Thermal Therapy Research Group, Department of Radiation Oncology, University of California at San Francisco, San Francisco, California 94143-1708, USA.
Int J Hyperthermia. 2010 Feb;26(1):39-55. doi: 10.3109/02656730903341332.
A patient-specific optimisation-based hyperthermia treatment planning program for catheter-based ultrasound technology was developed for a priori evaluation of proposed applicator implant strategies and determination of initial applied power settings. The interstitial and endocavity heating applicators, designed for delivering 3-D controllable hyperthermia within High Dose Rate (HDR) brachytherapy implants, consist of linear and sectored arrays of ultrasound transducers with variable power control in both length and angle. A 3D biothermal model, which incorporates relevant anatomical structures and implant geometries based upon HDR treatment planning, has been developed to simulate the temperature distributions induced by these ultrasound applicators within the catheter implants. A temperature-based constrained optimisation algorithm was devised and integrated within the finite-element thermal solver to determine the optimal applied power levels. A temperature-expressed objective function and constraints were employed to limit maximum temperature (T(max)), maximise target coverage (T(target)), and minimise thermal exposure to normal tissue and surrounding organs. The optimisation-based treatment planning was applied on representative examples of clinical HDR implants for endocavity treatment of cervix (n = 3) and interstitial treatment of prostate (n = 3). Applicator positioning and orientation, T(max), and T(target), were varied, and temperature volume and thermal dose volume histograms calculated for each plan. The optimisation approach provided optimal applied power levels (4-24 independent transducer sections) leading to conforming or tailored temperature distributions for all cases, as indicated with improved temperature index T(90) in the target volume and negligible temperature and thermal dose (t(43,max) < 1 min) exposure in surrounding non-targeted tissues, such as bladder and rectum. The precision of the optimised power estimates was shown to be within <5% for a range of starting levels and were similarly convergent. The execution times of this optimisation (<16 min) and forward thermal treatment planning (<22 min) is sufficiently fast to be integrated into the clinical setting. This optimisation-based treatment planning platform for catheter-based ultrasound applicators is a useful tool to provide feedback for applicator selection (sector angle, number of transducer sections along length), positioning (angle or orientation), optimal initial power settings, and has potential to significantly improve the delivery of hyperthermia in conjunction with HDR brachytherapy.
为了对提出的施源器植入策略进行预先评估并确定初始应用功率设置，我们开发了一种基于患者个体化优化的适用于基于导管的超声技术的高温治疗计划程序。设计用于在高剂量率（HDR）近距离治疗植入物中提供 3-D 可控高温的间质和腔内加热施源器，由超声换能器的线性和扇形阵列组成，在长度和角度上都具有可变功率控制。已经开发了一个 3D 生物热模型，该模型根据 HDR 治疗计划纳入了相关的解剖结构和植入物几何形状，以模拟这些超声施源器在导管植入物内引起的温度分布。设计了一个基于温度的约束优化算法，并将其集成到有限元热求解器中，以确定最佳应用功率水平。采用温度表达的目标函数和约束条件来限制最大温度（T(max)）、最大化目标覆盖（T(target)）以及最小化正常组织和周围器官的热暴露。基于优化的治疗计划应用于代表临床 HDR 植入物的示例，用于宫颈腔内治疗（n=3）和前列腺间质治疗（n=3）。改变施源器的定位和方向、T(max)和 T(target)，并为每个计划计算温度体积和热剂量体积直方图。优化方法提供了最佳的应用功率水平（4-24 个独立的换能器部分），为所有病例提供了一致或定制的温度分布，表现为目标体积中的温度指数 T(90)得到改善，以及周围非目标组织（如膀胱和直肠）中的温度和热剂量（t(43,max)<1 分钟）暴露可忽略不计。优化功率估计的精度在各种起始水平下都显示在<5%以内，并且收敛性相似。这种基于优化的导管超声施源器的治疗计划平台是一种有用的工具，可以为施源器选择（扇区角度、长度上的换能器部分数量）、定位（角度或方向）、最佳初始功率设置提供反馈，并有可能显著提高与 HDR 近距离治疗联合应用的高温治疗效果。
