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

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 xx 2.5 xx 5.0 mm <SU3 </SU. 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 similar to similar to 0.5 degrees A degrees C (0.2 degrees A degrees--0.8 degrees A degrees 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 degrees A degrees 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