FDG-PET/CT asserts itself for lung cancer imaging

PET/CT imaging has evolved in the past five years from an undefined new technology to an invaluable instrument that provides critical information for clinical decision making.

PET/CT has built its reputation primarily in oncology applications, which represent the majority of approved indications. The hybrid technique's impact has been greatest in diagnosis, evaluation, and management of non-small cell lung cancer (NSCLC). A study published last year showed that PET imaging of patients in a university-based lung cancer practice changed clinical management in more than 70% of cases (Chest 2005;128:698-703).

The impact has been almost as dramatic in the community hospital setting.

"We're just now collecting data in the lung cancer clinic, but I suspect that our findings will be similar [to those from the university-based study]," said Dr. Robert Jotte, medical director of the Lung Cancer Clinic of the Rockies in Denver. "I suspect the data will show that PET/CT changes clinical management in at least 50% of our cases."

The center has two mobile PET/CT scanners and has phased out use of its PET-only device. Between 80 and 90 patients arrive at the clinic each week. Most have a PET/CT study at some point in their clinical management.

PET/CT plays a role in evaluating patients with all stages of NSCLC. For those with stage 1 or stage 2 disease, PET/CT is used to rule out metastatic disease and determine whether patients are candidates for surgical resection. With stage 3 NSCLC, PET/CT studies focus on lymph node involvement; extent will determine appropriate therapy. For patients with stage 4 NSCLC, the test helps avoid unnecessary procedures and treatment when the primary clinical consideration is quality of life.

The ability to superimpose a CT image over a PET scan represents a major advance over the two individual imaging modalities, Jotte said. As an example, patients with stage 3 lung cancer frequently present with an obstructive airway lesion that causes collapse of the lung behind the lesion. Prior to PET/CT, clinicians were obligated to treat the lesion and the collapsed but normal lung tissue with radiation because the border between normal and malignant tissue could not be distinguished easily.

"Fused images will show increased glucose uptake in the tumor, and we can define where the tumor, stops and the normal collapsed lung begins," Jotte said.

At Radiology Associates of Tarrant County in Fort Worth, three or four lung cancer patients a day have PET/CT scans, including patients with single pulmonary nodules (SPN) and those diagnosed with lung cancer. Characterization of SPN was one of the first approved indications for PET and remains one of the most common applications of the hybrid technique.

PET/CT is used routinely to stage NSCLC patients, said Dr. Paul Shyn, a radiologist with the Fort Worth group. PET/CT guides treatment, particularly when it comes to making decisions about a patient's surgical candidacy. Radiation oncologists rely heavily on PET/CT images to develop their treatment protocols.

"The more precisely we can stage a patient, the more helpful we can be to the patient," Shyn said. "It seems that PET/CT is the most accurate way of doing that."

The expanding role of PET/CT in managing NSCLC patients is illustrated by the early experience of radiologists at Virginia Oncology Associates in Norfolk. When the organization launched its PET/CT service in April 2005, 21 NSCLC patients had scans during the first month of operation. The daily volume of lung cancer patients more than doubled over the next 12 months to 43 scans per month by April 2006.

"I think physicians like PET/CT imaging because it is one study that provides a very good way of looking for evidence of metastatic disease," said Dr. Paul Conkling, director of the early-phase research program at the Virginia facility. "In the initial staging, if an abnormality in the mediastinum is seen on both PET and CT, that's very powerful evidence of a positive node, and that may alter treatment plans. Instead of taking the patient straight to surgery, we might prefer to treat with chemotherapy or some other form of therapy first."

Because of its ability to identify disease in the center of the chest, PET/CT will probably help fuel the trend toward increased use of neoadjuvant chemotherapy in NSCLC, Conkling said. Patients with such centrally located lesions often receive a course of chemotherapy in an effort to downstage the disease and help the patient qualify for surgical resection. With the advent of PET/CT staging of NSCLC, more patients might become resectable.