Transurethral radiofrequency therapy for benign prostatic hyperplasia using a novel saline-liquid conductor: the virtual electrode

Needle-based ablation of renal parenchyma using microwave, cryoablation, impedance- and temperature-based monopolar and bipolar radiofrequency, and liquid and gel chemoablation: laboratory studies and review of the literature

BACKGROUND AND PURPOSE

Small renal tumors are often serendipitously detected during the screening of patients for renal or other disease entities. Rather than perform a radical or partial nephrectomy for these diminutive lesions, several centers have begun to explore a variety of ablative energy sources that could be applied directly via a percutaneously placed needle-like probe. To evaluate the utility of such treatment for small renal tumors/masses, we compared the feasibility, regularity (consistency in size and shape), and reproducibility of necrosis produced in normal porcine kidneys by different modes of tissue ablation: microwaves, cold impedance-based and temperature-based radiofrequency (RF) energy (monopolar and bipolar), and chemical. Chemoablation was accomplished using ethanol gel, hypertonic saline gel, and acetic acid gel either alone or with simultaneous application of monopolar or bipolar RF energy.

MATERIALS AND METHODS

A total of 107 renal lesions were created laparoscopically in 33 domestic pigs. Microwave thermoablation (N=12) was done using a Targis T3 (Urologix) 10F antenna. Cryoablation (N=16) was done using a single 1.5-mm probe or three 17F microprobes (17F SeedNet system; Galil Medical) (N=10 single probe and N=6 three probes); a double freeze cycle with a passive thaw was employed under ultrasound guidance. Dry RF lesions were created using custom-made 18-gauge single-needle monopolar probe with two or three exposed metal tips (GelTx) (N=12) or a single-needle bipolar probe (N=6) at 50 W of 510 kHz RF energy for 5 minutes. In addition, a multitine RF probe (RITA Medical Systems) was used in one set of studies (N=6). Both impedance- and temperature-based RF were evaluated. Chemoablation was performed with 95% ethanol (4 mL), 24% hypertonic saline (4 mL), and 50% acetic acid (4 mL) as single injections. In addition, chemoablation was tested with monopolar and bipolar RF (wet RF). Tissues were harvested 1 week after ablation for light microscopy.

RESULTS

In 11 of the 15 ablation techniques, there was complete necrosis in all lesions; however, three ethanol gel lesions had skip areas, three hypertonic saline gel lesions showed no necrosis or injury, and one monopolar RF and one bipolar RF lesion showed skip areas. In contrast to impedance-based RF, heat-based RF (RITA) caused complete necrosis without skip areas. All cryolesions resulted in complete tissue necrosis, and cryotherapy was the only modality for which lesion size could be effectively monitored using ultrasound imaging.

CONCLUSIONS

Cryoablation and thermotherapy produce well-delineated, completely necrotic renal lesions. The single-probe monopolar and bipolar RF produce limited areas of tissue necrosis; however, both are enhanced by using hypertonic saline, acetic acid, or ethanol gel. Hypertonic saline gel with RF consistently provided the largest lesions. Ethanol and hypertonic saline gels tested alone failed to produce consistent cellular necrosis at 1 week. In contrast, RITA using the Starburst XL probe produced consistent necrosis, while impedance-based RF left skip areas of viable tissue. Renal cryotherapy under ultrasound surveillance produced hypoechoic lesions, which could be reasonably monitored, while all other modalities yielded hyperechoic lesions the margins of which could not be properly monitored with ultrasound imaging.

Radiofrequency Interstitial Tissue Ablation: Wet Electrode

Minimally invasive methods for destroying tissue have been investigated for more than a decade, and growing interest has emerged in small probe or needle ablative techniques. Many energy sources that freeze or heat tissue have been studied. This paper discusses radiofrequency (RF) thermal therapy as delivered by the saline-augmented ("wet" or virtual) electrode. The technique modifies the electric field distribution and the resultant heat deposition within tissues by interstitially infusing a highly conductive electrolyte solution during the application of RF energy. We consider the mechanism of action of the saline-augmented probe, with emphasis on tissue electrical impedance, temperature distributions, and how the fluid circumvents the limitations of standard "dry" probes. If optimized for the particular application, the wet electrode can produce small to large ablation volumes quickly and controllably with a single needle stick. Because there is no desiccation or extremely high temperature, the tissue is not subjected to a phase shift of carbonization, which may reduce post-treatment inflammation and improve healing. The liquid RF electrode will find applications in the interstitial treatment of various tissues, including tumors.

Transurethral prostatic tissue ablation via a single needle delivery system: initial experience with radio-frequency energy and ethanol

We report an initial clinical experience to evaluate the safety and efficacy of outpatient prostatic ablation for the treatment of symptomatic benign prostatic hyperplasia (BPH) using local anesthesia (OPAL) with radio-frequency energy and intraprostatic absolute ethanol injection (EI). Twenty-three patients were treated with OPAL and five patients were treated with EI. Pre-operative data for all patients included international prostate symptom score (IPSS), quality of life score (QL), maximum flow rate (Q(max)), and post void residual determination. Prostate specific antigen (PSA) and transrectal ultrasound prostate volume determination were also done for EI patients. Needle deployment into the prostate was carried out at the 2, 4, 8 and 10 o'clock positions for lateral lobe hyperplasia and the 6 o'clock position for middle lobe hyperplasia. IPSS, QL, Q(max) and post void residual data were collected at 1, 3, 6 and 12 months post procedure. Both procedures resulted in statistically significant reductions of IPSS and QL. Trends towards improvement were seen both for Q(max) and post void residual, with Q(max) significantly improved after OPAL. Among EI patients, the prostate volume was reduced at 6 months post treatment to 37.2+/-17.9 g from 53.0+/-19.0 g (P=0.03) preoperatively. OPAL was safe but suffered from a high re-treatment rate. EI demonstrated encouraging results with regards to safety, symptom improvement and prostate volume reduction.

Hypertonic saline-augmented radiofrequency ablation of the VX-2 tumor implanted in the rabbit kidney: a short-term survival pilot study

OBJECTIVES

The increased incidental detection of small (less than 4 cm) renal tumors has stimulated investigations of minimally invasive therapies. Radiofrequency energy is a relatively new and evolving technology that has been used for a variety of experimental and clinical applications. We evaluate the efficacy of hypertonic interstitial saline-augmented radiofrequency therapy to ablate a malignant VX-2 tumor implanted in a rabbit kidney, as measured by the completeness of tumor destruction and progression to metastasis.

METHODS

The VX-2 tumor was surgically implanted into the left lower pole parenchyma of 18 New Zealand white rabbit kidneys. Ten days after implantation, hypertonic interstitial saline-augmented radiofrequency ablation was performed (n = 12) using a radiofrequency therapy system (RFT, United States Surgical Corp.). A sham operation was performed on a control group (n = 6). Animals were humanely killed at 5, 10, and 15-day intervals, and the clinical response and effect of radiofrequency energy on the malignant renal tissue was assessed.

RESULTS

No postoperative complications were encountered. The mean size of the implanted VX-2 tumor was 1.87 cm2. Kidneys in the treated group exhibited marked destruction of tumor tissue. Histologic analysis revealed coagulative necrosis of both malignant and normal renal tissue in the treated group. Three rabbits (1 control, 2 treated) died of metastatic disease.

CONCLUSIONS

Coagulative necrosis of renal parenchyma and tumor tissue was clearly demonstrated after radiofrequency ablation using the RFT system. The aggressive growth pattern of the VX-2 tumor often resulted in progression to metastatic disease while precluding complete tumor ablation. Hypertonic saline-augmented radiofrequency ablation is a promising new technology for the management of small, locally confined, renal tumors and has the potential for use with a minimally invasive approach.

Evaluation of thermal therapy in a prostate cancer model using a wet electrode radiofrequency probe

PURPOSE

To determine the temperature-time threshold of local cell death in vivo for thermal therapy in a prostate cancer animal model and to use this value as a benchmark to quantify global tissue injury.

MATERIALS AND METHODS

Two studies were designed in the Dunning AT-1 rat prostate tumor hind limb model. For both studies, a wet electrode radiofrequency (RF) probe was used to deliver 40 W of energy for 18 to 62 seconds after a 30-second infusion of hypertonic saline/Hypaque through the RF antenna. Thermal history measurements were obtained in tumors from at least two Fluoroptic probes placed radially 5 mm from the axis of a RF probe and 10 mm below the surface of the tissue. In study 1, the thermal history required for irreversible cell injury was experimentally determined by comparing the predicted injury accumulation (omega) with cell viability at the fluoroptic probe locations using an in vivo-in vitro assay. The omega value was calculated from the measured thermal histories using an Arrhenius damage model. In study 2, RF energy was applied for 40 seconds in all cases. At 1, 3, and 7 days after thermal therapy, triphenyltetrazolium chloride dye (TTC) and histologic analyses were performed to assess global tissue injury within a 5-mm radius from the axis of the RF probe.

RESULTS

Study 1 showed that cell survival dropped to 0 for 0.42 < omega < 0.7. This result was the basis for selection of 40 seconds of RF thermal therapy in study 2, which yielded omegaave = 0.5 in the tissue 5 mm from the probe axis. Both TTC and histology analysis showed that sham-treated tissue was not irreversibly injured. However, there was an inherent heterogeneity present in the tumor that accounted for as much as 15% necrosis in control or sham-treated tissue. In contrast, at 1, 3, and 7 days after therapy, significantly less enzyme activity was observed by TCC in thermally treated tissue compared with sham-treated tissue (35 v 85%; P < 0.001). Histologic analysis of thermally treated tissues revealed a gradual increase in the percent of coagulative necrosis (47%-70%) with a concomitant decrease in the percentage of shocked cells (53%-28%). At day 7, <3% viability was observed in treated tumors compared with 90% viability in sham-treated tissue.

CONCLUSION

The threshold of cellular injury in vivo corresponded to omega > 0.7 (> or =48 degrees C for 40 seconds). Global tissue injury could be conservatively predicted on the basis of local thermal histories during therapy.

Minimally invasive procedures as an alternative to medical management for lower urinary tract symptoms of benign prostatic hyperplasia

Data are reviewed relating to the safety and efficacy of minimally invasive transurethral microwave thermotherapy and medical management in patients with lower urinary tract symptoms of benign prostatic hyperplasia. Recent evidence is summarized indicating more pronounced long-term beneficial effects of microwave treatment. alpha-Blockade, however, offers the advantage of more rapid action than microwave treatment. Neoadjuvant and adjuvant alpha-blocker therapy can accelerate symptom and flow rate improvement in patients receiving microwave treatment. Compared with medical management, microwave treatment possesses greater versatility, allowing patients with severe baseline symptoms and small prostate sizes to be treated with a high probability of success.

Transurethral radiofrequency thermal ablation of prostatic tissue: a feasibility study in humans

OBJECTIVES

To evaluate the feasibility and efficacy of ablating prostatic tissue by inducing thermal lesions using radiofrequency (RF) energy delivered transurethrally through electrodes mounted on a Foley-like catheter.

METHODS

Twenty male patients, candidates for radical cystoprostatectomy to treat bladder carcinoma, underwent RF prostate ablation 1 to 8 days before surgery (mean 2.8). Stainless steel, internally cooled, 2-cm-long electrodes mounted on a Foley-like catheter were used to deliver RF energy to the prostatic tissue. Semicircular electrodes were used in 10 patients (group A) and circular electrodes were used in the remaining 10 patients (group B). The urethral, rectal, and prostatic tissue temperatures were recorded. Histologic step sections were performed on whole mounts of the prostates to define the volume of the thermal lesions.

RESULTS

The mean RF energy delivered was 36.5 kJ (range 26.4 to 53.1) in group A and 82.3 kJ (range 38 to 149) in group B. The intraprostatic temperatures were between 44 degrees C and 80 degrees C in group A and between 60 degrees C and 119 degrees C in group B. The urethral and rectal temperatures never exceeded 42 degrees C. No major complications occurred. After the RF procedure, 5 patients who received more than 75 kJ of energy could not void and required catheterization. The mean prostate volume was 11.54 cm(3) for group A and 24.02 cm(3) for group B. The mean volumes of the thermal lesions and their relative percentages in relation to the whole prostate in groups A and B were, respectively, 1.69 cm(3) and 15% and 6.91 cm(3) and 29% (P = 0.049). Analysis of variance showed a significant correlation between the thermal lesion volume and the energy delivered, regardless of the electrode shape (P = 0.001).

CONCLUSIONS

Satisfactory thermal ablation of prostatic tissue can be achieved using RF electrodes mounted on a Foley-like catheter. The procedure is effective, simple, and safe and, therefore, can be used in pilot clinical studies on patients with benign prostatic hyperplasia.