 chromosom pattern cancer patient treatment radiat damag chromosom human cell short-term cultur white blood cell damag assess patient cancer select studi larg portion blood-form tissu irradi cours treatment chromosom damag quantit variat normal number 46 qualit show structur aberr count chromosom cell cultur grown prior therapi interv treatment enabl determin variat stain prepar examin microscop allow recogn abnorm appar radiotherapi damag appear random chromosom cancer specif aberr differ cell cell correl appear persist aberr chromosom frequenc peak incid plateau remain unchang frequenc chang 