PET succeeds conventional imaging for hyperparathyroidism
Endocrine surgeons at the Mayo Clinic in Rochester, MN investigated whether C-11 choline PET/CT could identify abnormal parathyroid glands in patients who required further treatment after standard imaging and prior surgeries. The approach led to curative surgeries in 80% of patients, they found.
“C-11 choline PET/CT may be a useful adjunct for patients who have failed conventional imaging and who have previously had unsuccessful surgery,” wrote corresponding author Dr. Melanie Lyden.
Primary hyperparathyroidism causes high levels of calcium in the blood due to overproduction of parathyroid hormone and can lead to various health problems, including osteoporosis and cardiovascular complications. Surgery (parathyroidectomy) is the most common treatment.
Traditional preoperative imaging to locate abnormal glands may include ultrasound of the neck, SPECT/CT with iodine-123 sestamibi, and 4D CT. However, these three conventional imaging modalities are unable to achieve 100% accuracy in locating abnormal parathyroid glands, and their accuracy decreases significantly in the setting of reoperative parathyroidectomy where accurate localization is necessary for success. of the operation, the authors wrote.
In 2012, the Mayo Clinic received US approval for the use of C-11 choline PET for the restaging of biochemically recurrent prostate cancer and noted in case reports that the radiotracer of C-11 choline also appeared to accumulate in hyperfunctioning parathyroid cells. The group has since shown that the approach works well compared to standard imaging approaches in hyperparathyroid patients before surgery.
In this study, the group explored whether C-11 choline PET/CT is effective in patients in whom other approaches had failed to identify the disorder and who, perhaps as a result, underwent unsuccessful initial surgery.
Researchers looked at the outcomes of 43 patients who received C-11 choline PET/CT between 2017 and 2021 at the Mayo Clinic. Ultrasound, I-123 sestamibi, and 4D CT scans failed to localize the disorder in most patients, and 70% had previous operations at outside facilities. The C-11 choline radiotracer was produced in the hospital’s on-site cyclotron facility.
Of the 43 patients, 33 (77%) had positive C-11 choline PET/CT results, according to the results. Twenty-five patients were operated on and among these patients, 20 (80%) achieved intraoperative healing. Notably, 18 of the patients who underwent surgery (72%) had failed previous operations, the authors wrote. One patient had four prior failed operations and five patients had two prior failed operations.
Left is a C-11 choline PET/CT image used to identify a non-descended left parathyroid gland posterior to the submandibular gland; on the right, a comparative SPECT image which failed to identify the gland. Image reproduced with the kind permission of Operation.
Overall, in a highly selective cohort strongly geared towards patients with negative conventional imaging and failed surgery, imaging analysis showed that C-11 choline PET/CT achieved 64% sensitivity and a positive predictive value of 72%, the authors wrote.
“C-11 choline PET/CT is a useful adjunct for parathyroid localization in a complex patient population who have failed standard localization techniques which may include [ultrasound]I-123 sestamibi and/or 4D CT,” the authors wrote.
The authors noted several factors that may limit the widespread use of C-11 choline PET/CT. For one, C-11 choline has a short physical half-life of 20.4 minutes, which requires it to be produced and delivered locally. To date, including the Mayo Clinic, only Memorial Sloan Kettering and two non-academic centers offer C-11 choline PET/CT scans for primary hyperparathyroidism in the United States.
Second, the current cost of a C-11 choline PET/CT is nearly double that of I-123 sestamibi and SPECT/CT, although recent Medicare changes have reduced the cost to match to that of FDG PET/CT, the authors wrote.
Thus, it may be too early to suggest the routine inclusion of C-11 choline PET/CT imaging in the initial workup of primary hyperparathyroidism, they noted.
“However, it has shown promise as a powerful adjunct when conventional imaging modalities and exploratory operations have failed,” Lyden and colleagues concluded.
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