Probe Placements Research Articles

IS THERE A ROLE FOR CRYOABLATION OF THE PROSTATE IN THE MANAGEMENT OF LOCALIZED PROSTATE CARCINOMA?

It is impossible to adequately answer the question of whether there is a role for CSAP in the management of localized prostate carcinoma without considering the relative advantages and limitations of using other therapies to manage this disease (radical prostatectomy, radiation therapy, hormonal therapy, brachytherapy, expectant observation, and so on). Obviously, this is beyond the scope of this article. It is probably fair to point out, however, that the management of localized prostate carcinoma in the United States is generally quite controversial at the present time, and that despite a considerable amount of data pertaining to these therapeutic alternatives, it is difficult to discern a standard approach that can be broadly applied for all men with this disease. Therefore, if an absence of consensus on the management of localized prostate carcinoma does exist, it seems evident that investigations into alternative therapies are justified, and the preliminary results and efforts investigating CSAP fall well into this paradigm. In this context, several points can be made based on the available information. Significant numbers of patients who undergo CSAP can sustain undetectable levels of PSA for durable periods of time (more than 24 months). Thus, on a clinical level it seems possible to ablate the entire prostate with percutaneous CSAP, although rates of achieving this may be lower than originally anticipated. The reasons for persistence of carcinoma post CSAP are likely technical and related to the difficulties in determining the effective probe placements, number of probes to be used, number of freeze-thaw-freeze cycles to be used, and so on. Previous radiation exposure appears to confer an increased risk of CSAP-related morbidity, with incontinence, tissue sloughing, and rectal injury most prominent. Among nonradiated patients, incontinence is rare, and the most prominent postoperative concern involves BOO/tissue sloughing in a minority of patients. The longest follow-up data available on CSAP suggests that for patients with nonmetastatic prostate carcinoma, CSAP is associated with persistence of carcinoma in only 25% of patients. This compares favorably with the available biopsy data following external beam radiotherapy, in which most reports document positive biopsy results ranging between 30% and 100%, with the majority in the 40% to 50% range. Notably, the positive biopsy rate among patients with stage T3 disease following CSAP at 2 years can be less than 30%, which compares very favorably with previously reported positive biopsy result for these patients following external beam radiation therapy, which ranged between 40% and 100%. The management of patients with persistent carcinoma following CSAP poses fewer concerns to physicians than for those with persistent carcinoma following radiation therapy. Given the number of patients with prostate carcinoma who currently undergo radiotherapy as primary management, these data indicate that CSAP can now be considered a very viable therapeutic alternative for selected patients. With standardizations of technique as well as improved modifications in equipment, these preliminary CSAP results may well improve steadily in the near future. In the absence of randomized, comparative trials, it is difficult to draw meaningful comparisons between CSAP and radical prostatectomy. Based on available information, CSAP appears to be associated with a much lower incidence of stress and total incontinence than is radical prostatectomy. The rates of impotence following CSAP are somewhat comparable to those seen after radical prostatectomy, with wide variation among individual series. For patients who would be ideal candidates for radical prostatectomy (for example, less than stage T2c disease, PSA less than 10 ng/mL, and Gleason score of 7 or less), several authors have noted that the positive biopsy rate between 6 and 12 months is less than 10%.

Enhanced radiofrequency ablation of canine prostate utilizing a liquid conductor: the virtual electrode.

Conventional radiofrequency (RF) ablative techniques have shown promise for the treatment of symptomatic benign prostatic hyperplasia (BPH); however, present RF technology is limited by the small lesion size, necessitating several probe placements and heating cycles to achieve sizable lesions. This limitation is attributable primarily to a rapid increase in electrical impedance secondary to tissue desiccation and charring at the electrode tip. We devised a hollow screw-tip needle electrode that permits fixation to tissue, recording of temperature and impedance, infusion of fluid, and delivery of RF energy. Infusion of electrolyte solution (i.e., saline) into tissue prevents impedance rise by conducting RF energy away from the metal electrode and permits the creation of large lesions. By varying the conductivity of the perfusate (concentration and temperature), lesions of large diameter can be created in a controlled manner. To determine the long-term tissue effects, we applied this new modified RF technique to the prostates of five mongrel dogs in a chronic (0.5 to 8-week) study. The screw-tip electrode was serially embedded into each lobe of the perineally exposed glands with 1-minute infusion of 0.9% saline (2 mL/min) followed by application of RF energy (500 KHz, 50 W, 2-18 minutes) along with continuous saline infusion. Thermocouples were embedded 5 mm below and at the gland capsule, and RF application was discontinued when the temperature reached 50 degrees C at the periphery. Postoperatively, the animals were examined daily for clinical status and weekly for glandular changes using transrectal ultrasonography. At predetermined intervals, the animals were sacrificed and the prostates excised, measured, sectioned, and examined for histologic changes. Ablative tissue temperatures of 50 to 100 degrees C were produced while impedance remained stable. Four animals required a single catheterization for relief of urinary retention between days 2 and 3; otherwise, all animals demonstrated a quick and uneventful recovery with no edema detectable on day 7 ultrasound examination. The outside dimensions of the gland remained relatively constant throughout the study (+ or - 0.39 cm L + W + H). Histologic examination revealed coagulation necrosis (ablation) in both lobes of all prostates (69.94% + or - 16.62% of the gland) with tissueless cavities forming from the ablation area (28.71% + or - 8.24% of the gland) contained within the capsule surrounded by healthy tissue at the periphery. Intraprostatic lesions were obtained without any gross damage to surrounding tissue, including the bladder and rectal wall. Utilizing a liquid conductor in prostate tissue allows a single electrode-placement heating cycle for controlled ablation for the potential treatment of BPH. This new technique produces more extensive and uniform lesions than conventional RF procedures, and lesion size is limited only by the duration of RF energy application.

Thermodynamics of movable inductively heated seeds for the treatment of brain tumors

A thermodynamic study is presented of temperature distributions created by an inductively heated 6-mm-diam Ni sphere imbedded in vivo and in vitro into porcine brain tissue. This study was performed in support of the development of a system that creates localized heat-induced lesions in deep-seated brain tumors. In this system, a magnetic "seed" will be remotely repositioned within the brain by an externally produced magnetic field. Convective effects of a hot moving seed will produce a different thermodynamic situation than that arising from an array of static implants. In this work, a study is presented of part of the expected change, in which a static sphere is heated to high temperature. Measurements were made of the temporal and spatial dependence of the temperature rise in the vicinity of the heated sphere, in vivo in four animals and in one that was euthanized immediately prior to experimentation. These results are used for parameter estimation with a theoretical model based on a point source solution to a form of the thermal diffusion equation, i.e., the "bioheat transfer equation." With this model thermal distributions from a power source of arbitrary geometry can be found using appropriate integration methods, and the method has widespread applicability. Estimates of blood flow rates, tissue thermal conductivity, and seed power absorption were found using the parameter estimation algorithm. The estimated blood perfusion exhibits a step increase following the first heating in multiple heating experiments. Thermal conductivity estimated using data from the nonperfused (in vitro) animal is 0.6 W/m degrees C. Seed power absorption is estimated correspondingly to be 0.9 W, a result confirmed independently with calorimetry. Statistical uncertainty is established for the radial decrease of the tissue temperature rise created by this method. This result allows estimation of a cell death boundary uncertainty of 0.6 mm, caused by fluctuations in power delivered to the seed, uncertainty in the temperature probe placements, and thermal properties such as blood perfusion and tissue thermal conductivity.