An improved system and method for optimizing the planning, registration, targeting, and delivery of conformal, external beam radiation therapy of prostate cancer and other soft-tissue diseases. Real-time ultrasound imaging during planning and treatment is used forlocalization of soft tissue treatment targets and fused with radiographic or CT data for conformal treatment optimization. The fusion technique provides accurate localization of the prostate volume in real time. For treatment of prostate cancer, visualization of the prostate gland is achieved using transrectal ultrasonography and the fusion of that image in the precise location of the prostate within the pelvic region, accurately determining the location of the prostate target by transformation of the ultrasound image data on both the ultrasound and X-ray/CT images. The radiation field may be optimized to significantly reduce the volume of irradiated normal tissue, minimizing the exposure of the surrounding healthy tissues and increasing dosage delivered to the prostate treatment target.