A phosphor-containing drug activator activatable from a Monte Carlo derived x-ray exposure for treatment of a diseased site. The activator includes an admixture or suspension of one or more phosphors capable of emitting ultraviolet and visible light upon interaction with x-rays, wherein a distribution of the phosphors in the diseased target site is based on a Monte Carlo derived x-ray dose distribution. A system for treating a disease in a subject in need thereof, includes the drug activator and a photoactivatable drug, one or more devices which infuse the photoactivatable drug and the activator including the pharmaceutically acceptable carrier into a diseased site in the subject; and an x-ray source which is controlled to deliver the Monte Carlo derived x-ray exposure to the subject for production of ultraviolet and visible light inside the subject to activate the photoactivatable drug and induce a persistent therapeutic response, the dose comprising a pulsed sequence of x-rays delivering from 0.5-2 Gy to the tumor.