Objective: Microwave hyperthermia is a clinically validated adjunctive therapy in oncology, employing antenna applicators to selectively raise tumor tissue temperature to 40–44 °C. For deep-seated tumors, especially those in anatomically complex areas like the head and neck (H&N) region, phased array antennas are typically employed. Determining optimal antenna feeding coefficients is crucial to maximize the specific absorption rate (SAR) within the tumor and minimize hotspots in healthy tissues. Conventionally, this optimization relies on meta-heuristic global algorithms such as particle swarm optimization (PSO). Methods: In this study, we consider a deterministic alternative to PSO in microwave hyperthermia SAR-based optimization, which is based on the Alternating Projections Algorithm (APA). This method iteratively projects the electric field distribution onto a set of constraints to shape the power deposition within a predefined mask, enforcing SAR focusing within the tumor while actively suppressing deposition in healthy tissues. To address the challenge of selecting appropriate power levels, we introduce an adaptive power threshold search mechanism using a properly defined quality parameter, which quantifies the excess of deposited power in healthy tissues. Results: The proposed method is validated on both a simplified numerical testbed and a realistic anatomical phantom. Results demonstrate that the proposed method achieves heating quality comparable to PSO in terms of tumor targeting, while significantly improving hotspot suppression. Conclusions: The proposed APA framework offers a fast and effective deterministic alternative to meta-heuristic methods, enabling SAR-based optimization in microwave hyperthermia with improved tumor targeting and enhanced suppression of hotspots in healthy tissue.
目的：微波热疗是一种临床验证有效的肿瘤辅助疗法，通过天线辐射器选择性将肿瘤组织温度提升至40–44°C。针对深部肿瘤，尤其是头颈部等解剖结构复杂区域的肿瘤，通常采用相控阵天线系统。确定最优天线馈电系数对于最大化肿瘤内比吸收率（SAR）并最小化健康组织中的热点至关重要。传统优化方法主要依赖粒子群优化等元启发式全局算法。 方法：本研究提出一种基于交替投影算法的确定性优化方法，作为粒子群优化在微波热疗SAR优化中的替代方案。该方法通过迭代将电场分布投影至约束集，在预设掩模内重塑功率沉积分布，强制实现肿瘤内SAR聚焦，同时主动抑制健康组织中的能量沉积。针对功率水平选择的难题，我们引入基于精确定义质量参数的自适应功率阈值搜索机制，该参数可量化健康组织中沉积功率的超标程度。 结果：在简化数值测试平台和真实解剖模型上的验证表明，所提方法在肿瘤靶向性方面达到与粒子群优化相当的加热质量，同时显著提升热点抑制效果。 结论：提出的交替投影算法框架为元启发式方法提供了一种快速有效的确定性替代方案，能够在微波热疗中实现基于SAR的优化，在提升肿瘤靶向精度的同时增强对健康组织热点的抑制能力。
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