• Anni Gålne, Helen Almquist, Martin Almquist, Cecilia Hindorf, Tomas Ohlsson, Erik Nordenström, Anna Sundlöv, and Elin Trägårdh.
• Department of Medical Imaging and Physiology, Skåne University Hospital, Lund and Malmö, Sweden anni.galne@med.lu.se.
• J. Nucl. Med. 2019 Dec 1; 60 (12): 1717-1723.

AbstractPatients with neuroendocrine tumors (NETs) are often treated with somatostatin analogs (SSAs) for control of symptoms and tumor growth. Such therapy could theoretically lead to misinterpretation of somatostatin receptor imaging with 68Ga-DOTATATE PET/CT by interfering with tracer-receptor binding. Guidelines recommend an interval of 3-4 wk between the last dose and imaging. The aim of this study was to evaluate if long-acting (LA) SSA treatment changes the uptake of 68Ga-DOTATATE in patients with NETs. Methods: From 2013 to 2016, 296 patients with, or under evaluation for, NETs were included in this prospective observational study. The effect of LA SSA on tracer uptake was evaluated in 2 main patient populations: those undergoing 68Ga-DOTATATE PET/CT before starting LA SSA treatment and at least once afterward, and those receiving ongoing LA SSA therapy, in whom the effect of the interval between the last dose of LA SSA and the PET/CT exam was analyzed. A third, explorative, analysis was performed to evaluate if clinical disease progression, regression, or stable tumor status changed the uptake of 68Ga-DOTATATE. In the 3 analyses, measurements of SUVmax in normal liver and tumor lesions were compared. Results: The median SUVmax in normal liver was significantly higher before treatment (8.6; interquartile range, 7.4-10.2) than after treatment initiation (6.0; 4.7-8.0) (P < 0.001). No significant changes in SUVmax were seen in tumor lesions after treatment initiation. No significant differences in SUVmax were found in normal liver or tumor lesions dependent on the interval between last dose of LA SSA and PET/CT. Conclusion: Treatment with LA SSA does not change SUVmax in tumor lesions, whereas SUVmax in normal liver is significantly lower after treatment. The findings have implications for interpretation of 68Ga-DOTATATE PET/CT for response assessment after SSA therapy and for guidelines on discontinuation of treatment before PET/CT.© 2019 by the Society of Nuclear Medicine and Molecular Imaging.

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