Report from SNM: PET with C-11 choline shows versatility in prostate cancer
PET using carbon-11 choline is known to be more sensitive than FDG-PET for imaging the prostate. Research has focused on finding which specific applications use the tracer best.
Investigators at the Society of Nuclear Medicine meeting in Philadelphia on Tuesday showed that C-11 choline PET is sensitive to the effects of hormonal ablation and for the detection of local recurrence and diagnosis of primary and metastatic cancer.
Dr. Norbert M. Blumstein and colleagues at University Ulm in Germany prospectively examined 13 patients with localized prostate cancer who were receiving hormonal ablation therapy while awaiting brachytherapy.
PET/CT scans were performed prior to and several months after hormonal ablation treatment. C-11 choline PET/CT showed no evidence in any patient of extraprostatic tumor growth.
In 12 of 13 patients, at least one suspect lesion could be verified and located within the prostate before hormonal ablation. In contrast, C-11 choline PET/CT exams showed no suspect lesion in those patients under hormonal ablation.
The median standard uptake value (SUV) before and after hormonal therapy was 3.4 and 1.6, respectively. The median prostate-specific antigen (PSA) level before and after hormonal therapy was 7.6 ng/mL and 3.6 ng/mL, respectively. The reduction of SUV levels correlated well with the reduction of the PSA levels, Blumstein said.
"C-11 choline PET/CT can localize suspect lesions and lymph nodes, so we can use it to select low-risk patients to undergo brachytherapy," he said.
In another study led by Blumstein, researchers found C-11 choline sensitive in detecting local recurrence. C-11 choline PET/CT was performed in 34 patients with increasing PSA levels after radical prostatectomy, brachytherapy, or conformal radiation therapy.
In 32 of the patients, local recurrence could be detected with PET/CT. Focal uptake of C-11 choline was present in the prostate area with a mean SUV of 2.1. Mean lesion size in the CT scan was 14 mm. PET/CT findings were verified histologically in 20 patients.
Additional choline uptake in pelvic lymph nodes and para-aortic nodes was found in seven patients, indicating lymph node involvement. A solitary bone metastasis was present in one patient. A focal choline uptake in the prostate area was observed in the seven patients receiving hormone replacement therapy, Blumstein said.
"Only 8% of patients had a positive conventional diagnosis such as ultrasound or MR. In contrast, 94% had a positive identification of local recurrence using choline PET/CT," he said.
These findings have an important impact on therapy planning, including delivering a higher dose to the local relapse or to a single pelvic lymph node, he said.
Dr. Stefan Dresel and colleagues at the University of Munich examined 24 patients with C-11 choline PET and found that it diagnosedprostate cancer and its metastases with high sensitivity. Specificity suffered due to false-positive readings in two patients with prostatitis.
These patients, however, presented with lower SUVmax values compared with the cancer patients, Dresel said. It may be feasible to reduce false-positive readings through a better understanding of SUVmax threshold values between cancer and prostatitis.
