Added Value of SPECT/CT in Post Lu-177 Dotatate Treatment for Neuroendocrine Tumors

Objectives: The detection of NETs has been on the rise in the last 40 years with approximately 6/100,000 new cases per year and an estimated 103,312 cases in the United States (US). Theranostic approach using Ga-68 Dotatate (Ga-tate) for diagnosis and Lutetium-177 Dotatate (Lu-tate) for therapy is now FDA approved for detection and treatment of gastroenteropancreatic neuroendocrine tumors (GEP-NETs). The FDA guidelines for Lu-177 treatment are to give the same 4 doses of 200 mCi to every NET patient. The post therapy imaging of Lu-tate treatment using SPECT/CT is done in countries outside the US to examine the distribution of Lu-tate, confirm tumor targeting and help develop patient-tailored dose adjustment in future doses. However, post Lu-tate SPECT/CT is neither FDA required nor covered by insurance in the US. The objective of this study is to determine if SPECT/CT imaging for Lu-tate treatment adds value to the therapy patient.

Methods: For this study, literature on similar treatments was reviewed to compare how SPECT/CT imaging could add to the treatment with Lu-tate. SPECT/CT imaging on patients who have had Lu-tate treatment at a single institution was performed to assess potential impact on treatment protocol. A case study from this institution was reviewed to assess the added benefits of SPECT/CT post therapy imaging on a patient currently undergoing Lu-tate treatment. This institution has decided to perform same day imaging 4 hours post therapy and compare the post Lu-tate therapy SPECT/CT to baseline diagnostic Ga-tate PET/CT scan

Results: While reviewing the literature, it was found that there is no protocol for post Lu-177 therapy imaging in the US. However, outside the US the protocol is to image post therapy to help assess the distribution of Lu-tate to the NETs allowing for dosimetry analysis with SPECT/CT imaging at variable time points including 4, 24, 72 and 96 hours post Lu-tate therapy. At the observed case study from our local institution, comparing the 4 hours post Lu-tate SPECT/CT to the baseline Ga-tate PET/CT was very helpful to both the NM and the referring physicians as well as to the treated patient.

Conclusions: Imaging with SPECT/CT post therapy can give insight to the proper dosage for treatment while confirming the distribution of Lu-tate. While there are no guidelines in the US for post Lu-tate therapy SPECT/CT imaging, outside the US the protocol is to image post therapy to evaluate the dose of radiation that the tumor is absorbing versus the amount the organ at risk (i.e. kidney) is receiving. This protocol allows for a patient-tailored dose alteration of the Lu-tate to maximize treatment response and reduce radiation exposure to organ at risk.