MRI-guided interstitial ultrasound thermal therapy of the prostate: A feasibility study in the canine model

Department of Comparative Medicine, Stanford University, Palo Alto, California, United States
Medical Physics (Impact Factor: 2.64). 03/2005; 32(3):733-43. DOI: 10.1118/1.1861163
Source: PubMed


The feasibility of MRI-guided interstitial ultrasound thermal therapy of the prostate was evaluated in an in vivo canine prostate model. MRI compatible, multielement interstitial ultrasound applicators were developed using 1.5 mm diameter cylindrical piezoceramic transducers (7 to 8 MHz) sectored to provide 180 degrees of angular directional heating. Two in vivo experiments were performed in canine prostate. The first using two interstitial ultrasound applicators, the second using three ultrasound applicators in conjunction with rectal and urethral cooling. In both experiments, the applicators were inserted transperineally into the prostate with the energy directed ventrally, away from the rectum. Electrical power levels of 5-17 W per element (approximately 1.6-5.4 W acoustic output power) were applied for heating periods of 18 and 48 min. Phase-sensitive gradient-echo MR imaging was used to monitor the thermal treatment in real-time on a 0.5 T interventional MRI system. Contrast-enhanced T1-weighted images and vital-stained serial tissue sections were obtained to assess thermal damage and correlate to real-time thermal contour plots and calculated thermal doses. Results from these studies indicated a large volume of ablated (nonstained) tissue within the prostate, extending 1.2 to 2.0 cm from the applicators to the periphery of the gland, with the dorsal margin of coagulation well-defined by the applicator placement and directionality. The shape of the lesions correlated well to the hypointense regions visible in the contrast-enhanced T1-weighted images, and were also in good agreement with the contours of the 52 degrees C threshold temperature and t43 > 240 min. This study demonstrates the feasibility of using directional interstitial ultrasound in conjunction with MRI thermal imaging to monitor and possibly control thermal coagulation within a targeted tissue volume while potentially protecting surrounding tissue, such as rectum, from thermal damage.

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    • "The ability of catheter-based ultrasound devices to deliver conformal heating has been demonstrated in phantom, ex vivo, and in vivo using implanted thermometry and MR thermal imaging (Diederich et al 2004, Nau et al 2005b, Wootton et al 2009). Devices suitable for interstitial insertion can heat radially up to 10–15 mm (Diederich et al 2000, Nau et al 2005a). A catheter-based ultrasound device has been developed for endocervical insertion that can heat 2–4 cm diameter targets within the cervix (Wootton et al 2011), and the heating zone can potentially be extended to treat larger tumors by the additional implantation of interstitial devices in the periphery. "
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    ABSTRACT: Catheter-based ultrasound devices provide a method to deliver 3D conformable heating integrated with HDR brachytherapy delivery. Theoretical characterization of heating patterns was performed to identify implant strategies for these devices which can best be used to apply hyperthermia to cervical cancer. A constrained optimization-based hyperthermia treatment planning platform was used for the analysis. The proportion of tissue ≥41 °C in a hyperthermia treatment volume was maximized with constraints T(max) ≤ 47 °C, T(rectum) ≤ 41.5 °C, and T(bladder) ≤ 42.5 °C. Hyperthermia treatment was modeled for generalized implant configurations and complex configurations from a database of patients (n = 14) treated with HDR brachytherapy. Various combinations of endocervical (360° or 2 × 180° output; 6 mm OD) and interstitial (180°, 270°, or 360° output; 2.4 mm OD) applicators within catheter locations from brachytherapy implants were modeled, with perfusion constant (1 or 3 kg m(-3) s(-1)) or varying with location or temperature. Device positioning, sectoring, active length and aiming were empirically optimized to maximize thermal coverage. Conformable heating of appreciable volumes (>200 cm(3)) is possible using multiple sectored interstitial and endocervical ultrasound devices. The endocervical device can heat >41 °C to 4.6 cm diameter compared to 3.6 cm for the interstitial. Sectored applicators afford tight control of heating that is robust to perfusion changes in most regularly spaced configurations. T(90) in example patient cases was 40.5-42.7 °C (1.9-39.6 EM(43 °C)) at 1 kg m(-3) s(-1) with 10/14 patients ≥41 °C. Guidelines are presented for positioning of implant catheters during the initial surgery, selection of ultrasound applicator configurations, and tailored power schemes for achieving T(90) ≥ 41 °C in clinically practical implant configurations. Catheter-based ultrasound devices, when adhering to the guidelines, show potential to generate conformal therapeutic heating ranging from a single endocervical device targeting small volumes local to the cervix (<2 cm radial) to a combination of a 2 × 180° endocervical and directional interstitial applicators in the lateral periphery to target much larger volumes (6 cm radial), while preferentially limiting heating of the bladder and rectum.
    Full-text · Article · Jul 2011 · Physics in Medicine and Biology
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    • "Excellent results have been obtained (both experimentally and clinically) in inducing homogeneous and reproducible tumor destruction by thermal coagulation necrosis. Recently, several authors have suggested using miniaturized applicators for therapeutic ultrasound [7-9], which makes it an approach that is particularly appropriate for carcinoma of the esophageal ducts. "
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    ABSTRACT: Esophageal tumors generally bear a poor prognosis. Radical surgery is generally the only curative method available but is not feasible in the majority of patients; palliative therapy with stent placement is generally performed. It has been demonstrated that High Intensity Ultrasound can induce rapid, complete and well-defined coagulation necrosis. Thus, for the treatment of esophageal tumors, we have designed an ultrasound applicator that uses an intraluminal approach to fill up this therapeutic gap. Thermal ablation is performed with water-cooled ultrasound transducers operating at a frequency of 10 MHz. Single lesions extend from the transducer surface up to 10 mm in depth when applying an intensity of 14 W/cm2 for 10s. A lumen inside the therapy applicator provides path for an endoscopic ultrasound imaging probe operating at a frequency of 12 MHz. The mechanical rotation of the applicator around its axis enables treatment of sectorial or cylindrical volumes. This method is thus particularly suitable for esophageal tumors that may develop only on a portion of the esophageal circumference. Previous experiments were conducted from bench to in vivo studies on pig esophagi. Here we report clinical results obtained on four patients included in a pilot study. The treatment of esophageal tumors was performed under fluoroscopic guidance and ultrasound imaging. Objective tumor response was obtained in all cases and a complete necrosis of a tumor was obtained in one case. All patients recovered uneventfully and dysphagia improved significantly within 15 days, allowing for resuming a solid diet in three cases. This clinical work demonstrated the efficacy of intraluminal high intensity ultrasound therapy for local tumor destruction in the esophagus.
    Full-text · Article · Feb 2008 · Journal of Translational Medicine
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    ABSTRACT: It was hypothesized that the fiber-guided Nd:YAG laser with its incisional and hemostatic action, could be useful for meticulous tissue dissection in a subcapsular partial prostatectomy in dogs, and in laparoscopic surgery of dogs and cats. Prior to clinical use, its action was investigated in vitro. Spatial distribution of Nd:YAG laser-induced temperature distribution was investigated in a polyacrylamide gel using a dynamic color schlieren technique, comparing contact and free beam laser exposure. Short-term (up to 20s), laser-induced, thermal damage was investigated in ex vivo canine prostate tissue. Tissue temperature was measured using thermocouple probes. Prediction of thermal damage using Arrhenius theory was discussed and compared to the in vitro damage threshold, determined by histological evaluation. Contact mode laser application caused vaporization of tissue. Mean extend of tissue damage underneath the vaporization crater floor was <1 mm after 5, 10 or 20s of contact mode laser irradiation at 10W, whereas 20s of 20W non-contact exposure caused >4 mm coagulation necrosis. The tissue damage results were comparable to the schlieren temperature distributions, indicating that the schlieren technique can be used to model laser-tissue interaction. The laser was used in subcapsular partial prostatectomy in 4 mongrel dogs and in 8 dogs with prostate carcinoma (PCA). The urethra and dorsal capsule were spared and urinary continence was maintained postoperatively. It was concluded that laser assisted subcapsular partial prostatectomy is a potential palliative treatment for PCA in dogs and that the Nd:YAG laser is capable of precise prostate tissue dissection with acceptable thermal damage margins, comparable to the in vitro study. The Nd:YAG laser was compared to bipolar electrocoagulation (BEC) forceps in laparoscopic ovariectomy (lapOVE) in dogs and cats. The Remorgida forceps, combining BEC and sharp incision in one instrument, was compared to laser surgery in lapOVE in dogs. Laparoscopic laser ovariectomy was useful but did not have a significant advantage over BEC-OVE. The main reason for this is that blood vessels of >2 mm in diameter can not be properly coagulated with the laser, and BEC forceps were still needed to prevent mesovarial hemorrhage. The Remorgida forceps reduced surgical time, was not associated with an increased complication rate, produced less fume, and was used as a stand-alone device in ovariectomy. Under certain circumstances (pedicles containing much adipose tissue) the laser performed better than Remorgida. Laser surgery took more time (~2 min) than bipolar electrosurgery in lapOVE. Obesity significantly increased surgery duration in dogs, but not in cats because of the small amount of adipose tissue in the ovarian ligament of cats. No major difficulties or complications were encountered during or after surgery. In cats, low-pressure pneumoperitoneum, easy manipulation of the ovaries and a minimal amount of fat in the ovarian ligament facilitated excellent surgical access and outcome. The main conclusion is that the Nd:YAG laser is useful for precise open and laparoscopic soft tissue surgery, with minimal accompanying thermal tissue damage and adequate hemostasis, except for blood vessels of >2 mm in diameter which are best coagulated using bipolar forceps.
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