One measure of the effect of radiation is the amount of energy it deposits in a piece of tissue. This quantity is the absorbed dose. The units of absorbed dose is the gray (Gy).
In general, X-ray examinations are over-used throughout the world. Far too frequently, such examination, whether of the chest, the skeleton, or the abdomen, yields little information that is clinically useful. Many are given routinely, or without medical justification, and thus are 'not worthwhile', according to a report by a group of leading radiologists convened by the World Health Organization (WHO). So overused and misused are X-rays that they constitute a major source of population exposure to man-made ionizing radiation. They are also costly, accounting for an estimated 6 to 10% of a country's health expenditure.