18F-FLT-PET/CT adds value to 18F-FDG-PET/CT for diagnosing relapse after definitive radiotherapy in patients with lung cancer. Results of a prospective clinical trial

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Diagnosing relapse after radiotherapy for lung cancer is challenging. The specificity of both CT and 2-deoxy-2-[18F]fluoro-D-glucose (FDG)-PET/CT is low due to radiation-induced changes. 3'-deoxy-3'-[18F]fluorothymidine (FLT)-PET has previously demonstrated higher specificity for malignancy than FDG-PET. We investigated the value of FLT-PET/CT for diagnosing relapse in irradiated lung cancer. Methods: Patients suspected for relapse of lung cancer after definitive radiotherapy (conventional fractionated radiotherapy (cRT) or stereotactic radiotherapy (SBRT)) were included. Sensitivity and specificity were analysed within the irradiated high-dose volume (HDV) and patient-based. Marginal differences and inter-observer agreement were assessed. Results: Sixty-three patients who had received radiotherapy in 70 HDVs (34 cRT; 36 SBRT) were included. The specificity of FLT-PET/CT was higher than FDG-PET/CT (HDV: 96% [87-100] vs. 71% [57-83]; P = 0.0039; patient-based (90 % [73-98] vs. 55% [36-74]; P = 0.0020)). The difference between specificity of FLT-PET/CT and FDG-PET/CT was higher after cRT compared with SBRT. Sensitivity of FLT-PET/CT was lower than FDG-PET/CT (HDV: 69% [41-89] vs. 94% [70-100]; P = 0.1250; patient-based: 70% [51-84] vs. 94% [80-99]; P = 0.0078). Adding FLT-PET/CT when FDG-PET/CT was positive or inconclusive improved diagnostic value compared with FDG-PET/CT only. In cRT-HDVs, the probability of malignancy increased from 67% for FDG-PET/CT alone to 100% when both PETs were positive. Conclusion: FLT-PET/CT adds diagnostic value to FDG-PET/CT in patients with suspected relapse. The diagnostic impact of FLT-PET/CT was highest after cRT. We suggest adding FLT-PET/CT when FDG-PET/CT is inconclusive or positive within the previously irradiated volume to improve diagnostic value in patients where histological confirmation is not easily obtained.

Original languageEnglish
JournalThe Journal of Nuclear Medicine
Volume62
Issue number5
Pages (from-to)628-635
Number of pages8
ISSN0161-5505
DOIs
Publication statusPublished - 2021

ID: 249787371