Background and objectives

Image-guided medical interventions facilitates precise visualization at treatment site. The conformal prediction for sparing healthy tissue fringes precisely in the vicinity of irregular tumour anatomy remains clinically challenging. Pre-clinical image-based computational modelling is imperative as it helps in enhancement of treatment quality, augmenting clinical-decision making, while planning, targeting, controlling, monitoring and assessing treatment response with an effective risk assessment before the onset of treatment in clinical settings. In this study, the influence of heat deposition rate (SAR), exposure duration, and variable blood perfusion metrics for a patient-specific breast tumour is quantified considering the tumour margins thereby suggesting need of geometrically accurate models.

Methods

A three-dimensional realistic model mimicking dimensions of a female breast, comprising ~1.7 cm irregular tumour, was generated from patient specific two-dimensional DICOM format MRI images through image segmentation tools MIMICS 19.0® and 3-Matic 11.0® which is finally exported to COMSOL Multiphysics 5.2® as a volumetric mesh for finite element analysis. The Pennes bioheat transfer model and Arrhenius thermal damage model of cell-death are integrated to simulate a coupled biophysics problem. A comparative blood perfusion analysis is done to evaluate the response of tumour during heating considering thermal damage extent, including the tumour margins while sparing critical adjoining healthy tissues.

Results

The evaluated thermal damage zones for 1 mm, 2 mm and 3 mm fringe heating region (beyond tumour boundary) reveals 0.09%, 0.21% and 0.34% thermal damage to the healthy tissue (which is <1%) and thus successful necrosis of the tumour. The iterative computational experiments suggests treatment margins < 5 mm are sufficient enough as heating beyond 3 mm fringe layer leads to higher damage surrounding the tumour approximately 1.5 times the tumour volume. Further, the heat-dosage requirements are 22% more for highly perfused tumour as compared to moderately perfused tumour with an approximate double time to ablate the whole tumour volume.

Conclusions

Depending on the blood perfusion characteristics of a tumour, it is a trade-off between heat-dosage (SAR) and exposure/treatment duration to get desired thermal damage including the irregular tumour boundaries while taking into account, the margin of healthy tissue. The suggested patient-specific integrated multiphysics-model based on MRI-Images may be implemented for pre-treatment planning based on the tumour blood perfusion to evaluate the thermal ablation zone dimensions clinically and thereby avoiding the damage of off-target tissues. Thus, risks involving underestimation or overestimation of thermal coagulation zones may be minimised while preserving the surrounding normal breast parenchyma.

中文翻译：

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术前评估基于磁共振成像的复杂乳腺肿瘤解剖学中可变血流指标的消融余量：热疗法的模拟范例

背景和目标

图像引导的医疗干预措施可促进治疗部位的精确可视化。精确地在不规则肿瘤解剖结构附近保留健康组织条纹的保形预测在临床上仍然具有挑战性。临床前基于图像的计算模型势在必行，因为它有助于提高治疗质量，增强临床决策水平，同时在临床环境中开始治疗之前规划，靶向，控制，监测和评估治疗反应并进行有效的风险评估。在这项研究中，考虑到肿瘤的边缘，对患者特定乳腺肿瘤的热量沉积速率（SAR），暴露持续时间和可变血液灌注指标的影响进行了量化，从而表明需要几何精确的模型。

方法

通过图像分割工具MIMICS19.0®和3-Matic11.0®从患者特定的二维DICOM格式MRI图像中生成了一个模拟女性乳房的三维逼真的模型，包括约1.7 cm不规则肿瘤，最终被导出至COMSOL Multiphysics5.2®作为体积网格，用于有限元分析。将Pennes生物死亡的热传递模型和Arrhenius热损伤模型进行了整合，以模拟耦合的生物物理问题。考虑到热损伤的程度（包括肿瘤边缘，同时保留了重要的毗邻健康组织），进行了比较性血液灌注分析以评估加热期间肿瘤的反应。

结果

评估的1毫米，2毫米和3毫米边缘加热区域（超出肿瘤边界）的热损伤区域显示，对健康组织的热损伤为0.09％，0.21％和0.34％（<1％），从而成功破坏了组织。瘤。迭代的计算实验表明，<5 mm的处理余量就足够了，因为加热超过3 mm的条纹层会导致围绕肿瘤的更高损伤，约为肿瘤体积的1.5倍。此外，与中等程度灌注的肿瘤相比，高度灌注的肿瘤的热剂量需求高​​出22％，而消融整个肿瘤体积的时间大约是两倍。

结论

取决于肿瘤的血液灌注特性，在热剂量（SAR）与暴露/治疗持续时间之间进行权衡，以在考虑健康组织裕度的同时获得所需的热损伤，包括不规则的肿瘤边界。建议的基于MRI图像的特定于患者的综合多物理场模型可以用于基于肿瘤血液灌注的治疗前规划，从而在临床上评估热消融区域的尺寸，从而避免脱靶组织的损伤。因此，在保持周围正常乳房实质的同时，可以将涉及低估或高估热凝区的风险降至最低。