According to a new study, Combined positron emission tomography (PET) and computed tomography (CT) imaging of lymphoma patients is a more effective method to evaluate response to radiation therapy.

The study by researchers at the University of Southern California (USC) suggests that the procedure may help patients avoid unnecessary follow-up treatments.

The clinical study is the first to show the advantage of combined PET-CT imaging in evaluating radioimmunotherapy for patients with non-Hodgkin lymphoma, said Gary Ulaner, M.D., Ph.D., radiology resident and nuclear medicine fellow at the Keck School of Medicine of USC and the principal investigator of the study.

"Combined PET-CT imaging is more accurate in defining a complete response to radioimmunotherapy treatment," Ulaner said.

"Specifically, PET-CT is able to correctly label inactive scar masses, which are sometimes mistaken for active cancer when CT is used alone," Ulaner added.

Radioimmunotherapy is a type of radiation treatment that targets cancer cells through antibodies.

The therapy causes less harm to healthy cells and usually results in fewer side effects than other cancer treatments, Ulaner notes.

Typically, the treatment has been evaluated by use of CT imaging alone, which uses special X-ray equipment to produce multiple images of the inside of the body.

PET is a type of nuclear medicine imaging that uses very small amounts of radioactive material to diagnose or treat disease and other abnormalities. When PET and CT scans are combined they can produce a more complete image of the cancer metabolism, he says.

In the study, the research team evaluated five men and five women-ranging in age from 38 to 70 years-who underwent PET and CT imaging both several weeks before and several months after radioimmunotherapy for non-Hodgkin lymphoma.

After evaluation of CT images alone, eight of ten patients were classified as responders to treatment, and two patients were classified as having a complete response to the treatment.

After reevaluating with the fused PET-CT scans, researchers found that two patients who had residual lesions had been misclassified. Both of the patients were free of evident disease, and remained healthy after 18 or more months of follow up.

"Using this relatively novel hybrid imaging means that some patients will only require a one-day treatment of radioimmunotherapy instead of several rounds of chemotherapy," said Peter Conti, M.D, Ph.D., professor of radiology at the Keck School of Medicine.

"We will have a more accurate image that will identify the patients who have a complete response to the treatment," he added.

The study is published in the journal Radiology.