Certain "contrast agents" or probes may be used to aid in the simulation. The point of the exercise is to make all the necessary measurements to fix the precise location of the tumor . Marks will be made on your skin with a colored ink to outline the target the radiation oncologist will be aiming for—the "radiation port"—which has to be the same every day.
While the simulation is being done, the radiation oncologist may use the services of a clinical physicist and dosimetrist. The physicist is specially trained in the clinical application of radiation therapy and will give advice on technical matters that the radiation oncologist will incorporate into the plan. A dosimetrist is a person who, with the use of computers, helps design the specialized treatment plan developed for each individual.
Following the simulation, you will be ready to start treatment either that day or possibly several days later if your case is complex. The reason for the delay is that all the data from the simulation will be fed into a computer. The treatment team will need time to study the various plans and tailor-make any shielding or blocking devices that may be needed to keep radiation away from your healthy tissues.
The Dosage The amount of radiation you receive is measured in units that used to be called rads . The term used now is centigray (cGy) , but since one gray equals 100 rads the two terms are interchangeable.
Deciding what dosage of radiation to give is a critical part of the treatment plan. Careful planning allows the radiation oncologist to deliver the maximum effective dose to the visible tumor and any invisible tumor cells that might be nearby while protecting the surrounding normal tissues as much as possible.
