Final answer:
The position in which the patient is lying on their back with the right side turned 20 degrees towards the image receptor is the right anterior oblique position. This oblique position is defined with respect to the side of the body that is closer to the image receptor and the side that is elevated.
Step-by-step explanation:
When a patient is lying on their back facing the X-ray tube and the right side of their body is turned 20 degrees towards the image receptor, the position they are in is called the right anterior oblique position. The radiographic oblique positions are usually named based on the side of the body closer to the image receptor (in this case, anterior meaning the front part of the body) and the side of the body that is elevated (right side in the scenario described).
In contrast, if the patient were lying on their front, the position would be referred to as prone, where the face-down orientation is applied during certain examinations or medical procedures. Supine describes the face-up orientation, as in the described case, where the patient is lying on their back. Imaging techniques such as X-rays and CT scans greatly benefit from accurate patient positioning to provide precise diagnostic images.