Patients
Between June 10, 2015, and Dec 28, 2016, a total of 38 patients with unresectable stage III NSCLC were enrolled in the study. This prospective study was approved by the local ethics committee of Shandong Cancer Hospital and Institute, and each patient gave written and informed consent before inclusion in the study. All patients were treated in Shandong Cancer Hospital and met the following criteria: (1) NSCLC diagnosed by histological and imaging examination such as CT or 18F-fluorodeoxyglucose (FDG) PET/CT; (2) Eastern Cooperative Oncology Group (ECOG) score ≤1; (3) clearly measurable metastatic lymph nodes and primary tumors (RECIST); and (4) age >18 years. All patients were ready to undergo 18F-Alfatide Ⅱ PET/CT before chemotherapy or radiotherapy.
Radiotracer preparation
A simple lyophilized kit for labeling with PRGD2 peptide was purchased from the Jiangsu Institute of Nuclear Medicine, and the synthesis process was carried out as described in a previous study [12]. The radiochemical purity of the 18F-alfatide Ⅱ exceeded 99%, and its specific radioactivity exceeded 37 GBq (1,000 mCi)/μmol.
PET/CT scanning
Patients were given an intravenous injection of 4.81 MBq/kg (0.12 mCi/kg) 18F-alfatide Ⅱ and rested for about 60 minutes. Patients were not asked to fast or to confirm blood glucose levels. Scanning was performed with an integrated in-line PET/CT system (GEMINI TF Big Bore; Philips Healthcare). PET images were obtained from the head to the thigh, and the spiral CT component was performed with an X-ray tube voltage peak of 120 kV, 300 mAs. A full-ring dedicated PET scan of the same axial range followed. The patients continued normal shallow respiration during image acquisition. The images were attenuation-corrected with the transmission data from CT. The attenuation-corrected PET images, CT images, and fused PET/CT images, displayed as coronal, sagittal, and trans axial slices, were viewed on a MEDEX workstation (Beijing, China).
Image analysis
Two experienced nuclear medicine physicians assessed the 18F-alfatide Ⅱ PET/CT images visually, referring to PET fusion and CT images, until consensuses were reached. Acquired 18F-alfatide Ⅱ PET/CT data were transferred to the workstation in the DICOM format. The radiotracer concentration in the region of interest (ROI) was normalized to the injected dose per kilogram of each patient’s body weight to derive the standardized uptake values (SUVs). The SUVs were calculated according to the following formula: [measured activity concentration (Bq/ml) × body weight (g)]/injected activity (Bq).
PET/CT parameters, such as maximum SUV for primary tumor (SUVP) or metastatic lymph node (SUVLN), were generated using a vendor-provided automated contouring program. In addition, the maximal activity of 1 cm³ within the aortic arches was measured. Then the SUV ratios for primary tumor to aortic arches, metastatic lymph node to aortic arches, and primary tumor to metastatic lymph node were calculated, and denoted as TBRP, TBRLN, and T/LN, respectively.
Chemoradiotherapy
Patients were treated with two cycles of chemotherapy, followed by CCRT. Two additional cycles of chemotherapy were needed every 3 weeks after radiotherapy. An intensity-modulated radiotherapy technique (IMRT) or three-dimensional conformal RT (3D-CRT) was delivered to all patients with megavoltage equipment (6 MV). Radiotherapy was given as the conventionally fractionated regimen, 180–200 cGy for 5 days per week, and the total dose administered to patients ranged from 5040–6600 cGy (median dose, 6000 cGy). The chemotherapy administered was the cisplatin/docetaxel or cisplatin/pemetrexed regimen.
Response evaluation and survival assessments
Short-term outcome was assessed at 4 weeks after CCRT according to the revised RECIST criteria (v.1.1). According to the RECIST criteria, responders included patients with an outcome of complete response (CR) or partial response (PR), and patients who had an outcome of stable disease (SD) or progressive disease (PD) were classified as the non-responders.
PFS and OS were assessed for all NSCLC patients according to the RECIST criteria. OS and PFS were estimated from initiation of chemotherapy to death (for OS) and to progression or death (for PFS). Patients were followed up by enhanced CT every 6 weeks during treatment, every 2 months in the first year after treatment, and every 6 months from the second year after treatment.
Statistical analysis
Statistical analysis was performed using IBM SPSS Statistics for Windows version 20.0 (IBM, Armonk, NY, USA). Quantitative data for SUVP, SUVLN, T/LN, TBRP and TBRLN were expressed as mean ± standard deviation or median (range). Two-sample t test and Wilcoxon rank-sum tests were used to compare the PET/CT parameters between responders and non-responders. PET/CT parameters were tested by logistic regression analyses to identify the relationships between these variables and short-term outcomes or survival. Receiver-operating characteristic (ROC) curve analysis was used to determine the thresholds with the maximum Youden index as well as the predictive accuracy of 18F-Alfatide II PET/CT parameters for treatment response and survival. Both PFS and OS were assessed by Kaplan–Meier analysis. All tests were two-sided, and P<0.05 was considered statistically significant.