The effect of resolution on microwave hyperthermia focal quality

Abstract

Breast cancer remains one of the most prevalent forms of cancer affecting women globally, with over 2.5 million new cases reported annually. If not diagnosed and treated properly, it can be life-threatening. Fortunately, early diagnosis and advances in therapeutic approaches have significantly improved survival rates. Traditional treatment options include surgical methods such as lumpectomy and mastectomy, as well as non-invasive techniques like radiotherapy and chemotherapy. Recently, hyperthermia therapy—especially microwave hyperthermia—has emerged as a powerful adjunct to these modalities, aiming to increase treatment efficacy by elevating tumor temperature to damage or kill cancerous cells without harming surrounding healthy tissues. Among these factors, particular emphasis is placed on the effect of anatomical segmentation resolution on the focal quality of microwave hyperthermia. Microwave breast hyperthermia (MH) targets tumor regions by raising their temperature to therapeutic levels, typically between 41°C and 45°C. The effectiveness of MH relies heavily on the ability to focus energy precisely at the tumor site while minimizing unintended heating, or "hotspots," in adjacent healthy tissue. To ensure safety and efficacy, the distribution of Specific Absorption Rate (SAR)—which quantifies the amount of electromagnetic energy absorbed per kilogram of tissue—must be carefully optimized. The design of the hyperthermia system plays a pivotal role in achieving this goal, especially in scenarios where inter-patient anatomical variability introduces complexity into the treatment planning. In this study, a comprehensive numerical investigation was conducted to evaluate the sensitivity of SAR and temperature distributions to variations in tissue segmentation resolution. A realistic numerical breast model was constructed from MRI-based anatomical data and segmented using Gaussian filtering techniques to generate multiple representations with different resolution levels. By varying the Gaussian standard deviation ($\sigma$) parameters, the effect of segmentation resolution on electromagnetic energy deposition was quantitatively analyzed. It was observed that lower $\sigma$ values preserve anatomical detail and enhance SAR localization, whereas higher $\sigma$ values introduce excessive smoothing, leading to degraded focal quality. While SAR values varied with changes in permittivity and conductivity, the resulting temperature distributions remained relatively stable, indicating thermal diffusion dominates the ultimate heating pattern. Energy localization was achieved using a vector-based maximization strategy, in which the complex electric field contributions from individual antennas were coherently combined to maximize the resultant field intensity at the target location. In this approach, the excitation amplitudes were fixed for all antennas, and the phase of each antenna was set to zero at the target point. This phase setting enforces constructive interference at the target, allowing the electric field vectors to be added tip-to-tail in a consistent manner. The resulting fixed excitation configuration enables systematic scanning of the surrounding region, facilitating the assessment of focal quality robustness under varying segmentation resolutions. The findings of this study contribute to a deeper understanding of the impact of segmentation resolution on microwave hyperthermia focal quality, offering guidance for improving the robustness and reliability of image-based treatment planning in personalized breast cancer therapy.