## 4 Discussion  
Quantitative DWI and DCE-PWI analyses may portend the efficacy of CRT and early identification of potential treatment failure, resulting in an improvement in cancer management. In the current study, the quantitative analysis with DWI sequences allowed a reliable tumor assessment during the treatment phase. A low increase in ADC\({}_{\text{post-pre}}\) and ADC\({}_{\text{post-pre}}\) values was indicative of a high risk of residual cancer as directed by [PERSON] et al. [26]. ADC\({}_{\text{post/muscle post}}\) values \(>\) 0.85 and hypointense SI on DWIb800 images strongly correlated with post-CRT changes. Most of our patients with post-CRT changes (27/32, 84.3%) showed K(trans)\({}_{\text{post/pre/muscle}}\) values significantly lower (\(<\)0.85, 19 patients) or higher (\(>\)1.20, 8 patients) than all 5 patients with tumor persistence/recurrence. As for DWI [7], the aforementioned variations of DCE-PWI values could reflect the different tissue components, mainly fibrotic (Figure 3) or inflammatory (Figure 4) alterations, of post-treatment changes. Figure 2: Box plot for post-treatment residual tissue ADC values (ADCpost, **(A)**), AUCpost/(AUC muscle post):(AUC pre)/(AUC muscle pre) values (AUCpost/pre/muscle, **(B)**), and (K(trans) post)/(K(trans) muscle post):(K(trans) pre)/ (K(trans) muscle pre) values (K(trans)post/pre/muscle, **(C)**) in patients with tumor persistence/recurrence (blue box) and post-chemoradiotherapy (CRT) changes (red box). ADC: apparent diffusion coefficient. AUC: area under the curve. CRT: chemoradiotherapyotherapy. AUCpre: AUC values of primitive tumor. AUCpost: AUC values of the residual tissue after CRT. AUCmuscle pre: AUC values of ipsilateral trapezius muscle on pre-treatment magnetic resonance imaging. AUCmuscle post: AUC values of ipsilateral trapezius muscle on post-treatment magnetic resonance imaging. K(trans)pre: K(trans) values of primitive tumor. K(trans)post: K(trans) values of the residual tissue after CRT. K(trans)muscle pre: K(trans) values of ipsilateral trapezius muscle on pre-treatment magnetic resonance imaging. K(trans)muscle post: K(trans) values of ipsilateral trapezius muscle on pre-treatment magnetic resonance imaging. K(trans)muscle post: K(trans) values of ipsilateral trapezius ipsilateral trapezius muscle on post-treatment magnetic resonance imaging. Circles: drawing of comparison circles is a way to display whether or not the mean values of boxes in the box plot are significantly different from each other. Asterisk: asterisk is an indication that an extreme outlier is present in the data. Figure 4: Post-treatment magnetic resonance imaging (MRI) of a 36-year-old female patient affected by nasopharyngeal carcinoma with left lymph node metastasis (T3N3) and tumoral extension to bilateral Ronsemüller fossa, left nasal choana, and middle skull base, recently treated (3 months before) with chemoradiotherapy (CRT). Early post-treatment MRI demonstrated post-CRT inflammatory residual tissue (white striped arrows) in the left Ronsemüller fossa and ipsilateral nasal choana. Post-CRT inflammatory changes showed hyperintense signal on T2-weighted (**A**), T2-weighted fat-saturated (**B**), and diffusion-weighted b800 images (**C**); high apparent diffusion coefficient value (\(1.53\times 10^{-3}\) mm\({}^{2}\)/s) (**D**). After gadolinium contrast agent injection, post-CRT inflammatory residual tissue shows submucosal enhancement of 5 mm thickness (**E**), and very high K(trans) value (\(595.25\times 10^{-3}\) mm\({}^{2}\)/s) on dynamic contrast enhancement-perfusion weighted imaging (**F**). Ratio between K(trans) values of the primitive tumor and residual tissue after CRT, standardized with respect to K(trans) value of the ipsilateral trapezius (K(trans)post/pre/muscle), was 3.17. These findings suggested an increase in capillary permeability caused by CRT.