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Imaging-Guided Percutaneous Radiofrequency Ablation of Solid Renal Masses: Techniques and Outcomes of 38 Treatment Sessions in 32 Consecutive Patients

¹ All authors: Department of Diagnostic Imaging, Rhode Island Hospital, Brown Medical School, 593 Eddy St., Providence, RI 02903.

Received July 19, 2002; accepted after revision November 5, 2002.

 
Address correspondence to W. W. Mayo-Smith.

Abstract

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OBJECTIVE. The purpose of this study was to describe the treatment techniques and results of 38 consecutive imaging-guided percutaneous radiofrequency ablations of solid renal masses performed in 32 patients.

MATERIALS AND METHODS. Solid renal masses in 32 patients underwent 38 treatment sessions using imaging-guided percutaneous radiofrequency ablation. During 36 sessions, radiofrequency ablation was performed using CT guidance, and two, using sonographic guidance. The average patient age was 76 years (range, 52–87 years), and the average renal mass size was 2.6 cm (range, 1–5 cm). The average number of radiofrequency treatments per solid mass at each session was 2.4 (range, 1–6 treatments), and the average time per treatment was 9.2 min (range, 3–14 min). A single electrode was used in 12 sessions, and a cluster electrode was used in 26 sessions. The average follow-up time was 9 months (range, 1–36 months).

RESULTS. Twenty-six of 32 patients had successful treatment of the solid renal mass using percutaneous imaging-guided radiofrequency ablation after one treatment session. Successful treatment was defined as lack of enhancement of the treated region on follow-up CT. Six of 32 patients had residual enhancing tissue after the first treatment session and returned for a second session. Five of these six retreatments were successful. Masses requiring a second treatment session were significantly larger than masses treated in a single session (3.5 vs 2.4 cm, respectively; p = 0.0013). Two patients had perinephric hematomas (which did not require transfusion), and one patient developed a 5-mm skin metastasis at the electrode insertion site, which was resected without recurrence.

CONCLUSION. Percutaneous imaging-guided radiofrequency ablation shows promise in the treatment of solid renal malignancies.

Introduction

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Solid renal masses are being detected more frequently with the increased use of cross-sectional imaging [1, 2]. Approximately 25–49% of renal cell carcinomas are now detected incidentally on cross-sectional imaging [3]. The treatment for solid renal masses that cannot definitively be classified as benign by imaging criteria has traditionally been nephrectomy. More recently, nephron-sparing surgery or partial nephrectomy has been performed in appropriate surgical candidates at tertiary referral centers [4, 5]. In addition, laparoscopic nephrectomy is a new treatment technique that is less invasive than traditional open nephrectomy [6]. Although these newly introduced procedures are less invasive than traditional nephrectomy, they all require hospital admission, general anesthesia, and operating room time, along with their attendant risks and costs.

Radiofrequency ablation is a new technique that has been used most extensively to treat liver neoplasms [7, 8, 9] and has been described in laboratory animals [10, 11, 12, 13, 14, 15, 16]. It has more recently been described in treating a limited number of patients with solid renal masses [17, 18, 19, 20, 21, 22, 23, 24, 25]. If it can be shown to cause complete tumor eradication, renal radiofrequency ablation may hold promise as a new minimally invasive technique to treat renal malignancies on an outpatient basis without the need for hospital admission or general anesthesia.

Our purpose was to describe our experience in 38 consecutive treatment sessions of solid renal masses using percutaneous imaging-guided radiofrequency ablation and to describe techniques, complications, and results in these patients.

Materials and Methods

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Patient Recruitment
This retrospective study was approved by our institutional review board, and informed consent was obtained from all patients before the procedure. Thirty-three consecutive patients were referred to one institution for percutaneous imaging-guided radiofrequency ablation of solid renal masses. All patients either refused surgery or were not considered surgical candidates because of advanced age or comorbid conditions. Imaging-guided radiofrequency ablation was performed from 1998 to 2002. One patient had an exophytic mass in the left kidney that abutted the descending colon. The mass could not be separated from the colon despite multiple attempts of patient repositioning during CT, and radiofrequency ablation was not performed because of risk of injury to the adjacent colon. The remaining 32 patients referred to our service were treated and compose the cohort for this study. There were 21 men and 11 women with an average age of 76 years (range, 52-87 years).

Tumor Characteristics
Of the 32 patients, 18 had pathologic confirmation of the diagnosis from imaging-guided biopsy performed either in advance or at the time of the radiofrequency ablation. The pathologic results from the biopsies were 14 renal cell carcinomas, two oncocytomas, one angiomyolipoma that did not contain macroscopic fat, and one metastatic angiosarcoma. Fourteen patients did not have pathologic confirmation of the renal lesion, but the mass was either solid on renal sonography (with homogeneous internal echoes) or showed over 15 H of enhancement at dedicated contrast-enhanced renal CT. The average size of treated renal masses was 2.6 cm (range, 1–5 cm). Twenty renal masses were treated in the right kidney, and 12 were treated in the left. Three tumors were located in the anterior renal cortex; 15, in the lateral renal cortex; 13, in the posterior cortex; and one lesion, in the superior cortex.

The location (or macroscopic morphologic location) of renal neoplasms was defined by Gervais et al. [20] as either exophytic, mixed, or central depending on the relationship of the tumor to the perinephric fat, renal parenchyma, and renal sinus fat. Exophytic renal masses were defined as at least 25% of the tumor extending beyond the renal contour and not abutting the renal sinus fat. Central masses extended into the renal sinus fat and were limited to the confines of the renal contour. The mixed category included tumors that were located adjacent to the renal sinus fat and distorted the renal contour. According to this definition, 29 of the treated tumors in our series were exophytic (Figs. 1A, 1B, 2A, 2B, 2C, 3A, 3B, 3C, 3D), and three were mixed.

View larger version (171K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A. —79-year-old woman with biopsy-proven renal cell carcinoma of right kidney. Contrast-enhanced CT scan obtained before treatment shows enhancing exophytic mass (arrow) along posterior medial border of right kidney.

View larger version (165K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B. —79-year-old woman with biopsy-proven renal cell carcinoma of right kidney. CT image obtained 2 months after radiofrequency treatment shows decreased size of mass and no enhancement. Note mild dilatation of upper pole calyx (arrow), which is presumably due to heat-induced stricture of collecting system.

View larger version (125K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A. —68-year-old man with solid enhancing mass in left kidney. Contrast-enhanced CT scan obtained before treatment shows enhancing exophytic mass (arrow) in lateral left kidney.

View larger version (155K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B. —68-year-old man with solid enhancing mass in left kidney. CT fluoroscopic image obtained during treatment shows cluster electrode (arrow) along medial aspect of mass. Patient required three separate 6-min treatments of mass at separate locations during treatment session to cause complete necrosis.

View larger version (122K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2C. —68-year-old man with solid enhancing mass in left kidney. Contrast-enhanced CT scan obtained 1 month after radiofrequency treatment shows complete tumor necrosis with no enhancement.

View larger version (161K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A. —74-year-old woman with biopsy-proven renal cell carcinoma requiring two radiofrequency treatments. Contrast-enhanced CT scan obtained before treatment shows enhancing exophytic mass (arrow) in posterior lower pole of right kidney.

View larger version (136K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B. —74-year-old woman with biopsy-proven renal cell carcinoma requiring two radiofrequency treatments. CT fluoroscopic image from first radiofrequency ablation shows single electrode in medial portion of lesion.

View larger version (108K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3C. —74-year-old woman with biopsy-proven renal cell carcinoma requiring two radiofrequency treatments. Contrast-enhanced CT scan obtained 2 months after original radiofrequency ablation shows residual enhancing tumor (arrow).

View larger version (124K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3D. —74-year-old woman with biopsy-proven renal cell carcinoma requiring two radiofrequency treatments. Contrast-enhanced CT scan obtained 6 months after second radiofrequency treatment shows no residual enhancing tissue at site of tumor (arrow).

Radiofrequency Technique
For the first 2 years of the study, all patients were interviewed immediately before the treatment by an interventional radiologist. For the past year, our interventional service has employed a dedicated nurse practitioner who helps coordinate referrals, gathers relevant outside radiologic studies, and coordinates the pre- and posttreatment communication with both the patient and referring physician. Currently, all patients referred for a renal radiofrequency ablation have a dedicated visit to our service in advance of the treatment, at which time the procedure is explained in detail by the nurse practitioner who also obtains a brief history and performs a physical examination. An interventional radiologist then interviews the patient to further explain the technique and answer any questions. All patients had chest, abdominal, and pelvic CT performed before the radiofrequency ablation to stage the cancer.

The procedure was performed in all patients using conscious sedation (droperidol, midazolam and fentanyl) administered by dedicated nursing personnel. Continuous monitoring of heart rate, ECG tracing, oxygen saturation rate, and respiratory rate was performed, and blood pressure was taken every 3–5 min according to the conscious sedation protocol at our hospital. In 1998, at the beginning of our study, two patients were admitted for observation after the radiofrequency procedure. Since that time, all patients have been discharged on the day of the procedure after appropriate monitoring because of conscious sedation. No patient received prophylactic antibiotics before or after the procedure.

We defined a session as a visit to the radiology department when a renal mass was treated with radiofrequency ablation. A radiofrequency treatment referred to the placement of a radiofrequency probe into the lesion and application of radiofrequency energy. Thus, a patient could undergo more than one radiofrequency treatment in a single session. All radiofrequency ablations were performed with an internally cooled radiofrequency system. The radiofrequency generator (Cosman coagulator-1, Radionics, Burlington, MA) produces a maximal output of 200 W, and internal cooling of the electrode is performed with a peristaltic pump that recirculates ice water (80 mL/min) keeping the electrode tip temperature below 20°. A cluster electrode (three 2.5-cm active-tip electrodes) was used in 26 sessions, and a single electrode (2- to 3-cm active tip) in 12 sessions. When the cluster electrode was used, four grounding pads were placed on the patient's thighs; with the single electrode, two grounding pads were used. The average number of radiofrequency treatments per renal mass was 2.4 (range, 1–6 treatments) at each session, and the average treatment time was 9.2 min (range, 3–14 min). The time of treatment was determined by posttreatment intratumoral temperature. As has been described by Goldberg et al. [26], a temperature of greater than 50° was considered adequate to induce tissue necrosis. The average tumor baseline impedance was 64 (range, 50–91 ), power deposition was 141 W (range, 96–164 W), and current was 1.5 A (range, 0.8–2.0 A). The average maximum intratumoral temperature achieved immediately after radiofrequency treatment was 78.1° (range, 59–96°). The radiofrequency electrode tract was not coagulated at the time of radiofrequency electrode withdrawal.

Follow-Up
After the ablation session, patients were followed up on contrast-enhanced CT, usually performed at 1-, 3-, and 6-month intervals after the original session. We obtained follow-up information by direct interview of the patient, contact with the referring urologist, examination of the radiology reports, or, if necessary, follow-up in the patient's medical chart.

Statistical comparison of patients treated with one versus two sessions for lesion size, number of radiofrequency treatments, radiofrequency treatment time, and posttreatment temperature was performed using the unpaired Student's t test. Comparison of the type of electrode used (single vs cluster electrode) between the patients treated in one versus two sessions was performed using the chi-square test. Statistical analysis was performed using the software program Statview version. 5.0.1 (SAS Institute, Cary, NC). A p value of less than 0.05 was considered statistically significant.

Results

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There were 38 sessions of radiofrequency ablation of solid renal masses in 32 patients. Twenty-six patients were treated in a single session each; six patients each had two treatment sessions. Originally, sonographic guidance was used in the first two patients with small renal masses. After gaining more experience, we preferred CT guidance because the electrode was more reliably placed and the production of gas at the treatment site did not obscure the lesion for additional treatments. Originally, we used a single electrode for treatment of small lesions but currently use the cluster electrode for all treatments because the area of tumor necrosis is greater, thus reducing the need for multiple treatments per session. The average treatment time was 9.2 min (range, 3–14 min), and the average treatment temperature was 78.1° (range, 59–96°). All treatments resulted in a posttreatment intratumoral temperature greater than 50°, which we considered to be an effective end point because this temperature has been shown to be tumoricidal [26].

All patients tolerated the procedure with no major complications. Two patients had a transient episode of hypertension during the procedure (mean blood pressure, 215/100 mm Hg), which resolved spontaneously after the procedure. Two patients had small perinephric hematomas after the procedure, which resolved and did not require transfusion. One patient with a biopsy-proven renal cell carcinoma had a dilated upper pole calyx on follow-up CT, presumably from a stricture induced by the treatment (Figs. 1A, 1B). One patient had a single 5-mm metastasis in the skin at the electrode insertion site, which was resected, and no recurrent tumor has been identified during the follow-up period of 16 months. Several patients had pain or paresthesias in the periumbilical region for several weeks after the procedure, which resolved spontaneously. This presumably was due to transient damage to the intercostal or lumbar nerves in the affected dermatome. All patients received a prescription for oral pain medications (acetaminophen and hydrocodone bitartrate) at the time of discharge from the hospital, but fewer than 50% of the patients had the prescription filled, and few required analgesia for more than several days after the procedure. No patient experienced the postablative pain syndrome (pain, fevers, malaise, elevated WBC) described after hepatic radiofrequency ablation [27], and no patient required readmission to the hospital after the original treatment session. No patient received antibiotics before, during, or after the procedure.

Patients were imaged with contrast-enhanced CT at approximately 1, 3, and 6 months after the original treatment session. If there was no residual enhancement at the 6-month follow-up, patients were then imaged at 6-month intervals. The average follow-up interval for all patients was 9 months (range, 1–36 months). Twenty-six patients have shown no residual enhancing tumor on follow-up CT (Figs. 1A, 1B and 2A, 2B, 2C). Six patients did show residual enhancing tumor at follow-up and were treated a second time (Figs. 3A, 3B, 3C, 3D). On average, the second session occurred 4 months after the first session (range, <1–11 months). After the second treatment, five of these six patients showed no residual enhancement. One showed a small amount of residual enhancement, but the patient refused a third treatment. The small (<1 cm) area of enhancement in this patient has been stable for 18 months and is being followed up. Renal masses requiring a second treatment session (3.5 cm, range 2–5 cm) were significantly larger than masses that did not require a second session (2.4 cm, range 1–4 cm; p = 0.0031). There was not a significant difference in type of electrode used, number of treatments per session, posttreatment temperature, or treatment time between tumors treated in one session and those treated in two sessions.

Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
Imaging-guided radiofrequency ablation shows promise as a minimally invasive therapy for the treatment of solid renal masses. Our results show minimal morbidity and no mortality associated with this procedure. These findings are similar to those reported by Gervais et al. [20]. Our preliminary experience suggests that the procedure can be performed safely on an outpatient basis using conscious sedation. We found no need for prophylactic antibiotics because none of our patients developed an infection after the procedure.

We have found that CT is the preferred imaging modality for performing renal radiofrequency ablations because both the renal mass and electrode location are reliably seen. In addition, the production of air bubbles at the electrode tip during radiofrequency treatment actually aids in determining the area treated using CT and can obscure both the lesion and localization of the electrode tip using sonography. On the basis of our experience in this small cohort of patients, we recommend using a cluster electrode for treatment of all renal masses because the area of tumor kill is greater than that using a single electrode and fewer treatments should be needed per session. To the best of our knowledge, the duration of each radiofrequency treatment has not been studied in treating renal masses. A treatment time of 12 min with the cooled-tip electrode system in both experimental and human models has been advocated for hepatic lesions [6, 26, 27]. This treatment time in the liver is based on the dual blood supply of the liver, which can dissipate heat generated by the radiofrequency electrode, also known as the "heat sink" effect. We have found that treatment times of 6 min can reliably induce temperatures after treatment of 50° in the lesion, which has been shown to induce tumor necrosis [26]. Depending on the lesion location, treatment times as short as 3 min (in small lesions surrounded by perinephric fat) caused tumor necrosis and lack of enhancement on follow-up imaging. For larger renal lesions, imaging-guided overlapping treatments and measurement of temperature at the electrode tip before retreatment provided reliable guidance for complete tumor ablation, as has been described in a study of radiofrequency ablation of the liver [27].

Eighteen of our patients had pathologic proof of diagnosis, whereas 14 were treated on the basis of imaging characteristics of enhancement of greater than 15 H on contrast-enhanced CT or of a solid renal mass shown on sonography. Sonographic findings and tumor enhancement patterns on CT have been shown to be reliable indicators of a solid renal mass [3, 28]. The role of biopsy before ablation is to document either a benign lesion that does not need treatment or a malignant lesion that does require treatment. The need for biopsy before renal radiofrequency ablation is controversial because renal biopsies can result in indeterminate or false-negative results.

Minimal complications were associated with renal radiofrequency ablation in our study. Two patients had a perinephric hematoma, which did not require a transfusion, and two patients had a transient episode of hypertension during the procedure, which resolved spontaneously. No patient had an episode of macroscopic hematuria. One patient had a 5-mm skin metastasis at the electrode insertion site, which was subsequently resected. These findings underscore the importance of both clinical and radiologic follow-up. One patient had dilatation of an upper pole calyx after the procedure, which may have been due to heat-induced stricture to the collecting system (Figs. 1A, 1B). We know of no other reports of collecting-system stricture caused by this technique. Renal radiofrequency ablation was generally well tolerated by our patients, who required only minimal oral pain medication after treatment.

Although the optimal time for imaging follow-up has not been determined, we currently schedule the patient for dedicated renal contrast-enhanced CT (using 5-mm collimation) at 1-, 3-, and 6-month intervals after the original treatment session. If there is no evidence of enhancement at 6 months, we then follow up at 6-month intervals. The optimal time intervals for follow-up should be investigated in future studies.

Analysis of tumor location showed that most lesions (29/32) were exophytic (> 25% of the tumor margin adjacent to the perinephric fat) (Figs. 1A, 1B, 2A, 2B, 2C, 3A, 3B, 3C, 3D). Three lesions were mixed (margins adjacent to the renal sinus and perinephric fat), and none of the lesions in our patients were purely central (tumor abutting the renal sinus fat and limited to the confines of the renal contour). We treated 32 of 33 patients referred for renal radiofrequency ablation and did not view location of the tumor within the cortex as a contraindication to treatment. One patient referred for renal radiofrequency ablation could not be treated because the exophytic lateral left renal mass was adjacent to the descending colon, but all other referred patients were treated. Thus, we found that most patients with solid renal masses are candidates for this procedure. That most lesions were exophytic and relatively small probably reflects the fact that most were discovered incidentally on imaging, although we did not study this feature specifically. Most lesions treated were either lateral (n = 15) or posterior (n = 13). These locations are optimal for treatment because the lesion is easily accessible using a posterior approach with the patient in the prone position.

Small renal masses have been shown to grow slowly, and a case can be made to follow up elderly debilitated patients because they may die of other causes before death from the renal cell carcinoma [29, 30, 31]. Indeed, nephrectomy may have a higher morbidity and mortality rate than watchful waiting in this patient cohort. The purpose of this study was not to decide whether patients should be observed or treated with radiofrequency ablation but to evaluate the technique of radiofrequency ablation and document its effectiveness. If renal radiofrequency ablation is shown to be comparable to surgical resection, then the appropriate patients for treatment should be investigated in future randomized trials.

In summary, we have found that imaging-guided percutaneous radiofrequency ablation shows great promise in treating solid renal malignancies. The procedure can be performed on an outpatient basis with minimal morbidity. Long-term follow-up should be maintained, and appropriate patient selection criteria should be determined by future studies.

Acknowledgments
 
We thank the urologists, John Maynard, John Marcaccio, Joeseph Callaghan, and Bradley Miller, who referred patients for radiofrequency treatment; Glenn A. Tung for his timely statistical analysis; and Steve Hopkins for his tireless assistance in image restoration.

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				C. J. Simon, D. E. Dupuy, T. A. DiPetrillo, H. P. Safran, C. A. Grieco, T. Ng, and W. W. Mayo-Smith Pulmonary Radiofrequency Ablation: Long-term Safety and Efficacy in 153 Patients Radiology, April 1, 2007; 243(1): 268 - 275. [Abstract] [Full Text] [PDF]

				T. D. Atwell, M. A. Farrell, M. R. Callstrom, J. W. Charboneau, B. C. Leibovich, D. E. Patterson, G. K. Chow, and M. L. Blute Percutaneous Cryoablation of 40 Solid Renal Tumors with US Guidance and CT Monitoring: Initial Experience Radiology, April 1, 2007; 243(1): 276 - 283. [Abstract] [Full Text] [PDF]

				E. Liapi and J.-F. H. Geschwind Transcatheter and Ablative Therapeutic Approaches for Solid Malignancies J. Clin. Oncol., March 10, 2007; 25(8): 978 - 986. [Abstract] [Full Text] [PDF]

				M. D. Beland, W. W. Mayo-Smith, D. E. Dupuy, J. J. Cronan, and R. A. DeLellis Diagnostic Yield of 58 Consecutive Imaging-Guided Biopsies of Solid Renal Masses: Should We Biopsy All That Are Indeterminate? Am. J. Roentgenol., March 1, 2007; 188(3): 792 - 797. [Abstract] [Full Text] [PDF]

				G. E. Wile, J. R. Leyendecker, K. A. Krehbiel, R. B. Dyer, and R. J. Zagoria CT and MR Imaging after Imaging-guided Thermal Ablation of Renal Neoplasms RadioGraphics, March 1, 2007; 27(2): 325 - 339. [Abstract] [Full Text] [PDF]

				S. Kawamoto, S. Permpongkosol, D. A. Bluemke, E. K. Fishman, and S. B. Solomon Sequential Changes after Radiofrequency Ablation and Cryoablation of Renal Neoplasms: Role of CT and MR Imaging RadioGraphics, March 1, 2007; 27(2): 343 - 355. [Abstract] [Full Text] [PDF]

				W. S. McDougal, N. E. Tolkoff-Rubin, M. D. Michaelson, P. R. Mueller, and K. Braaten Case 28-2006 -- A 59-Year-Old Man with Masses in Both Kidneys N. Engl. J. Med., September 14, 2006; 355(11): 1161 - 1167. [Full Text] [PDF]

				S. G. Silverman, Y. U. Gan, K. J. Mortele, K. Tuncali, and E. S. Cibas Renal Masses in the Adult Patient: The Role of Percutaneous Biopsy Radiology, July 1, 2006; 240(1): 6 - 22. [Abstract] [Full Text] [PDF]

				J. P. McGahan, K. M. Ro, C. P. Evans, and L. M. Ellison Efficacy of transhepatic radiofrequency ablation of renal cell carcinoma. Am. J. Roentgenol., May 1, 2006; 186(5 Suppl): S311 - S315. [Abstract] [Full Text] [PDF]

				J. D. Bojarski, D. E. Dupuy, and W. W. Mayo-Smith CT Imaging Findings of Pulmonary Neoplasms After Treatment with Radiofrequency Ablation: Results in 32 Tumors Am. J. Roentgenol., August 1, 2005; 185(2): 466 - 471. [Abstract] [Full Text] [PDF]

				S. G. Silverman, K. Tuncali, E. vanSonnenberg, P. R. Morrison, S. Shankar, N. Ramaiya, and J. P. Richie Renal Tumors: MR Imaging-guided Percutaneous Cryotherapy--Initial Experience in 23 Patients Radiology, August 1, 2005; 236(2): 716 - 724. [Abstract] [Full Text] [PDF]

				D. A. Gervais, F. J. McGovern, R. S. Arellano, W. S. McDougal, and P. R. Mueller Radiofrequency Ablation of Renal Cell Carcinoma: Part 1, Indications, Results, and Role in Patient Management over a 6-Year Period and Ablation of 100 Tumors Am. J. Roentgenol., July 1, 2005; 185(1): 64 - 71. [Abstract] [Full Text] [PDF]

				D. A. Gervais, R. S. Arellano, F. J. McGovern, W. S. McDougal, and P. R. Mueller Radiofrequency Ablation of Renal Cell Carcinoma: Part 2, Lessons Learned with Ablation of 100 Tumors Am. J. Roentgenol., July 1, 2005; 185(1): 72 - 80. [Abstract] [Full Text] [PDF]

				K. Ahrar, S. Matin, M. J. Wallace, S. Gupta, and M. E. Hicks Percutaneous Transthoracic Radiofrequency Ablation of Renal Tumors Using an Iatrogenic Pneumothorax Am. J. Roentgenol., July 1, 2005; 185(1): 86 - 88. [Abstract] [Full Text] [PDF]

				E. M. Merkle, S. G. Nour, and J. S. Lewin MR Imaging Follow-up after Percutaneous Radiofrequency Ablation of Renal Cell Carcinoma: Findings in 18 Patients during First 6 Months Radiology, June 1, 2005; 235(3): 1065 - 1071. [Abstract] [Full Text] [PDF]