考虑基于导管的超声源的热消融的理论建模：对治疗计划、监测和控制的影响。
Considerations for theoretical modelling of thermal ablation with catheter-based ultrasonic sources: implications for treatment planning, monitoring and control.
机构信息
Thermal Therapy Research Group, Department of Radiation Oncology, University of California-San Francisco, CA 94143, USA.
出版信息
Int J Hyperthermia. 2012;28(1):69-86. doi: 10.3109/02656736.2011.630337.
PURPOSE
To determine the impact of including dynamic changes in tissue physical properties during heating on feedback controlled thermal ablation with catheter-based ultrasound. Additionally, we compared the impact of several indicators of thermal damage on predicted extents of ablation zones for planning and monitoring ablations with this modality.
METHODS
A 3D model of ultrasound ablation with interstitial and transurethral applicators incorporating temperature-based feedback control was used to simulate thermal ablations in prostate and liver tissue. We investigated five coupled models of heat dependent changes in tissue acoustic attenuation/absorption and blood perfusion of varying degrees of complexity. Dimensions of the ablation zone were computed using temperature, thermal dose, and Arrhenius thermal damage indicators of coagulative necrosis. A comparison of the predictions by each of these models was illustrated on a patient-specific anatomy in the treatment planning setting.
RESULTS
Models including dynamic changes in blood perfusion and acoustic attenuation as a function of thermal dose/damage predicted near-identical ablation zone volumes (maximum variation < 2.5%). Accounting for dynamic acoustic attenuation appeared to play a critical role in estimating ablation zone size, as models using constant values for acoustic attenuation predicted ablation zone volumes up to 50% larger or 47% smaller in liver and prostate tissue, respectively. Thermal dose (t(43) ≥ 240 min) and thermal damage (Ω ≥ 4.6) thresholds for coagulative necrosis are in good agreement for all heating durations, temperature thresholds in the range of 54°C for short (<5 min) duration ablations and 50°C for long (15 min) ablations may serve as surrogates for determination of the outer treatment boundary.
CONCLUSIONS
Accounting for dynamic changes in acoustic attenuation/absorption appeared to play a critical role in predicted extents of ablation zones. For typical 5-15 min ablations with this modality, thermal dose and Arrhenius damage measures of ablation zone dimensions are in good agreement, while appropriately selected temperature thresholds provide a computationally cheaper surrogate.
目的
确定在基于导管的超声热消融中，在加热过程中包含组织物理特性的动态变化对反馈控制热消融的影响。此外，我们比较了几种热损伤指标对该模式下消融区预测范围的影响，以用于规划和监测消融。
方法
使用 3D 模型模拟经皮和经尿道应用程序的超声消融，该模型包含基于温度的反馈控制，以模拟前列腺和肝脏组织的热消融。我们研究了五种不同复杂程度的热依赖性组织声衰减/吸收和血液灌注变化的耦合模型。使用温度、热剂量和阿累尼乌斯热损伤指标（凝固性坏死）计算消融区的尺寸。在治疗计划设置中，通过比较每个模型的预测值来展示这些模型的预测结果。
结果
包括热剂量/损伤函数中的血液灌注和声衰减的动态变化的模型预测了几乎相同的消融区体积（最大变化<2.5%）。考虑到动态声衰减似乎在估计消融区大小方面起着关键作用，因为使用声衰减常数值的模型分别预测肝脏和前列腺组织的消融区体积大了 50%或小了 47%。在所有加热时间下，凝固性坏死的热剂量（t(43)≥240 分钟）和热损伤（Ω≥4.6）阈值是一致的，对于短（<5 分钟）持续时间消融，温度阈值在 54°C 范围内，对于长（15 分钟）消融，温度阈值在 50°C 范围内，可作为确定治疗边界的替代指标。
结论
在预测消融区范围方面，考虑声衰减/吸收的动态变化似乎起着关键作用。对于该方法的典型 5-15 分钟消融，热剂量和阿累尼乌斯损伤指标对消融区尺寸的测量结果一致，而适当选择的温度阈值提供了一种计算成本更低的替代指标。
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