PET/CT more accurate for selecting patients for radionuclide therapy

Metrics based on PET/CT imaging can identify neuroendocrine tumor patients who may benefit from peptide receptor radionuclide therapy (PRRT) better than traditional imaging-based scoring measures, according to a study published in the September issue of The Journal of Nuclear Medicine.

The Krenning score—a quantitative estimate of the expression of somatostatin receptors (SSTR) based on 111In-pentetreotide scintigraphy—typically guides patient selection for PRRT. Scores derived from PET/CT imaging, however, were “significantly” higher and more accurately detected neuroendocrine patients eligible for radionuclide therapy.

“In the past, physicians relied on 111In-pentetreotide imaging with planar scintigraphy and single photon emission computed tomography (SPECT) to determine whether or not a patient is eligible to receive 177Lu-dotate PRRT,” said Thomas A. Hope, MD, associate professor of radiology at the University of California, San Francisco, in a statement. “However, limited literature is available on the accuracy of PET/CT in determining 177Lu-dotate PRRT eligibility. Our study aimed to compare the Krenning scores derived from the various imaging modalities and assess the impact on treatment decision-making.”

Hope and colleagues included 150 patients with suspicion or biochemical evidence of neuroendocrine tumors in their study. Participants received both 68Ga-dotate PET/CT and 111In-pentetreotide imaging (planar scintigraphy and SPECT) within a week. Three physicians reviewed and graded the images, assigning each a Krenning score based on the lesion with the highest uptake; a consensus grade was given to each exam.

After comparing the Krenning scores to the volume and extent of tumor burden, lesion size and maximum standardized uptake value in each patient, the researchers found the detection rate of SSTR-positive disease was 23% for 111In-pentetreotide planar imaging, 38% for SPECT and 72% for 68Ga-dotate PET/CT.

“It is important for patients to realize, however, that although one may have a high Krenning score informed by 68Ga-dotate PET/CT, it does not always mean that 177Lu-dotate PRRT is appropriate as the next treatment,” the researchers concluded. “There is a great amount of work left in order to understand how to use 68Ga-dotate PET/CT to select patients for treatment moving forward.”