Prostate cancer is a major cause of cancer related deaths in American men. Standard treatment of prostate cancer has been whole-gland treatment including radical prostatectomy and radiation therapy. There is growing evidence that prostate cancer is over-treated and prostate cancer may not be clinically evident during the natural life span of many patients who are aggressively treated. Whole-gland treatment methods have also been associated with high risk of complications altering quality of life such as incontinence and impotence. Based on these facts, focal treatment methods which are not associated with serious complications but aim to control the cancer at the outset have been suggested as alternative treatment methods for low-risk prostate cancer. Among these methods, MRI guided laser induced thermal therapy (LITT) is a promising technique with certain advantages over the other focal therapy methods. It can create accurate, predictable and reproducible ablation zones within the prostate and induces minimal change outside the targeted ablation zone. It is compatible with MRI and therefore, can benefit from superior soft tissue contrast resolution for treatment planning and MR thermography for real time therapy monitoring. Our group has recently completed a Phase I study and demonstrated the technical feasibility and confirmed the initial safety of this procedure. The goal of the present proposal is to conduct a phase II clinical trial with MRI-guided LITT for targeted focal destruction of prostat cancer. We hypothesize that MR-guided LITT will effectively ablate target areas of prostate cancer, exhibit an exceptional long term safety profile, and will not alter urinary or sexual qualiy-of-life. The specific aims are (1) We will conduct a Phase II non-randomized, single-arm clinical trial to rigorously assess oncologic effectiveness of MRI guided LITT in patients with newly diagnosed prostate cancer. Primary endpoint will be confirmation of lack of cancer within the treatment zone by an MR guided biopsy performed 3 months after laser ablation. Secondary endpoints will be oncologic efficacy based on biopsy of the treatment zone at 12 months following treatment and treatment-related safety and toxicity measured with validated instruments. (2) We will implement quantitative and anatomic MR imaging to follow each treated region and surrounding tissue to define alterations in the MR imaging features of the ablation zone. Dynamic contrast enhanced (DCE) imaging, diffusion weighted imaging (DWI), quantitative T2-weighted imaging and high resolution anatomic imaging will be collected prior to treatment and at 3 months and 12 months following treatment. The results of post-treatment MRI's will be compared to biopsies performed at 3 months and 12 months following the procedure. At the completion of this project, we will have treated 27 patients using MR-guided LITT and will have gained highly valuable information regarding oncologic efficacy, safety, and predictive role of MRI. We will subsequently use these results to support the design of a larger multi-center trial to evaluate the comparative effectiveness of this new focal treatment paradigm.