Understanding Radiation Therapy

+ -Text Size

TOPICS

External radiation therapy

How does your doctor plan your treatment?

After a physical exam and a review of your medical history and test results, the doctor will pinpoint the area to be treated. This is done a few days before starting radiation therapy in a process called simulation. You will be asked to lie still on a table while the radiation therapist uses a special x-ray machine to define your treatment field (also called the treatment port). These are the exact places on your body where the radiation beams will be aimed.

Radiation beams are aimed very precisely. A special mold, mask, or cast of a body part may be made to help you stay still during treatment. These will also help get you in the same position for each treatment. The radiation therapist may mark the treatment field with freckle-sized dots of semi-permanent ink. The marks will likely fade away over time, but they are needed until your treatment is finished. Don’t use soap on or scrub these marks. Sometimes the area may be marked with permanent dots like a tattoo. (These can later be removed with a laser if you like.)

Based on the simulation, other tests, and your medical diagnosis, the doctor will decide how much radiation is needed, how it will be given, and how many treatments you should have.

External radiation therapy is usually given with a machine called a linear accelerator (often called a “linac” for short), which is described below.

How long does the treatment take?

In most cases the total dose of radiation needed to kill a tumor can’t be given all at once. This is because it’s very hard to give radiation therapy without harming normal cells nearby. A dose of radiation given all at once can cause more damage to normal tissues. This can cause more side effects than giving the same dose over many treatments.

Because of this, the total dose of external radiation therapy is usually divided into smaller doses called fractions. The most common way to give it is daily, 5 days a week (Monday through Friday) for 5 to 8 weeks. Weekend rest breaks allow time for normal cells to recover. The total dose of radiation and the number of treatments can vary, based on:

  • The size and location of your cancer
  • The type of cancer
  • The reason for the treatment
  • Your general health
  • Any other treatments you are getting

Other radiation schedules may be used in certain cases. For example, radiation therapy may last only a few weeks (or less) when it’s being given to relieve symptoms, because the overall dose of radiation is lower. In some cases, radiation might be given as 2 or more treatments each day (called hyperfractionated radiation). Or it might be given as split-course therapy, which allows for several weeks off in the middle of treatments to give the body time to recover while the cancer shrinks.

What happens during each treatment visit?

External radiation is a lot like having a regular x-ray. The treatment itself is painless and takes only a few minutes. But each session can last 15 to 30 minutes because of the time it takes to set up the equipment and put you in position.

Depending on the area being treated, you may need to undress, so wear clothes that are easy to take off and put on. You’ll be asked to lie on a treatment table next to the radiation machine (the linear accelerator or linac). The machine has a wide arm that extends over the table. The radiation comes out of this arm. The machine can move around the table to change the angle of the radiation, if needed.

The radiation therapist may put special heavy shields between the machine and parts of your body that are not being treated to help protect normal tissues and organs.

Once you are in the correct position, the radiation therapist will go into a nearby room to operate the machine and watch you on a TV monitor. The room is shielded, or protected from the radiation so that the therapist is not exposed to it. You will be able to talk with the therapist over an intercom. You’ll be asked to lie still during the treatment. You do not have to hold your breath—just breathe normally.

The radiation therapy machine will make clicking and whirring noises and may sometimes sound like a vacuum cleaner as it moves to aim the radiation beam from different angles. The radiation therapist controls the movement and checks to be sure it’s working properly. If you are concerned about anything that happens in the treatment room, ask the therapist to explain. If you feel ill or uncomfortable during the treatment, tell the therapist right away. The machine can be stopped at any time.

Will I be radioactive during or after external radiation treatment?

External radiation therapy affects cells in your body only for a moment. Because there’s no radiation source in your body, you are not radioactive at any time during or after treatment.

Newer forms of external radiation therapy

Today, scientists have developed newer, more precise ways of giving external radiation therapy. These approaches allow doctors to better focus the radiation on the tumors and do less damage to normal tissues. This allows doctors to use higher doses of radiation. Because these methods are newer, their long-term effects are still being studied.

The machines allow doctors to shape (conform) the radiation beam to match the shape of the tumor. With conformal radiation, a special computer uses imaging scans (like CT scans) to map the location of the cancer in the body in 3 dimensions (3-D). Radiation beams can then be shaped (or conformed) to match the shape of the cancer. This helps to better protect the normal tissues around the cancer.

Three-dimensional conformal radiation therapy (3D-CRT) delivers shaped beams at the cancer from different directions. Patients are fitted with a mold or cast to keep the body part still so the radiation can be aimed more accurately. By aiming the radiation more precisely, it may be possible to reduce radiation damage to normal tissues and better kill the cancer by increasing the radiation dose to the tumor.

Intensity modulated radiation therapy (IMRT) is a newer method much like 3D-CRT. It conforms to the tumor shape like 3D-CRT, but also allows the strength of the beams to be changed in some areas to lessen damage to normal body tissues. This gives even more control in reducing the radiation that reaches normal tissue and allows a higher dose to the tumor. It may result in fewer effects on sensitive tissues nearby.

A form of IMRT called helical tomotherapy uses a linear accelerator inside a large “donut” that spirals around the body while you lie on the treatment table. It can deliver radiation from many different angles around the body. This may allow for even more precisely focused radiation.

Conformal proton beam radiation therapy is much like conformal therapy, but it uses proton beams instead of x-rays. Protons are parts of atoms that cause little damage to tissues they pass through but are very good at killing cells at the end of their path. This means that proton beam radiation may be able to deliver more radiation to the tumor while reducing side effects on normal tissues. Protons can only be put out by a special machine called a cyclotron or synchrotron. This machine costs millions of dollars and requires expert staff. This is why proton beam therapy costs a lot and is not yet found in many radiation treatment centers. At this time, it’s most often used for prostate cancer, and so far outcomes are much the same using proton therapy versus IMRT. More studies are needed to find out if proton radiation gives better results in certain cancers than other types of radiation treatment.

Intraoperative radiation therapy (IORT) is external radiation given directly to the tumor or tumors during surgery. It may be used if the tumors can’t be totally removed or if there is a high risk the cancer will come back in the same area. The surgeon finds the cancer while the patient is under anesthesia (drugs that are used to make the patient sleep and not feel pain). Normal tissues are moved out of the way and protected with special shields, so IORT lets the doctor give one large dose of radiation to the cancer and limit the effects on nearby tissues. IORT is usually given in a special operating room that has radiation-shielding walls.

Stereotactic radiosurgery is not really surgery, but a type of radiation treatment that gives a large dose of radiation to a small tumor area in one session. It’s mostly used for brain tumors and other tumors inside the head. In some cases, a head frame or shell may be used to help keep the patient’s head still. Once the exact location of the tumor is known from the CT or MRI scans, radiation is sent to the area from a machine. The radiation is very precisely aimed to affect nearby tissues as little as possible.

There are 3 different ways stereotactic radiosurgery can be given:

  • The most common type uses a movable linear accelerator that is controlled by a computer. Instead of sending out many beams at once, the machine moves around to target the tumor from different angles. Several machines do stereotactic radiosurgery in this way, with names such as X-Knife, CyberKnife®, and Clinac®.
  • The Gamma Knife® uses a large dose of high-energy radiation that is precisely focused at the tumor from many different angles for a short period of time in one treatment session. Again, it does not use a knife and there is no cutting.
  • A third type uses heavy charged particle beams (like protons and helium ions) to deliver radiation to the tumor. Also aimed at the tumor from different angles, the particles allow most of the radiation’s energy to be delivered to more precise depths, at the end of their paths.

Most of the time, stereotactic radiosurgery uses one session to give the whole radiation dose, but it may be repeated if needed. Sometimes doctors give the radiation in many smaller treatments to deliver the same or slightly higher dose (fractionation). This is sometimes called fractionated radiosurgery or fractionated stereotactic radiotherapy.

Clinical trials are being done to look at how well stereotactic radiosurgery and stereotactic radiotherapy work alone and when used along with other types of radiation therapy.


Last Medical Review: 01/24/2013
Last Revised: 01/24/2013