What is radiation therapy?
Radiation therapy uses focused, high-energy photon beams to destroy cancer cells. More than half of cancer patients will undergo some sort radiation therapy. It can be used as a standalone treatment or in combination with other therapies, shrinking tumors before surgery or chemotherapy or destroying any cancer cells that might remain after other treatments.
Radiation is produced by a linear accelerator, or LINAC. It employs microwave energy to accelerate electrons to nearly the speed of light within a contained area. The electrons collide with a metal barrier, creating powerful X-rays called photons. The photons are shaped into beams and delivered to the patient through a gantry that moves 360 degrees around the treatment table.
A single dose of radiation is called a fraction. Most radiation treatments require several fractions. A typical radiation treatment plan has five fractions a week for 4-6 weeks.
Radiation therapy requires careful planning to ensure the tumor is targeted with the least amount of impact on surrounding tissues. CT scanners simulate treatments by testing various beam fields and immobilization devices used to keep the patient from moving during treatment. Data from the simulators help calculate the appropriate dose before treatment begins.
Types of Radiation Therapy
Brachytherapy, or internal radiation, involves radioactive material that is implanted in the body. Dozens of tiny "seeds" containing radioactive iodine are placed at the tumor site with a special needle or catheter. In permanent brachytherapy, the seeds are left inside the body to release radiation over time. For temporary brachytherapy, the seeds are inserted for several minutes or hours and removed afterward, usually in an outpatient procedure.
3D conformal radiation therapy is a technique that uses three-dimensional scans to determine the exact shape and size of the tumor. The radiation beams are shaped by tiny metal leaves that are arranged to fit the tumor dimensions (multi-leaf collimator), minimizing the side effects to healthy tissue.
Intensity modulated radiation therapy (IMRT) focuses multiple radiation beams of different intensities directly on the tumor for the highest possible dose. Radiation oncologists use special planning software to make sure the patient is properly positioned for the most accurate treatment.
Intraoperative radiation therapy (IORT) is used to treat an exposed tumor during cancer surgery. IORT is performed with a treatment unit that delivers a high dose of radiation to a surgically exposed treatment area. Surrounding healthy organs and tissues protected by lead shields or moved out of the radiation field.
Proton therapy uses energy from protons instead of photons. Protons deliver their maximum amount of energy to the tumor with no entrance or exit dose, resulting in fewer side effects than standard radiation therapy. MD Anderson’s Proton Therapy Center treats several types of cancer. Read more about proton therapy
Stereotactic radiosurgery (SRS) uses dozens of tiny radiation beams to treat tumors in the head and neck with a single radiation dose. MD Anderson uses the Gamma Knife® SRS system. Read more about stereotactic radiosurgery
Stereotactic body radiation therapy (SBRT) links CT scans of the tumor site with treatment-planning software to determine beam direction and intensity, accounting for tumor motion and anatomy changes during the treatment procedure. Read more about SBRT
Stereotactic spine radiotherapy uses guidance from CT scans for the highest possible dose to tumors on the spine. The CT machine moves on rails around the treatment table to constantly confirm the tumor location. Radiation beams can be instantly adjusted to account for any changes during the procedure.
BY Devon Carter
May 09, 2017
More than half of cancer patients will receive radiation therapy, but what is it? Does it hurt? And what are the side effects?
We spoke with Cullen Taniguchi, M.D., Ph.D., to answer some common questions about radiation therapy. Here’s what he had to share.
How does radiation therapy work?
Radiation therapy uses high-energy waves, like those used with an X-ray, but at a higher energy that damages tumor cells’ DNA....