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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.
Radiation therapy may be recommended to treat a pituitary tumor if:
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.
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.
The main ways to give radiation therapy for pituitary tumors are:
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.
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.
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.
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.
Radiation therapy can sometimes affect nearby normal structures, which can lead to side effects. For example:
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Lee CC, Kano H, Yang HC, et al. Initial Gamma Knife radiosurgery for nonfunctioning pituitary adenomas. J Neurosurg. 2014;120(3):647-654.
Li X, Li Y, Cao Y, et al. Safety and efficacy of fractionated stereotactic radiotherapy and stereotactic radiosurgery for treatment of pituitary adenomas: A systematic review and meta-analysis. J Neurol Sci. 2017;372:110-116.
Loeffler JS, Shih HA. Radiation therapy for pituitary adenomas. UpToDate. 2022. Accessed at https://www.uptodate.com/contents/radiation-therapy-of-pituitary-adenomas on August 4, 2022.
National Cancer Institute. Physician Data Query (PDQ). Pituitary Tumors Treatment. 2020. Accessed at https://www.cancer.gov/types/pituitary/hp/pituitary-treatment-pdq on August 16, 2022.
van Westrhenen A, Muskens IS, Verhoeff JJC, Smith TRS, Broekman MLD. Ischemic stroke after radiation therapy for pituitary adenomas: A systematic review. J Neurooncol. 2017 Jun 28.
Last Revised: October 10, 2022