Sunnybrook Health Sciences Centre, 2075 Bayview Avenue, Toronto, Ontario M4N 3M5, Canada.
Med Phys. 2010 Jun;37(6):2862-75. doi: 10.1118/1.3426313.
MRI-guided transurethral ultrasound therapy can generate highly accurate volumes of thermal coagulation conforming to 3D human prostate geometries. This work simulated, quantified, and evaluated the thermal impact of these treatments on the rectum, pelvic bone, neurovascular bundles (NVBs), and urinary sphincters because damage to these structures can lead to complications.
Twenty 3D anatomical models of prostate cancer patients were used with detailed bioacoustic simulations incorporating an active feedback algorithm which controlled a rotating, planar ultrasound transducer (17, 4 x 3 mm2 elements, 10 W(acoustic)/cm2). Heating of the adjacent surrounding anatomy was evaluated at 4.7, 9.7, and 14.2 MHz using thermal tolerances reported in literature.
Heating of the rectum posed the most important safety concern, influenced largely by the water temperature of an endorectal cooling device (ECD); depending on anatomy, temperatures of 7-37 degrees C were required to limit potential damage to less than 10 mm3 on the outer 1 mm layer of the rectal wall. Heating of the pelvic bone could be important at 4.7 MHz. A smaller sized ECD or a higher ultrasound frequency in sectors where the bone was less than 10 mm from the prostate reduced heating in all cases below the threshold for irreversible damage. Heating of the NVB was significant in 75% of the patient models in the absence of treatment planning; this proportion was reduced to 5% by increasing treatment margins up to 4 mm. To avoid damaging the urinary sphincters, the transducer should be positioned at least 2-4 mm from the sphincters, depending on the transurethral cooling temperature.
Simulations show that MRI-guided transurethral therapy can treat the prostate accurately, but in the absence of treatment planning, some thermal impact can be predicted on the surrounding anatomy. Treatment planning strategies have been developed, which reduce thermal injury to the surrounding anatomy.
MRI 引导经尿道超声治疗可以产生高度精确的热凝固体积，与 3D 人体前列腺几何形状相符。这项工作模拟、量化和评估了这些治疗对直肠、骨盆骨、神经血管束 (NVB) 和尿括约肌的热影响，因为这些结构的损伤可能导致并发症。
使用 20 个前列腺癌患者的 3D 解剖模型，结合主动反馈算法进行详细的生物声学模拟，该算法控制旋转平面超声换能器 (17 个，4 x 3mm2 元件，10 W(声)/cm2)。在文献中报道的热耐受范围内，使用 4.7、9.7 和 14.2MHz 评估相邻周围解剖结构的加热情况。
直肠加热是最重要的安全关注点，主要受直肠内冷却装置 (ECD) 的水温影响；根据解剖情况，需要 7-37°C 的温度，以将直肠壁外 1mm 层的潜在损伤限制在 10mm3 以下。在 4.7MHz 时，骨盆骨的加热可能很重要。在骨骼距离前列腺小于 10mm 的区域，使用较小尺寸的 ECD 或更高的超声频率可以降低所有情况下的加热，使其低于不可逆损伤的阈值。在没有治疗计划的情况下，75%的患者模型中 NVB 的加热是显著的；通过将治疗边缘增加到 4mm，可以将这个比例降低到 5%。为了避免损伤尿括约肌，换能器应至少距离括约肌 2-4mm，具体取决于经尿道冷却温度。
模拟结果表明，MRI 引导经尿道治疗可以精确治疗前列腺，但在没有治疗计划的情况下，周围解剖结构可能会受到一定的热影响。已经制定了治疗计划策略，可以减少周围解剖结构的热损伤。
