3D versus 2D steering in patient anatomies: a comparison using hyperthermia treatment planning.

PURPOSE: In this study hyperthermia treatment planning is used to investigate whether the target temperature during hyperthermia treatment can be increased using the 3D AMC-8 instead of the 2D AMC-4 system (AMC: Academic Medical Center). METHODS AND MATERIALS: The heating ability of the AMC-4 and AMC-8 system was analysed for five patients with cervix uteri carcinoma. Dielectric and thermal models were generated, based on a hyperthermia planning computerised tomography (CT), at a resolution of 2.5 × 2.5 × 5.0 mm(3). Calculation of the electric fields with the finite-difference time-domain method was followed by SAR- and temperature-based optimisation. The ability to correct for axial shifts of the patient by phase/amplitude steering was investigated for both systems. Finally, it was investigated whether adjusting the ring-to-ring distance of the AMC-8 system can be used for further optimisation. RESULTS: An average increase in T(90) of ∼0.5°C (0.2°-0.8°C) was found for the AMC-8 system compared to the AMC-4 system. The gain in T(50) and T(10) was also 0.5°C on average. The additional power required to achieve this gain was 36% to 71% of the power required for the AMC-4 system. The AMC-8 system has the capability of correcting changes in axial position (-8 cm, +8 cm), contrary to the AMC-4 system. For both systems the axial position should be known within 1-2 cm. CONCLUSIONS: Hyperthermia treatment with the AMC-8 system can lead to a clinically relevant increase of the target temperature compared to treatment with the AMC-4 system. The AMC-8 system provides large freedom in the axial positioning of the patient.