As you suspected, astronauts that travel between planets would be subjected to much higher doses of radiation than we get here on Earth, and even different from low Earth orbit, where the International Space Station is. One solution would be to protect the astronauts with shielding. This requires a heavy metal wall between the astronauts (or Martian dwellers!) and space. However, there's an obvious difficulty, which is that a big heavy wall (let's say big enough to cover an entire Martian colony) is hard to take with you all the way to another planet! Coming up with a material than can be lighter but still effective in shielding from radiation is a difficult problem that you can read more about in this NASA article: https://www.nasa.gov/feat...ce-radiation-on-mars