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PET scan shows during treatment if radiation is shrinking lung tumor, U-M study shows

July 19, 2007

Finding suggests treatment could be changed early if tumor not responding

ANN ARBOR, Mich. - Lung cancer patients may not need to wait till their radiation treatment is over to know if it worked. A PET scan several weeks after starting radiation treatment for lung cancer can indicate whether the tumor will respond to the treatment, according to a new study by researchers at the University of Michigan Comprehensive Cancer Center.

Traditionally, PET, or positron emission tomography, has been used after radiation treatment for lung cancer to assess whether the tumor responded to treatment and whether the patients will have a chance of being cured. Using PET several weeks into treatment, researchers found a strong correlation between tumor responses during treatment and response three months after completion of the treatment. This could potentially allow doctors to change the radiation treatment plan before treatment ends to improve the outcome.

Results of the study appear in the July 20 issue of the Journal of Clinical Oncology.

"This demonstrates that PET scans can be performed earlier during the course of radiation treatment, which will allow us to modify the treatment regimen before the treatment is completed. Our sample size was small, but the results are very promising," says lead study author Feng-Ming Kong, M.D., Ph.D., assistant professor of radiation oncology at the U-M Medical School.

In a pilot study of 15 people with early-stage non-small-cell lung cancer, researchers administered FDG-PET scans before beginning radiation therapy, three to four weeks into treatment and three months after completing treatment. An FDG-PET scan uses radioactive labeled glucose, which is drawn to cells that are being metabolized quickly. If a tumor is responding to radiation treatment, it would show decreased FDG activity in the cells.

The concern in the past has been that normal lung tissue reacts to the radiation and may be in the way of determining through PET scan whether the tumor is shrinking. Kong's study found this was not an issue.

"The confounding effect on normal tissue is not as significant during treatment as it is after treatment, which is a big surprise. This is the part I'm most excited about: The confounding effect is actually more remarkable after the treatment. That's counter to our traditional assumptions. We always assumed the confounding effect would be worse during treatment," Kong says. She says this finding makes sense, as normal lung tissue is slow to react to the assault of radiation therapy and typically there is a delay before lung inflammations or other problems develop.

"The PET scan is better to perform during the course of treatment instead of months after treatment. It avoids the normal tissue confounding effect and allows the radiation therapist to modify the doses if necessary," Kong says.

The researchers are continuing to study PET scans in a larger number of patients to verify the pilot findings. The next step is to assess whether changing the treatment regimen based on mid-treatment PET scan findings would lead to better tumor control and survival rates. If continued studies bear out the initial data, Kong is hopeful this work could eventually lead to a change in standard practice guidelines regarding PET for lung cancer.

University of Michigan Health System