permanent record on your body.

Once the simulation is complete, you will be given an appointment for your first treatment. This usually occurs 1-3 days later, provided you are medically ready to begin them. During this interval of time, the physicist and physician work to finalize the treatment plan. Also, custom designed blocks that will shield normal tissues are fashioned and mounted on trays that will be attached to the machine for use during your treatment. The therapist will instruct you on where you will go to change and receive your first treatment.