OBJECTIVETo 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).

METHODSTwenty-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 (K(trans), 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.

RESULTSThe K(trans) 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 K(trans) value for Pre-RT (P=0.005) but negatively with the K(trans) 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 K(trans), kep, or Ve were found between the groups with different prognosis.

CONCLUSIONSThe 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. K(trans) 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.