Positron emission tomography with [¹⁸F]FDOPA and [¹⁸F]FDG in the imaging of small cell lung carcinoma: preliminary results

Small cell lung carcinomas (SCLC) express neuroendocrine markers, and dihydroxyphenylalanine (DOPA) is known to accumulate in neuroendocrine tumours. This study was performed with the aim of evaluating the uptake of 3,4-dihydroxy-6-¹⁸F-fluoro-phenylalanine ([¹⁸F]FDOPA) by SCLC, based on comparison with the results of fluorine-18 fluorodeoxyglucose ([¹⁸F]FDG) positron emission tomography (PET) and standard imaging procedures. [¹⁸F]FDG PET and [¹⁸F]FDOPA PET were performed on four patients with newly diagnosed SCLC. There was agreement between the results of [¹⁸F]FDOPA PET and [¹⁸F]FDG PET in four tumoural sites out of 11, whereas [¹⁸F]FDG PET and standard imaging procedures were in full agreement. A semi-quantitative analysis based on standardised uptake values (SUVs) was performed in order to compare [¹⁸F]FDG and [¹⁸F]FDOPA tumour uptake. The median [¹⁸F]FDG SUV_max was 5.9 (with a 95% confidence interval from 4.4 to 9.2), while the median [¹⁸F]FDOPA SUV_max was 1.9 (with a 95% confidence interval from 1.6 to 3.8). The difference between [¹⁸F]FDG SUV_max and [¹⁸F]FDOPA SUV_max was significant (P<0.01). [¹⁸F]FDOPA PET appeared less sensitive than [¹⁸F]FDG PET and standard imaging procedures in the staging of SCLC. No clear relation between [¹⁸F]FDOPA uptake and positivity of neuroendocrine markers on immunohistochemistry emerged from these preliminary results; however, since [¹⁸F]FDOPA uptake may reflect better differentiation of the tumour, and possibly a better prognosis, this point warrants clarification in a larger study.