Radiation Therapy for Pituitary Tumors
Radiation therapy uses high energy x-rays or particles 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 is not an option, if a pituitary tumor remains or comes back after surgery, or if the tumor causes symptoms that aren’t relieved by medicines.
Radiation therapy is much like getting an x-ray, although 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 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.
Conventional 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 is not painful. Each session lasts about 15 to 30 minutes. Much of that time is spent making sure the radiation is aimed correctly. The actual treatment time each day is much shorter.
This therapy can be very effective, but it also has some drawbacks:
- It works slowly, so it can take months or years before the tumor growth and/or excess hormone production is fully controlled.
- It can damage the remaining normal pituitary. In most cases, normal pituitary function will be lost over time, requiring treatment with hormones.
- 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, resulting in impaired vision.
- The radiation may increase the risk of developing a brain tumor later in life, although this risk is still likely to be low.
These risks are likely to be lower with the use of newer techniques that focus the radiation more precisely on the pituitary, such as intensity modulated radiation therapy (IMRT), stereotactic radiation, and proton beam therapy. The use of these techniques might be limited for some tumors that are very close to the optic nerves.
Intensity modulated radiation therapy (IMRT)
IMRT is an advanced form of three-dimensional radiation therapy. It uses a computer-driven machine that actually moves around the patient as it delivers the radiation. IMRT lets the doctor shape the radiation beams and aim them at the tumor from several angles. The intensity (strength) of the beams can also be adjusted to limit the dose reaching the most sensitive nearby normal tissues. This may result in 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 a single session (radiosurgery) or in a few sessions (radiotherapy). It targets the tumor more precisely than standard radiation, causing less harm to the remaining normal pituitary gland and limiting the 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 aim the radiation beams very precisely. (The areas on the scalp where the frame is attached are numbed first.) Sometimes a 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:
- In one approach, 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.
- Another approach uses a movable linear accelerator (a machine that creates radiation) that is controlled by a computer. 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 a single session, though it may be repeated if needed. (There is no actual surgery involved in this treatment.) 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 benefit of stereotactic radiation is usually seen a bit sooner than with other forms of radiation therapy, although 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. 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 nearby 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 is not widely available – there are only a handful of proton beam centers in the United States at this time. It is not a standard treatment for pituitary tumors. Studies are still needed to see if it is safer or more effective than stereotactic radiosurgery or stereotactic radiotherapy.
For more general information about radiation therapy, see the Radiation Therapy section of our website.
Last Medical Review: May 8, 2014 Last Revised: December 17, 2014