Abstract: System for treatment by photodynamic therapy comprising: —an illuminating device (10) including a light emitting surface for illuminating an internal surface to be treated with a light adapted to activate a photosensitizer compound, the light emitting surface emitting light with a distribution of light power comprising fractions of light power decreasing from a maximum at the light emitting surface, the light emitting surface having a determined illumination profile that provides respective illuminated areas for a plurality of the fractions of light power, —a positioning system (40) adapted to position in real-time the light emitting surface within a reference frame, —an electronic unit (45) connected to the positioning system (40) and adapted to monitor in real-time a dose of light energy delivered to the internal surface based on the illumination profile and the position of the light emitting surface.