Gray

A Gray is the unit of measurement of ionising radiation energy absorbed by a material (in radiation-oncology the material in question is biological tissue or a tumour) (named after Stephen Gray, an English physician). 1 Gy = 100 rad (an English term meaning radiation absorbed dose). The intensity of radiotherapy treatment is given in Gy. For example, a total dose of 60 Gy administered in fractionated doses during daily sessions for six weeks.