Predictive Value of Diffusion, Glucose Metabolism Parameters of PET/MR in Patients With Head and Neck Squamous Cell Carcinoma Treated With Chemoradiotherapy

Abstract

Purpose: This study aims to evaluate the predictive value of the pretreatment, metabolic, and diffusion parameters of a primary tumor assessed with PET/MR on patient clinical outcomes. Methods: Retrospective evaluation was performed using PET/MR image data sets acquired using the single tracer injection dual imaging of 68 histologically proven head and neck cancer patients 4 weeks before receiving definitive chemoradiotherapy (CRT). PET/MR was performed before the CRT and 12 weeks after the CRT for response evaluation. Image data (PET and MRI diffusion-weighted imaging [DWI]) was used to specify the maximum standard uptake value, the peak lean body mass corrected, SUV_max, the metabolic tumor volume, the total lesion glycolysis (SUV_max, SUL_peak, MTV, and TLG), and the mean apparent diffusion coefficient (ADC_mean) of the primary tumor. Based on the results of the therapeutic response evaluation, two patient subgroups were created: one with a viable tumor and another without. Metabolic and diffusion data, from the pretreatment PET/MR and the therapeutic response, were correlated using Spearman's correlation coefficient and Wilcoxon's test. Results: After completing the CRT, a viable residual tumor was detected in 36/68 (53%) cases, and 32/68 (47%) patients showed complete remission. However, no significant correlation was found between the pretreatment parameter, ADC_mean (p = 0.88), and the therapeutic success. The PET parameters, SUV_max and SUL_peak, MTV, and TLG (p = 0.032, p = 0.01, p < 0.0001, p = 0.0004) were statistically significantly different between the two patient subgroups. Conclusion: This study found that MRI-based (ADC_mean) data from FDG PET/MR pretreatment could not be used to predict therapeutic response although the PET parameters SUV_max, SUL_peak, MTV, and TLG proved to be more useful; thus, their inclusion in risk stratification may also be of additional value.

Keywords: ADC; MTV; PET/MR; SUV; TLG; clinical outcome; predictive value; squamous cell carcinoma.

Figure 1

Flowchart of excluded patients.

Figure 2

Axial Dixon fat suppressing (FS) T1-weighted turbo spin echo (TSE) sequence (A) used as an anatomical map. On the corresponding apparent diffusion coefficient (ADC)-map (B) the area of low signal intensity, epiglottic primary tumor's (left white arrow) mean ADC (ADC_mean: 777.5 + -42.2 10⁻⁶ s/mm²) delineated (with left green ellipse), and the metastasis of largest lymph node (right white arrow) on the left side of the neck.

Figure 3

Complete Remission (CR): sagittal PET (A₁), coronal (B₁), and axial (C₁) PET/MR images and axial MR-diffusion weighted imaging (DWI) apparent diffusion coefficient (ADC) map of the tumor (D₁) show the glottic tumor spread over the supra-, and infraglottic regions, pretreatment maximum of standardized uptake value (SUV_max): 14.12, peak lean body mass corrected SUV_max (SUL_peak): 8.93, total lesion glycolysis (TLG): 25.46, metabolic tumor volume: 2.97 cm³, mean ADC (ADC_mean): 867.22 + -53.52 × 10⁻⁶ s/mm². Post-treatment sagittal PET (A₂), coronal (B₂), and PET/MR and DWI ADC axial (D₂) images show complete remission (CR); without any pathologic FDG accumulation, and diffusion restriction on the observed volume.

Figure 4

Correlation plots (lower triangle), histograms (diagonal), and Spearman correlation coefficients in the upper triangle are shown in the plot-matrix of pretreatment maximum of standardized uptake value (SUV_max), peak lean body mass corrected SUV_max (SUL_peak), total lesion glycolysis (TLG), metabolic tumor volume (MTV), mean apparent diffusion coefficient (ADC_mean). The significance levels are denoted by stars (**p < 0.01, ***p < 0.001, no star: no significant).

Figure 5

Boxplots show the distributions of maximum of standardized uptake value (SUV_max) (A), peak lean body mass corrected SUV_max (SUL_peak) (B), total lesion glycolysis (TLG) (C), metabolic tumor volume (MTV) (D), mean apparent diffusion coefficient (ADC_mean) (E) parameters in the therapy response based subgroups, patients who achieve complete remission and non-complete remission. The p-value of the Wilcoxon rank-sum test is shown in the upper part of the plot.