DCEMRI of spontaneous canine tumors during fractionated radiotherapy: A pharmacokinetic analysis

PurposeTo estimate pharmacokinetic parameters from dynamic contrast-enhanced magnetic resonance (DCEMR) images of spontaneous canine tumors taken during the course of fractionated radiotherapy, and to quantify treatment-induced changes in these parameters.Materials and methodsSix dogs with tumors in the oral or nasal cavity received fractionated conformal radiotherapy with 54 Gy given in 18 fractions. T1-weighted DCEMR imaging was performed prior to each treatment fraction. Time–intensity curves in the tumor were extracted voxel-by-voxel, and were fitted to the Brix pharmacokinetic model. The dependence of the pharmacokinetic parameters on the accumulated radiation dose was calculated.ResultsThe Brix model reproduced the time–intensity curves well. A reduction in the kep parameter with accumulated radiation dose was found for five (three significant) out of six cases, while the results for the A parameter were less consistent. Both pre-treatment kep and the change in kep with accumulated dose correlated significantly with tumor regression.ConclusionsPharmacokinetic parameters derived from DCEMR images taken during fractionated radiotherapy may predict response to radiotherapy. This may potentially impact on patient stratification and monitoring of treatment response for image-guided treatment strategies.