Prostate cancer - are there side effects of radiation therapy?

YES. External beam: skin becomes red, swollen, warm, and sensitive, as if sunburn which subsides gradually in four to six weeks. Possible side effects: erectile dysfunction and urinary symptoms of frequency, bleeding, or, rarely, incontinence.
Yes. Fatigue, urinary and bowel symptoms are common with external beam radiation but are typically mild and transient. Urinary symptoms may be more intense with "seeds" (brachytherapy) but quality of life studies show return to baseline symptoms within months after implant. Long term side effects may include blood in urine or stool or development of bladder cancer (after 10-20 years).