Materials and Methods HIFU Equipment

For this study, we used a modified second- and third-generation device called the Sonablate 200 and 500 (Focus Surgery, Indianapolis, IN, USA) in 35 and 50 patients, respectively. A treatment module includes the ultrasound power generator, multiple transrectal probes of different focal depths, the probe positioning system, and a cooling system (Fig. 1). The transrectal HIFU probes use proprietary transducer technology with low-energy ultrasound (4 MHz) for imaging of the prostate and for the delivery of high-energy ablative pulses (site intensity, 1300-2200W/cm2). The single piezoelectric crystal alternates between high-energy ablative (1-4sec) and low-energy (6-12 sec) ultrasound for a total cycle of 7-16sec.

Fig. 1. The Sonablate 500 type device consists of an operator's console, imaging monitor, transrectal probe, and an automatic continuous cooling system

Fig. 1. The Sonablate 500 type device consists of an operator's console, imaging monitor, transrectal probe, and an automatic continuous cooling system

Fig. 2. High-intensity ultrasound was focused on the specific lesion (3 x 3 x 10 mm)

Before the start of treatment, the operator uses longitudinal and transverse sonograms by imaging of the prostate and selects the prostate tissue volume to be ablated by a set of cursors on these images. The probe houses a computer-controlled positioning system that directs each ablative pulse to the targeted region of the prostate. Each discrete high-energy focused ultrasonic pulse ablates a volume of 2 x 2 x 10mm3 in a single beam for 2.5-, 3.0-, 3.5-, 4.0-, and 4.5-cm focal length probes with Sonablate 200, and 3 x 3 x 10 mm (Fig. 2) of tissue in a split beam for 3.0- and 4.0-cm focal length probes with Sonablate 500 [15-18]. For a single beam, the operation power density is set by the computer using the tissue depth measurements. In the split-beam mode, the total acoustic power is initially set at 24 and 37W for 3.0- and 4.0-cm focal length probes, respectively. The individual focal lesion produces almost instantaneous coagulative necrosis of the tissue due to a temperature rise of 80° to 98°C in the focal zone [17,18]. Under computer control, the ultrasound beam is steered mechanically to produce consecutive lesions in a manner such that all focal lesions overlap lat-

Fig. 3. The computer-controlled transducer ablates the entire prostate tissue. Focal lesions are overlapped in linear rows (left) at each of the lateral sector positions (right) to create a volume lesion

erally and longitudinally to ensure necrosis of the entire targeted prostate volume (Fig. 3). A semiautomatic or automatic cooling device is used during treatment to maintain a constant baseline temperature of less than 37° and 18°C in the transrectal probe that helps to prevent thermal injury of the rectal mucosa with the Sonablate 200 and 500, respectively.

Was this article helpful?

0 0

Post a comment