Simulating Hyperthermia Treatment: How CST Helps Design Safer RF Cancer Therapy

Introduction
Hyperthermia (RF/microwave-based heating of tumor tissue to ~42–47 °C) is an established adjunct therapy that can sensitize tumors to radiotherapy and chemotherapy. Designing clinically safe and effective treatments requires careful control of where RF energy is deposited to avoid overheating healthy tissue. Simulation enables engineers and clinicians to evaluate antenna placements, phasing strategies, and patient-specific outcomes before trials.

Model Setup in CST Studio Suite
The simulation uses a voxel patient model (named ‘Laura’ in the setup) placed on a simple support table. A cylindrical water bolus surrounds the region of interest (Pelvic region) and eight dipole antennas are arranged around this bolus. The dipoles act as the RF applicators. Key components modeled in CST:

• Voxel patient model (skin, fat, muscle, tumor regions)
• Eight dipole applicators placed symmetrically around the pelvic region
• Cylindrical water bolus between antennas and skin (impedance matching and maximizing the energy deposition to the targeted tumor tissue region)
• Simple supporting table geometry to capture structural reflections
• The geometry is inspired by common clinical phased-array hyperthermia devices.

2) Electromagnetic (HF) Solver Workflow & Settings
Solver and domain settings used in the HF stage:

• Solver: Time Domain (Transient) solver in CST Microwave Studio
• Frequency sweep range: 0 – 100 MHz (main operating frequency ~90 MHz)
• Boundary conditions: Open (add space) on all six sides to mimic free‑space radiation
• Mesh type: Hexahedral FIT
• Solver accuracy (stopping criterion): −40 dB (residual energy)
• Excitation: simultaneous multi‑port excitation (Ports 1–8) with amplitude = 1.0 and phase = 0° for each port
• Excitation signal: Gaussian pulse covering the 0–100 MHz band (broadband excitation to extract frequency response)

EM High‑Frequency Results
S-parameters:

The S-parameter plot (Ports 1–8) shows the resonance and matching behaviour across 0–100 MHz band. Around the therapeutic band (~90 MHz), the return losses (S11…S88) are mostly below −10 dB, indicating acceptable matching. At some resonant peaks between 70–80 MHz, certain ports reach values near −40 dB, which reflects excellent coupling. Overall, the results confirm that the dipole array is well matched in the treatment frequency band, ensuring that most of the input power is delivered into the targeted tumour tissue rather than being reflected back.

E-field (f=90MHz)

POWER LOSS DENSITY (f=90MHz)

EM → Thermal Coupling: Exporting Losses
The HF solver’s volumetric power loss density (W/m³) is exported and used as the volumetric heat source for the thermal solver. This export step uses the ‘Thermal Loss Calculation’ post processing template in CST to convert EM absorption into thermal loads.
Using the HF-derived volumetric losses as heat sources, the thermal solver produced steady-state temperature maps that show a localized hot spot at the tumor location and safe temperature levels in surrounding tissue.

• Maximum temperature in tumor region: ≈ 48.6 °C (note: different runs/scaling produced values ≈46.6–48.6 °C depending on power scaling)
• Minimum temperature in peripheral regions: ≈ 24.0–24.4 °C
• Healthy tissue near the tumor remains close to baseline (~37 °C in our model)

Interpretation: A tumor temperature in the 42–47 °C range is considered therapeutic for hyperthermia treatments. The solver reproduced selective heating behavior, with the tumor reaching the therapeutic range while surrounding tissue remained at safe physiological levels.

Temperature result

Heat flow result

Conclusion
This study demonstrates how CST Studio Suite can accurately link electromagnetic and thermal simulations to predict the outcome of hyperthermia treatments. By modelling patient anatomy, antenna arrays, and heat transfer, engineers can validate antenna performance and temperature distribution before clinical trials, reducing design risks and improving patient safety.

We Urge You To Call Us For Any Doubts & Clarifications That You May Have. We Are Eager to Talk To You

Call Us: +91 7406663589