UK question - what cream to use during radiotherapy and how?

A friend in the UK had a UMX without reconstruction a few weeks ago and will be having several weeks of radiotherapy/radiation treatment shortly. She doesn't use any social media tools so asking this on her behalf.

I never had radiation, just surgery for my BC but remember reading that there is a cream to use during that treatment to soothe the skin, help prevent burn damage (not to mention pain?). So, I'd appreciate it if someone in the UK who knows about this could please tell me the name of a product that was effective for them (which I can hopefully order for her on Amazon UK) And also advise on when should she use it - do you use anything before you get a treatment? After a treatment (how long after)? Sorry for being clueless, appreciate any info you can provide on this.

Thank you - Abigail