Immobilizing your body

Before you begin external beam radiation treatment, your radiation therapy team carefully plans every aspect of your treatment in a process called radiation simulation. Radiation therapy 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 30 minutes.

A variety of immobilizers may be used to ensure you'll be in the same position for each radiation therapy treatment. A cushion-like device called a Vac-Lok bag (shown here) — similar to a beanbag with the air removed — holds its shape, cradling you in the best position.