Journal
JOURNAL OF NUCLEAR MEDICINE
Volume 62, Issue 5, Pages 628-635Publisher
SOC NUCLEAR MEDICINE INC
DOI: 10.2967/jnumed.120.247742
Keywords
lung cancer; radiotherapy; relapse; F-18-FDG PET/CT; F-18-FLT PET/CT
Funding
- Danish Cancer Society [R134-A8543-15-S42]
- Department of Clinical Physiology, Nuclear Medicine, and PET, Rigshospitalet, University of Copenhagen, Denmark
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Diagnosing relapse after radiotherapy for lung cancer is challenging. While F-18-FLT PET/CT demonstrated higher specificity for malignancy than F-18-FDG PET, the sensitivity was lower. The addition of F-18-FLT PET/CT improved diagnostic value, particularly after conventional fractionated radiotherapy.
Diagnosing relapse after radiotherapy for lung cancer is challenging. The specificity of both CT and F-18-FDG PET/CT is low because of radiation-induced changes. 3'-deoxy-3'-F-18-fluorothymidine (F-18-FLT) PET has previously demonstrated higher specificity for malignancy than F-18-FDG PET. We investigated the value of F-18-FLT PET/CT for diagnosing relapse in irradiated lung cancer. Methods: Patients suspected of relapse of lung cancer after definitive radiotherapy (conventional fractionated radiotherapy [cRT] or stereotactic body radiotherapy [SBRT]) were included. Sensitivity and specificity were analyzed both within the irradiated high-dose volume (HDV) and on a patient basis. Marginal differences and interobserver agreement were assessed. Results: Sixty-three patients who had received radiotherapy in 70 HDVs (34 cRT; 36 SBRT) were included. The specificity of F-18-FLT PET/CT was higher than that of F-18-FDG PET/CT (HDV, 96% [95% CI, 87-100] vs. 71% [95% CI, 57-83] [P 5 0.0039]; patient-based, 90% [95% CI, 73-98] vs. 55% [95% CI, 36-74] [P = 0.0020]). The difference in specificity between F-18-FLT PET/CT and F-18-FDG PET/CT was higher after cRT than after SBRT. The sensitivity of F-18-FLT PET/CT was lower than that of F-18-FDG PET/CT (HDV, 69% [95% CI, 41-89] vs. 94% [95% CI, 70-100] [P = 0.1250]; patient-based, 70% [95% CI, 51-84] vs. 94% [95% CI, 80-99] [P = 0.0078]). Adding F-18-FLT PET/CT when F-18-FDG PET/CT was positive or inconclusive improved the diagnostic value compared with F-18-FDG PET/CT alone. In cRT HDVs, the probability of malignancy increased from 67% for F-18-FDG PET/CT alone to 100% when both tracers were positive. Conclusion: F-18-FLT PET/CT adds diagnostic value to F-18-FDG PET/CT in patients with suspected relapse. The diagnostic impact of F-18-FLT PET/CT was highest after cRT. We suggest adding F-18-FLT PET/CT when F-18-FDG PET/CT is inconclusive or positive within the previously irradiated volume to improve diagnostic value in patients for whom histologic confirmation is not easily obtained.
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