The Utility of Post-Treatment FDG PET/CT Metrics In the Evaluation of Head And Neck Squamous Cell Carcinoma

Abstract

18F-Fluorodeoxyglucose (FDG) positron-emission tomography–computed tomography (PET/CT) imaging is a valuable imaging procedure for tumour staging, restaging, assessing the response to therapy, and in follow-up surveillance among patients diagnosed with head and neck squamous cell carcinoma (HNSCC). While qualitatively assessing PET/CT images has become widely adopted, quantitative analyses have also been introduced to overcome several limitations of visual analysis, enabling a more objective and easier examination of inter- and intra-patient variations. This thesis presents research to investigate the role of FDG PET/CT quantitative metrics in HNSCC. A systematic review and three retrospective studies were undertaken to assess the utility of PET/CT quantitative metrics, including maximum standardised uptake value (SUVmax) and peak standardised uptake value (SUVpeak) derived at three months following the completion of chemoradiotherapy (CRT) in HNSCC. These studies confirmed the continuous use of the SUVmax in post-treatment HNSCC and developed further insights regarding the diagnostic and prognostic value of these metrics in this setting. It also provided more insight into the impact of utilising different body size metrics as well as relative metrics in SUV normalisation. Specifically, the systematic review aimed to evaluate the evidence base in the literature on the diagnostic performance and prognostic value of post-treatment FDG PET/CT metrics derived from primary tumour and lymph node sites to discriminate residual disease and predict survival outcomes in patients with HNSCC. This review revealed inconsistent results, requiring further investigation to determine the value of these metrics in the post-treatment setting. The first study aimed to identify the normalisation method that is least sensitive to body size measurements when reporting PET/CT parameters in patients with HNSCC. It was found that variations in body size might have a limited impact on those metrics; therefore, the use of any body size factors appears to be acceptable when analysing post-treatment FGD PET/CT quantitative metrics in HNSCC. The second study sought to assess the diagnostic performance of these quantitative metrics for distinguishing HNSCC residual disease. It was found that all metrics could discriminate between residual disease at the primary and nodal sites at certain thresholds. It was also found that the use of lean body mass (LBM) and body surface area (BSA), as well as a second normalisation of the FDG uptake in the background regions, did not improve their performance. Lastly, the third study investigated the prognostic utility of these quantitative metrics in predicting survival outcomes, as well as the effect of human papilloma virus (HPV) status on their prognostic value. Regardless of HPV status, post-treatment primary tumour and lymph node SUV metrics were found to be significant prognostic factors for predicting three-year progression-free survival (PFS). However, the analysis of five-year overall survival (OS) showed inconclusive findings. Overall, it was concluded that the use of either total body weight, LBM, or BSA in SUV normalisation is suitable for analysing post-treatment scans of HNSCC. This includes the evaluation of quantitative metrics for prognostication and discriminatory ability. Importantly, an increase in post-treatment SUVmax and SUVpeak values higher than the thresholds presented in this thesis, could potentially signify an augmented likelihood of disease progression. Patients with lesions exhibiting SUVmax and SUVpeak values that surpass the specified thresholds should thus be closely monitored.