Thermal Therapy Research Group, Department of Radiation Oncology, University of California, San Francisco, California 94115, USA.
Med Phys. 2011 Feb;38(2):598-611. doi: 10.1118/1.3512803.
The clinical success of hyperthermia adjunct to radiotherapy depends on adequate temperature elevation in the tumor with minimal temperature rise in organs at risk. Existing technologies for thermal treatment of the cervix have limited spatial control or rapid energy falloff. The objective of this work is to develop an endocervical applicator using a linear array of multisectored tubular ultrasound transducers to provide 3-D conformal, locally targeted hyperthermia concomitant to radiotherapy in the uterine cervix. The catheter-based device is integrated within a HDR brachytherapy applicator to facilitate sequential and potentially simultaneous heat and radiation delivery.
Treatment planning images from 35 patients who underwent HDR brachytherapy for locally advanced cervical cancer were inspected to assess the dimensions of radiation clinical target volumes (CTVs) and gross tumor volumes (GTVs) surrounding the cervix and the proximity of organs at risk. Biothermal simulation was used to identify applicator and catheter material parameters to adequately heat the cervix with minimal thermal dose accumulation in nontargeted structures. A family of ultrasound applicators was fabricated with two to three tubular transducers operating at 6.6-7.4 MHz that are unsectored (360 degrees), bisectored (2 x 180 degrees), or trisectored (3 x 120 degrees) for control of energy deposition in angle and along the device length in order to satisfy anatomical constraints. The device is housed in a 6 mm diameter PET catheter with cooling water flow for endocervical implantation. Devices were characterized by measuring acoustic efficiencies, rotational acoustic intensity distributions, and rotational temperature distributions in phantom.
The CTV in HDR brachytherapy plans extends 20.5 +/- 5.0 mm from the endocervical tandem with the rectum and bladder typically <8 mm from the target boundary. The GTV extends 19.4 +/- 7.3 mm from the tandem. Simulations indicate that for 60 min treatments the applicator can heat to 41 degrees C and deliver > 5EM(43 degrees C) over 4-5 cm diameter with Tmax < 45 degrees C and 1 kg m(-3) s(-1) blood perfusion. The 41 degrees C contour diameter is reduced to 3-4 cm at 3 kg m(-3) s(-1) perfusion. Differential power control to transducer elements and sectors demonstrates tailoring of heating along the device length and in angle. Sector cuts are associated with a 14-47 degrees acoustic dead zone, depending on cut width, resulting in a approximately 2-4 degrees C temperature reduction within the dead zone below Tmax. Dead zones can be oriented for thermal protection of the rectum and bladder. Fabricated devices have acoustic efficiencies of 33.4%-51.8% with acoustic output that is well collimated in length, reflects the sectoring strategy, and is strongly correlated with temperature distributions.
A catheter-based ultrasound applicator was developed for endocervical implantation with locally targeted, 3-D conformal thermal delivery to the uterine cervix. Feasibility of heating clinically relevant target volumes was demonstrated with power control along the device length and in angle to treat the cervix with minimal thermal dose delivery to the rectum and bladder.
热疗辅助放疗的临床成功取决于肿瘤内足够的温度升高，同时最大限度地降低危及器官的温度升高。现有的宫颈热治疗技术对空间控制或能量快速衰减的限制。本研究的目的是开发一种使用多节管状超声换能器线性阵列的经阴道施源器，以提供 3-D 适形、局部靶向的热疗，同时与宫颈癌放疗相结合。该基于导管的设备集成在 HDR 近距离治疗施源器内，以方便顺序和潜在的同时热和辐射输送。
对 35 例接受 HDR 近距离治疗局部晚期宫颈癌的患者的治疗计划图像进行检查，以评估围绕宫颈的辐射临床靶区（CTV）和大体肿瘤体积（GTV）的尺寸以及危及器官的接近程度。生物热模拟用于确定施源器和导管材料参数，以在非靶向结构中最小热剂量积累的情况下充分加热宫颈。制造了一系列具有两个到三个工作在 6.6-7.4MHz 的管状换能器的超声施源器，这些换能器未分段（360 度）、双分段（2 x 180 度）或三分段（3 x 120 度），以控制能量在角度和沿装置长度的沉积，以满足解剖限制。该设备安装在一个 6 毫米直径的 PET 导管中，带有冷却水流动，用于经阴道植入。通过测量声效率、旋转声强分布和在体模中的旋转温度分布来对设备进行表征。
HDR 近距离治疗计划中的 CTV 从阴道内管延伸 20.5 ± 5.0mm，直肠和膀胱通常距靶边界 <8mm。GTV 从阴道内管延伸 19.4 ± 7.3mm。模拟表明，对于 60 分钟的治疗，施源器可以加热到 41°C，并在 4-5cm 直径上输送 >5EM（43°C），最大温度 <45°C，1kg m(-3) s(-1)血液灌注。在 3kg m(-3) s(-1)灌注下，41°C 轮廓直径减小到 3-4cm。对换能器元件和扇形区的差动功率控制演示了沿装置长度和角度的加热定制。扇形区切割与 14-47 度的声死区有关，具体取决于切割宽度，导致在死区内部的最大温度以下降低 2-4°C。死区可以定向以保护直肠和膀胱免受热损伤。制造的设备的声效率为 33.4%-51.8%，声输出在长度上很好地准直，反映了扇形区策略，并与温度分布强烈相关。
开发了一种基于导管的超声施源器，用于经阴道植入，具有局部靶向、3-D 适形热疗，用于子宫颈。通过沿装置长度和角度的功率控制，对临床相关靶区进行加热，以最小的热剂量输送到直肠和膀胱，从而实现治疗宫颈的可行性。
