Research
Diagnostic Imaging Online
March 28, 2006
Report from AMI: F-18 choline
Less than stellar results characterized one of the first large human trials of F-18 choline PET/CT for prostate cancer staging and management.
A study involving 219 patients examined over two years found the technique was unable to detect small metastases and produced false negatives in 14 cases. Dr. Werner Langsteger, director of nuclear medicine and endocrinology at the Hospital of the Merciful Sister in Linz, Austria, reported the results at the 2006 Academy of Molecular Imaging meeting in Orlando Monday.
Langsteger’s assessment was not entirely grim. On the plus side, he found that PET/CT detected more lesions than CT. The PET procedures identified 93 lesions, compared with 53 lesions for CT.
Of 61 biopsy-confirmed cases scheduled for surgery, six were upstaged because of metastatic lymph nodes or bone metastases uncovered with F-18 choline PET/CT. Overall sensitivities and specificities were not announced, but the test was 57% sensitive and 94% specific for lymph node metastases larger than 5 mm. Sensitivity and specificity for metastases smaller than 2 mm were 22% and 93%, respectively.
“For preoperative staging, the results were disappointing,” Langsteger said.
Among patients with a Gleason score of less than 7, one false-negative lymph node escaped detection. Five false negatives appeared among patients with a Gleason score above 7. In patients with prostate-specific antigen results below 50, five false negatives appeared. Two patients who had a PSA score above 50 had positive lymph nodes that were overlooked.
Several factors appeared to create opportunities for false positives: variations in standard uptake value readings during the eight-minute dynamic scan, late-enhancement imaging performed two hours after F-18 choline injection, and whole-body imaging.
In a sample case, the SUV of a suspected 10-mm-diameter lesion measured with CT was initially 6.6. The SUV then fell in readings acquired in each of the next seven minutes to 2.1. An F-18 choline PET/CT exam performed 12 months earlier had produced an SUV of 2.6 in the region of interest. CT indicated that the mass had grown.
For follow-up management, SUV increases were observed in the late images of more than half of the metastases among patients with elevated PSA. SUV increases did not appear for patients under hormone therapy for lymph node metastases.
Cancer mapping included in the trial produced promising results, Langsteger said.
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