Radiation Therapy for Pituitary Tumors

Radiation therapy uses high-energy rays or particles to kill tumor cells. It is sometimes used to treat pituitary tumors. For this type of treatment, you'll see a doctor called a radiation oncologist.

When might radiation therapy be used for pituitary tumors?

Radiation therapy might 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 often works 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 a simulation, is used to determine the correct angles for aiming the radiation beams, the shape of the beams, and the proper dose of radiation.

A custom-fitted mask of plastic mesh might be made to hold your head in the exact same position for each treatment. The mask has many openings to allow you to breathe normally.

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 5 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.

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

This type of treatment delivers a large, precise radiation dose to the tumor area. It might be given by:

• SRS, which typically delivers the whole radiation dose in 1 session, though it might be repeated if needed.
• SRT (sometimes called fractionated radiosurgery), in which doctors give the radiation in several treatments to deliver the same or a slightly higher dose. This might be safer for tumors near sensitive structures.

Despite the name, there is no actual surgery. The goal is to focus radiation very precisely on the tumor, limiting exposure to nearby structures and the rest of the brain.

In this technique, radiation is focused on the tumor from many different angles.

Examples of stereotactic systems

Gamma Knife aims many radiation beams at the tumor from 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. To keep your head completely still, it might be held in place with either a custom-fitted mask or a temporary head frame that is attached to the scalp.

Machines such as CyberKnife, Zap-X, and ExacTrac use a single, computer-controlled beam from a movable linear accelerator (LINAC, a machine that creates radiation). Instead of delivering many beams at once, the machine moves around the head to deliver a thin beam of radiation to the tumor from many different angles.

Limitations of SRS/SRT

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

This type of radiation therapy might not be ideal for tumors that:

• Are very close to the optic nerves
• Are very large
• Have a complex or unusual shape

Possible side effects of radiation therapy

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

• Feeling tired or irritable during the course of radiation therapy might happen to some people.
• Nausea, vomiting, and headaches are possible but are not common.
• Loss of pituitary function might occur if radiation damages the remaining normal parts of the pituitary gland. Treatment with hormones might be needed.
• Impacts on mental function might appear after several years if radiation damages normal brain tissue near the pituitary.
• Vision changes are possible if radiation damages the optic nerves.
• A brain tumor might occur years after radiation, although this risk is low in adults.