Department of Radiation Oncology, Duke University, Durham, NC, USA.
Phys Med Biol. 2010 Apr 7;55(7):1949-69. doi: 10.1088/0031-9155/55/7/011. Epub 2010 Mar 12.
The aim of this study was to investigate temperature and thermal dose distributions of thermobrachytherapy surface applicators (TBSAs) developed for concurrent or sequential high dose rate (HDR) brachytherapy and microwave hyperthermia treatment of chest wall recurrence and other superficial diseases. A steady-state thermodynamics model coupled with the fluid dynamics of a water bolus and electromagnetic radiation of the hyperthermia applicator is used to characterize the temperature distributions achievable with TBSAs in an elliptical phantom model of the human torso. Power deposited by 915 MHz conformal microwave array (CMA) applicators is used to assess the specific absorption rate (SAR) distributions of rectangular (500 cm(2)) and L-shaped (875 cm(2)) TBSAs. The SAR distribution in tissue and fluid flow distribution inside the dual-input dual-output (DIDO) water bolus are coupled to solve the steady-state temperature and thermal dose distributions of the rectangular TBSA (R-TBSA) for superficial tumor targets extending 10-15 mm beneath the skin surface. Thermal simulations are carried out for a range of bolus inlet temperature (T(b) = 38-43 degrees C), water flow rate (Q(b) = 2-4 L min(-1)) and tumor blood perfusion (omega(b) = 2-5 kg m(-3) s(-1)) to characterize their influence on thermal dosimetry. Steady-state SAR patterns of the R- and L-TBSA demonstrate the ability to produce conformal and localized power deposition inside the tumor target sparing surrounding normal tissues and nearby critical organs. Acceptably low variation in tissue surface cooling and surface temperature homogeneity was observed for the new DIDO bolus at a 2 L min(-1) water flow rate. Temperature depth profiles and thermal dose volume histograms indicate bolus inlet temperature (T(b)) to be the most influential factor on thermal dosimetry. A 42 degrees C water bolus was observed to be the optimal choice for superficial tumors extending 10-15 mm from the surface even under significant blood perfusion. Lower bolus temperature may be chosen to reduce the thermal enhancement ratio (TER) in the most sensitive skin where maximum radiation dose is delivered and to extend the thermal enhancement of radiation dose deeper. This computational study indicates that well-localized elevation of tumor target temperature to 40-44 degrees C can be accomplished by large surface-conforming TBSAs using appropriate selection of coupling bolus temperature.
本研究旨在探讨为胸壁复发和其他浅表疾病的同期或序贯高剂量率（HDR）近距离放疗和微波热疗而开发的热短距放疗表面敷贴器（TBSA）的温度和热剂量分布。使用稳态热力学模型结合水囊的流体动力学和热疗敷贴器的电磁辐射，对人体躯干椭圆形模型中的 TBSA 可实现的温度分布进行了特征描述。使用 915MHz 共形微波阵列（CMA）敷贴器沉积的功率来评估矩形（500cm2）和 L 形（875cm2）TBSA 的比吸收率（SAR）分布。在双输入双输出（DIDO）水囊中组织内的 SAR 分布和流体流动分布被耦合起来，以求解 TBSA 的稳态温度和热剂量分布。矩形 TBSA（R-TBSA）用于治疗皮肤下 10-15mm 处的浅表肿瘤靶区。针对水囊入口温度（T(b)=38-43°C）、水流量（Q(b)=2-4Lmin(-1)）和肿瘤血液灌注（ω(b)=2-5kgm(-3)s(-1)）的范围进行热模拟，以确定其对热剂量学的影响。R-TBSA 和 L-TBSA 的稳态 SAR 模式证明了在肿瘤靶区内产生适形和局部化功率沉积的能力，同时保护周围正常组织和附近的关键器官。在 2Lmin(-1)的水流量下，新的 DIDO 水囊的组织表面冷却和表面温度均匀性变化可以接受。温度深度分布和热剂量体积直方图表明，水囊入口温度（T(b)）是热剂量学的最主要影响因素。观察到 42°C 的水囊是从表面延伸 10-15mm 的浅表肿瘤的最佳选择，即使在有显著血液灌注的情况下也是如此。为了在最大辐射剂量处的最敏感皮肤中降低热增强比（TER），并将辐射剂量的热增强延伸得更深，可选择较低的水囊温度。这项计算研究表明，通过适当选择耦合水囊温度，大的表面适形 TBSA 可以将肿瘤靶区温度升高到 40-44°C，实现良好的局部升温。
