Question: how does radio therapy help destroy cancer cells?

Hywel Owen answered on 14 Jun 2012:

There are basically two kinds of radiotherapy:

1) You put a small bead of radioactive material next to the tumour, and the radiation from it kills the tumour cells and other things next to the bead. The hard part is sometimes you can’t get the bead next to the tumor, as when you inject it it might damage tissues on the way in.

2) You fire a beam of particles, either X-rays or protons (or sometimes even other things like carbon ions) and as the particles travel through the patient they deposit energy. The trick here is to make sure the energy is only deposited at the tumour. Protons are great because they’re like little bombs of energy – after they enter the body, they slow down without doing too much damage, and then when they stop they give nearly all their effect over a small range of about 2mm. You can adjust how deep this happens by changing the initial energy (or speed) of the protons. By firing protons in from a number of different directions you can minimise the effect on the parts of the body that aren’t tumour (i.e. most of it!).

The other bit that you should know is that radiotherapy isn’t done all at once. You go in for repeat sessions (which are called ‘fractions’) where radiation is delivered a bit at a time. There are usually around 30-50 of these sessions. Cancer tissue is more sensitive than healthy tissue, so if you get the dose right each time the cancer is gradually killed off while the healthy tissue has time to recover. Combine that with the different directions idea and you can make a good treatment.