<sup>11</sup>C-Hydroxyephedrine Positron Emission Tomography in the Postoperative Management of Pheochromocytoma and Paraganglioma

<b><i>Aim:</i></b> Accurate detection of recurrent disease and restaging are essential in the postoperative surveillance of many patients with pheochromocytomas (PHEOs) and paragangliomas (PGLs). In this study, the impact of positron emission tomography (PET) and PET/computed tomography (CT) with ¹¹C-hydroxyephedrine (HED) was evaluated for the postoperative surveillance and diagnosis of recurrent disease and for functional monitoring of locoregional and systemic therapy. <b><i>Methods:</i></b> One hundred and eleven HED-PET and PET/CT examinations performed in 48 patients after surgical intervention for PHEO/PGL were analyzed retrospectively. In a subgroup of 16 patients who underwent systemic and locoregional therapies, the tracer uptake in tumors was also measured as the functional volume (FV), maximum standardized uptake value (SUV_max), mean SUV (SUV_mean) and as the total catecholamine transporter tumor volume (TCTTV) calculated as TCTTV = FV × SUV_mean. The PET imaging results were correlated with CT/magnetic resonance imaging findings and biochemical and clinical follow-up data. <b><i>Results:</i></b> In the first postoperative examination, HED-PET was positive in 24/48 and negative in 24/48 patients with no false-positive results, yielding 92.3% sensitivity and 100% specificity. For the 16 patients, there was a significant correlation between FV and SUV_max and SUV_max and TCTTV. TCTTV correlated significantly with plasma and urinary catecholamines. In 11/16 patients, SUV_max and TCTTV increased/decreased in parallel but not in the remaining 5 patients. <b><i>Conclusion:</i></b> HED-PET and PET/CT were found to be valuable in the postoperative follow-up in detecting recurrent and metastatic disease. In a subgroup of patients, functional monitoring of systemic and locoregional therapies was feasible by assessing the changes of the TCTTV, and therefore warrants further prospective evaluation.