Study questions timing of PET imaging for radiation therapy planning

PET imaging of non-small cell lung cancer prior to receiving radiation therapy should not be the basis for determining areas that may benefit from higher doses of radiation, according to research presented this week at the 2009 American Society of Radiation Oncology meeting.

Some studies suggest that areas that of avid FDG uptake on PET images before treatment are also the regions most likely to have intense metabolic activity after treatment, according to Dr. Nitin Ohri, a radiation oncology resident at Thomas Jefferson University Hospital.

“Investigators are looking to PET imaging to find ways to predict if any part of the tumor would benefit from a higher radiation dose,” Ohri said. “I wanted to see if residual activity on a scan after treatment correlates with the activity pattern on a scan done before treatment.”

PET scans of 43 patients, of which 15 showed significant activity on the scans both before and after treatment, were examined. Ohri set up a coordinate system that divided tumors into nine regions, or 17 regions for larger tumors. Metabolic FDG activity in the regions both before and after treatment was then compared.

Ohri found the regions of intense FDG uptake for some patients didn’t change after treatment. However, some patients showed activity in completely different regions before and after treatment.

“It’s not sufficient to increase the dose to areas that are especially active on PET imaging before treatment and expect that to improve the control rate,” Ohri said in a release. “It may be more appropriate to do a scan halfway through treatment and plan additional radiation dose around that.”