Naked Science Forum

General Science => General Science => Topic started by: katieHaylor on 05/10/2018 09:35:07

Title: How does proton beam therapy work?
Post by: katieHaylor on 05/10/2018 09:35:07

Andrew says:

I recently heard a story about proton beam therapy.  The advantage of this technique is that the protons are supposed to stop inside the tumour being treated and give up all of their energy there.  As a result, they damage the tumour but none of the tissue between the skin and the tumour.

How does the physics of this work?  If the protons are slowing as a result of passing through tissue on the way to the tumour, how is it that they don't give up a proportional amount of their energy along the way?

Can you help?

Title: Re: How does proton beam therapy work?
Post by: alancalverd on 05/10/2018 18:00:46

Some energy is deposited all along the track, but the interaction crossection increases as the proton slows down, so a lot of energy is deposited at the end of the track. Wikipedia has a good entry under "proton bragg peak".

For a crude analogy, imagine a hot cannon ball flying through a mountain of butter. Initially, it is travelling quickly so there is very little time to transfer heat energy to each meter of butter, but when it stops moving, it can deposit all its residual heat at one point.  So the butter will re-congeal along the track but form a molten pool around the stationary missile.