Preliminary retrospective investigation of FDG-PET/CT timing in follow-up of ablated lung tumor

The aim of this study was to clarify the most appropriate follow-up initiation time point for positron emission tomography (PET)/computed tomography (CT) following radio frequency ablation (RFA) of lung tumors, and the cutoff values of maximum standard uptake value (SUVmax) to evaluate local tumor progression. We enrolled 15 patients (8 men, median age 62 years) with 60 tumors, who were treated with RFA of lung tumors and underwent fluorodeoxyglucose (FDG)-PET/CT following RFA. Local tumor progression was assessed by periodic chest CT images prior to and following intravenous administration of a contrast medium. The SUVmax of three periods, namely, 0-3 months, 3-6 months, and 6-9 months after RFA, was evaluated. The appropriate time point for follow-up initiation and the cutoff value of SUVmax were determined using receiver-operating characteristic (ROC) analysis. The median follow-up period was 357 days. Of 60 tumors, 10 showed local progression. The area under the ROC curve (Az) for the 6-9 months (P=0.044) was the largest and almost equal to that of the 3-6 months (P=0.024). Az for the 0-3 months was the smallest and statistically insignificant (P=0.705). The cutoff value of 1.5 of SUVmax at 3-9 months after RFA showed 77.8% sensitivity and 85.7-90.5% specificity. The appropriate follow-up initiation time point is at least 3 months following RFA. Thus, SUVmax is a useful and reliable predictive indicator. (author)