What is the monthly treatment couch position indicator tolerance?

• A. 2 mm / 1°
• B. 2 mm
• C. 1°
• D. 1 mm

Answer: (A)

Monthly treatment couch position indicator tolerance is a dual requirement that covers both translational and rotational accuracy of the couch. In practice, the couch readings must stay within 2 millimeters of the intended translational position and within 1 degree of the intended rotation. The 2 mm limit keeps the patient’s alignment to the isocenter precise, minimizing setup and beam targeting errors. The 1° limit controls orientation so that couch angles don’t introduce positioning or edge effects that could shift the beam relative to the planned plan. That combination—2 mm and 1°—is the standard to ensure accurate, repeatable couch positioning.