There are quite a few videos on Youtube for how to construct a personal statement. But its basically - short intro section about why you want to do diagnostic radiography, longer middle section talking about yourself, your skills and values and how they apply to your chosen course, and finally a short conclusion section. I don't know where you're applying to, but I'm doing Therapeutic Radiography at Sheffield Hallam and they have pre-application days (probly online now) where they go through the application process including how to do your personal statement.
You're a mature student, so you have loads of life experience. You've worked so you know about working in a team, timekeeping, deadlines etc. Working in a prison I'm sure requires loads of unique qualities, different styles of communication, safeguarding etc. Travelling round Australia for 2 years shows independence, self-reliance, flexibilty etc. And then try and relate some of these skills/experiences back to Diagnostic Radiography.
When I wrote mine, I did a massive list of everything I wanted to include, then it was a case of whittling it down, removing the bits that weren't relevant to make a coherent PS.