A patient is being set up for a posterior oblique chest field, and the plan calls for the couch top rotated 30° so the rails clear the beam at a 315° gantry angle. The collimator must stay at 0°, and the isocenter has to remain at the same point in the patient after the rotation. Department protocol requires image guidance, not surface imaging alone, to verify internal position after couch rotation. Which couch and console checks confirm the setup before the beam is delivered?

The correct setup aligns the planned isocenter with the couch rotation axis before rotating the couch top 30°. This geometry helps keep the isocenter at the same point in the patient as the couch turns; the specified rotation provides rail clearance at the 315° gantry angle while preserving the required 0° collimator setting. Image guidance verifies internal position after rotation, and checking the gantry, collimator, and couch values on the console confirms that the current machine settings match the plan. A setup that uses the setup record for the couch angle still performs the alignment, rotation, and image-guided verification, but the record does not confirm the couch’s current console setting. Surface imaging can help assess positioning, but it does not replace the protocol-required image guidance for checking internal position after rotation. Positioning the patient at the planned isocenter with room lasers does not establish that the isocenter lies on the couch rotation axis; subsequent imaging cannot substitute for setting up that rotational geometry. Exam caveat: distinguish couch-top rotation from gantry rotation, and do not assume the collimator angle may change when it is specified to remain fixed. Practical check: before beam delivery, compare the displayed gantry, collimator, and couch values with the plan and review the post-rotation image match under local protocol.