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

Advancements in microwave ablation for tumor treatment and future directions

Microwave ablation (MWA) is a minimally invasive treatment that uses thermal energy to target and destroy tumors. Compared to other ablation methods, such as radiofrequency ablation (RFA), MWA operates at higher frequencies, allowing for faster ablation and larger treatment areas. In addition to its direct tumor-destroying effects, MWA has been shown to activate immune responses, contributing to long-term antitumor effects. MWA can also be combined with surgery, chemotherapy, and immunotherapy to enhance treatment outcomes. This review examines the current research on MWA's technical innovations, clinical applications, and its potential in improving cancer treatment efficacy.

Two Cases of Strictures after Percutaneous CT-Guided Radiofrequency Ablation for Renal Cell Carcinoma

Percutaneous radiofrequency ablation is a safe and effective minimally invasive treatment option in selected patients with T1a tumors of the kidney with a low complication rate. We describe two cases that developed the rare but severe complication of thermal injury-induced strictures of the upper urinary tract and its consecutive management.

[Ablative therapy of small renal masses]

Renal cell cancer is nowadays predominantly diagnosed in early stages due to the widespread use of sectional imaging for unrelated symptoms. Small renal masses (<4 cm) feature a largely indolent biology with a very low risk for metastasis or even a benign biology in up to 30% of the cases. Consequently, there is a need for less invasive therapeutic alternatives to nephron-sparing surgery. Meanwhile, there is a broad portfolio of local ablation techniques to treat small renal tumors. These include the extensively studied radiofrequency ablation and cryoablation techniques as well as newer modalities like microwave ablation and irreversible electroporation as more experimental techniques. Tumor ablation can be performed percutaneously under image guidance or laparoscopically. In particular, the percutaneous approach is a less invasive alternative to nephron-sparing surgery with lower risk for complications. Comparative studies and meta-analyses report a higher risk for local recurrence after renal tumor ablation compared to surgery. However, long-term oncological results after treatment of small renal masses are promising and do not seem to differ from partial nephrectomy. The possibility for salvage therapy in case of recurrence also accounts for this finding. Especially old patients with an increased risk of surgical and anesthesiological complications as well as patients with recurrent and multiple hereditary renal cell carcinomas may benefit from tumor ablation. Tumor biopsy prior to intervention is associated with very low morbidity rates and is oncologically safe. It can help to assess the biology of the renal mass and prevent therapy of benign lesions.

Outcomes of Radiofrequency Ablation for Kidney Cancer

BACKGROUND

The incidence of small (< 4 cm) solid enhancing renal masses has been rising, and the majority (60% to 80%) of these tumors are renal cell carcinomas (RCCs) when pathologic analysis is performed. Needle ablation for small incidental renal masses is an attractive therapeutic option. Reasons include its decreased morbidity, shorter convalescence, and the ability to avert the higher risk of extirpative surgery in an aging patient population. Radiofrequency ablation (RFA) is a thoroughly studied needle ablative method used for RCC.

METHODS

The current published literature on renal tumor RFA was reviewed. The in vitro experiments, animal studies and clinical experience with RFA for treatment of small RCCs were analyzed and various controversies in renal RFA are presented for discussion.

RESULTS

Percutaneous and laparoscopic renal RFA can be safely performed and can eradicate small RCCs with cancer specific survival rates over 90% to 95% in many series. While long-term (5 years or greater) cancer control data are not yet available, these intermediate-term results are similar to those achieved with traditional nephron-sparing surgical options. However, the optimal method to perform RFA for renal masses is still evolving.

CONCLUSIONS

While long-term cancer control data are not yet available, the current literature suggests that RFA can effectively eradicate small RCCs. Further research is needed to elucidate the influence of various treatment variables, including impedance vs temperature-controlled RFA, sonographic vs computed tomographic guidance, general anesthetic vs conscious sedation, and radiologist vs urologist delivery of renal RFA.

Treatment of liver cancer of middle and advanced stages using ultrasound-guided percutaneous ethanol injection combined with radiofrequency ablation: A clinical analysis

Liver cancer is a malignancy of the digestive system and has a high morbidity and mortality rate. Local intervention has become a viable option in identifying liver treatment. The aim of the present study was to analyze the clinical effects of treating liver cancer in middle and advanced stages using ultrasound-guided percutaneous ethanol injection (PEI) in tumors combined with radiofrequency ablation (RFA). A total of 100 patients with stage III-IV liver cancers were selected to participate in the study. Patients were divided into groups. In group A, treatment was initiated with PEI and after 1-2 weeks RFA was applied while in group B treatment was initiated with RFA and after 1-2 weeks PEI was applied. Patients in group C received PEI and RFA simultaneously. The clinical effects in the 3 groups were compared after 6-month follow ups. The volume of tumor ablation necrosis in group A was significantly greater than that in the groups B and C, while the size was significantly smaller compared to groups B and C after ablation. For group A, the complete ablation rate was significantly higher than that in groups B and C, and the differences were statistically significant (P<0.05). Liver damage indices, including raising levels of glutamic-pyruvic transaminase and total bilirubin, were significantly decreased in group A (P<0.05). The survival rate in group A was also significantly higher than in groups B and C (P<0.05). In conclusion, for patients with liver cancer in middle and advanced stages, the treatment method using PEI followed by RFA was more beneficial in terms of improving the tumor ablation rate, alleviating liver damages and increasing survival rates.

Enhanced visualization of fine needles under sonographic guidance using a MEMS actuator

Localization of a needle tip is important for biopsy examinations in clinics. However, the needle tip is sometimes difficult to discern under the guidance of sonography due to its poor visibility. A mini actuator that radiates a low-intensity ultrasound wave was manufactured using micro-electro-mechanical system (MEMS) technology. Interference between the radiated and diagnostic ultrasound pulses was observed as bright lines in the B-mode ultrasound image, from which the mini actuator could be recognized with ease. Because the distance between the mini actuator and the needle tip is fixed, the needle tip can be determined despite its inconsistent appearance in the sonography. Both gel phantom and ex vivo tissue evaluation showed that the needle tip can be determined reliably utilizing the acoustic interference pattern.

Renal cell carcinoma

The treatment of renal cell carcinoma (RCC) has changed greatly over the past 15 years. Progress in the surgical management of the primary tumor and increased understanding of the molecular biology and genomics of the disease have led to the development of new therapeutic agents. The management of the primary tumor has changed owing to the realization that clean margins around the primary lesion are sufficient to prevent local recurrence, as well as the development of more sophisticated tools and techniques that increase the safety of partial nephrectomy. The management of advanced disease has altered even more dramatically as a result of new agents that target the tumor vasculature or that attenuate the activation of intracellular oncogenic pathways. This review summarizes data from prospective randomized phase III studies on the surgical management and systemic treatment of RCC, and provides an up to date summary of the histology, genomics, staging, and prognosis of RCC. It describes the management of the primary tumor and offers an overview of systemic agents that form the mainstay of treatment for advanced disease. The review concludes with an introduction to the exciting new class of immunomodulatory agents that are currently in clinical trials and may form the basis of a new therapeutic approach for patients with advanced RCC.

Microwave ablation of renal tumors: state of the art and development trends

In the last decades an increased incidence of new renal tumor cases has been for clinically localized, small tumors <2.0 cm. This trend for small, low-stage tumors is the reflection of earlier diagnosis primarily as a result of the widespread and increasing use of non-invasive abdominal imaging modalities such as ultrasound, computerized tomography, and magnetic resonance imaging. Renal tumors are often diagnosed in elderly patients, with medical comorbidities whom the risk of surgical complications may pose a greater risk of death than that due to the tumor itself. In these patients, unsuitable for surgical approach, thermal ablation represents a valid alternative to traditional surgery. Thermal ablation is a less invasive, less morbid treatment option thanks to reduced blood loss, lower incidence of complications during the procedure and a less long convalescence. At present, the most widely used thermal ablative techniques are cryoablation, radiofrequency ablation and microwave ablation (MWA). MWA offers many benefits of other ablation techniques and offers several other advantages: higher intratumoral temperatures, larger tumor ablation volumes, faster ablation times, the ability to use multiple applicators simultaneously, optimal heating of cystic masses and tumors close to the vessels and less procedural pain. This review aims to provide the reader with an overview about the state of the art of microwave ablation for renal tumors and to cast a glance on the new development trends of this technique.

Analysis of the effect of renal excretory system cooling during thermal radiofrequency ablation in an animal model

OBJECTIVE

Analysis of renal excretory system integrity and efficacy of radiofrequency ablation with and without irrigation with saline at 2°C (SF2).

MATERIALS AND METHODS

The median third of sixteen kidneys were submitted to radiofrequency (exposition of 1 cm) controlled by intra-surgical ultrasound, with eight minutes cycles and median temperature of 90°C in eight female pigs. One excretory renal system was cooled with SF2, at a 30mL/min rate, and the other kidney was not. After 14 days of post-operatory, the biggest diameters of the lesions and the radiological aspects of the excretory system were compared by bilateral ascending pyelogram and the animals were sacrificed in order to perform histological analysis.

RESULTS

There were no significant differences between the diameters of the kidney lesions whether or not exposed to cooling of the excretory system. Median diameter of the cooled kidneys and not cooled kidneys were respectively (in mm): anteroposterior: 11.46 vs. 12.5 (p = 0.23); longitudinal: 17.94 vs. 18.84 (p = 0.62); depth: 11.38 vs. 12.25 (p = 0.47). There was no lesion of the excretory system or signs of leakage of contrast media or hydronephrosis at ascending pyelogram.

CONCLUSION

Cooling of excretory system during radiofrequency ablation does not sig¬nificantly alter generated coagulation necrosis or affect the integrity of the excretory system in the studied model.

Attenuation and de-focusing during high-intensity focused ultrasound therapy through peri-nephric fat

High-intensity focused ultrasound (HIFU) is an attractive therapy for kidney cancer, but its efficacy can be limited by heat deposition in the pre-focal tissues, notably in fat around the kidney (peri-nephric fat), the acoustic properties of which have not been well characterized. Measurements of attenuation were made using a modified insertion-loss technique on fresh, unfixed peri-nephric fat obtained from patients undergoing kidney surgery for cancer. The de-focusing effect of changing the position of the fat layers was also investigated using fresh subcutaneous fat from euthanized pigs. The mean attenuation of human peri-nephric fat was found to be 11.9 ± 0.9 Np/m (n = 10) at 0.8 MHz, the frequency typically used for HIFU ablation of kidney tumors, with a frequency dependence of f(1.2). A typical 2- to 4-cm thickness of peri-nephric fat would result in a de-rated intensity of 3% - 62% at 0.8 MHz compared with a hypothetical patient with no peri-nephric fat. Through the use of freshly excised porcine subcutaneous fat, the presence of fat 100 mm in front of the focus was found to have a de-focusing effect of approximately 1 mm in both transverse directions, which corresponds to a full HIFU beam width off-target. Peri-nephric fat may significantly affect both the intensity and accuracy of HIFU fields used for the ablation of kidney cancer.

Electrolysis - a new method of renal ablation?

OBJECTIVE

• To present a novel method of renal ablation using direct current electrolysis, using a porcine model to assess the safety and efficacy of the technique.

MATERIALS AND METHODS

• In all, 20 anaesthetised pigs were used, after receiving ethical approval. The pigs were housed and managed in accordance with Institute of Medical and Veterinary Science guidelines. • A single 6 F catheter incorporating cathode and anode was inserted directly into the renal parenchyma via a loin incision. A direct current of 100 mA was applied for varying times. • Several treatments were performed in each pig and a total of 72 treatments were analysed. • The pigs were recovered and observed for 3 days with an analysis of electrolytes and creatinine after ablation. The pigs were humanely killed at 3 days and the kidneys submitted for histological analysis.

RESULTS

• Complete tissue destruction was seen in the area of kidney treated with no viable cells. • A sharp line of demarcation was noted between normal renal parenchyma and the area of coagulative necrosis. The area of tissue ablation was reliably predicted from the duration of application of the electrolytic current. • One pig developed a secondary haemorrhage.

CONCLUSIONS

• Renal electrolysis is a new method of focal renal ablation. The procedure may be carried out using a fine ablation catheter (6 F) allowing for the development of minimal intervention treatment of small renal masses. • This study shows the technique to be effective and safe. As with other renal ablative techniques there is a small risk of postoperative haemorrhage.

[Microwave tumor ablation. New devices, new applications?]

CLINICAL ISSUE

The majority of patients with hepatic malignancies are not amenable to surgical resection. In some of these cases minimally invasive ablative therapies are a treatment option.

STANDARD TREATMENT

Besides radiofrequency ablation, the most common ablative therapies are cryoablation, laser ablation and microwave ablation.

TREATMENT INNOVATIONS

The classic fields of application of microwave ablation are the treatment of malignancies of the liver, kidneys and lungs. Furthermore, cases of treatment of bone tumors and tumors of the adrenal gland have been reported as well as treatment of secondary hypersplenism.

PERFORMANCE

The manufacturers of microwave systems pursue different strategies to reach an optimal ablation zone, such as water or gas cooling of the antenna, the simultaneous use of different antennas or an automatic modulation of the microwave energy and frequency.

ACHIEVEMENTS

In contrast to other tumor ablation methods microwave ablation causes a direct heating of a tissue volume, thus this method is less vulnerable to the cooling effect of vessels in the ablation zone. Moreover the electric conductivity of the treated tissue does not influence microwave radiation so that microwave ablation has advantages for the treatment of high-resistance organs, such as the lungs or bone. Some publications have shown that microwave ablation causes larger ablation zones in less time in comparison to radiofrequency ablation.

PRACTICAL RECOMMENDATIONS

Classic indications for microwave ablation are the treatment of malignancies of the liver, lungs and kidneys. Initial technical problems have been solved, so that an increasing significance of the microwave ablation among the ablative therapies is to be expected.

Percutaneous radiofrequency ablation of renal parenchyma: experimental study on the optimal temperature and the impact of vasoactive drugs

BACKGROUND AND PURPOSE

Radiofrequency (RF) is an efficient, inexpensive, safe, and friendly option for the management of small renal tumors. The objective was to evaluate the ideal temperature for renal cell destruction in dogs by RF and to verify whether the injection of vasoactive drugs, such as prostaglandin E1 and adrenaline, can help to improve the results, compared with "dry" RF ablation.

MATERIALS AND METHODS

The study was divided into three phases: Initially, 16 dogs of comparable weight underwent RF ablation of the renal parenchyma at temperatures of 80°C, 90°C, and 100°C. After that, seven other dogs received adrenaline (vasoconstrictor) and seven received prostaglandin E1 (vasodilator). Finally, the results from 14 animals were compared with those of the 16 (dry RF) dogs at the optimum temperature found. After 14 days, the animals underwent nephrectomy to evaluate the size of the lesions (width and depth), histology examination, and were then sacrificed.

RESULTS

There were no clinical or surgical complications in any of the dogs, and none died before the 14th day after the procedure. The optimum temperature was found to be 90°C. Prostaglandin E1 resulted in significantly larger lesions (in depth and width) than adrenaline, with lower impedance. Prostaglandin did not increase the lesions compared with dry RF. All the kidneys presented total coagulation necrosis, with no viable cells in the histologic analysis of the treated tissue.

CONCLUSION

In the ablation of renal cells by RF, prostaglandin produced larger lesions (in depth and width) than the same procedure using adrenaline, and its performance was similar to that of RF without injection of drugs.

Small renal mass: what the urologist needs to know for treatment planning and assessment of treatment results

OBJECTIVE

Small renal mass is a new distinct clinical entity. Detection of these tumors has increased with increased use of imaging.

CONCLUSION

We know that a proportion of these tumors are not renal cell carcinoma, and imaging-guided biopsy is being increasingly used for treatment planning. The objectives of this review are to provide an update on our current understanding of the biology of small renal masses and to review approaches to the diagnosis and treatment of these lesions.

[US-guided percutaneous radio frequency in kidney cancer: our experience]

The radio frequency ablation of kidney cancer showed satisfactory results at a short follow-up with the use of a new RF generator system. Radio frequency is an alternative procedure with the intention of producing heat damage to tissue by electromagnetic energy.

METHODS

From January 2009 to July 2010, at our operative unit, ten patients (age range: 50-83 years) underwent percutaneous radio frequency. All tumors were primitive without secondarism. The lesion diameter ranged from 15 to 35 mm. Only in two cases the treatment was open due to difficulties in finding the lesion.

RESULTS

At six months' treatment, two patients had a complete remission and one patient an incomplete one; at eight months, five patients are with a complete remission and one patient with complete remission; at twelve months, one patient showed an incomplete remission.

CONCLUSIONS

There are no studies with a long-term follow-up and it is prudent to limit this therapy to those patients who can not undergo surgical treatment. A correct post-operative imaging evaluation is essential to ensure an effective treatment.

In vivo microwave-induced porcine kidney thermoablation: results and perspectives from a pilot study of a new probe

OBJECTIVE

To test the in vivo effects (toxicity, completeness of necrosis, dimensions of the lesion) of microwave thermoablation on porcine kidneys, using the Amica Probe v3 (Hospital Service SpA, Aprilia, Italy), in a refrigerated 17-G microwave applicator, that can be used to induce a spherical necrotic area.

PATIENTS AND METHODS

Six pigs were used; each kidney was treated, with no kidney pedicle clamping, by microwave thermoablation at least in three different zones with different exposure times and power, during open surgery. Twelve kidneys had 32 microwave thermoablations overall. The kidneys were then surgically removed, and necrotic lesions measured and evaluated microscopically. The sphericity index (SI) was also calculated to evaluate lesion reproducibility. Areas of renal tissue that were missed were then microscopically evaluated by NADH in vivo staining.

RESULTS

In all, 32 thermoablations were applied; the mean (sd) lesion diameter ranged from 1.2 (0.3) to 4.2 (0.1) cm and changed in relation to both power and time of exposure. The 50-W power particularly induced necrotic renal lesions ranging from 1.9 (0.2) to 4.2 (0.1) cm as a function of the time of exposure and the optimal SI (1.04). Pathological evaluation showed no skipped areas in the context of the lesion, or healthy kidney tissue damage close to necrotic lesions.

CONCLUSIONS

Thermoablation with the Amica probe is safe and showed excellent in vivo effects in this porcine model. Increasing the exposure time at 50 W power could be a useful percutaneous minimally invasive treatment for small solid masses (<4.2 cm), avoiding the risk of missing tumour areas or kidney parenchymal damage from microwave treatment.

Microwave tumor ablation: mechanism of action, clinical results, and devices

Microwave ablation uses dielectric hysteresis to produce direct volume heating of tissue. Microwaves are capable of propagating through many tissue types, even those with high impedance such as lung or bone, with less susceptibility to "heat-sink" effects along vessels. Microwaves are highly conducive to the use of multiple applicators, showing the synergy seen with other energies, but also the potential capability for phasing of the electromagnetic field. As a result, larger, more customizable ablation zones may be created in less time. Although multiple microwave ablation systems are currently available, further study and continued development are needed.

Effects of microwave ablation of the kidney

INTRODUCTION

Thermal ablative therapy with cryotherapy and radiofrequency ablation is currently being utilized for treatment of small renal masses. Recently, microwave ablation (MWA) has been investigated for soft tissue destruction, with limited clinical experience for renal masses. This study was designed to evaluate the effectiveness of a new microwave system in the porcine kidney.

MATERIALS AND METHODS

MWAs were performed in vivo on six pigs using the Evident Microwave Ablation System (Valleylab, Boulder, CO) with a 3.7 cm active tip percutaneous antenna. Ablations were performed in both upper and lower poles at 45 W for 3, 5, and 10 minutes. Three pigs died; three pigs survived for 7 days. After necropsy the kidneys were harvested, ablation zones were measured, and histological analysis was performed.

RESULTS

The ablated zones at each time interval were inconsistent. The gross appearance of the lesions in both groups was similar. The antenna tract was charred, the collecting system was damaged, and there was asymmetry of the zones of ablation. Histological analysis revealed coagulative necrosis in the area of the ablation with sloughed and denuded urothelium.

CONCLUSION

MWA of the kidney utilizing this model yields inconsistent geometrical lesions when applied near the renal collecting system. Additionally, microwave energy may be preferentially absorbed by the increased water content in the collecting system resulting in damage to it. Further study is needed to assess the attenuation of the microwave field in the kidney at different locations due to the kidneys heterogeneity.

A critical analysis of the actual role of minimally invasive surgery and active surveillance for kidney cancer

CONTEXT

The incidence of renal cell carcinomas (RCCs) has increased steadily-most rapidly for small renal masses (SRMs). Paralleling the changing face of RCC in the past 2 decades, new, less invasive surgical options have been developed. Laparoscopic radical nephrectomy (LRN) is an established procedure for the treatment of RCC. Treatment of SRMs includes open partial nephrectomy (OPN), laparoscopic partial nephrectomy (LPN), thermal ablation, and active surveillance.

OBJECTIVE

To present an overview of minimally invasive treatment options and data on surveillance for kidney cancer.

EVIDENCE ACQUISITION

Literature and meeting abstracts were searched using the terms renal cell carcinoma, minimally invasive surgery, laparoscopic surgery, thermal ablation, surveillance, and robotic surgery. The articles with the highest level of evidence were identified with the consensus of all the collaborative authors and reviewed.

EVIDENCE SYNTHESIS

Renal insufficiency, as measured by the glomerular filtration rate, occurs more often after radical nephrectomy than partial nephrectomy (PN). OPN and LPN show comparable results in long-term oncologic outcomes. The treatment modality for SRMs should therefore be nephron-sparing surgery (NSS). In select patients, thermal ablation or active surveillance of SRMs is an alternative.

CONCLUSIONS

LRN has become the standard of care for most organ-confined tumours not amenable to NSS. Amongst NSS options, PN is the treatment of choice, yet remains underutilised in the community. Initial data during its learning curve revealed that LPN had higher urologic morbidity. However, current emerging data indicate that in experienced hands, LPN has shorter ischaemia times, a lower complication rate, and equivalent long-term oncologic and renal functional outcomes, yet with decreased patient morbidity compared to OPN. Robotic partial nephrectomy is being explored at select centres, and cryotherapy and radiofrequency ablation are options for carefully selected tumours. Active surveillance is an option for selected high-risk patients. Percutaneous needle biopsy is likely to gain increasing relevance in the management of small renal tumours.

Adjuvant approaches to enhance cryosurgery

Molecular adjuvants can be used to enhance the natural destructive mechanisms of freezing within tissue. This review discusses their use in the growing field of combinatorial or adjuvant enhanced cryosurgery for a variety of disease conditions. Two important motivations for adjuvant use are: (1) increased control of the local disease in the area of freezing (i.e., reduced local recurrence of disease) and (2) reduced complications due to over-freezing into adjacent tissues (i.e., reduced normal functional tissue destruction near the treatment site). This review starts with a brief overview of cryosurgical technology including probes and cryogens and major mechanisms of cellular, vascular injury and possible immunological effects due to freeze-thaw treatment in vivo. The review then focuses on adjuvants to each of these mechanisms that make the tissue more sensitive to freeze-thaw injury. Four broad classes of adjuvants are discussed including: thermophysical agents (eutectic forming salts and amino acids), chemotherapuetics, vascular agents and immunomodulators. The key issues of selection, timing, dose and delivery of these adjuvants are then elaborated. Finally, work with a particularly promising vascular adjuvant, TNF-alpha, that shows the ability to destroy all cancer within a cryosurgical iceball is highlighted.

Ablation of bull prostate using novel bipolar radiofrequency ablation probe

PURPOSE

We describe the use of a novel bipolar radiofrequency (RF) system for the destruction of prostate tissue in an ex vivo model.

MATERIALS AND METHODS

A bipolar RF delivery system (Trod Medical, France) was linked to a 500 kHz generator. Eight lesions were created in an ex vivo bull prostate model using 7-mm (n = 4) and 10-mm probes (n = 4). Ablation was performed for 150 seconds. Temperature was recorded at the center of the lesion (Tc) and at the periphery (Tp) of the prostate. Tissue damage, both within and without the intended destruction zones, was assessed. The distance from Tc to Tp was recorded.

RESULTS

All lesions created with either the 7-mm or 10-mm bipolar RF ablation (RFA) probes demonstrated complete tissue destruction only within the intended zone. Using the 7-mm probe, the mean Tc was 82 degrees C and the mean Tp 34 degrees C. The mean distance from the edge of the lesion to the periphery was 5 mm. Impedance was 62 Ohm, and power was 4 watts during ablation with the 7-mm probe. With the 10-mm probe, the mean Tc and Tp were 70 degrees C and 41 degrees C, respectively. The mean distance from the edge of the lesion to the periphery was 5 mm. Impedance was 78 Ohm, and power was 4.5 watts during ablation with the 10-mm probe.

CONCLUSIONS

In an ex vivo model, bipolar RFA is capable of producing lesions with precise margins. Spread of heat is limited, evidenced histologically and by significant temperature drop off. This technology holds promise in the management of benign and malignant urologic diseases.

Determination of the most efficient temperature for radiofrequency ablation of renal cells: a prospective study in dogs

BACKGROUND AND PURPOSE

Radiofrequency (RF) ablation of renal tumors is a major technique for tumor cell destruction while preserving healthy renal parenchyma. There is no consensus in the literature regarding the optimal temperature, impedance, and time for RF application for effective cell destruction. This study investigated two variables while keeping time unchanged: Temperature for RF cell destruction and tissue impedance in dog kidneys.

MATERIALS AND METHODS

Sixteen dogs had renal punctures through videolaparoscopy for RF interstitial tissue ablation. A RF generator was applied for 10 minutes to the dog's kidney at different target temperatures: 80 degrees C, 90 degrees C, and 100 degrees C. On postoperative day 14, the animals were sacrificed and nephrectomized. All lesions were macroscopically and microscopically examined. The bioelectrical impedance was evaluated at three different temperatures.

RESULTS

Renal injuries were wider and deeper at 90 degrees C (P < 0.001), and they were similar at 80 degrees C and 100 degrees C. The bioelectrical impedance was lower at 90 degrees C than at the temperatures of 80 degrees C and 100 degrees C (P < 0.001). Viable cells in the RF ablation tissue area were not found in the microscopic examination.

CONCLUSION

The most effective cell destruction in terms of width and depth was achieved at 90 degrees C, which was also the optimal temperature for tissue impedance. RF ablation of renal cells eliminated all viable cells.

Imaging findings of genitourinary tumors in the elderly

Aging-correlated pathologies are atherosclerosis, arterial hypertension, diabetes mellitus, bacterial infections, and malnutrition. The progressive impairment of renal function is the cause of the drug-induced renal pathologies: direct damage induced by nephrotoxic drugs or indirect damage induced by decreased renal excretion of serum molecules. In the elderly, an increase in different pathologies occurs in the genitourinary tract. Among these pathologies, an increase in neoplastic disorders is present; at the same time, several non-neoplastic pathologies are more frequent in old patients. This article considers first the neoplastic genitourinary pathologies and second the non-neoplastic genitourinary pathologies.

Percutaneous renal cryoablation: current status

Over the last 13 years, renal cryoablation has emerged as a promising technique for the treatment of solid renal tumors. The improvement in imaging modalities such as ultrasound, computed tomography and MRI, as well as the introduction of thinner probes, has led to the spread of the minimally invasive percutaneous approach. We review the historical background of percutaneous renal cryoablation (PRC), present its basic principles, mention the contemporary clinical data and outcomes of this technique and suggest future directions for its wider application in renal tumors. Early results have demonstrated that it may offer an alternative for the treatment of small renal masses with the advantages of minimal complications, spared renal function, decreased overall costs and equivalent oncologic efficacy. Long-term results are required in order to apply this minimally invasive technique to a broader spectrum of patients.

Radiofrequency ablation of renal tumors

Development of cross-sectional imaging has led to a significant increase in diagnosis of small renal tumors. Nephron-sparing surgery has proven to be effective in the management of these small tumors. Could radiofrequency ablation be as effective in the management of these patients, after showing promising results in a selected group of patients? In this article we discuss the principles of radiofrequency ablation and present results in a selected group of patients. We also outline future perspectives of this noninvasive technique.

Combined Percutaneous Radiofrequency Ablation and Ethanol Injection of Renal Tumours: Midterm Results

OBJECTIVES

To evaluate the safety and efficacy of combined percutaneous, image-guided, radiofrequency (RF) ablation and ethanol injection of renal tumours, and to present our midterm results.

METHODS

Since February 2002, 27 consecutive patients (22 men, 5 women; age range: 39-84 yr; mean: 69) with 28 renal tumours (mean diameter: 2.87cm) were treated with combined percutaneous RF and ethanol ablation, and were prospectively evaluated. Twenty-five patients were considered nonsurgical candidates because of comorbid conditions (16 patients) or had previous nephrectomy (9 patients), and 2 had refused surgery. Thirty-three ablation sessions were performed, with computed tomography (26 sessions), ultrasound (6), or combined magnetic resonance imaging/fluoroscopic guidance in 1. Absolute ethanol (0.5-3ml; mean: 1.7) was injected into the tumour immediately before treatment with radiofrequency. Mean follow-up period was 18.6 mo (range: 3-56).

RESULTS

Twenty-seven of the 28 tumours were completely ablated with either one (21 tumours) or two treatment sessions (6 tumours). One patient with residual disease refused further treatment. Only three minor complications, including a subcapsular haematoma and two patients with loin pain, occurred; all three patients were treated conservatively. None of the complications was related to the ethanol injection. During the follow-up period, no evidence of local recurrence or metastatic disease was seen. Creatinine levels have not changed significantly in any of the patients following ablation.

CONCLUSIONS

Combined use of percutaneous RF and ethanol ablation is a safe and effective alternative treatment for selective patients with renal tumours.

Oncologic outcomes for ablative therapy of kidney cancer

Needle ablative therapies for small incidental renal masses are emerging as alternatives to traditional extirpative surgery. Reasons include their associated decreased morbidity, shorter convalescence, and the ability to avert the higher risk of extirpative surgery in an aging patient population. Cryoablation (CA) and radiofrequency ablation are the two most thoroughly studied needle ablative methods used for renal cancer. High-intensity focused ultrasound has also been studied but with limited published human experience at this time. For both radiofrequency ablation and CA, in vitro experiments, animal studies, and (increasingly) human experience have been published, allowing us to define appropriate candidates for such therapies, their oncologic outcomes, and the potential pitfalls. While long-term data is being collected, the current literature suggests that CA and radiofrequency ablation can be safely performed and can effectively eradicate small renal cancers with cancer-specific survival rates similar to those of traditional surgical options.

Cryoablation of renal cancer: variables involved in freezing-induced cell death

The detection of renal tumors has increased significantly over recent years resulting in a greater demand for novel, minimally invasive techniques. Cryoablation has emerged as a valuable treatment modality for the management of renal cancer. In an effort to detail the effects of freezing in renal cancer, the human renal cancer (RCC) cell line, 786-O, was evaluated in vitro. 786-O cells were exposed to a range of freezing temperatures from -5 to -40 degrees C and compared to non-frozen controls. The data show that freezing to -5 degrees C did not affect 786-O cell viability, while -10 degrees C, -15 degrees C, and -20 degrees C results in a significant loss of viability (23, 70, and 91%, respectively). A complete loss of cell viability was evident at temperatures of -25 degrees C and colder. Following this analysis, variables involved in the success of cryoablation were investigated. For each of the temperatures tested, extended freeze hold times and passive thawing rates resulted in more extensive cell damage. Additionally, a double freeze-thaw cycle significantly increased cell death compared to a single cycle (62% vs. 22% at -10 degrees C; 89% vs. 63% at -15 degrees C, respectively). While these variables play an important part in the effective application of cryoablation, a molecular understanding of the cell death involved is critical to improving efficacy. Apoptotic inhibition afforded 12% (-10 degrees C), 25% (-15 degrees C), and 11% (-20 degrees C) protection following freezing. Using fluorescence microscopy analysis, the results demonstrated that apoptosis peaked at six hours post-thaw. Next, apoptotic initiating agents including 5-FU and resveratrol (RVT) applied prior to freezing exposure resulted in a significant increase in cell death compared to either application alone. Importantly, the combination of RVT and freezing was noticeably less effective when applied to normal renal cells. The results herein demonstrate the efficacy of freezing and describe a novel therapeutic model for the treatment of renal cancer that may distinguish between cancer and normal cells.

?Skipping? is still a problem with radiofrequency ablation of small renal tumours

OBJECTIVE

To evaluate the homogeneity and extent of necrosis obtained with next-generation radiofrequency ablation (RFA) equipment and techniques, as incomplete tumour necrosis, or 'skipping', has been documented after RFA of renal tumours and subsequent partial nephrectomy, but this was assumed to result from insufficient energy deposition with first-generation low-energy generators.

PATIENTS AND METHODS

In all, 17 patients with solitary renal tumours of <or=4 cm were treated with RFA under laparoscopic control. A state-of-the-art monopolar RFA generator and 15 G multi-tined needle probes were used. The probe tines were deployed to create an ablation zone>0.5-1.0 cm beyond the sonographically controlled tumour borders. Target temperatures of 105 degrees C were applied in three cycles for 10-30 min at up to 150 W. Tumours were then removed by laparoscopic partial nephrectomy and specimens evaluated by detailed histology.

RESULTS

The mean (range) resected tumour size was 22 (11-40) mm, the mean RFA time was 39 (27-59) min and the mean surgical resection time was 25 (12-45) min. In 13 patients, haemostasis was sufficient to avoid the renal pedicle being clamped. Intraoperative repeated positive margins in one patient required a laparoscopic radical nephrectomy. Thirteen (76%) renal masses showed histologically complete ablation of the entire tumour. Of the four RFA failures, three tumours were >3 cm in diameter, two were highly vascularized and three had a very heterogeneous tissue texture.

CONCLUSION

Even with state-of-the-art technology, skipping remains a problem with RFA for small renal masses and renders the technique unreliable.

Energieablative Therapie von Nierentumoren

Solid renal tumours with a diameter <4 cm may be effectively cured by partial nephrectomy but this is associated with a complication rate of 15-20%. In addition, these tumours are more frequently diagnosed in the elderly (<70 years) and 26% are aggressive G3 and potentially hazardous tumours. Since these tumours are frequently unifocal, spherical, peripherally located and easily accessible for minimally invasive approaches, energy ablative techniques are attractive less invasive therapeutic options. These tumours may be treated by freezing (cryoablation) or by heat (radiofrequency ablation, high intensified focused ultrasound). Cryoablation seems to be the most reliable technique with a 1.6% recurrence rate over 3 years follow-up but only 1.8% complications. Conversely skipping renders RFA unreliable in highly vascularised tumours >3 cm with 23% vital tumours to be found at histological work-up. Laparoscopic HIFU is still experimental. Percutaneous techniques are less effective as compared with laparoscopy with recurrence rates ranging between 13-21% (cryoablation) and 14-18% (RFA). In addition, oncological follow-up relies solely on radiological measurements, frequently without histological verification thus making percutaneous techniques unpredictable.