Study of a thermal model for cancer treatment with laser ablation Development of a feedback system to optimize optical and thermal liver parameters using an integrated temperature monitoring technique

The rising in importance of minimally invasive surgical techniques goes unfortunately side by side with the increasing number of cancer cases worldwide, especially in poor countries. The fact that not every healthcare system can guarantee proper cures to all the citizens underline the importance of research in finding always cheaper protocols. Laser ablation is a new frontier that could open access to curing cancer also for those that nowadays cannot afford other treatments for the high cost of hospitalisation and therapies as well. Cancer is a pathological condition where the proliferation of cells in organs and tissues modifies the normal functioning and structure; for this reason any typology of mini-invasive surgical treatment, either hyper-thermal or hypothermal, has the aim of forcing cells' necrosis. 
The purpose of this master thesis have been to develop a thermal model that could help recreating the temperature distribution of liver during ablation. Moreover, the confrontation of the model with the experimental measures made during ex-vivo ablation gave the chance to evaluate liver optical and thermal parameters of the liver. The future goal will be to build an integrated sensing system in the delivery probe that calibrates the power real-time during the ablation. Nowadays temperature monitoring, hence the effect of the power applied on the tissue, is mostly done with thermal Magnetic Resonance, while the integrated sensing system abovementioned is made with an array of Fibre Bragg Gratings. The linear relationship between temperature and the characteristic parameter of the gratings, the Bragg wavelength, simplifies the evaluation of the temperature distribution in the target. These sensors have been used in the thesis' experiments after a previous characterisation of FBGs made with MicronOptics and thermocouple in order to find the parameters to find the Bragg wavelength. Two kinds of array have been used: an ultradense array with 20 distributed FBGs staggered with respect to the core and an array with 20 FBGs in axis with the core. The former has helped to sense temperatures close to the tip of the laser, especially for the points along the trajectory; the latter instead was used for sensing temperature orthogonally in respect to the laser. The model was made using MATLAB PDE toolbox: this tool gives the possibility to solve Partial Differential Equations in different fields such as the study of thermal conductivity. The liver was modelled as a 2D cylinder section considering the delivery fibre along the central axis. The toolbox divides the section in a mes and works solving the heat equation for each area. The heat source has been modelled as punctual and with a Gaussian behaviour radially and an exponential decay along the axis. The optical parameters taken in account are scattering and absorption; the thermal parameter is the conductivity.
Once obtained the temperature distribution it has been compared to the measurements took during ablation with an optimisation algorithm, fminsearc, to find parameters of absorption, scattering and conductivity that fit better the real problem.