11C-5-hydroxytryptophan positron emission tomography after radiofrequency ablation of neuroendocrine tumor liver metastases

• Aim: The aim was to assess the feasibility of C-11-5-hydroxy-tryptophan positron emission tomography ( C-11-5-HTP-PET) in the follow-up after radiofrequency ablation (RFA) of liver metastases from neuroendocrine tumors (NETS). Background: Contrast-enhanced computed tomography (CECT) and contrast-enhanced ultrasound (CEUS) are commonly used to evaluate the liver after RFA of NETs. In general, C-11-5-HTP-PET is more sensitive in the visualization of NETs, but no studies have investigated its role after RFA.Methods: Six consecutive patients with liver metastases from NETs were subjected to RFA treatment. All patients underwent baseline imaging before RFA and on two occasions (1-2 and 6-11 months) after RFA. The imaging consisted of C-11-5-HTP-PET, CEUS and CECT on all three occasions.Results: Thirty RFA areas were evaluated, and residual tumors (RTs) were depicted in eight areas (22%). C-11-5-HTP-PET depicted RTs after RFA with maximum sensitivity (100%) and specificity (100%), using radiological follow-up as the gold standard. C-11-5-HTP-PET detected five out of eight RTs earlier than CECT or CEUS. In general, the sensitivity of C-11-5-HTP-PET exceeded that of CECT and CEUS for early visualization of NET liver metastases.Conclusion: C-11-5-HTP-PET can be used in the follow-up after RFA for the purpose of detecting RT, and it provides additional information to CEUS and CECT by detecting new lesions.

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