FDG PET and evaluation of posttherapeutic residual tumors in pediatric oncology: preliminary experience.

INTRODUCTION: Residual masses are an important problem in oncology. The determination of their nature (fibrosis or active tumor) is crucial. The place of 18F-fluorodeoxyglucose -positron emitting tomography (PET) as a new imaging device remains to be determined in this context. OBJECTIVES: To evaluate the place of 18F-fluorodeoxyglucose -PET in the prediction of the nature of residual masses in children with solid tumors. PATIENTS AND METHODS: Between January 2004 and January 2006, 238 PETs were performed in children followed up in the pediatric oncology and hematology departments. This was a monocentric retrospective review of the medical files of 18 children, in whom the main objective of the PET was to evaluate a residual mass. The sex ratio was 1/5; the median age 100 months (range, 34 to 180 mo). The underlying diseases were Hodgkin disease (n=5), lymphomas (n=5), osteosarcomas (n=3), rhabdomyosarcomas (n=2), and others (n=3). The final diagnostic (remission or persistent disease) was given by follow-up (median, 18 mo; range, 18 to 40), together with clinical, radiologic, and biopsy (in 6 cases) data. RESULTS: PET was negative in 13 cases and positive in 5, among them 4 patients relapsed. Among the 13 negative PETs, there was 1 relapse and 12 remissions. The respective value of PET sensibility and specificity were 0.8 and 0.92, respectively. Positive and negative predictive values were 0.8 and 0.92, respectively. CONCLUSION: On the basis of these preliminary results, PET seems to be an interesting tool to assess the nature of posttherapeutic residual masses in children, regardless of the underlying malignancy. Its role needs to be confirmed and further explored by multicentric studies tailored according to the underlying disease.

Comparison between PET and PET/CT in recurrent head and neck cancer and clinical implications.

The aim of this retrospective study was to compare the diagnostic accuracy between positron emission tomography (PET) and combined PET/computed tomography (PET/CT) in the detection of recurrent head and neck squamous cell carcinoma (HNSCC) and to evaluate the degree of interobserver agreement. Thirty-two patients who had undergone curative treatment for HNSCC and who presented with a suspicion of recurrent local disease were studied with fluoro-2-deoxy-D-glucose (FDG)-PET imaging. All patients had undergone an inconclusive conventional workup (nasofibroscopy, CT scan and/or MRI). PET and PET/CT were reviewed by two nuclear medicine physicians independently. Performances of PET and PET/CT were compared using biopsy and/or clinical follow-up of at least 8 months as gold-standard. ROC curves were employed for statistical analysis. Out of 32 patients, 18 (56%) had a local recurrence. Intraclass correlation coefficients were strong (>90) and statistically significant (P < 0.0001) for the two reviewers in all cases. The sensitivity, specificity and accuracy of PET were found to be 94%, between 36 and 50% and between 69 and 75%, respectively, depending on the consideration of equivocal cases. Results for PET/CT were found to be 94, 57 and 78%. The utility scores of PET and PET/CT were 0.72 and 0.78, respectively. PET/CT could have a direct impact on patient care with the avoidance of 8/14 (57%) unnecessary invasive procedures (panendoscopy under general anaesthesia). Combined PET/CT is more accurate than PET alone for detection of recurrent HNSCC. The findings of this study are reinforced by the strong interobserver agreement in the interpretation of the results.

Positron emission tomography with [(18)F]FDOPA and [(18)F]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-(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.