Before you begin radiation treatment, your radiation therapy team carefully plans your treatment in a process called radiation simulation. Treatment planning usually involves positioning your body, making marks on your skin and taking imaging scans.

Your radiation therapy team determines whether you'll lie on your back, stomach or side during treatment. It's crucial to find a position that optimizes your treatment, but is comfortable enough to hold for 15 to 45 minutes.

A variety of immobilizers may be used to ensure you'll be in the same position for each radiation therapy treatment. Here, a special cushionlike device that holds its shape is used.

Another type of immobilization device used during radiation therapy is a thermoplastic mask. This mask might be used if you're receiving radiation to your head or neck. The firm plastic mask is molded to your face and secured to the table, so it gently holds your head in place. Some masks may extend to cover your shoulders, as well.

Once you're correctly positioned, your radiation therapy team takes computerized tomography (CT) images of the area of your body to be treated. This helps your radiation oncologist determine the exact areas where treatment will be focused.

To indicate the area where radiation should be aimed, your radiation therapy team uses a combination of laser lights and marks on your body. This also ensures that your body is precisely aligned and positioned properly for each treatment session.

What type of mark you receive depends on your cancer and your treatment. In certain cases, marks are drawn on your skin with a marker. You can wash these marks off once your final treatment is completed.

Most of the time, marks are permanent. Tiny tattoos — small dots of ink under your skin — are permanent marks that can't be accidentally rubbed off or washed away. This photo shows how small the tattoos are — about the size of a freckle. Sometimes you'll need multiple tattoos. If you're concerned about receiving tattoos, talk with your radiation therapy team.

Once planning is complete, you can begin radiation therapy.

During treatment, you'll be placed on a table in the same position that you were placed in during the radiation simulation. The immobilization devices used in simulation will now be used during your radiation therapy. This ensures you'll be in the same position established during simulation and that no movement will occur while the radiation beam is delivering treatment.

The radiation therapy treatment planning process provides a good opportunity for you to ask questions about what will happen during your treatment. Be sure to ask your treatment team about any concerns you might have. That way, you'll know what's occurring as you begin your radiation therapy.