Positron emission tomography, or PET scans, can help clinicians diagnose and treat some cancers, but it is not clear yet whether the imaging technology helps people with cancer live longer and healthier lives, according to a comprehensive review by the UK National Health Service.

PET scans are one of the latest tools used to detect and determine a cancer’s activity in the body. PET is generally more accurate than other imaging technologies such as computerized tomography (CT) or magnetic resonance imaging (MRI) scans. Using tiny radioactive elements, a PET scan can zero in on the distinctive biochemical fingerprints that distinguish cancerous cells from normal tissue.

The most common type of PET scan, called FDG-PET, appears to lead to the best therapy for patients who have a newer diagnosis of non-small cell lung cancer and in those who have undergone treatment for Hodgkin’s lymphoma, the study authors, led by Karen Facey, an evidence-based health policy researcher, said. FDG-PET can also help identify the best treatment for patients with colorectal cancer, and it can detect small, potentially malignant lung growths called solitary pulmonary nodules, they said.

“For other cancers, PET can often improve the accuracy of detecting a tumor, but it is unclear how this affects a patient’s treatment and ultimately their outcome,” Facey said.

She said the most reliable evidence suggests that FDG-PET is cost-effective (in the UK) in non-small cell lung cancer and Hodgkin’s lymphoma.

Facey and her colleagues combed through the results of six systematic reviews and 158 primary studies that examined the effect of PET scans on the management of breast, colorectal, head and neck, lung, lymphoma, melanoma, esophageal and thyroid cancers. For many of the cancers examined in the review, the answers are still inconclusive and require larger, more careful study, the authors said.

"For instance, did PET scans diagnose these cancers better than an MRI or CT scan?" Facey said. "Could a PET scan give a better idea of a cancer’s severity or spread" Would they be better than other imaging techniques at detecting the recurrence of a cancer or monitoring a tumor’s response to treatment?"

While research continues, physicians are already using combination PET/CT scans to help diagnose and treat cancer patients. Facey and her colleagues also reviewed this technology. They said the PET/CT scans appear to be “slightly more accurate” so far.

In September, the Society of Nuclear Medicine, whose members use PET technology, updated its "scope of practice" guidelines to reflect this trend.

“Since many of the state-of-the-art nuclear medicine cameras as well as PET scanners have CT scanners attached to them, performing CT scans becomes one of the nuclear medicine technologist’s tasks,” said Cindi Luckett-Gilbert, chair of the society’s special task force on the scope of practice.

Facey said this is the first comprehensive review of PET for determining how well patients are responding to chemotherapy and for determining the sites for radiation therapy.

“It has identified many interesting new studies, but these are difficult to interpret given their different designs, so there’s a real need for larger, better quality studies of this kind to be performed in the UK,” she said.

The review was published in Health Technology Assessment, the international journal series of the Health Technology Assessment program part of the National Institute for Health Research in the UK (Facey K, et al. Overview of the clinical effectiveness of positron emission tomography imaging in selected cancers. Health Technology Assessment 11(44), 2007).

For more information, visit: http://www.hta.ac.uk