Radiation Therapy for Pituitary Tumors

Radiation therapy uses high energy x-rays or particles to kill tumor cells. For this type of treatment, you'll see a doctor called a radiation oncologist. Radiation is directed at the tumor from a source outside the body.

When might radiation therapy be used?

Radiation therapy may be recommended to treat a pituitary tumor if:

• Surgery isn't an option for some reason
• Some of the pituitary tumor remains or comes back after surgery
• The tumor causes symptoms that aren’t controlled with medicines

Radiation therapy can work well, especially in controlling tumor growth. However, it tends to work more slowly in controlling excess pituitary hormone production. It can often take months or even years before excess hormone production is fully controlled.

How is radiation therapy given?

Radiation therapy is much like getting an x-ray, but the doses of radiation used are much stronger.

Before your treatments start, the radiation team will get imaging tests such as MRI scans to map out the exact location, size, and shape of the tumor. This planning session, called simulation, is used to determine the correct angles for aiming the radiation beams, the shape of the beams, and the proper dose of radiation.

The treatment itself is not painful. You lie on a special table while a machine delivers the radiation from precise angles. Each session typically 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.

Types of radiation therapy

The main ways to give radiation therapy for pituitary tumors are:

• Fractionated radiation therapy
• Stereotactic radiosurgery (SRS)/stereotactic radiation therapy (SRT)

The choice of which one to use depends on factors such as the size and location of the tumor, if the tumor is making excess hormones, and the availability of nearby treatment facilities.

Fractionated radiation therapy

In this approach, the total dose of radiation is broken up (fractionated) into smaller doses, which are usually given 5 times a week over 4 to 6 weeks.

Higher doses of radiation can damage normal brain tissue, so doctors try to deliver the radiation to the tumor while giving the lowest possible dose to normal surrounding brain areas. Some newer techniques can help doctors focus the radiation more precisely.

Intensity modulated radiation therapy (IMRT): IMRT is an advanced form of 3D radiation therapy. It uses the results of imaging tests such as MRI and special computers to map the location of the tumor precisely. Then a computer-driven machine moves around the patient to deliver 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.

Proton beam radiation therapy: This form of treatment uses beams of protons rather than x-rays to kill tumor cells. Protons are positive parts of atoms.

Unlike x-rays, which release energy both before and after they hit their target, protons 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 brain tissue.

Proton beam radiation therapy requires highly specialized equipment and isn't available everywhere – there are a limited number of proton beam centers in the United States at this time.

Stereotactic radiosurgery (SRS)/stereotactic radiation therapy (SRT)

This type of treatment delivers a large, precise radiation dose to the tumor area, either in one treatment session (for SRS) or in a few sessions (for SRT). There is no actual surgery in this treatment. Radiosurgery targets the tumor precisely, limiting the radiation exposure to nearby structures and the rest of the brain.

A head frame might be attached to the skull to help aim the radiation beams. (Sometimes a mesh face mask is used to hold the head in place instead.) Once CT or MRI scans have shown the exact location of the tumor, radiation is focused on it from many different angles.

• In one approach, thin radiation beams from a machine are focused on 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's controlled by a computer. Instead of delivering many beams at once, this machine moves around the patient's head to deliver a thin beam of radiation to the tumor from many different angles. Several machines with names such as X-Knife, CyberKnife, and Clinac are used for this type of stereotactic radiosurgery.

SRS typically delivers the whole radiation dose in one session, though it may be repeated if needed. For SRT (sometimes called fractionated radiosurgery), doctors give the radiation in several treatments to deliver the same or a slightly higher dose.

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 might not be a good option for tumors that are very close to the optic nerves. It also might not be helpful for tumors that have an unusual shape.

Possible side effects of radiation therapy

Radiation therapy can sometimes affect nearby normal structures, which can lead to side effects. For example:

• Some people might feel tired or irritable during the course of radiation therapy.
• Nausea, vomiting, and headaches are possible but are not common.
• Radiation might damage the remaining normal parts of the pituitary gland. This could result in the loss of pituitary function over time, so treatment with hormones might be needed.
• Radiation might damage normal brain tissue near the pituitary, which could affect mental function years later.
• Radiation might damage the optic nerves, which could lead to vision changes.
• Radiation may increase the risk of developing a brain tumor later in life, although this risk is low in adults.