PET scans may help in leukemia care

Is the chemotherapy working? Is the radiation therapy shrinking the tumor?

The sooner doctors know the answers to those questions, the better they can tailor cancer treatment. Now a UW–Madison research team is finding that non-invasive PET scans may provide the answers early during treatment — in contrast to the current long wait needed to determine clinical outcome.

With five clinical trials in progress, researchers in the School of Medicine and Public Health (SMPH) recently reported a promising advance at the 2008 annual meeting of the American Association of Physicists in Medicine. It was a small study involving adult patients with acute leukemia.

The team, led by Robert Jeraj, assistant professor of medical physics, with Mark Juckett, associate professor of hematology, found that a PET scan performed during the first few days of treatment using a substance taken up by leukemia cells predicted which patients were going to respond to chemotherapy and which were not.

“By knowing whether chemotherapy will work or not for a patient right after treatment is started, physicians could stop the ineffective treatment and possibly change to a more effective regimen,” says Jeraj.

Almost one-third of leukemia patients do not respond to chemotherapy, which kills the cancerous cells that originate in bone marrow as well as healthy bone marrow cells. The treatment often severely compromises patients’ immune systems, leaving them highly vulnerable to infections.

Unfortunately, doctors can’t tell how the treatment is going until they perform a bone marrow biopsy — typically on the pelvic bone — after a weeklong course of chemotherapy. Two weeks later, a second biopsy is usually taken to confirm that the disease is in remission.

The researchers took PET scans after injecting study participants with tiny amounts of the radioactive tracer fluoro-L-thymidine (FLT), which is readily taken up by cells during growth. In the scans, FLT shows up as a bright contrasting color in all bones in which bone marrow cells — the most proliferative in the body — are functioning. The researchers compared the scans to biopsy results.

“The scans were completely dark in patients who were responding,” says Jeraj, “while we saw residual bone marrow activity in the scans when the chemo was not successful.”

What’s more, a PET scan shows a total-body picture of bone marrow activity, while a bone marrow biopsy shows activity in only the spot that is tested.

“A measurement at one site doesn’t necessarily represent all activity,” says Jeraj.

The FLT PET scans may also be used to assess how well chemo or radiation therapy is proceeding in the treatment of tumors.

“Tumors exhibit more proliferation than the rest of the cells in the body, so you can see that activity very clearly on a FLT PET scan,” Jeraj says.