Diagnostic impact of additional O-(2-[18F]fluoroethyl)-L-tyrosine (18F-FET) PET following immunotherapy with dendritic cell vaccination in glioblastoma patients

Objective: Vaccination therapy using tumour antigen-loaded, autologous dendritic cells (DC) is a promising therapeutic approach alongside standard treatment for glioblastoma (GBM). However, reliable diagnostic criteria regarding therapy monitoring are not established. Here, we analysed the impact of additional F-18-fluoroethyl-tyrosine positron emission tomography (F-18-FET PET) imaging following DC vaccination therapy. Methods: We analysed data of GBM patients who received DC vaccination therapy. Following MRI diagnosis of tumour recurrence, additional static and dynamic F-18-FET PET imaging was performed. Vaccination was performed five times by intradermal injections, either weekly between concomitant radio/-chemotherapy and intermittent chemotherapy or after tumour recurrence, before re-radiation therapy. MRI and F-18-FET PET results were compared and correlated with clinical data. Results: Between 2003 and 2016, 5 patients were identified who received DC vaccination and F-18-FET PET imaging (1 female/4 males; mean age: 44 +/- 14 y). 3/5 patients showed congruent results of tumour progression. In three patients F-18-FET PET indicated treatment related changes, which was in contrast to MRI findings that indicated tumour progression. In these patients F-18-FET PET results could be confirmed by either neuropathological diagnosis or according to the RANO criteria Conclusions: Despite the small patients number our results indicate an additional impact of F-18-FET PET for monitoring outcome following vaccination therapy.