Whole brain radiation dose: think about it.

I have always wondered about the tolerance of brain tissue to radiation. Whole brain radiation can be “safely” given up to 54-60 Gy (in the previous protocols for glioblastoma- NO LONGER used). Brainstem dose, in the current QUANTEC era, is not exceeded to 54Gy as a point dose (disregard the 10cc volume for a minute).

The whole brain mean dose is preferably not exceeded beyond a mean dose of 28Gy which we are propagating in the post-hippocampal era (so as to say).

It brings me back to the original question. Why is a focused radiation dose exceeding 60Gy (for example) more injurious than whole brain dose to the same effect? And why brainstem isn’t affected in that scenario?

Another question. If a phased plan is executed, is it sufficient to only add up the mean doses? This is because both the phases have used different calculation subsets; radiation delivery is also going to be markedly different.

Well, no easy answers!