2. Photon fluence and dose

In radiology, the term "dose" has traditionally been used to refer to different physical quantities. Originally, it refers to the quantity of energy absorbed by a unit volume of matter (tissue, gas, etc.) through which ionizing radiation, in this case X-rays, passes. From this definition have been derived two other uses of the same word: to quantify the fluence of X-rays passing through a surface, and to estimate the health impact of ionizing radiation penetrating biological tissue. Context generally helps us understand what we're talking about, but some texts can be ambiguous.