Depends on technique
Classic radiation is given via external beams to whole breast over 6-7 weeks with primarily local affect like mild repeated sunburn
(redness, irritation-more extreme may incl.
Blistering or peeling). Newer techniques if a larger daily dose cn be given can reduce the time to 3-4 weeks. Other option is accelerated partial breast usually w/implanted device and seeds over 5 days.