Radiation Therapy for Pituitary Tumors

Radiation therapy uses high energy x-rays or particle waves to kill tumor cells. This type of treatment is given by a doctor called a radiation oncologist. Radiation is directed at the tumor from a source outside the body.

Radiation therapy may be recommended if surgery isn't an option, if some of a pituitary tumor remains or comes back after surgery, or if the tumor causes symptoms that aren’t controlled with medicines.

Radiation therapy is much like getting an x-ray, but the doses of radiation used are much higher. Before your treatments start, the radiation team will get imaging tests such as MRI scans to define the exact location, size, and shape of the tumor. This is used to determine the correct angles for aiming the radiation beams, the shape of the beams, and the proper dose of radiation.

Standard radiation is usually given in a series of treatments 5 times a week over 4 to 6 weeks. At each session, you lie on a special table while a machine delivers the radiation from precise angles. The treatment doesn't hurt. Each session lasts about 15 to 30 minutes. Much of that time is spent making sure you are in the right position so the radiation is aimed correctly. The actual time you're getting the treatment is much shorter.

Radiation can work well, but it has some drawbacks:

  • It works slowly, so it can take months or even years before the tumor growth and/or excess hormone production is fully controlled.
  • It can damage the remaining normal pituitary. In many cases, normal pituitary function will be lost over time, so treatment with hormones will be needed.
  • It may damage some normal brain tissue, particularly near the pituitary gland, which could affect mental function years later.
  • The optic nerves may be damaged, causing vision changes.
  • The radiation may increase the risk of developing a brain tumor later in life, but this risk is low in adults.

Newer radiation therapy techniques

Newer techniques help lower the risks of radiation therapy. These techniques focus the radiation more precisely on the pituitary. However, some of these techniques might not be possible for some tumors that are very close to the optic nerves.

Intensity modulated radiation therapy (IMRT)

IMRT is an advanced form of 3-D radiation therapy. It uses a computer-driven machine that moves around the patient as it sends out the radiation. IMRT lets the doctor shape the radiation beams and aim them at the tumor from many angles. The intensity (strength) of the beams can also be adjusted to limit the dose reaching nearby normal tissues. This may mean fewer side effects. Many major hospitals and cancer centers now use IMRT.

Stereotactic radiosurgery/stereotactic radiation therapy

This type of treatment delivers a large, precise radiation dose to the tumor area in one treatment. Though this is called radiosurgery, no cutting or surgery is involved. In some cases, the treatment might be done in a few sessions (called stereotactic radiotherapy). Radiosurgery targets the tumor more precisely than standard radiation, causing less harm to the normal pituitary gland and limiting radiation exposure to the rest of the brain.

For this treatment, a lightweight metal frame is often attached to the head with small pins or screws to help hold the head still and aim the radiation beams very precisely. (The areas on the scalp where the frame is attached are numbed first.) Sometimes a mesh face mask is used to hold the head in place instead of a frame. Once the exact location of the tumor is known from CT or MRI scans, radiation is focused at the tumor from many different angles. This can be done in 2 ways:

  • Thin radiation beams from a machine are focused at the tumor from hundreds of different angles for a short period of time. Each beam alone is weak, but they all converge at the tumor to give a higher dose of radiation. An example of such a machine is the Gamma Knife.
  • A movable linear accelerator (a machine that creates radiation) that's controlled by a computer is used. Instead of delivering many beams at once, this machine moves around the head to deliver radiation to the tumor from different angles. Several machines do stereotactic radiosurgery in this way, with names such as X-Knife, CyberKnife, and Clinac.

Stereotactic radiosurgery typically delivers the whole radiation dose in one session, though it may be repeated if needed. Sometimes doctors give the radiation in several treatments to deliver the same or a slightly higher dose. This is called fractionated radiosurgery or stereotactic radiotherapy.

The benefits of stereotactic radiation are usually seen a bit sooner than with other forms of radiation therapy, but it can still take months to be fully effective.

Unfortunately, this therapy can’t be used for tumors that are very close to the optic nerves. It also might not be helpful for tumors that have an unusual shape.

Proton beam radiation therapy

This form of treatment uses a beam of protons rather than x-rays to kill cancer cells. Protons are positive parts of atoms.

X-rays release their energy both before and after they hit their target, which can damage nearby healthy tissues and the tissues they pass through to reach the tumor. Protons, on the other hand, cause little damage to tissues they pass through and only release their energy after traveling a certain distance. Doctors can use this property to deliver more radiation to the tumor with less damage to normal tissues. Like stereotactic radiation, it has the advantage of focusing the radiation more precisely on the pituitary tumor.

But proton beam radiation therapy requires highly specialized equipment and isn't widely available – there are only a handful of proton beam centers in the United States at this time. It's not a standard treatment for pituitary tumors. Studies are still needed to see if it's safer or more effective than stereotactic radiosurgery or stereotactic radiotherapy.

More information about radiation therapy

To learn more about how radiation is used to treat tumors, see Radiation Therapy.

 

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

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Last Medical Review: November 2, 2017 Last Revised: November 2, 2017

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