What is external beam radiation therapy and how does the radiation oncologist plan your treatment?
After a physical exam and a review of your medical history and test results, the radiation oncologist will have you undergo a simulation, this is the planning process. Radiation beams are aimed very precisely. A special mold called an alpha cradle or a mask, may be made during the simulation to help you stay still during treatment. These devices will also help get you in the same position for each treatment. After the simulation is done and based on other tests and your medical diagnosis, the radiation oncologist will decide how much radiation is needed, how it will be given, and how many treatments you should have.
External beam radiation therapy is usually given with a machine called a linear accelerator.
In most cases the total dose of radiation needed to kill a tumor can’t be given all at once. This is because it is very hard to give radiation therapy without harming some 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 radiation therapy is daily, 5 days a week during the weekdays, but weekends off for most patients, for 5 to 8 weeks. Weekend rest breaks allow time for normal cells to recover. Other radiation fractionation 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 allow the body time to recover while the cancer shrinks. 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, for instance cure versus palliation.
Your general health, if you are very ill with other health issues such as heart disease or breathing issues not from the cancer.
Any other treatments you are getting such as chemotherapy or dialysis.
External beam radiation treatment is painless. It is like having a regular x-ray. The treatment itself 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. You will be asked to lie on a treatment table under the linear accelerator. 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, you do not need to move.
Once you are in the correct position, the radiation therapist will go to the console area outside of the room to operate the linear accelerator and watch you on a TV monitor, there is also an intercom system so the radiation therapist can hear you and talk to you if need be. The room is shielded, or protected from the radiation so that the therapist is not exposed to it. You will be asked to lie still during the treatment. You do not have to hold your breath in most cases, just breathe normally and try to relax as best you can.
The radiation therapy machine will make clicking and whirring noises as it moves to aim the radiation beam from different angles. The radiation therapist controls the movement from the console area and watches the linear accelerator be sure it is moving properly. If you are concerned about anything that happens in the treatment room, ask the radiation therapist to explain, you are not bothering them, do not be shy, the radiation therapist is there to help. If you feel ill or uncomfortable during the treatment, tell the therapist right away. The machine can be stopped at any time.
A common question is will I be radioactive during or after external beam radiation treatment? The answer is no, external beam radiation therapy affects cells in your body only for a moment. Because there is no radiation source in your body, you are not radioactive at any time during or after treatment.
Technology today has made more precise ways of giving external beam radiation therapy. These approaches allow radiation oncologists to focus the radiation more directly on the tumors.
Three-dimensional conformal radiation therapy (3D-CRT) delivers shaped beams at the cancer from different directions. 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. Newer machines allow radiation oncologist, physicist and or dosimetrist to shape (conform) the radiation beam to match the shape of the tumor. With conformal radiation, a special computer uses imaging scans (like CT/PET 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. These newer forms of radiation do less damage to normal tissues. This allows radiation oncologists to use higher doses directed only at the tumors.
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.
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 nearby 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. More studies are needed to figure out if proton radiation gives better results in certain cancers than the usual photon radiation treatment.
Intraoperative radiation therapy (IORT) is external beam radiation given directly to the tumor or tumors during surgery. It may be used if the tumors cannot be totally removed or if there is a high chance of the cancer coming back in the same area. The surgeon finds the cancer while the patient is under anesthesia. Normal tissues can be moved out of the way and protected with special shields, so IORT lets the radiation oncologist give one large dose of radiation to the cancer and not affect 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 is mostly used for brain tumors and other tumors inside the head. The radiation is very precise and nearby tissues are affected 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 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®.
The Gamma Knife® uses high-energy radiation that is precisely focused at the tumor from many different angles for a short period of time. This large dose of radiation is given exactly to the tumor 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 stereotactic radiation to the tumor. Most of the time, stereotactic radiosurgery uses one session to give the whole radiation dose, but it may be repeated if needed. Sometimes radiation oncologist 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.