Use of 18F-FDG-PET-CT for Assessment of Response to Neoadjuvant Chemotherapy in Children With Wilms Tumor.

PURPOSE: The aim of this study was to evaluate the predictive value of fluorine-18-fluorodeoxyglucose positron emission tomography with computed tomography (F-FDG-PET-CT) in the assessment of histologic response to neoadjuvant chemotherapy in children with Wilms tumors (WTs). MATERIALS AND METHODS: We prospectively registered 12 patients with WTs who were treated with 2 cycles of neoadjuvant chemotherapy and surgery. All patients underwent sequential F-FDG-PET-CT before (PET-CT1) and after (PET-CT2) neoadjuvant chemotherapy. Maximum standardized uptake value (SUVmax) was measured on PET-CT1 (SUV1) and PET-CT2 (SUV2). The percentage change in SUVmax (SUVmax reduction) was calculated. After surgery the effects of neoadjuvant chemotherapy were graded histopathologically: ≥90% necrosis indicated a good response and <90% necrosis was considered a poor response. The correlation between SUVmax reduction and histologic response was estimated using the Spearman correlation coefficient. RESULTS: Among the 12 patients who underwent PET-CT before and after chemotherapy, SUVmax reduction was significantly different between the good response group and the poor response group (P=0.035). A significant, in terms of P value, correlation was found between pathologic response and SUVmax reduction (r=0.700; 95% confidence interval, 0.060-0.935; P=0.011). A threshold of 66% reduction in SUVmax was identified, with which partition, there were 8 good histologic responders (≥66% decrease in SUVmax) and 4 poor responders. The histologic complete response rate of the good responders was 87.5%, whereas that of poor responders was 0%. SUV1≥7 and SUV2≥2.4 were both considered to be with high risk of recurrence. In patients with SUV1≥7, 4/5 cases relapsed and 4/6 patients with SUV2≥2.4 relapsed. CONCLUSIONS: As there seems to be a good correlation of changes in SUVmax and histologic response, PET-CT has the potential of predicting the response to neoadjuvant chemotherapy in children with WT. SUV1 and SUV2 by themselves might be a good prognosticator of the clinical outcome of WT pediatric patients treated with International Society of Pediatric Oncology protocols, although the reduction rate of SUVmax is much less powerful for prognosis.