Doctors at the University of Maryland Medical Center are using a new method to treat cancerous tumors in various parts of the body with a higher dose of radiation, while sparing surrounding organs and tissue. The method called, Intensity Modulated Arc Therapy, IMAT, has proven effective in delivering a higher, more uniform concentration of radiation than conventional radiation therapies. The results were presented at the 42nd annual meeting of the American Society for Therapeutic Radiology and Oncology (ASTRO) in Boston on October 25.
"The major question with cancer treatment is always, how do you treat the cancer effectively without hurting the surrounding structures. If someone has cancer next to a structure that cannot take much radiation, then that presents a problem," says Cedric Yu, D.Sc., director of Medical Physics at the University of Maryland Medical Center in Baltimore, who designed IMAT. "With the IMAT method, the radiation rotates around the critical organs while the beam remains fixed on the tumor. This allows a higher concentration of radiation to be delivered to the tumor while the nearby structures are spared."
Using a linear accelerator, a sophisticated machine used to deliver radiation treatment, Dr. Yu has designed IMAT to deliver intensity-controlled radiation beams to cancerous tumors in a rotational manner that allows a higher dose of radiation to get to the cancer. Because the beams are rotated, the surrounding tissues and structures receive only minimal radiation exposure. Dr. Yu pioneered this method and the University of Maryland Medical Center is the only medical center in the country using it.
Conventional fixed beam radiation is administered in straight columns that go either up and down or across. This method requires doctors to use less radiation because it cuts across healthy tissue and critical organs. For this reason, there's also a higher chance that the cancer could return. Combining fixed beam radiation, however, with other therapies offers more success.
Other intensity-modulated rotational methods require patients to move during treatment and use thinner beams to deliver the radiation. IMAT however does not require patient movement and uses open beams, which allow more radiation photons to pass through.
In the study, 25 patients with various types of cancers, including prostate cancer, head and neck cancer, and nasal/pharynx cancer, and cancers of the central nervous system received therapy for an average of 30 days. A treatment plan was designed using the patient's CT scans that were fed into special computers. Before each procedure, a practice treatment was performed to ensure accuracy. The study results show that the IMAT method delivers a more uniform, higher concentration of radiation for different sites in the body. Also patients spend less time, about seven minutes, on the treatment table.
"Using conventional methods to treat prostate cancer, for example, the dose you can safely deliver is about 66Gy, the cure rate is about 65 percent for lower risk patients. Now if we can give a higher dose of radiation, above 75Gy, the cure rate could be over 90 percent," says Dr. Yu. "The IMAT method provides a way to deliver a higher radiation dose to the tumor that would have been too dangerous to do before."
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