Final answer:
An alternative position for sternum imaging if the RAO position is not possible is the Left Anterior Oblique (LAO) position, which similarly visualizes the sternum by placing the patient's left side closest to the image receptor.
Step-by-step explanation:
If a patient cannot assume the recumbent Right Anterior Oblique (RAO) position, an alternative position for imaging the sternum is the Left Anterior Oblique (LAO) position. In the LAO position, the patient's left side is placed closest to the image receptor, which allows for a similar oblique view of the sternum compared to the RAO. The other options mentioned, such as Left Posterior Oblique (LPO), Left Lateral Decubitus, and Right Posterior Oblique (RPO), do not provide the same degree of visualization of the sternum as the RAO or the LAO position.