Nov. 18, 2007 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 U.K. 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. 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, say review authors led by Karen Facey.
"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," said Facey, an evidence-based health policy researcher.
The most reliable evidence "would suggest that FDG-PET is cost-effective [in the United Kingdom] in non-small cell lung cancer and Hodgkin's lymphoma," she added.
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 U.K.," she said.
The review is published in the latest issue of Health Technology Assessment, the international journal series of the Health Technology Assessment programme, part of the National Institute for Health Research in the United Kingdom.
Facey and 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 instance, did PET scans diagnose these cancers better than an MRI or CT scan" 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"
For many of the cancers examined in the review, the answers are still inconclusive and require larger, more careful study, the HTA authors found.
While research continues, physicians are already using combination PET/CT scans to help diagnose and treat cancer patients. Facey and colleagues also reviewed this new technology and say that 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, the chair of the society's special task force on the scope of practice.
Journal reference: Facey K, et al. Overview of the clinical effectiveness of positron emission tomography imaging in selected cancers. Health Technology Assessment 11(44), 2007
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