Pre-treatment FLT-PET parameters as a prognostic tool for patients with locally advanced recurrent nasopharyngeal carcinoma salvaged by carbon-ion radiotherapy: a pilot study

BACKGROUND: Although carbon-ion radiotherapy (CIRT) may improve outcome for patients with locoregionally recurrent nasopharyngeal carcinoma (LR-NPC), local progression still remains one of the major failure patterns. This suggests an unmet need of markers for predicting disease control after re-irradiation and potentially guiding tailored treatment. The purpose of this study was to explore the predictive value of pre-treatment 3’-deoxy-3’-[(18)F]fluorothymidine (FLT)-positron emission tomography (PET) for patients with locally advanced LR-NPC. METHODS: In this retrospective analysis, LR-NPC patients with locally advanced stage (stage III/IV) who received pre-treatment FLT-PET between June, 2015, and August, 2017, were retrospective reviewed and included in this study. OS and local progression-free survival (LPFS) were calculated using the Kaplan-Meier method. Univariable and multivariable Cox regression analyses of LPFS were performed. FLT-derived parameters, including SUV(max), metabolic tumor volume (MTV), and total lesion thymidine (TLT) were examined. The relationship between FLT-derived parameters and mucosal necrosis was tested by the Wilcoxon test. RESULTS: A total of 27 patients with a median follow-up of 31.3 months were included in this analysis. The 2-year OS and LPFS rates were 85.2% and 47.9%, respectively. In multivariable analysis, except for TLT-40% (P=0.059), all pre-treatment MTVs (P=0.040 for MTV-40%; P=0.021 for MTV-50%; P=0.026 for MTV-60%) and TLTs (P=0.043 for TLT-50%; P=0.048 for TLT-60%) were significantly related to LPFS. Moreover, MTVs and TLTs with various boundaries (except for MTV-40%) were also associated with the development of mucosal necrosis after CIRT. CONCLUSIONS: In the current study, a significant association between pre-treatment FLT-PET and LPFS was observed in patients with locally advanced LR-NPC. Further investigations are warranted to confirm the predictive role of FLT-PET.