Advances in radiation therapy for cancer have made it possible to fine-tune radiation beams so they match the shape and position of a patient's tumor nearly anywhere in the body. But the pinpoint accuracy of modern radiation treatments would be worthless if the tumor wasn't in the spot where the radiation beams were aimed.
So tumors that move, such as those in the lung which can change position during each breath are a special problem for radiation oncologists. A group at Washington University School of Medicine in St. Louis has studied the way lung tissues move during breathing in hopes of improving radiation as a treatment for lung cancer.
Lung cancer is diagnosed in about 170,000 people in the United States each year. While surgical removal of a malignant tumor is the preferred way to treat lung cancer, surgery may not be feasible if medical conditions make the operation very risky or if the tumor has grown into structures that cannot be removed. In such cases, as long as the cancer has not metastasized, radiation therapy offers a real chance for cure. In addition, radiation therapy is sometimes used to control a tumor that can't be cured to improve a patient's comfort. Studies show that three-dimensional techniques that deliver high doses of radiation in the precise shape of the tumor are more effective than older techniques.
"Ideally, the radiation should be delivered to as small an area as possible so normal tissue near the tumor isn't damaged," says Daniel Low, Ph.D., professor of radiation oncology and director of the Medical Physics Division. "But with a lung tumor, you need to irradiate a larger area if you want to encompass the tumor as it moves. One option to avoid this is to just turn on the radiation beams during a certain phase of the breathing cycle, but that assumes that patients breathe regularly and the tumor returns to the same place with each breath."