Report from AMI: Melanoma PET/CT need not cover brain or uninvolved extremities

Results from a University of California, Los Angeles study suggest that imaging the brain and uninvolved extremities during routine whole-body PET/CT of melanoma wastes scanner time and exposes patients to unnecessary radiation.

A retrospective examination of 296 cases found scanner efficiency can be improved without jeopardizing the diagnostic power of the scan or patient safety, according to chief investigator, Dr. Esther Choi, a nuclear medicine resident. She reported the results at the 2006 Academy of Molecular Imaging meeting in Orlando.

Before the trial, melanoma patients at UCLA Medical Center were routinely scanned head to toe. PET/CT scans were performed in about 30 minutes, while dedicated PET scans required up to 75 minutes. Protocols involved intravenous administration of 0.21 mCi/kg F-18 FDG, injected 60 minutes before imaging. A weight-based PET protocol was used. Patients weighing less than 130 pounds were imaged in one minute per bed position. Patients weighing over 200 pounds were imaged in five minutes per bed position.

By correlating pathologic data with positive imaging findings, Choi learned that the primary sites of melanoma were head and neck (54 patients), lower extremities (27), upper extremities (18 patients), trunk (29), and unknown (9).

Out of nearly 300 studies, however, only three revealed metastases in initially uninvolved extremities and/or the brain, Choi said. All three patients also had widely metastatic disease with extensive visceral involvement. Six studies showed new hypermetabolic foci in the same extremities involved by the primary melanoma. False-negative PET scans (four brain lesions and one extremity lesion) were reported for five patients, while 11 false-positive extremity findings occurred.

The results led Choi and supervising researcher, Dr. Johannes Czernin, director of nuclear medicine, to conclude that routine inclusion of the brain and initially uninvolved extremities is of no significant benefit, compared with the information already obtained by the whole-body FDG study from the base of the skull to midthigh.

"Melanoma patients should, therefore, be scanned in the same manner as other oncology patients," she said.