Implementation of a control system for SAR and temperature focusing in a head and neck cancer hyperthermia applicator

Hyperthermia therapy is exploited in the medicine field combined with the most known cancer treatments - radiotherapy and chemotherapy - to improve their effectiveness. During hyperthermia treatments, the tumor tissues are heated up to 42/43°C through non-ionizing microwave radiation generated by proper antenna applicators. Overheating makes the cells more sensitive to ionizing radiations and enhances drug delivery without adding further toxicity. These benefits have been demonstrated for tumor sites like cervix, breast, head and neck, skin, bladder, and esophagus. For the treatment of internal tumors, properly phased antenna arrays are currently used in the clinical practice to maximize the specific absorption rate (SAR) (and hence the temperature increase) in the tumor target, while avoiding formation of hotspots in the surrounding healthy tissues. This is achieved by means of proper optimization routines based on numerical simulations and an active electronic control system able to provide the optimized antenna feedings to the antennas of the array during the whole heating session. The main focus of the present thesis concerns the implementation of the electronic control system needed to maintain the proper SAR focusing on a target region in an experimental mock-up reproducing a hyperthermia applicator for tumors in the neck region. The considered mock-up includes a circular array made of eight patch antennas surrounding a phantom of the human neck and immersed in the waterbolus, i.e., a cooling system which favors the radiation coupling into the neck and avoids overheating of the skin. The entire prototype is modelled and simulated with the software COMSOL Multiphysics. The performed simulations are used to find the antenna feedings which maximize the SAR in a target region inside the phantom by means of an optimization procedure, and to provide the optimized temperature maps for comparison with the experimental measurements. Real-time temperature monitoring is performed during the experimental sessions using fiber optic sensors (FOS), inserted in different positions of the neck phantom to verify the expected heating in the target region and the minimization of hotspots in the surrounding areas. Simulations and experimental sessions move forward together to fix the setup and the corresponding numerical model that better match the expectations in terms of SAR and electric field focusing, temperature measurements and surrounding boundary conditions.