In standard prostate brachytherapy treatment, the seeds are placed throughout the prostate to treat the entire gland. This is done because, in the past, it was impossible to know where the cancer was located within the prostate. Multiparametric magnetic resonance imaging (MRI) can identify tumor(s) with a high degree of accuracy. This trial will assess whether using MRI to guide prostate brachytherapy can result in less chronic toxicity by allowing lower doses to be delivered to the regions of the prostate without tumor while simultaneously allowing higher doses to the tumor. Subjects enrolled in this study will then be followed over two years and evaluated for toxicity. In addition, after two years they will undergo an MRI and a biopsy to assess the cancer control rate of the treatment.