Ideal doses of IMRT defined to reduce treatment side effects for head and neck cancer

10/17/05

DENVER, Oct. 18 – Results from a University of Pittsburgh study evaluating intensity modulated radiation therapy (IMRT) for head and neck cancer determined the ideal doses for lessening treatment side effects. The findings were presented today at the 47th Annual Meeting of the American Society for Therapeutic Radiology and Oncology (ASTRO) in Denver.

"Despite major advances in chemotherapy and radiation for the treatment of head and neck cancers, many patients continue to suffer debilitating side effects that greatly impact their quality of life," said Dwight E. Heron, M.D., study co-author and associate professor of radiation oncology, University of Pittsburgh School of Medicine and director of radiation oncology, University of Pittsburgh Medical Center. "While these high-energy beams are targeted to the tumor site as precisely as possible, they often inadvertently injure healthy tissue that surrounds the tumor site, limiting the doses of radiation that can be used to effectively destroy cancer cells. With this study, we sought to discover whether tightly focused radiation beams, such as those provided by IMRT, would make a difference in the severity of side effects associated with treatment and found a distinct dose-response relationship in the oral cavity of patients treated with IMRT in addition to chemotherapy."

In the study, 70 patients with head and neck cancer were treated with IMRT using the Eclipseâ Planning System, Varian Medical Systems and chemotherapy. Patients were treated from April 2002 through September 2004 and were evaluated for grade level of oral mucositis, or inflammation, based on the volume of IMRT dose administered. Oral mucositis not only causes pain, but also can affect speech, the ability to eat or drink and to take oral medication. Patients with severe cases may require tube feeding.

Results indicated that the severity of side effects, or the grade of oral mucositis, was directly correlated with the volume of the radiation dose administered to the oral cavity, and the researchers defined an ideal dose volume of IMRT at which the incidence of acute oral mucositis was lessened.

"We found that if we constrain the dose of IMRT, we reduce the toxic effects of treatment," said Dr. Heron. "These results are encouraging evidence that head and neck cancer patients can benefit from IMRT at specific doses. With more homogenous and conformal treatment, head and neck cancer patients may be spared side effects from standard radiotherapy that can be significant."

During radiation therapy, high-energy beams are aimed at cancer cells to destroy them by permanently damaging their underlying genetic material. Unlike standard radiation therapy, IMRT administers a radiation field that consists of several hundred small beams of varying intensities that pass through normal tissue without doing significant damage, but converge to give a precise dose of radiation at the tumor site. IMRT can potentially limit the adverse side effects from radiation while increasing the intensity of doses that can be given to effectively destroy cancer cells.

IMRT is combined with a process called inverse treatment planning to determine the best way to treat a patient. It relies on CT (computed tomography) data from patients that is processed and analyzed by a complex computer system to produce the ideal radiation dose distribution for that patient.

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