| Objective:Lung cancer is one of the leading causes of death worldwide. About 80% percents of them are non-small cell lung cancer(NSCLC). It was found that about two third of those patients was too late to be on operation or intolerant of operation for their first visit to a doctor. Therefore, to improve the final outcomes, a reliable prognostic test is required to predict treatment response before its onset, to allow a more aggressive treatment strategy. A dual modality18F-FDG PET/CT allows the fusion of all diagnostic information from CT and PET scans with utmost accurate alignment, which helps to detect primary tumors and metastases by morphologic and functional characteristics. It has been used to evaluate focal pulmonary nodules and the stages of the lung cancer, and to detect a recurrent tumor. However, the potential of serial 18F-FDG PET/CT for being a prognostic factor has yet to be determined. The purpose of the present study was to evaluate if SUV was a significant predictor for local or regional recurrence, either before or after treatment. We also want to determine if the changes of SUV was a reliable predictor for prognosis. At the same time, we attempted to retrospectively determine a cut-off SUV to increase the accuracy in predicting prognosis in our study.Methods:This is a prospective study of 47 consecutive patients with locally advanced non small cell lung cancer (stageШA/ШB) who were treated with chemoradiotherapy in the department of radiotherapy of the Shandong Cancer Hospital and Institute from February 2005 to March 2006. All patients had at least two serial 18F-FDG PET/CT scans: one was performed before start of treatment (SUVbefore), and the other approximately 1-3 months after finishing of treatment (SUVafter). The maximum standardized uptake value(SUVmax)of the primary lung lesion was calculated in both pretreatment and post-treatment PET/CT to obtain the SUVbefore and SUVafter.. We also want to determine if the changes of SUV was a reliable predictor for prognosis. The value changes of SUV before and after treatment were calculated according to the following equation:△SUV=(SUVbefore-SUVafter)×100% / SUVbefore. We recorded the following variables: age, gender, histology type and clinical stage of all the patients. Follow-up examinations were planned their completion of therapy. Recurrence or metastasis was considered when there an abnormal finding suggesting recurrence or metastasis on serial imaging studies or pathologically confirmed malignancy. Statistical software (SPSS, version 11.0; SPSS Ins.) was used for the analysis. Logistic regression analysis was applied to assess the effects of the following variables: age, gender, histology type, clinical stage, SUVmax, and△SUV. The receiver operating characteristic(ROC) curve was constructed to determine an optimal cut-off value to differentiate different prognosis with the best trade-off between sensitivity and specificity.Results:After a median follow-up of 20.5 months, patients were classified into two categories: group A included the patients who had local and regional recurrence or metastasis. The other patients who had no local and regional recurrence or metastasis were group B. Before treatment, the SUV for group A and group B were 11.60±2.55,8.49±4.12 respectively, There was significant difference between the two groups (p =0.005). After treatment, the SUV for group A was 5.60±2.25 and for group B 2.79±0.86. Thus, the SUV was significantly lower in group B than those in group A (p =0.000); Also, the SUVmax were present in squamous cell carcinoma and adenocarcinoma. There were no significant differences between different histologies, either before treatment or after treatment in both group A and group B. The decreases in SUVmax between baseline and 1-3 months after completion of therapy were 52.56%±22.07% for group A . For group B, the decreases in SUVmax between baseline and 1-3 months after completion of therapy were 60.95%±19.64%.There was no significant difference between these two groups (p =0.155); Using the SUVmax of 8.5 as the cut-off for differentiating between the two groups, pretreatment PET/CT showed an overall sensitivity of 96% ,a specificity of 67%,a positive predictive value of 78%, a negative predictive value of 93% and an overall accuracy of 83%. The sensitivity,specificity,positive predictive value,negative predictive value and overall accuracy for post-treatment PET/CT scans were 73%,95%,86%,72% and 79% respectively when we used 4.5 as the cut-off; Logistic regression analysis was applied to assess the effects of the following variables: age, gender, histology type, clinical stage, SUVmax, and△SUV. SUVbefore and SUVafter were significant factors correlated with recurrence and metastasis(p1=0.003, p2=0.000). In contrast, histology,age,gender,stage and△SUV were not significant.Conclusions:18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) can measure and image the glucose metabolism quantitatively using 18F-FDG and may be more sensitive than CT because the alterations in tissue metabolism measured by PET generally precede anatomical changes .This study has shown that 18F-FDG PET/CT SUVmax was an important complementary prognostic factor for inoperable NSCLC patients and was useful in predicting the outcome of chemoradiotherapy in patients with locally advanced NSCLC. In this study, patients with high SUVs were observed to have a worse outcome. Quantitative evaluation of 18F-FDG PET/CT scans before and after treatment might help to determine the most appropriate treatment strategy, and consequently improve treatment efficiency. Due to the limited number of patients in this study, a clinical study with a larger group of patients is warranted.
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