From Our 2008 Archives

Study Finds Variations in Doses of Radiation Therapy

By Amanda Gardner
HealthDay Reporter

TUESDAY, Feb. 26 (HealthDay News) -- Procedures to carry out a highly refined, complex radiation treatment for killing tumors and sparing healthy tissue may vary more widely from one medical center to the next than previously thought, a new study suggests.

"This study raises a very large and serious problem for the radiation oncology community because you cannot compare doses and hence clinical outcome between treatment centers," said study lead author Indra J. Das, a professor of radiation oncology at the University of Pennsylvania.

Das and his co-authors are calling for national and international guidelines for the use of so-called intensity-modulated radiation therapy (IMRT). Their study findings are published online in the Feb. 26 issue of the Journal of the National Cancer Institute.

Dr. Candice Aitken, assistant professor of radiation oncology at Dartmouth Hitchcock Medical Center in Lebanon, N,H., agreed, saying the "point of the article is that we need to come up with methods of reporting doses so that we can interpret studies performed at different institutions better."

IMRT is the latest development in the field of radiation oncology. It uses very small beams of radiation ("beamlets"), each with a controlled radiation intensity, aimed at a tumor from many angles. The beams can change shape hundreds of times during any given treatment. The idea is to spare healthy tissue as much as possible while still delivering the needed dose to malignant tissue, according to the Mayo Clinic.

"Some people call it 'dose painting,' where you can give high doses to certain regions depending on what's clinically needed," Aitken explained. "Instead of a uniform field, you can vary intensity pixel by pixel... If you have a brain tumor that sits next to the optic nerve, IMRT can help us sculpt the dose around an odd-shaped tumor next to a critical structure. That's the real value of IMRT."

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."

SOURCES: Indra J. Das, Ph.D., professor of radiation oncology, University of Pennsylvania, Philadelphia; Eric Horwitz, M.D., vice chairman and clinical director of radiation oncology, Fox Chase Cancer Center, Philadelphia; Candice Aitken, M.D., assistant professor of radiation oncology, Dartmouth Hitchcock Medical Center, Lebanon, N.H.; Feb. 26, 2008, Journal of the National Cancer Institute, online

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