Simulation is what the radiation oncologist does to the patient before the radiation therapy starts. It is usually a much longer session than the therapy sessions.

During the simulation, the patient lies down on the radiation machine, and the radiation therapy try to define the treatment field, drawing lines on the body with different colors. These lines are crucial for keeping the treatment within the defined field every time the patient comes for radiation therapy. The patinet is instructed not to take a tub bath during the treatment period (whcih may be several weeks) and to protect these lines from erasure when taking a shower. If the lines smudge a littel or become faint during the treatment period, they can be redrawn, but if they erase completely, then the patient needs to be simulated again, which is quite a hassle, not to mention very expensive.

Some treatment plans require re-defining the radiation field during the treatment, so the patient may be resimulated for that purpose.

Immediately after simulation, the patient signs the consent form and is given the treatment schedule and the final instructions.

When I worked at M.D. Anderson Cancer Center, the medical interpreters sometimes used the word تخطيط, instead of تمثيل, but that led to confusion to the "therapy planning session," which is different.