NeoTect has long shown promise for evaluating the pulmonary arteries. Targeted to somatostatin receptors, the thallium-based probe seemed ideally suited to noninvasively differentiate benign from malignant solitary pulmonary nodules. The agent has not realized its original promise, however. Studies have shown that NeoTect scintigraphy generates sensitivity rates as high as 95% for this application, but its specificity is less impressive. While lung cancer cells have six times more somatostatin receptors on their surfaces than normal cells, other cell types have somatostatin receptors as well, so the specificity level for the standard clinical protocol falls in the low 70% range. As a result, acceptance has been limited.
A new, semiquantitative approach to measuring the effectiveness of NeoTect may come to the rescue. Developed in the nuclear medicine department at Brooke Army Hospital in San Antonio, the technique compares the scintigraphy activity in a region of interest (ROI) around the suspicious nodule and a corresponding region in the contralateral lung. Dr. Ryan T. Zucker, a former nuclear medicine fellow at Brooke, presented results of a study on the new protocol Thursday. The lesion is considered malignant when there is a positive ratio of more than two to one for the ROI around the lesion compared to the ROI around normal tissue.
A retrospective study was performed on 76 patients in whom CT had previously identified an indeterminate solitary pulmonary nodule. Exams were obtained on a dual-headed SPECT camera two to three hours after intravenous injection of 20 millicuries of technetium-99m-depreotide.
Whole-body planar imaging disclosed that 72 of the 76 patients had nodules. Thirty-eight of the masses had lesion to normal lung parenchyma ratios greater than two to zero. The findings were then confirmed using transthoracic needle biopsy, CT-guided biopsy, or thoracotomy at the time of surgery.
The new technique boosted the sensitivity of the test significantly, Zucker said. The protocol had a specificity rate of 97.2% and sensitivity rate of 91.4%. Its positive predictive value was 96.9%, and the negative predictive value was 92.1%. Its overall 94% accuracy rate stands up well against the 88% accuracy rate for FDG-PET.
"Given the results of our study, NeoTect may in the future become the new gold standard for evaluating indeterminate solitary pulmonary nodules," Zucker said.
