IMRT can also take into account patient movement, such as swallowing, as well as set-up error, Das said. "The problem is that this is dependent on the treatment planning process," he said.
For the new study, the researchers reviewed data on 803 patients treated with IMRT between October 2004 and July 2006. Twelve percent of the participants had brain cancer, 26 percent had head and neck cancer, while 62 percent had prostate cancer. The patients were treated at five different medical centers, each using different planning systems for the therapy.
"They looked at how different institutions actually implement their IMRT by looking at plan details," Aitken said.
Basically, the original prescribed dose was compared with the "planned" -- or delivered -- dose.
A total of 46 percent of patients received a maximum dose that was 10 percent higher than the prescribed dose, while 63 percent of patients received a dose more than 10 percent lower than the prescribed dose. The study could not evaluate how large of an area received a too-low dose. While it's important for comparative purposes, a 10 percent variability over small volumes has not been proven to be clinically significant, Aitken said.
Other experts, however, feel the variations have a value in and of themselves.
"This is quantifying something we already know," said Dr. Eric Horwitz, vice chairman and clinical director of radiation oncology at Fox Chase Cancer Center in Philadelphia. "As a radiation oncologist, we take that radiation into account. We know that variation exists and sometimes we use it to our advantage."
The U.S. National Cancer Institute has more on radiation therapy for cancer.
SOURCES: Indra J. Das
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