How does Radiation Therapy Work?
Radiation therapy, or radiotherapy, is the use of various forms of radiation to safely and effectively treat cancer and other diseases. Radiation therapy works by damaging the genetic material within cancer cells and limiting their ability to successfully reproduce. When these damaged cancer cells die, the body naturally eliminates them. Normal cells are also affected by radiation, but they are able to repair themselves in a way that cancer cells cannot. In addition, your radiation oncologist will develop a plan to deliver the radiation to the tumor area, shielding as much surrounding normal tissue as possible.
Your radiation oncologist may recommend using radiation therapy in a number of different ways. Sometimes the goal is to cure the cancer. In this case, radiation therapy may be used to:
- Destroy tumors that have not spread to other parts of your body and cure you of disease.
- Reduce the risk that cancer will return after you undergo surgery or chemotherapy by killing small amounts of cancer that might remain.
- Shrink the cancer before surgery.
In other cases, the goal is to reduce the symptoms caused by growing tumors and to improve your quality of life. When radiation therapy is administered for this purpose, it is called palliative care or palliation. In this instance, radiation may be used to:
- Shrink tumors that are interfering with your quality of life, such as a lung tumor that is causing shortness of breath.
- Relieve pain by reducing the size of a tumor.
It is important for you to discuss the goal of your treatment with your radiation oncologist.
Some patients are concerned that radiation therapy will cause another cancer. In fact, the risk of developing a second tumor because of radiation therapy is very low. For many people, radiation therapy can cure the cancer. This benefit far outweighs any small risk that the treatment could cause a later cancer. However, you should discuss the risks and benefits of all of your treatments with your treatment team. If you smoke, the most important thing you can do to reduce your risk of a second cancer is to quit smoking.
External Beam Radiation Therapy
During external beam radiation therapy, a beam (or multiple beams) of radiation is directed through the skin to the cancer and the immediate surrounding area in order to destroy the main tumor and any nearby cancer cells. To minimize side effects, the treatments are typically given five days a week, Monday through Friday, for a number of weeks. This allows doctors to get enough radiation into the body to kill the cancer while giving healthy cells time to recover.
The radiation beam is usually generated by a machine called a linear accelerator. The linear accelerator, or linac, is capable of producing high-energy X-rays or electrons for the treatment of your cancer. Using treatment planning computers and software, your treatment team controls the size and shape of the beam, as well as how it is directed at your body, to effectively treat your tumor while sparing the surrounding normal tissue.
Intensity Modulated Radiation Therapy (IMRT)
Intensity modulated radiation therapy, or IMRT, is a specialized form of 3D-CRT that allows radiation to be more exactly shaped to fit the tumor. With IMRT, the radiation beam can be broken up into many “beamlets,” and the intensity of each beamlet can be adjusted individually. Using IMRT, it may be possible to further limit the amount of radiation received by healthy tissue near the tumor. In some situations, this may also safely allow a higher dose of radiation to be delivered to the tumor, potentially increasing the chance of a cure.
Proton Beam Therapy
Proton beam therapy is a form of external beam radiation treatment that uses protons rather than electron X-rays to treat certain types of cancer and other diseases. The physical characteristics of the proton therapy beam allow the radiation oncologist to more effectively reduce the radiation dose to nearby healthy tissue. Proton therapy is available at only a few centers in the country and is used in unique clinical situations.
Once you are positioned correctly, the therapist will leave the room and go into the control room next door to closely monitor you on a television screen while giving the radiation. There is a microphone in the treatment room so you can always talk with the therapist if you have any concerns. The machine can be stopped at any time if you are feeling sick or uncomfortable.
The radiation therapist may move the treatment machine and treatment table to target the radiation beam to the exact area of the tumor. The machine might make noises during treatment that sound like clicking, knocking or whirring, but the radiation therapist is in complete control of the machine at all times.
Image Guided Radiation Therapy (IGRT)
Radiation oncologists use image guided radiation therapy, or IGRT, to help better deliver the radiation to the cancer since tumors can move between treatments due to differences in organ filling or movements while breathing. IGRT involves conformal radiation treatment guided by imaging, such as CT, ultrasound or X-rays, taken in the treatment room just before the patient is given the radiation treatment on a daily basis.
All patients first undergo a CT scan as part of the planning process. The information from the CT scan is then transmitted to a computer in the treatment room to allow doctors to compare the earlier image with the images taken just before treatment. During IGRT, doctors compare these images to see if the treatment needs to be adjusted. This allows doctors to better target the cancer while avoiding nearby healthy tissue. In some cases, doctors will implant a tiny marker in or near the tumor to pinpoint it for IGRT. This helps to account for organ/tumor motion even if the body is immobilized by a casting device.