But even with the more collimation a chest x-ray is 2 imges and a ct chest is easily more.
Ct exposes the patient to more radiation just based on how it functions, combined with the scout images. so a CT chest would have two scouts which are the closest to plain film x-ray and thats before the actual cT slicing and exposure.
Or I don't understand the question, but this seems to be a trend of poorly conceptulized questions.