The key here is the field of radiation being applied. This includes where it comes in and where it goes out. They shoot the radiation from a number of different angles so only the tumor gets the maximum dose. The parotid is behind the tissue at the back of the throat and is not connected to the tongue so it will not be a place the cancer will spread, but it will be in the field where the radiation is either going in or out.

The reason it is damaged is because it falls in the field of radiation needed to treat the tumor. By changing the angles they shoot the radiation into the tumor (they hit me from 5 different angles every treatment), they can change the field to minimize the effect on the parotid, but if they change the angle too much they will not hit the tumor with enough radiation.

I still think that the question at hand is how much of the parotid they will be losing to radiation. I lost half but have good saliva from the other salivary glands, so my dry mouth is not that bad (it�s not a good thing either).

Also, different people react to radiation in different ways. People here will tell you that we all have different outcomes from radiation.

Hope this helps