Average doses in radiotherapy
Radiotherapy doses are expressed in grays. These are average doses because the doses prescribed may vary from one patient to another. The use of gray as a unit instead of the Sievert is necessary because in therapy we are talking about doses of energy locally delivered to the tumor. Sievert and its sub-multiples are units planned for radiation protection, not for the energy deposited evaluation in a tumor for its destruction.
IN2P3/ Source K.G.Gerber - Unscear 2000