Ga-68 Dotatoc versus In-111 Ocreotide.

Aim: This abstract aims to evaluate whether Ga-68 dotatoc is, in fact, a more comprehensive and accurate study for detecting neuroendocrine tumors versus the more familiar method, In-111 octreotide scan. Both radiopharmaceuticals are used to localize, diagnose, and follow patients with neuroendocrine tumors (NETs). NETs are rare tumors found in neuroendocrine cells that can spread throughout the body. If caught in the early stages, NETs may be curable. Overall survival rate usually varies depending on the stage or grade. Ga-68 dotatoc localizes in tumors by receptor binding. It has a half-life of just 68 minutes with an energy of 511 KeV. The typical dose is 4-6 mCi. IV with uptake of approximately 45 minutes to 1 hour. The patient is positioned supine, head first, and imaged skull base to thigh. Ga-68 dotatoc is an extremely useful radiopharmaceutical because of the rapid isotope localization, quick scanning time of 20-25 minutes, and the short half-life. In-111 octreotide has a half-life of 67 hours and an energy of 171 KeV and 245 KeV. The recommended dose of In-111 octreotide is approximately 6 mCi IV. The patient returns 4 hours later for imaging. The first set of whole-body images take approximately 20 - 30 minutes. After these images are acquired, SPECT imaging is often required which takes an additional 20 - 30 minutes. The patient returns in 24 hours for the same set of pictures including SPECT. If high intestinal activity is detected on the first set of images, the patient may be asked to take a mild laxative before they go to bed to reduce interfering activity on the 24-hour images. If high background persists, the patient may need to return for 48-hour imaging and SPECT. Ga-68 dotatoc has many advantages over In-111 octreotide imaging. Ga-68 dotatoc is extremely quick because the patient is injected and imaged within an hour. The complete test is over within 2 hours. With In-111octreotide, localization of the radioisotope is slow, multiple images must be acquired up to 24 and even 48 hours, delaying time to final results and diagnosis. A disadvantage of Ga-68 dotatoc is that it is more expensive. Both Ga-68 dotatoc and In-111 octreotide imaging are clinically useful for detecting neuroendocrine tumors. However, Ga-68-dotatoc, as PET tracer, has been shown to be more accurate with higher sensitivity (96% vs. 86%) and specificity (93% vs 50%) than In-111 octreotide. Subject 1: 57-year-old patient with ileal carcinoid, status post-surgery, radiation therapy for metastases in the breast and left femur, rising serotonin.References: (For Picture) Graham MM, Gu X, Ginader T, Breheny P, Sunderland JJ. 68Ga-DOTATOC Imaging of Neuroendocrine Tumors: A Systematic Review and Metaanalysis. 2017;58(9):1452-1458.

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