Abstract: Objective To study the changes in quantitative kinetic parameters in dynamic contrast-enhanced magnetic resonance
imaging (DCE-MRI) during radiotherapy and their value for efficacy evaluation in patients with nasopharyngeal carcinoma
(NPC). Methods Twenty-four patients with NPC that had been pathologically confirmed as poorly differentiated squamous
cell carcinoma underwent conventional MRI and DCE-MRI scans 1-2 days before radiotherapy (Pre-RT), during radiotherapy
(RT 50 Gy), and upon completion of radiotherapy (RT 70 Gy). Based on the two-compartment model and using the arterial
input function deconvolution technique, we calculated the quantitative kinetic parameters of DCE-MRI (Ktrans, kep, and Ve) of the
tumor tissues, examined the correlation between the tumor regression rate (RS0-50) and the parameters on Pre-RT and RT 50
Gy, and compared the parameters for RT 70 Gy among the groups with different prognosis. Results The Ktrans value of the
tumor tissue decreased after radiotherapy and showed a significant difference between Pre-RT and RT 70 Gy, but not between
Pre-RT and RT 50 Gy. The kep value decreased and Ve value increased after radiotherapy. The tumor regression rate was found
to be positively correlated with the Ktrans value for Pre-RT (P=0.005) but negatively with the Ktrans value for RT 50 Gy (P=0.001).
During the follow-up for 3 years, 5 patients died and 3 patients had distant metastases. No statistical differences in Ktrans, kep, or
Ve were found between the groups with different prognosis. Conclusions The kinetic parameters in DCE-MRI, which vary
significantly during radiotherapy, allow monitoring of tumor angiogenesis and vascular permeability and quantitative
assessment of treatment efficacy for NPC. Ktrans value for Pre-RT and RT 50 Gy can serve as an indicator for early efficacy
assessment of radiotherapy and for treatment adjustment, but its relation with the long-term outcomes awaits further study.