A fixed or variable focal distance unit used to project a light pattern, e.g., grid or crosshatch, that aids in the positioning of patients during diagnostic imaging, radiation therapy, or treatment planning procedures. It is intended to enable precise and reproducible 1, 2, or multi-dimensional alignment of a selected portion(s) of the patient's anatomy with respect to the radiation beam or beams used for diagnostic or therapeutic procedures. Light-based positioning units can be freestanding units or incorporated as a component to a diagnostic imaging or radiation therapy system. It typically includes: a light bulb, a grid to shape the pattern, and mechanical/electronic controls.