[18f]fmiso pet in metastatic neuroendocrine tumours: a pilot study

Objective(s): the phenomenon of peripheral [68ga]dotatate avidity without central avidity (which we have termed a “donut) has been observed in neuroendocrine neoplasm (nen) lesions. there has been speculation as to whether this is due to hypoxia, de-differentiated disease or other causes. the presence of hypoxia may have prognostic and therapeutic implications, and was evaluated in these lesions using the pet hypoxia imaging biomarker [18f]fmiso.methods: prospective pilot study in patients with metastatic nens with at least one donut lesion (central [68ga]dotatate non-avidity). [18f]fdg and [18f]fmiso scans were acquired within 60 days of the [68ga]dotatate pet/ct. [18f]fmiso scans were acquired as a dynamic scan over 20 mins from injection with a delayed image at 2 hours. the dynamic acquisition was analysed quantitatively using a graphical approach yielding parametric images of influx rate constant and volume of distribution. [18f]fmiso uptake within the identified donut hole on the 2 hr delayed scan was qualitatively scored by two experienced nuclear medicine physicians as: 0 (no uptake), 1 (uptake less than normal liver), 2 (uptake equal to normal liver), or 3 (uptake greater than normal liver).results: ten patients were enrolled with primary sites including pancreas (n=3), small bowel (n=3), rectum (n=2), duodenum (n=1) and lung (n=1).  six subjects were scored 1, three subjects were scored 2, and one subject was scored 3. all lesions evaluated were located in the liver. quantitative [18f]fmiso parametric imaging showed evidence of increased uptake rate (ki) in the photopenic areas of the donut lesions in 8/10 subjects. surrounding uptake rate in normal liver was extremely low. in the qualitative delayed image assessment, only one subject demonstrated [18f]fmiso uptake greater than surrounding normal liver (small bowel primary, g2).conclusion: only one of ten patients with donut lesions demonstrated increased [18f]fmiso uptake rate on delayed static imaging. in contrast, dynamic imaging demonstrated increased [18f]fmiso uptake rate in the region of [68ga]dotatate photopenia on 8 of 10 patients. future research using [18f]fmiso in nen patients should incorporate dynamic imaging.