MRI before and after external beam intensity-modulated radiotherapy of patients with prostate cancer: the feasibility of monitoring of radiation-induced tissue changes using a dynamic contrast-enhanced inversion-prepared dual-contrast gradient echo sequence.

Abstract

To identify and quantify suitable pharmacokinetic MRI parameters for monitoring tissue changes after external beam intensity-modulated radiotherapy of prostate cancer. Six patients with biopsy-proven prostate cancer (initial PSA, 6.0-81.4 ng/ml) underwent MRI at 1.5 T using a combined endorectal/body phased-array coil and a dynamic contrast-enhanced inversion-prepared dual-contrast gradient echo sequence (T1/T2(*)w; 1.65 s temporal resolution). MRI was performed before and immediately after radiotherapy, at 3 months and at 1 year. Perfusion, blood volume, mean transit time, delay, dispersion, interstitial volume, and extraction coefficient were calculated in prostate cancer and normal prostate for all four time points using a sequential 3-compartment model. Prostate cancer and normal prostate tissue showed a statistically significant decrease in perfusion (p=0.006, p=0.001) and increase in extraction coefficient (p=0.004, p<0.001). For prostate cancer, there was also a decrease in vascular volume (p=0.034). The other parameters investigated showed no statistically significant changes. Statistically significant differences between prostate cancer and normal prostate tissue were only observed before radiotherapy, when prostate cancer showed significantly higher perfusion (1.84 vs. 0.12 ml/cm(3)min, p=0.028) and a smaller extraction coefficient (0.42 vs. 0.64, p=0.028). Two pharmacokinetic parameters, perfusion and extraction coefficient, appear to be suitable candidates for monitoring the response to percutaneous intensity-modulated radiotherapy of prostate cancer.