¹⁸F-FDG PET/CT In Delineating The Gross Target Volume And Early Evaluation Of Radiotherapy Response In Patients With Esophageal Carcinoma

Objective To evaluate 18F-fluorodeoxyglucose(FDG) PET/CT in delineating the gross target volume(GTV) of and early assessment of radiotherapy response in patients with esophageal carcinoma.Method PartⅠSixteen patients with nasopharyngeal carcinoma undergoing precise radiotherapy were recruited. The diagnosis of all cases was confirmed with cytology or histology. before radiotherapy delivery, 18F-FDG PET/CT scan was performed. Images were coregistered and transferred to Philips Pinnacle3 planning system for contouring. One radiation oncologists,one nuclear medicine physician and one radiaotherapy engineer defined the GTV by visualization independently. The GTV was defined according to CT image alone (GTV(CT)) and PET/ CT images (GTV(PET/CT)) respectively. The GTV include the primary tumor of esophagus (GTVt) and metastatic lymph nodes (GTVn ).The GTV defined with different image modalities and by different persons was compared using SPSS 13.0 statistic software.PartⅡSixteen patients with esophagus carcinoma during three-dimensional conformal radiotherapy were enrolled into the study from Mon. 2009 to Jan.2010. 18F-FDG PET/CT imaging were performed at one week before radiotherapy, during radiotherapy(DT 50Gy/25F, the fifth week),within one week after radiotherapy(DT 60Gy/35F, the sixth week)and one month after radiotherapy, respectively. The maximum standard uptake value (SUVmax) and SUV decline percentage was calculated according to 18F-FDG PET/CT imaging . Comprehensive evaluation of radiotherapy response was performed one month after radiotherapy.Results PartⅠFirstly, on the whole, GTV(PET/CT) was significantly larger than GTV(CT) .Secondly, there was a significant change of GTV contoured between CT and PET/CT image modilities. Thirdly, there was no statistically significant difference of GTV defined by different contourers, but the variability of GTV defined by PET/CT was smaller than CT.PartⅡThe clinical response was obtained for 16 patients based on clinical examination and CT after the completion of radiotherapy . There were 4 patients with CR(complete remission), 9 with PR(partial remission) and 3 with NR(no change) .The mean SUVmax before radiotherapy, in mid radiotherpy and after radiotherapy was 14.9±6.8, 5.6±2.9 and 3.2±1.6, respectivelly. There was a sgnificant decline.(F=31.55,P<0.001). In the patients with clinical CR the mean SUVmax before radiotherapy was 22.4±6.6, that in mid radiotherapy was 4.7±2.6, that after radiotherapy was 2.6±0.6. In the patients with PR the mean SUVmax before radiotherapy was 11.7±5.3, that in mid radiotherapy was 6.4±3.2,and after radiotherapy was 3.3±1.8. In the NR group ,the mean SUVmax before radiotherapy was 14.8±3.2, that in mid radiotherapy was 4.2±2.2,and that after radiotherapy was 3.7±2.2.There was significant differences in mean SUVmax before radiotherapy among the patients with clinical CR,PR and NR(F=5.012,P=0.026);while the mean SUVmax in mid and after radiotherpy among the CR,PRand NR group had no statistic difference(F=0.846,P=0.451,F=0.448,P=0.0648).Conclusions 18F-FDG PET/CT may more accurately guide GTV contouring in patients with esophageal carcinoma. Moreover, the variability of GTV contoured with PET/CT between observers may be smaller. PET/CT image may improve the overall accuracy and precision of GTV delineation in patients with esophageal carcinoma. 18F-FDG PET/CT may early detect radiotherapy response of esophageal carcinoma and help to decide the following treatment plan. It may provide valuable information for planning radiotherapy. With the limitation of relatively short follow-up period in this study , a larger sample of cases and longer follow-up remain to be investigated.