October 27, 2009

By Aleea Farrakh

Posted in: Radiotherapy | radiation

Tags: accelerator, beam, brachytherapy, external, particle, proton, radiation, systemic, therapy, x-ray

Radiation therapy is a type of cancer treatment that uses beams or particles of energy to kill cancer cells and/or reduce tumor size. Radiation therapy damages cells by affecting the genetic material that controls how cells grow and divide. Even though healthy cells are sometimes destroyed during radiation therapy, the ultimate goal is to target cancerous cells only.

Radiation therapy is mainly used to treat solid tumors and has been most effective in cancers of the brain, breast, cervix, larynx, lung, pancreas, prostate skin, spine, stomach and soft tissue sarcomas. It also can be used to treat leukemia and lymphoma.

Not only are there different types of radiation, there are also different ways to deliver it. Deciding what type of radiation a patient needs depends on various factors; type of cancer, location of the cancer, how far into the body the radiation will need to go, the patient’s medical history, and other treatments being administered before or after radiation.

External radiation therapy employs a machine such as an accelerator to collect and aim high-energy rays at the tumor in a localized part of the body. In addition to being used to treat tumors, this form of radiation therapy can also relieve pain or slow down cancers that have already spread. One form of external radiation is external beam radiation therapy that is delivered by means of a linear accelerator.

Linear accelerators use powerful generators to create the high energy for external beam radiation therapy. The linear accelerator has a special set of lead shutters, called collimators, which focus and direct the radiation to the tumor, in an attempt to destroy it. Since it is challenging to give radiation therapy to the tumor without harming normal cells nearby, in most treatment cases, the total dose of radiation needed to kill a cancerous growth can’t be given all at once. For this reason, the total dose of radiation is usually divided into smaller doses, or fractions. Commonly, fractionated doses are delivered over a span of five to eight weeks, and the patient does not have to stay in the hospital during this time period. When aiming to relieve pain, radiation is used to destroy as much of a growing tumor as is feasible. Often the tumor is invading or pressing on bones, nerves, or other organs, needed by the body to survive, so completely destroying the tumor often might cause too much collateral damage.

In contrast to external radiation, internal radiation, or brachytherapy, uses radiation that is sealed in a container, known as an implant, which is placed either close to (interstitial), or inside the body cavity (intracavitary) where the tumor is located. This is done so that very few normal cells are exposed to the radiation. When delivering intracavitary radiation, implants are placed in body cavities or body tissues using applicators. The applicators are put in by a doctor using an imaging test (such as an x-ray or MRI) to look at the exact area where the radiation needs to go. Implants are left in place from anywhere between one and seven days, depending on the dosage and tumor size. Smaller implants (such as the seeds or pellets) may be left in the body permanently. Over the course of several weeks the implants stop giving off radiation. Since it does take a few weeks, patients who have received brachytherapy are advised to stay away from pregnant women and to avoid holding young children. If implants are left in, the patient can go home the same day they are placed inside the body. This technique is commonly used to treat patients with prostate, uterine or vaginal cancers.

When choosing between external and internal radiation, doctors sometimes let the patient decide. If the patient is healthy enough to receive general anesthesia and doesn’t want to receive five to eight weeks of treatment, brachytherapy is used. On the other hand, if a patient prefers an outpatient procedure, he or she may decide on external beam radiation.

Systemic radiation is a form of nuclear medicine. It uses radioactive drugs known as radiopharmaceuticals –such as iodine 131 and strontium 89. These drugs are usually in liquid form and can be taken by mouth or given intravenously. The radioactive molecules are coupled with agents that recognize biological markers located on cells in specific regions of the body, so they travel through the blood stream and home in on the specific organ or area where the tumor is located. The radiopharmaceutical then binds to the organ and delivers radiation to kill the cancer cell. This technique is most commonly used to treat thyroid cancer or non-Hodgkin lymphoma.

The most common side effects associated with most types of radiation are nausea, fatigue, skin damage and digestive problems. These effects can occur a few days after the treatment or can last for a few weeks, depending on the patient. Other side effects can vary depending on the area of the body being treated. When receiving radiation therapy to the head and neck, dry mouth and difficulty swallowing may occur. If radiation is directed to the chest, patients sometimes suffer shortness of breath and skin irritation. When directed at the pelvis, women may feel bladder irritation. If the ovaries have been exposed to radiation, infertility or early menopause can result. For men, radiation therapy to an area that includes the testes can reduce both the number of sperm and their ability to function. In severe cases, erectile dysfunction can also occur. If the cancer has spread to many sites in the brain, and the entire brain is being treated with radiation, severe side effects can occur including vomiting, hearing loss, memory loss, hair loss, seizures and headaches.

Patients receiving radiation therapy should discuss the possibility of all side effects with their doctor. To reduce side effects like nausea and vomiting, antiemetic drugs are given to patients. Used most often to bring relief to patients undergoing chemotherapy, antiemetics are improving the quality of care for patients undergoing radiation as well.