![]() The majority of the patient’s lesions should have uptake greater than the liver background to be eligible for the therapy. The assessment of SSTR expression is based on 111In-pentetreotide (OctreoScan) gamma-camera and SPECT imaging or, preferably, 68Ga-DOTATATE PET imaging. Those in the Ki-67 range of 20% to 50% may have high-enough SSTR expression to warrant PRRT, while those above 50% generally do not. This is typically true for well-differentiated tumors ( 23, 24), which is why the NETTER-1 trial required patients to have either low- or intermediate-grade tumors (Ki-67 20%) are more variable in their SSTR expression. The therapy is most effective in patients who have high expression of SSTRs on their tumor cells ( 22). ![]() Tumor grade and SSTR density based on imaging are linked concepts. The worst outcomes were very small percentages of patients developing acute leukemia (<1%) or myelodysplastic syndrome (<2%), in the context of PFS of 29 months and overall survival (OS) of 63 months ( 17, 18). Lu-177) and low levels of significant toxicity otherwise, with the suggestion for individual predilections toward radiation ( 16). Recent publications from these groups focus on long-term tolerability and outcomes (again in larger groups of 400-800 patients), showing favorable toxicity profiles regarding the kidneys and bone marrow (with greater renal toxicity in those treated with Y-90 vs. (PFS), and low G3 and G4 toxicities ( 15). Follow-up studies in much larger (500-600 patients, but single institution) cohorts continued to show favorable outcomes with 30% objective response rates, 40-month progression-free survival There are still some areas that are struggling with the availability of Ga68-DOTATATE locally, or insurance denials, but these issues will become less in the future.Įven very early prospective studies on 177Lu-DOTATATE with only 35-50 patients showed partial response rates of 10% to 25%, as well as improvements in QoL measures in those with metastatic NET who were refractory to traditional therapies ( 13, 14). In fact, in all key aspects (resolution, imaging time, radiation dose, sensitivity, and resultant change in clinical management), 68Ga-DOTATATE is superior to 111In-pentetreotide and should, therefore, be used whenever possible. Aside from the improved resolution of positron emission tomography (PET) over planar as well as SPECT gamma camera imaging, the imaging protocol is also much more favorable as the whole-body scan is done at 60 min post injection. In June 2016, 68Ga-DOTATATE (NetSpot, Advanced Accelerator Applications ) was FDA approved, thereby providing a PET-imaging alternative to the long-used 111In-pentetreotide ( Figs. Three peptides based on this concept include DOTA-TATE, DOTA-TOC, and DOTA-NOC. The next generation of imaging agents used the positron-emitting isotope Gallium-68 ( 68Ga) bound to either octreotide or octreotate using the DOTA-linker ( 6). Even further delayed imaging is sometimes necessary and the patient is requested to have regular bowel movements during this time (with the use of over-the-counter laxatives if needed) to increase the specificity of the scan. The imaging protocol is somewhat cumbersome as the radiopharmaceutical injection is followed 24 and (often) 48 h afterward with whole-body planar imaging with or without SPECT/CT. ![]() In-111 allows for gamma-imaging and this has been the mainstay of nuclear imaging of NETs since the 1980s. Historically, the first approach to both nuclear imaging and therapy of NETs was with Indium-111 DTPA-octreotide (or In111-pentetreotide Octreoscan TM) ( 5).
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