Positron emission tomography (PET) with fluorine-18 fluorodeoxyglucose (FDG) is a very useful technique for the imaging of lymphomas in the adult population. It provides unique information about the behaviour of malignant cells and contributes to more accurate staging of the illness and better assessment of response to therapy. The purpose of this study was to evaluate the usefulness of FDG PET in childhood lymphoma compared with conventional imaging methods (CIMs) and clinical data. Between July 1998 and August 2001, 42 FDG PET examinations were performed using a dedicated PET system (27 examinations) or a hybrid coincidence PET system (15 examinations) for initial tumour staging ( n=7), restaging ( n=5) or assessment of response to therapy or residual masses ( n=30) in 27 children with Hodgkin's disease (HD) ( n=20) or non-Hodgkin's lymphoma (NHL) ( n=7). FDG PET results were compared with CIM findings and clinical data. Since 2000, a standardised questionnaire for evaluation of the clinical impact of FDG PET on both staging and therapy has been sent to the 16 referring physicians and 13 have replied. In all children, FDG PET was performed without any side-effects. FDG PET was found to be very sensitive (Se=12/12) for staging and restaging of the illness, showing more lesions than CIMs, with a 50% patient upstaging rate (6/12). It was very accurate for monitoring response to therapy and for characterisation of residual masses. False-positive results were observed in two NHL patients with thymic uptake and one false-negative result was obtained in a patient whose NHL relapsed 1 month after a negative FDG PET. The questionnaire emphasised the impact of FDG PET on clinical management, which was modified on the basis of the FDG PET results in 23% of patients. As previously demonstrated in the adult population, FDG PET appeared to be a very sensitive imaging technique for staging and restaging of lymphoma in children and was very useful for monitoring the response to therapy.

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-(18)F-fluoro-phenylalanine ([(18)F]FDOPA) by SCLC, based on comparison with the results of fluorine-18 fluorodeoxyglucose ([(18)F]FDG) positron emission tomography (PET) and standard imaging procedures. [(18)F]FDG PET and [(18)F]FDOPA PET were performed on four patients with newly diagnosed SCLC. There was agreement between the results of [(18)F]FDOPA PET and [(18)F]FDG PET in four tumoural sites out of 11, whereas [(18)F]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 [(18)F]FDG and [(18)F]FDOPA tumour uptake. The median [(18)F]FDG SUV(max) was 5.9 (with a 95% confidence interval from 4.4 to 9.2), while the median [(18)F]FDOPA SUV(max) was 1.9 (with a 95% confidence interval from 1.6 to 3.8). The difference between [(18)F]FDG SUV(max) and [(18)F]FDOPA SUV(max) was significant ( P<0.01). [(18)F]FDOPA PET appeared less sensitive than [(18)F]FDG PET and standard imaging procedures in the staging of SCLC. No clear relation between [(18)F]FDOPA uptake and positivity of neuroendocrine markers on immunohistochemistry emerged from these preliminary results; however, since [(18)F]FDOPA uptake may reflect better differentiation of the tumour, and possibly a better prognosis, this point warrants clarification in a larger study.

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For detection of recurrent colorectal carcinoma, a 2-D coincidence gamma camera with 19 mm thick crystals and optimized acquisition and reconstruction parameters provides similar results in terms of accuracy, both per patient and per site, to those of an Nal PET camera.