Procedure (200) of support, by computer, for planning a treatment of a patient future photodynamic therapy, during which a predefined photosensitive substance to be administered to future patient then subjected to a light at a predetermined wavelength by means of a number of identical optical fibers suitable to be inserted into an insertion length of the area to be treated as a position on a grid brachytherapy (1), each optical fiber of the type that emits a high intensity in a perpendicular to the longitudinal axis of the fiber, comprising address: - a step of modeling the elementary volume of theoretical action of an optical fiber in association with said photosensitive substance by a cylinder range R and length L corresponding to said insertion length, said range R determined by the performance of steps if lowing: - building (110) a computer database from data from a plurality of clinical trials conducted in different patients using said photosensitive substance associated with at least one optical fiber, each clinical trial associated with a set of being parameters corresponding to the actual conditions of the clinical trial and comprising at least the number of optical fibers used, their position relative to a grid brachytherapy, and the insertion length of each of the fibers in the area to be treated, consisting of such construction memorizing for each patient, in the database, a first digital file corresponding to a series of digital images of the area to be treated before the clinical trial, a second digital file corresponding to a series of digital images of the area after the clinical trial, and said set of parameters corresponding to the actual test conditions Clíni co； - measuring (120), for each patient in the database, the volume of the necrotic area effectively during the clinical trial, from said first and second digital files； - calculating (130) for each patient database, the total theoretical volume of action depending on the parameters of said se
