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

Aim: The aim was to assess the feasibility of 11C-5-hydroxy-tryptophan positron emission tomography (11C-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, 11C-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 11C-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%). 11C-5-HTP-PET depicted RTs after RFA with maximum sensitivity (100%) and specificity (100%), using radiological follow-up as the gold standard. 11C-5-HTP-PET detected five out of eight RTs earlier than CECT or CEUS. In general, the sensitivity of 11C-5-HTP-PET exceeded that of CECT and CEUS for early visualization of NET liver metastases. Conclusion: 11C-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.