Numerical and experimental assessment of the influence of thermocouple orientation on temperature measurements for radiative superficial hyperthermia

BACKGROUND: Radiative oncological hyperthermia (HT) is a medical therapy for cancer treatment aimed at inducing temperatures up to 40-44 °C for 1h in pathological tissues. This aim is achieved through the application of an electromagnetic (EM) field radiated by antennas located on the body surface. According to tumor location, hyperthermia is typically classified in deep or superficial HT. In both cases, temperature measurements are typically performed during treatment for verification purposes and in validation procedures to assess HT device performance. Temperature monitoring is typically carried out using thermocouples or thermistors, both of which transmit the information through a signal along metallic wires; when thermocouples are used, their readings are performed while discontinuing EM radiation to avoid electromagnetic interference. PURPOSE: This work aims to study the effect that temperature sensors systems have on the EM field and temperature distributions produced by the HT device. In particular, the effect of the orientation of the metallic wires was analyzed. METHODS: Experimental measurements and a numerical analysis were performed using two different setups, based on a phantom equipped with catheters for temperature probe insertion and a commercial hyperthermia antenna. RESULTS AND CONCLUSION: Results showed that wires oriented orthogonally to the electric field do not induce a significant change in the EM-temperature distributions. Instead, the presence of wires oriented parallel to the main electric field component induces a significant perturbation of the EM field and temperature distributions, with a reduction of the penetration depth. These results evidence that care must be taken when placing temperature sensors in HT procedures.