To be most effective, radiation therapy must be aimed precisely at the same target or targets each and every time treatment is given. The process of measuring your anatomy and marking your skin to help your team direct the beams of radiation safely and exactly to their intended locations is called 3D simulation.
The simulation process begins with your doctor deciding the best treatment position for you to lie in each day. An immobilization device is then created to help secure you into that position which helps keep you from moving during a treatment. There are many different devices used specially designed to secure different positions and areas of the body. They are specifically designed for each patient in order to accurately reproduce your treatment position each and every day.
Once you are comfortably in position, we perform a CT scan in order to create 3-dimensional information of your body. This is done by entering the CT scan into state-of-the-art software which allows the doctor and dosimetry team the ability to view your body from virtually any angle. Often other outside diagnostic studies such as MRI and PET-CT scans are integrated into the simulation to gather as much detail as possible to target the disease. All this data gives your team the ability to create the most conformal angles to treat with while avoiding healthy normal tissue.
Your radiation oncologist will write a prescription dictating the amount of radiation to be given over a specified amount of time. This will also include the technique used to deliver the radiation. This decision is based on all information gathered during your workup including surgical notes, pathology reports, diagnostic reports, physical exams, and close consultation with your other doctors.
The dosimetry team will then develop an isodose treatment plan to match the doctor’s written prescription. This plan displays to the radiation oncologist exactly where and how the radiation is absorbed by the body and how well normal tissue has been spared. Utilizing the IMRT delivery technique to deliver the radiation will yield very conformal isodose plans which help to spare normal tissues.
Once a plan is approved for treatment and all quality assurance tests have been met the plan information is entered into a “record and verify” system for the therapists to use for treatment each day. This system ensures that all parameters of the plan are being met on the treatment machine before the delivery of dose. You are now ready to come in begin treatments.
Although simulation is typically only one session, your physician may schedule additional sessions depending on the type of cancer you have and the type of radiation therapy that is being used.