Studies support targeted use of C-11 PET/CT in prostate cancer evaluation

C-11 choline PET/CT substantially improved sensitivity for lesion detection in the re-staging of patients with prostate cancer, according to a study presented May 23 at the annual meeting of the American Urological Association in Atlanta. However, its utility was limited in the initial staging of men with high-risk prostate cancer. R. Jeffery Karnes, MD, from the Mayo Clinic in Rochester, Minn., and colleagues presented three studies exploring potential applications of C-11 choline PET/CT in prostate cancer at the annual meeting.

“We found C-11 to be most helpful and much more sensitive than other exams available in patients who require re-staging,“ Karnes told Health Imaging in an interview.

In one study, Karnes and colleagues assessed the capability of C-11 choline PET/CT to delineate the extent and distribution of disease after failed therapy. The researchers retrospectively analyzed 176 patients who underwent C-11 choline PET/CT after primary treatment failure from September 2007 to November 2010.

Sensitivity, specificity, positive predictive value and negative predictive value were 93 percent, 76 percent, 91 percent and 81 percent, respectively. In 32 percent of cases, the PET study detected treatable lesions not identified via conventional imaging and triggered changes in management, according to the abstract.

In another study, Karnes et al analyzed data for 36 patients who underwent salvage surgery after failed initial treatment. Among these men, C-11 choline PET/CT provided a sensitivity of 88 percent and positive predictive value of 94 percent, indicating that the approach is accurate for detection of localized disease recurrences.

However, when Karnes and colleagues sought to explore the role of C-11 choline PET/CT in the initial staging of high-risk prostate cancer, the method was accurate but did not offer additional diagnostic value for patients who had undergone prior x-ray-based staging exams.

In this study, the researchers retrospectively analyzed data for 45 patients with high-risk prostate cancer who underwent C-11 choline PET/CT from September 2007 to November 2010, and compared the results with findings from conventional imaging, targeted biopsy or surgical resection.

Although PET/CT delivered sensitivity, specificity and positive predictive value of 100 percent for each measure, and negative predictive value of 93 percent, the researchers suggested that C-11 choline PET/CT may not outperform conventional imaging.

Performing a C-11 choline PET/CT scan on a patient with high-risk prostate cancer who presents with at least a bone scan and a CT or MRI exam usually does not reveal anything more than the initial scans, Karnes said.

The researchers did not complete a cost-effectiveness analysis, and Karnes noted that the PET/CT study might supplant conventional imaging. However, “it isn’t additive,” he said. In addition, C-11 exams produced two false-negative results in this cohort, both in patients on androgen deprivation therapy. The method should be used with caution in this population, the researchers wrote in the abstract.

As pioneers detail potential roles for C-11 scanning, Karnes noted its limited availability. C-11 has a 20-minute half-life, so its use requires an onsite cyclotron.