Temperature Map Reconstruction in Head and Neck Cancer Hyperthermia

Hyperthermia treatment (HT) is a thermal treatment which uses non-ionizing electromagnetic radiation, like microwaves, to rise the temperature in the tumor region (where cells reach 42/44°C) creating tissue damage. Recent studies show that HT can sensitize cancer cells to both chemotherapy and radiotherapy treatments, increasing their efficacy without providing new dose exposition. During HT, it is crucial to limit the heating process only in the tumor site while maintaining the temperature values in the surrounding healthy tissues around the physiological level. For internal cancers, phased antenna arrays are properly designed to focus the electromagnetic radiation on the tumor region, avoiding hotspots, i.e., dangerous overheated regions far from the tumor site, which could be harmful especially in the treatment of head and neck (H&N) cancers. In the clinical practice, a water-bolus (plastic bag filled with cold water) is introduced between the antenna applicator and the patient to avoid overheating of the skin, where temperature must remain tolerable, and improve the radiation coupling into the body. Good clinical outcomes are achieved using a patient-specific treatment planning, where the antenna feedings are optimized by means of numerical simulations using patient-specific phantoms derived from MRI and CT scans of the patient. After optimizing the power deposition on the tumor target, thermal solvers are used to generate the temperature map distribution in the numerical phantom. Although the solvers produce high valuable results, they are often not reliable per se. The dielectric and thermal parameters assigned to the different tissues of the phantom are currently known with high uncertainty. These values, reported in the Literature and derived from ex-vivo measurements, can introduce inaccuracies in the simulations, leading to incorrect temperature maps of the patient. For this reason, during HT treatments it is essential to quantify the temperature in the heated tissues with invasive temperature probes (inserted into closed-tip catheters), which cause great discomfort to the patient and provide limited spatial information. The goal of the present Master Thesis is to validate and improve the accuracy of the simulated 3D temperature map from few known temperature values during HT treatments in the H&N cancer scenario. A realistic numerical phantom is used for the thesis purpose; then, via the Sim4Life software and Python and MATLAB scripts, simulations are performed to maximize the specific absorption rate (SAR) on the tumor target and to generate the corresponding temperature map. Assuming to know few temperature values (along the direction of a catheter) of different target maps corresponding to random combinations of the tissue parameters, a numerical reconstruction method is applied to retrieve the target maps in the whole region of interest. This method employs high-performance simulations of the temperature map (to be performed prior to treatment). An in-depth analysis is carried out to estimate the number of such simulations needed to ensure a sufficiently good reconstruction, for different scenarios, i.e., when a different number of parameters of a given number of tissues are supposed to be different from their baseline values. Finally, the quality of the reconstruction is also discussed for different directions of insertion of the catheter in the region of interest.