Dynamic gadolinium-enhanced perfusion MRI of prostate cancer: assessment of response to hypofractionated robotic stereotactic body radiation therapy.

Abstract

The purpose of this study was to evaluate the utility of dynamic gadolinium-enhanced perfusion MRI for monitoring the response to robotic stereotactic body radiation therapy for prostate cancer. Eighty-seven patients with prostate cancer underwent dynamic gadolinium-enhanced MRI before robotic stereotactic body radiation therapy, and prostate volume was calculated. Pharmacokinetic analysis postprocessing software was used to generate colorized parametric maps showing perfusion of enhancing tumors. The transfer constant K(trans) was calculated for identified tumors. Follow-up MRI was performed 2 months after treatment for 22 patients, 6 months for 71 patients, 12 months for 54 patients, and 24 months for 27 patients with repeated measurements of prostate volume and K(trans). Perfusion MRI depicted focal enhancing prostate tumors that correlated with the biopsy results in 82 of 87 patients (94%). The median K(trans) of tumors before robotic stereotactic body radiation therapy was 1.79 minutes(-1). Follow-up MRI showed decreases in the size and degree of enhancement of tumors. The median tumor K(trans) decreased to 1.21 minutes(-1) 2 months, 0.39 minutes(-1) 6 months, 0.30 minutes(-1) 12 months, and 0.22 minutes(-1) 24 months after treatment. Prostate volume had decreased 23% 2 months, 26% 6 months, 33% 12 months, and 37% 24 months after robotic stereotactic body radiation therapy. The corresponding median prostate-specific antigen concentration before treatment was 6.45 ng/mL. After treatment, the concentration was 2.90 ng/mL at 2 months, 1.30 ng/mL at 6 months, 1.10 ng/mL at 12 months, and 0.59 ng/mL at 24 months. Dynamic gadolinium-enhanced MRI is a useful tool for monitoring the response of prostate cancer to robotic stereotactic body radiation therapy, yielding both qualitative and quantitative data.