Abstract
Background: Neuro-endocrine tumor due to uncommon and multi-centric origin, pose a clinical challenge for their diagnosis and treatment. Developing countries where 68Ga-DOTA-TOC/NOC PET imaging is very limited and costly, 99mTc based SSR imaging can be used as the key tool for its diagnosis and assessment of therapy response. In this study we used two different 99mTc-octreotide radiopharmaceuticals designated as RP-1 and RP-2 for clinical assessment of somatostatin receptors imaging in histo-pathologically proven NET patients, and later the localization of 177Lu-DOTA-TATE which was synthesized manually using acetate buffer was evaluated. 99mTc- labeled RP-1 and RP-2 sensitivity, specificity; positive and negative predictive values were calculated and compared by SPECT/CT images for utilization in peptide receptor radionuclide therapy (PRRT).
Method: Sodium-pertechnetate was used for labeling of both radiopharmaceuticals while 177Lu(0.04 N HCl)DOTA-TATE was synthesized by 0.1M ammonium acetate/ascorbic acid. 75 patients of known primary NET imaging with RP-1 and RP-2 were evaluated for somatostatin receptor avidity and 3 were selected for PRRT. All images were correlated with either 68Ga-DOTA-TOC, (most of the patients) histopathology, CT and/or MRI reports.
Results: Out of 75, 39 patients were performed with RP-1, found 23 as true positive, 7 as true negative with sensitivity, specificity, PPV and NPV of 71.87%, 100%, 100% and 43.75%, whereas 36 images with RP-2, calculated 22 T/P, 6 as T/N, 8 as F/N, with 75.8%, 100%, 100% and 50%respectively. Their 177Lu-DOTA-TATE SPECT/CT revealed specific localization of therapeutic radionuclide.
Conclusion:99mTc-imaging of RP-2 as compared to RP-1 had better efficiency and sensitivity and can be used as an alternate of 68Ga-DOTA/TOC PET imaging.

Key words: 177Lu-DOTA-TATE, 99mTc-HYNIC-TATE/HYNIC-TOC, 99mTc base somatostatin receptor diagnostic agent, Peptide Receptor Radionuclide Therapy, comparative assessment of 99mTc-Octreotide.