Complex sentence: It is a physical quantity, and does not take into account any biological context, and unlike the pre- 1971 non-SI roentgen unit of dose, the gray is defined independently for any target material.
Split into simpler sentences: It is a physical quantity, and does not take into account any biological context. Unlike the pre- 1971 non-SI roentgen unit of radiation exposure, the gray is defined independently of any target material.