A Photodynamic Therapy (PDT) system with an elongated interventional device (IDV) with a bundle of optical fibers (F1, F2, F3) forming respective light exit ports which can be individually accessed. The bundle has an optical shape sensing fiber (OSS), e.g. including Fiber Bragg Gratings, arranged for sensing position and orientation (P_O) of the light exit ports. A processor executes a control algorithm which generate a light dose signal (LDS) to allow generation of light outputs (LD1, LD2, LD3) to the plurality of optical fibers (F1, F2, F3) accordingly. The control algorithm generates the light dose signal (LDS) in response to the determined position and orientation of the light exit ports (P_O), and three-dimensional body anatomy image information obtained by a first image modality (I1), e.g. X-ray, MRI, CT, ultrasound, or PET-CT. This combination allows precise application of a light dose distribution for PDT treatment of a tumor with a minimal destruction of connective tissue. In embodiments, the control
