Response Prediction Using<sup>18</sup>F-FAPI-04 PET/CT in Patients with Esophageal Squamous Cell Carcinoma Treated with Concurrent Chemoradiotherapy
Xinying Hu, Tao Zhou, Jiazhong Ren, Jinghao Duan, Hongbo Wu, Xiaoli Liu, Zhengshuai Mu, Ning Liu, Yuchun Wei, Shuanghu Yuan
Abstract
This prospective study examined whether imaging results obtained using the tracer <sup>18</sup>F-AlF-NOTA-fibroblast activation protein inhibitor (FAPI)-04 (denoted as <sup>18</sup>F-FAPI-04) in PET/CT can predict the short-term outcome in patients with locally advanced esophageal squamous cell carcinoma (LA-ESCC) treated with concurrent chemoradiotherapy (CCRT). <b>Methods:</b> The 18 enrolled LA-ESCC patients underwent <sup>18</sup>F-FAPI-04 PET/CT scanning before CCRT. The SUV<sub>max</sub>, SUV<sub>mean</sub>, SUV<sub>peak</sub>, metabolic tumor volume, and total lesion fibroblast activation protein expression of the primary tumor were recorded. Additionally, the SUV<sub>max</sub> of the primary tumor and SUV<sub>mean</sub> of normal tissue (muscle and blood) were measured, and their ratios were denoted as target-to-background ratios (TBR<sub>muscle</sub> and TBR<sub>blood</sub>). Patients were classified as responders or nonresponders according to RECIST (version 1.1), and variables were compared between the 2 groups. <b>Results:</b> The TBR<sub>blood</sub>, TBR<sub>muscle</sub>, and SUV<sub>mean</sub> were significantly higher in nonresponders than in responders (all <i>P</i> < 0.05). Receiver-operating-characteristic curve analysis identified TBR<sub>blood</sub> (area under the curve [AUC], 0.883; <i>P</i> = 0.008), TBR<sub>muscle</sub> (AUC, 0.896; <i>P</i> = 0.006) and SUV<sub>mean</sub> (AUC, 0.870; <i>P</i> = 0.010) as significant predictors of the response to CCRT, with cutoffs of 10.68, 10.95, and 6.88, respectively. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were also determined for TBR<sub>blood</sub> (100.0%, 72.7%, 66.7%, 88.9%, and 77.8%, respectively), TBR<sub>muscle</sub> (100.0%, 72.7%, 66.7%, 88.9%, and 77.8%, respectively), and SUV<sub>mean</sub> (85.7%, 81.8%, 75.0%, 90.0%, and 83.3%, respectively). On univariate logistic regression analysis, TBR<sub>blood</sub> (<i>P</i> = 0.026), TBR<sub>muscle</sub> (<i>P</i> = 0.036), SUV<sub>mean</sub> (<i>P</i> = 0.045), and tumor site (<i>P</i> = 0.032) were significantly correlated with the short-term outcome. On multivariable logistic regression analysis, TBR<sub>blood</sub> (<i>P</i> = 0.046) was an independent prognostic factor for short-term outcome. <b>Conclusion:</b> A higher baseline TBR<sub>blood</sub> on <sup>18</sup>F-FAPI-04 PET/CT scans was associated with a poor response to CCRT in LA-ESCC patients, and thus, TBR<sub>blood</sub> may be useful for screening LA-ESCC patients before CCRT treatment.