This study is being done to evaluate the use of MRI during radiation treatment planning to identify areas of tumor within the prostate to aid in future treatment planning and targeting of prostate cancer. This study will be conducted at the University of Pennsylvania Health System. The study is projected to run for 18 months. Subjects will be male 18 or older with a prostate cancer diagnosis and treatment plansat the Department of Radiation Oncology.

Inclusion Criteria:

• Age 18 or older
• Male
• Biopsy proven prostate cancer without evidence of metastatic disease
• Planned definitive external beam RT with daily ERB and implanted Visicoil fiducial markers.
• Prior fMRI-ec documenting an IPL 25 mm2 in axial bidimensional diameter product, concordant with intraprostatic tumor location as documented on transrectal ultrasoundbiopsy
• Subject capable of giving informed consent for standard external beam RT and for the study.
• No current contraindication that would prevent MRI or gadolinium contrast.

Exclusion Criteria:

• Metastatic disease
• Lack of fMRI-ec documeneting an IPL 25 mm2 in axial bidimensional product, concordant with intraprostatic tumor location as documented on transrectal untrasound biopsy
• Neoadjuvant androgen deprivation therapy greater than 10 weeks, defined from date of LHRH analog injection to date of fMRI-sim
• Contraindication that would prevent MRI or gadolinium contrast
• GFR 30 mL/min/1.73m2 per Crockoft-Gault formula.