(Adapted in part from National Cancer Institute website)
Radiation Oncology (also called radiation therapy, x-ray therapy, or irradiation) is the use of a certain type of energy (called ionizing radiation) to kill cancer cells and shrink tumors. Radiation therapy injures or destroys cells in the area being treated (the “target tissue”) by damaging their genetic material, making it impossible for these cells to continue to grow and divide. Although radiation damages both cancer cells and normal cells, most normal cells can recover from the effects of radiation and function properly. The goal of radiation therapy is to damage as many cancer cells as possible, while limiting harm to nearby healthy tissue.
There are different types of radiation and different ways to deliver the radiation. There are two broad categories of radiation therapy; external radiation therapy (teletherapy) and isotope therapy (brachytherapy, internal radiation, and in some cases, systemic radiation). The most common forms of external beam radiation therapy used in clinical practice are X-rays and electrons. X-rays, for example, can penetrate deeply into the body and can treat deep seated tumors. Electron beam treatment is often useful for treating superficial tumors such as skin cancer.
About half of all cancer patients receive some type of radiation therapy. Radiation therapy may be used alone or in combination with other cancer treatments, such as chemotherapy or surgery. In some cases, a patient may receive more than one type of radiation therapy.
Radiation therapy may be used to treat almost every type of solid tumor, including cancers of the brain, breast,cervix,larynx,lung, pancreas,prostate, skin, spine,stomach,uterus, or soft tissue sarcomas.Radiation can also be used to treat leukemiaand lymphoma (cancers of the blood-forming cells and lymphatic system, respectively). Radiation dose to each site depends on a number of factors, including the type of cancer and whether there are tissues and organs nearby that may be damaged by radiation.
For some types of cancer, radiation may be given to areas that do not have evidence of cancer. This is done to prevent cancer cells from growing in the area receiving the radiation. This technique is called prophylactic radiation therapy.
Radiation therapy also can be given to help reduce symptoms such as pain from cancer that has spread to the bones or other parts of the body. This is called palliative radiation therapy.
Most people who receive radiation therapy for cancer have external radiation. Some patients have both external and internal or systemic radiation therapy, either one after the other or at the same time.
External radiation therapy usually is given on an outpatient basis; most patients do not need to stay in the hospital.
External radiation therapy is used to treat most types of cancer, including cancer of the bladder, brain, breast, cervix, larynx, lung, prostate, and vagina. In addition, external radiation may be used to relieve pain or ease other problems when cancer spreads to other parts of the body from the primary site. There are several methods of administering external radiation therapy delivery.
Two-dimensional (2-D) radiation therapy
In the past, the planning of radiation treatments was done in two dimensions (width and height). Today this is used in the minority of cases.
Three-dimensional (3-D) conformal radiation therapy
Three-dimensional (3-D) conformal radiation therapy uses computer technology to allow doctors to more precisely target a tumor with radiation beams (using width, height, and depth).
A 3-D image of a tumor can be obtained usingcomputed tomography (CT)magnetic resonance imaging (MRI) or positron emission tomography (PET). Using information from these images, special computer programs design radiation beams that “conform” to the shape of the tumor. Because the healthy tissue surrounding the tumor is largely spared by this technique, higher doses of radiation can be used to treat the cancer. Improved outcomes with 3-D conformal radiation therapy have been reported for many cancers.
In our centers, the radiation is delivered by linear accelerators that are equipped with multileaf collimators (a collimator helps to shape or sculpt the beams of radiation). The equipment can be rotated around the patient so that radiation beams can be sent from the best angles. The beams conform as closely as possible to
the shape of the tumor allowing very accurate treatment.
Intensity-modulated radiation therapy (IMRT)
IMRT is a new type of 3-D conformal radiation therapy that uses radiation beams (usually x-rays) of varying intensities to deliver different doses of radiation to small areas of tissue at the same time. The technology allows for the delivery of higher doses of radiation within the tumor and lower doses to nearby healthy tissue. IMRT may also lead to fewer side effects during treatment. IMRT has proven to be a remarkably effective way to treat cancer and improve patients’ lives during treatment and beyond.
One revolution is all it takes. RapidArc delivery uses a dynamic MLC, variable dose rate, and variable gantry speed to generate IMRT-quality dose distributions in a single optimized arc around the patient. Clinicians can now deliver continuously modulated dose to the entire tumor volume while sparing normal, healthy tissue. RapidArc dramatically reduces the amount of time patients spend on the treatment couch.
Image Guided Radiation Therapy (IGRT)
IGRT provides high-resolution, three-dimensional images to pinpoint tumor sites, adjust patient positioning when necessary, and improves the overall precision of the radiation therapy treatment. It is often used together with IMRT.
Isotope Therapy (brachytherapy, internal radiation and in some cases systemic radiation)
Isotope therapy or brachytherapy) uses radiation that is placed very close to or inside the tumor. Internal radiation is usually delivered in one of several ways, each of which is described below.
Interstitial radiation therapyis when sealed radioactive isotopes are inserted into tissue at or near the tumor site. It is used to treat tumors of the head and neck, prostate, cervix, ovary, breast, and perianal and pelvic regions.
Intracavitary or intraluminal radiation therapy is when sealed radioactive isotopes are inserted into a body cavity with an applicator. It is commonly used in the treatment of uterine and cervix cancer.
Systemic radiation therapy uses radiopharmaceuticals, to treat cancer, including thyroid cancer, and pain caused by the spread of cancer to the bone (bone metastases). The most commonly used radiopharmaceuticals are samarium 153 (Quadramet®) and strontium 89 (Metastron™). These drugs are approved by the FDA to relieve pain caused by bone metastases. Both agents are given intravenously (by injection into a vein), usually on an outpatient basis; sometimes they are given in addition to external beam radiation.
Another radiopharmaceutical, Iodine 131, is used to treat thyroid cancer and benign thyroid disorders such as Graves Disease and some types of goiters. It is usually given orally.
You can find more information about radiation therapy in the National Cancer Institute (NCI) booklet Radiation Therapy and You: Support for People With Cancer. This publication is available on the NCI Publications Locator Website.