Here's my layman's understanding, your medical team may be better able to explain it.

Radiosensitizers are chemicals or pharmaceutical agents that can enhance the killing effect on tumor cells by accelerating DNA damage and producing free radicals indirectly.

Don't ask me to explain that, in school, biology was not my thing and medical school was never a part of my career path.

Not all PCa cells will die off when on ADT, if imaging shows where PCa is, my understanding is the radiation can "kill" thus eliminating perhaps some of those cells that survive in a low T environment. My understanding is that's why one starts with ADT and several months after, begins radiation.

Kevin