Lack of testosterone weakens the cancer cells, prevents their moving around and reproducing and stops cancer cells from advancing in state (like G4 to G5). It is believed that while so weakened, the radiation treatments are more effective in killing the cancer cells.
I deal with my inclination to depression by maintaining a rigid (somewhat extreme) daily exercise regimen as part of a seriously structured daily task schedule. I carry a lot of constant pain. Getting in a daily 7 mile run dumps sufficient quantities of endorphins into my blood stream to dull my perception of that pain and to prevent my mood from going foul or depressive. Discovering this many years ago has saved my life, for sure.
My Lovely Lady Labrador enjoys it as well.