Optimization of the Clinical Setting Using Numerical Simulations of the Electromagnetic Field in an Obese Patient Model for Deep Regional Hyperthermia of an 8 MHz Radiofrequency Capacitively Coupled Device in the Pelvis

SIMPLE SUMMARY: Several randomized controlled trials have shown that the concurrent use of hyperthermia with radiotherapy results in a significant increase in local control rates. However, in studies that analyzed thermal parameters, the radiosensitizing effect required a favorable increase in tumor temperature. A good temperature increase is more difficult to achieve in deep-seated tumors than in superficial tumors. In this study, the reduction of subcutaneous fat overheating, which is a weak point of the deep heating of a capacitively coupled heating system, and the optimization of temperature distribution in the deep regional hyperthermia in the pelvis were investigated using electromagnetic field numerical simulations. In conclusion, the use of overlay boluses, the salt solution concentration in the overlay boluses, and the intergluteal cleft bolus insertion were found to be important for optimizing the temperature distribution. Further studies with numerical simulations based on the patient’s body shape and tumor location are expected. ABSTRACT: Background: The purpose of this study was to evaluate the effectiveness of the clinical setting for deep regional hyperthermia of an 8 MHz radiofrequency (RF) capacitively coupled device in the pelvis by using numerical simulations of the electromagnetic field. Methods: A three-dimensional patient model of cervical cancer of the uterus in an obese patient was reconstructed with computed tomography data. The specific absorption rate (SAR) and temperature distributions among the various heating settings were evaluated using numerical simulations. Results: The averaged SAR value of the deep target tumor was similar between with or without overlay boluses (OBs), and that of the subcutaneous fat (SF) at the edges of cooling boluses with OBs was lower than that of the SF without OBs. The use of OBs reduced the overheating of the SF. The 0.5% salt solution in the OB produced the least overheated areas outside the deep target tumor compared with the other concentrations. The insertion of the intergluteal cleft (IGC) bolus could improve the temperature concentration of the deep target tumor. Conclusions: The use of OBs and the salt solution concentration in the OB were important to optimize the temperature distribution. IGC bolus might contribute to temperature optimization. Further studies with individualized numerical simulations in each patient are expected.