The purpose of this study was to evaluate the value of an (18)F-FDG PET/CT-based interpretation system (Hopkins criteria) to assess the therapy response and survival in lung cancer.
Methods: This is an Institutional Review Board-approved, retrospective study. A total of 201 patients with biopsy-proven lung cancer, who underwent therapy assessment (18)F-FDG PET/CT within 6 mo (mean, 7.5 wk) of completion of treatment, were included. Patients were primarily treated with surgical resection, chemotherapy, radiation therapy, or a combination of these treatments. PET/CT studies were interpreted by 2 nuclear medicine physicians, and discrepancies were resolved by a third interpreter. The studies were scored using a qualitative 5-point scale for the primary tumor, mediastinum, distant metastatic site, if present, and overall assessment. Scores 1, 2, and 3 were considered negative and scores 4 and 5 were considered positive for residual disease. Patients were followed for a median of 12 mo (up to 128 mo). Kaplan-Meier plots with a Mantel-Cox log-rank test were performed considering death as the endpoint.
Results: Overall, the PET/CT studies were positive in 144 (71.6%) and negative in 57 (28.4%) patients. There was substantial agreement between 2 interpreters (R1, R2), with a κ of 0.78 (P < 0.001). The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of the Hopkins scoring system were 89%, 80%, 92.8%, 71.4%, and 86.7%, respectively. Overall, PET/CT resulted in starting a new treatment plan in 70.8% of patients with positive residual disease on therapy assessment PET/CT. There was a significant difference in overall survival (OS) between patients who were categorized as positive in comparison to those who were categorized as negative (hazard ratio [HR] = 2.12; 95% confidence interval = 1.44-3.12), which remained significant after adjustment for disease stage, prior clinical suspicion, and primary treatment. Subgroup analysis according to the tumor histology showed that positive Hopkins scoring could significantly predict the OS in both small cell lung cancer (HR = 2.88; log-rank, P = 0.02) and non-small cell lung cancer (HR = 2.01; log-rank, P = 0.001). Similarly, there was a significant difference in OS between patients with positive and negative Hopkins score both in those who had surgical resection as part of the primary treatment (HR = 6.09; log-rank, P < 0.001) and in those who were treated with chemotherapy with or without radiation (HR = 1.60; log-rank, P = 0.02).
Conclusion: The 5-point qualitative therapy response interpretation for lung cancer has substantial interinterpreter agreement and high accuracy and could significantly predict survival in lung cancer, irrespective of tumor histology and treatment modality.
Keywords: PET/CT; lung cancer; survival; therapy assessment.
© 2016 by the Society of Nuclear Medicine and Molecular Imaging, Inc.