RT Journal Article
SR Electronic
T1 <sup>18</sup>F-FLT PET/CT Adds Value to <sup>18</sup>F-FDG PET/CT for Diagnosing Relapse After Definitive Radiotherapy in Patients with Lung Cancer: Results of a Prospective Clinical Trial
JF Journal of Nuclear Medicine
JO J Nucl Med
FD Society of Nuclear Medicine
SP 628
OP 635
DO 10.2967/jnumed.120.247742
VO 62
IS 5
A1 Tine Nøhr Christensen
A1 Seppo W. Langer
A1 Gitte Persson
A1 Klaus Richter Larsen
A1 Annika Loft
A1 Annemarie Gjelstrup Amtoft
A1 Anne Kiil Berthelsen
A1 Helle Hjorth Johannesen
A1 Sune Høgild Keller
A1 Andreas Kjaer
A1 Barbara Malene Fischer
YR 2021
UL http://jnm.snmjournals.org/content/62/5/628.abstract
AB Diagnosing relapse after radiotherapy for lung cancer is challenging. The specificity of both CT and 18F-FDG PET/CT is low because of radiation-induced changes. 3′-deoxy-3′-18F-fluorothymidine (18F-FLT) PET has previously demonstrated higher specificity for malignancy than 18F-FDG PET. We investigated the value of 18F-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 18F-FLT PET/CT was higher than that of 18F-FDG PET/CT (HDV, 96% [95% CI, 87–100] vs. 71% [95% CI, 57–83] [P = 0.0039]; patient-based, 90% [95% CI, 73–98] vs. 55% [95% CI, 36–74] [P = 0.0020]). The difference in specificity between 18F-FLT PET/CT and 18F-FDG PET/CT was higher after cRT than after SBRT. The sensitivity of 18F-FLT PET/CT was lower than that of 18F-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 18F-FLT PET/CT when 18F-FDG PET/CT was positive or inconclusive improved the diagnostic value compared with 18F-FDG PET/CT alone. In cRT HDVs, the probability of malignancy increased from 67% for 18F-FDG PET/CT alone to 100% when both tracers were positive. Conclusion: 18F-FLT PET/CT adds diagnostic value to 18F-FDG PET/CT in patients with suspected relapse. The diagnostic impact of 18F-FLT PET/CT was highest after cRT. We suggest adding 18F-FLT PET/CT when 18F-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.