The Invention relates to a method (200) for assistance in planning a Treatment with Photodynamic Therapy for a patient,During which a PhotoSensitive substance default should be administered to the patient and then subjected to Light to a Predetermined Wavelength through a number of Optical Fibers adapted to be introduced over a length of Insertion in the treatment area. Uerdo with a position associated with a Grid of brachytherapy.The Method performs a measurement (230) of the volume of the treatment area by the volume Reconstruction from contours of the Digital Processing introduced directly into a series of digital images of the area, then a determination (250) made the calcul Ar the number of Optical Fibers used,Its position on the Grid of brachytherapy and its insertion length that optimizes the correspondence of a total volume of Action Theoretical calculated with the measured volume of the treatment Area, the volume of total Theoretical action that is calculated based on the position of Each FibreAnd a volume of Basic Theoretical Action of a Fibre which corresponds to the volume of a Cylinder with RADIUS R and height default, which corresponds to the insertion length of Fiber.The Invention also relates to a method of modeling 100) the radius of Action of an optical fiber which uses the correlation of measured volumes of necrotic areas from a Plurality of current clinical trials in patients with different volumes calculated Theoretical part Go the same sets of parameters used in clinical trials and the volume of Basic Theoretical actionA Fiber.La invención se relaciona con un método de asistencia (200) para planeación de un tratamiento con terapia fotodinámica para un paciente, durante el cual una sustancia fotosensible predeterminada se debe administrar al paciente y luego se somete a iluminación a una longitud de onda predeterminada a través de un número de fibras ópticas adaptado para ser introducido sobre una longitud de inserción en el área de tratamiento
