MINIMALLY-INVASIVE TEMPERATURE MONITORING IN HYPERTHERMIA TREATMENT OF INTERNAL TUMORS VIA DETAILED NUMERICAL PHANTOMS

The aim of thermal therapies in cancer treatment is to significantly alter the temperature of the target (tumor) region without damaging the healthy tissues. Microwave hyperthermia (HT) consists in heating locally the region of interest up to 42-44°C by means of an antenna applicator, while keeping the heat in the surrounding area at a tolerable level for the tissues and therefore for the patient himself. Hyperthermia is used in association with conventional cancer therapies, being able to sensitize tumors to radiotherapy and chemotherapy (cancer therapies are more effective at the same dose) without adding toxicity. In order to improve the clinical outcome of hyperthermia treatments, a patient-specific treatment planning is needed, where a numerical model of the patient is created, the baseline thermal and dielectric parameters (i.e., the values found in the Literature) are assigned to the different tissues, the antenna feedings are optimized using an EM simulation solver, and the corresponding temperature map is obtained by solving the bioheat equation. Unfortunately, tissues parameters are characterized by great uncertainty, which can significantly affect the simulated temperature maps. Hence, for safety reasons, invasive temperature probes inserted into closed-tip catheters are necessary during treatment to provide some (limited) temperature measurements. The present Master Thesis is part of a research aim to monitor and predict the temperature in, and around a cancer volume during HT in a minimally invasive method, obtaining a 3D temperature map from a single catheter (fiber-optic) thermometer. The specific focus is in simulating the operation in silico, with a highly realistic phantom of the neck region; simulations were performed with the highly specialized commercial software Sim4Life, and with temperature-reconstruction algorithms in MATLAB. For the treatment of internal tumors, the hyperthermia applicator is usually composed by an array of antennas, properly fed to focus the specific absorption rate (SAR) – and hence the temperature increase – on the tumor region. An accurate model of the device has been built for a human phantom in Sim4Life. Then, the microwave heating was focused within the tumor region, through a SAR-based optimization of the antenna feedings. The influence of thermal parameters such as perfusion rate and thermal conductivity, as well as the dielectric ones, i.e., permittivity and electrical conductivity, on the resulting temperature maps is analysed by solving the bioheat equation in Sim4Life for different values of the constituent parameters, changed by means of a Python interface. Once found the most critical parameters, a numerical reconstruction is implemented to obtain a more reliable temperature map of the whole region of interest starting from a set of few known temperature values – mimicking those experimentally known along the catheters during the clinical treatment.