Why is a linear accelerator used in external beam radiotherapy?

A linear accelerator, often called a linac, generates high-energy radiation outside the body. The treatment team uses planning images and measurements to shape the beam and direct it toward the target from selected angles. The machine can rotate around the treatment couch, while supports and positioning marks help place the body consistently for each session.

The radiation plan is designed around the target and nearby organs. Beam shaping and treatment checks help the team deliver the prescribed plan accurately, but the machine does not decide the treatment on its own. A radiation oncologist, medical physicist and radiation therapists work together to plan, check and deliver care. You do not feel the radiation beam while it is being delivered, although treatment effects can develop over time.

Attend planning and verification appointments and follow instructions about clothing, skin products, bladder or bowel preparation, and medicines. Wear comfortable clothing that allows the treatment area to be positioned as directed. During treatment, remain as still as you can and tell the therapist if you feel unwell or cannot maintain the position. Keep the treatment area clean and use only skin products approved by your team.

Tell the team about new or worsening pain, skin breakdown, difficulty swallowing, persistent vomiting, unusual bleeding, or symptoms that interfere with eating, drinking, breathing or daily activity. Seek emergency help for severe breathing difficulty, sudden weakness, confusion or uncontrolled bleeding. The right response depends on the treated body area, so use the contact number in your radiotherapy instructions.

Ask what the machine will treat, how positioning will be checked, which normal tissues are near the target, and which changes should be reported between sessions. Ask whether you need special preparation on treatment days.