Hair loss from radiotherapy happens only on the part of the body that is being treated. This is not the same as hair loss from chemotherapy, which happens all over the body.
If your mum is not having radiotherapy to her head area then it should be fine for her to colour her hair before her radiotherapy treatment. However, she may find after radiotherapy her skin may be more sensitive, so it's always best to do a patch test first and leave it for a while to see if she develops any skin reactions.
I hope this is of some help. Give us a ring if you would like to talk anything over. The number to call is Freephone 0808 800 4040 and the lines are open from 9am till 5pm Monday to Friday.
