Is this the same kind of radiation that spread in Japan, Chernobyl and Three Mile Island?

No.  The main health issue with industrial radiation accidents is that airborne radioactive particles can be swallowed or inhaled which can be absorbed into your body for long periods of time leading to multiple health problems.

Treatment of prostate cancer is a targeted treatment using a temporary emission of radiation using electricity to produce photons.  There are no photons when the electricity is turned off.  Therefore, you are never “radioactive.”  Instead your prostate is targeted with high energy X-rays for about 90 seconds when you are being treated and there are no radioactive particles after that 90 seconds is completed.