Use of Diffuser Fibres in the Treatment of Prostate Cancer by Interstitial Photodynamic Therapy

Sammanfattning: SpectraCure AB is a start-up company aiming at treating internal solid tumours such as prostate tumours with an innovative technology called ‘Interstitial Photodynamic Therapy’. This treatment requires the use of fibres to deliver the amount of light required to activate a drug injected to the patient which leads to the destruction of the tumours. This treatment is patient-based which means that the amount of light, modulated by the irradiation time, is dependent on the characteristics of the tissue for each patient. In order to do so, the critical parameters to estimate are the optical properties and among them, a particular attention will be given to the effective attenuation coefficient μ_eff, which characterises the tissue to be treated. Those parameters are then used as inputs of an algorithm calculating the appropriate irradiation time for each light delivery fibre based on the minimal dose the tissue is supposed to receive to permit the activation of the drug. So far, SpectraCure AB has been using 400 μm bare end fibres assumed to be point sources to perform the light delivery; eighteen of those are required to have a good estimation of the optical properties of the tissue and enough light in all the region to be treated. The idea now is to introduce diffuser fibres, modelled as an array of point sources, to be able to increase the power delivered by the fibres and in the meantime reducing the number of fibres. The aim of this thesis is to evaluate the performance of diffuser fibres in interstitial photodynamic therapy. A finite element method (FEM) solver called Nirfast for near IR (Infrared) fluorescence and spectral tomography has been used. The study has shown that the properties of the tissue remain well determined for 5 and 7 mm diffuser fibres while they become less accurate for a higher fibre length. Furthermore, the diffusion approximation, which is the simplest approximation for the light propagation in homogeneous tissues, has been applied in the case we have a heterogeneous medium and has lead to correct enough results to enable the treatment with the P18 system developed by SpectraCure AB. We intended to change the power delivered by the fibre but no satisfying conclusion could be drawn.