oth percutaneous radiofrequency ablation (RFA) and cryoablation have shown favorable local tumor

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1 Vascular and Interventional Radiology Original Research Atwell et al. Radiofrequency Ablation and Cryoablation of Small Renal Masses Vascular and Interventional Radiology Original Research Thomas D. Atwell 1 Grant D. Schmit 1 Stephen A. Boorjian 2 Jay Mandrekar 3 A. Nicholas Kurup 1 Adam J. Weisbrod 1 George K. Chow 2 Bradley C. Leibovich 2 Matthew R. Callstrom 1 David E. Patterson 2 Christine M. Lohse 4 R. Houston Thompson 2 Atwell TD, Schmit GD, Boorjian SA, et al. Keywords: ablation, complications, cryoablation, radiofrequency, renal cell carcinoma, survival DOI: /AJR Received January 24, 2012; accepted after revision April 20, M. R. Callstrom has received research grants from Siemens Healthcare and Endocare. Presented at the 2012 annual meeting of the ARRS, Vancouver, BC, Canada. 1 Department of Diagnostic Radiology, Mayo Clinic, 200 First St SW, Rochester, MN Address correspondence to T. D. Atwell (atwell.thomas@mayo.edu). 2 Department of Urology, Mayo Clinic, Rochester, MN. 3 Department of Biostatistics, Mayo Clinic, Rochester, MN. 4 Department of Biomedical Statistics and Informatics, Mayo Clinic, Rochester, MN. AJR 2013; 200: X/13/ American Roentgen Ray Society Percutaneous Ablation of Renal Masses Measuring 3.0 cm and Smaller: Comparative Local Control and Complications After Radiofrequency Ablation and Cryoablation OBJECTIVE. The purpose of this article is to compare the efficacy and complication rates of percutaneous radiofrequency ablation (RFA) and cryoablation in the treatment of renal masses measuring 3.0 cm and smaller. MATERIALS AND METHODS. A retrospective review was performed of 385 patients with 445 tumors measuring 3.0 cm or smaller treated with thermal ablation from 2000 through Two hundred fifty-six tumors in 222 patients were treated with RFA (mean [± SD] tumor size, 1.9 ± 0.5 cm), and 189 tumors in 163 patients were treated with cryoablation (mean tumor size, 2.3 ± 0.5 cm). Major complications and efficacy as measured by technical success and local tumor recurrence rates were recorded. RESULTS. There were five (1.1%) technical failures, including one (0.4%) among tumors treated with RFA and four (2.1%) among tumors treated with cryoablation (p = 0.17). Of the 218 tumors treated with RFA and with follow-up beyond 3 months, seven (3.2%) developed local tumor recurrence, at a mean of 2.8 years after treatment (range, years). Of the 145 tumors treated with cryoablation and with follow-up beyond 3 months, four (2.8%) developed local tumor recurrence at a mean of 0.9 years after treatment (range, years). For biopsy-proven renal cell carcinoma, estimated local recurrence-free survival rates at 1, 3, and 5 years after RFA were 100%, 98.1%, and 98.1%, respectively, compared with 97.3%, 90.6%, and 90.6%, respectively, after cryoablation (p = 0.09). Major complications occurred after 4.3% (10/232) of RFAs and 4.5% (8/176) of cryoablation procedures (p = 0.91). CONCLUSION. RFA and cryoablation are both effective in the treatment of renal masses measuring 3 cm or smaller. Major complications with either procedure are infrequent. B oth percutaneous radiofrequency ablation (RFA) and cryoablation have shown favorable local tumor control according to short- and intermediate-duration follow-up [1 4]. However, two landmark meta-analyses published in 2008 by Kunkle et al. [5, 6] found a considerable discrepancy in the rate of local tumor recurrence between RFA and cryoablation. Specifically, local recurrence was reported following 12% of RFAs and 5% of cryoablations. Although, at first glance, these results suggest inferiority of RFA compared with cryoablation, it is important to recognize a generally accepted limitation of RFA in treating large (> 3 cm) renal masses. Specifically, excellent outcomes have consistently been reported in the treatment of renal masses smaller than 3 cm using RFA [4, 7, 8]. This of particular importance when one recognizes the now defined role of thermal ablation in the current American Urological Association guidelines in treating the small renal mass [9] and the challenges faced in appropriate triage of patients to ablation. The purpose of this article is to compare the complication rate and efficacy of percutaneous RFA and cryoablation in the treatment of renal masses measuring 3.0 cm and smaller. Materials and Methods Approval for this retrospective study was obtained from our institutional review board, and the study was compliant with the HIPAA. Informed consent was waived by the institutional review board. Patient Selection After institutional review board approval, patients who underwent percutaneous ablation of a renal mass 3.0 cm or smaller with curative intent between May of 2000 and November of 2010 were identified for study. Four hundred forty-five tumors in 385 patients were treated, including 256 (58%) tumors treated with RFA and 189 (42%) tumors treated with cryoablation. AJR:200, February

2 Atwell et al. Patient Triage for Ablation Patients were initially evaluated in the Department of Urology for formal urologic consultation. If the patient and urologist deemed that ablation was a reasonable treatment alternative to surgery (e.g., in most cases because of high surgical risk or prior renal surgery), the pertinent radiographic images were reviewed with a radiologist experienced with renal ablation. If the tumor was deemed technically amenable to ablation, the patient was scheduled for treatment with either RFA or cryoablation. RFA was introduced into our practice in 2000, and cryoablation was introduced in Since 2003, larger tumors (typically those > 3 cm) and those more centrally located within the kidney or near the ureter tended to be triaged to cryoablation at the discretion of the treating physician. General prescreening guidelines for patients before ablation included serum international normalized ratio (< 1.6) and platelet counts (> /L). Antiplatelet therapy was held for 5 7 days before treatment. Tumor Characteristics All patients had CT or MRI at presentation that revealed an indeterminate solid or complex cystic renal mass concerning for malignancy. Maximum tumor size was determined according to the largest measurement obtained using the modality that best depicted the tumor margin. Tumors were classified as described elsewhere [10]. Tumors were classified as exophytic, intraparenchymal, or central, depending on their position relative to the renal parenchyma. Any tumor that contacted the renal sinus fat was classified as a central tumor. The remaining tumors were classified as either exophytic or intraparenchymal. Exophytic tumors were defined as tumors where 50% or greater of the circumference extended beyond the renal capsule, and intraparenchymal tumors were defined as tumors where less than 50% of the tumor circumference extended beyond the capsule. Triage Between RFA and Cryoablation Since 2003, both RFA and cryoablation have been used at our institution as treatment options for patients with a small renal mass. The choice of treatment modality was left to the discretion of the treating physician, although with time, there was a general trend to treat larger tumors and central tumors with cryoablation. Ablation Procedure Verbal and written informed consent for the ablation was obtained. All renal ablations were performed with the patient under general anesthesia. Since 2000, we have used two RFA devices. From 2000 to 2002, we primarily used the RITA device (Angiodynamics). Since 2002, we have used an impedance-based internally cooled RFA device (Cool-tip, Covidien). We have performed cryoablation since 2003; the Endocare cryoablation system (HealthTronics) was used in all treatments. After induction of general anesthesia, ultrasound (Acuson Sequoia, Siemens Healthcare) was used to guide the ablation applicator (electrode or cryoprobe) into the renal tumor. CT was used to confirm accurate applicator placement and proximity of adjacent structures. Hydrodisplacement was performed in the treatment of 95 tumors to displace the tumor from critical adjacent structures, such as bowel, adrenal gland, or body wall. Ureteral stents were placed in 20 patients to allow retrograde irrigation of the ureter to minimize risk of ureteral or collecting system injury. Immediately before initiating the ablation process, an 18-gauge core biopsy device (Monopty Biopsy Instrument, C. R. Bard) was used to obtain one or two samples from the tumor using ultrasound or CT guidance. In a few cases, obscuration TABLE 1: Characteristics of Renal Tumors Treated With Radiofrequency Ablation (RFA) or Cryoablation Feature RFA (n = 256) Cryoablation (n = 189) p Size (cm) < Mean ± SD 1.9 ± ± 0.5 Median (range) 1.8 ( ) 2.4 ( ) Location Right 147 (57) 82 (43) Left 108 (42) 105 (56) Transplant 1 (< 1) 1 (< 1) Horseshoe 0 1 (< 1) Position < Exophytic 144 (56) 58 (31) Intraparenchymal 95 (37) 54 (29) Central 17 (7) 77 (41) Biopsy performed 152 (59) 140 (74) Classification result of biopsy (n = 292) 0.15 RCC 82 (54) 79 (56) Oncocytoma 23 (15) 25 (18) Oncocytic neoplasm 10 (7) 7 (5) Angiomyolipoma 4 (3) 3 (2) Suspicious for RCC 1 (1) 5 (4) Metastasis 5 (3) 0 Atypical 3 (2) 0 Spindle cell neoplasm 1 (1) 0 Nondiagnostic 23 (15) 21 (15) Diagnostic result of biopsy (n = 292) 0.89 Malignant 102 (67) 91 (65) Benign 27 (18) 28 (20) Nondiagnostic 23 (15) 21 (15) Technical outcome 0.17 Success 255 (> 99) 185 (98) Failure 1 (< 1) 4 (2) Local recurrence All tumors 7/218 (3.2) 4/145 (2.8) 0.48 RCC 1/75 (1.3) 3/61 (4.9) 0.09 Note Data are no. (%) of tumors, except where noted otherwise. RCC = renal cell carcinoma. 462 AJR:200, February 2013

3 Radiofrequency Ablation and Cryoablation of Small Renal Masses of the renal tumor by the applicator precluded a safe biopsy. Early in our practice, we did not routinely biopsy all renal tumors. The tumor was then ablated per manufacturer recommendations: temperature-based RFA for the RITA system, impedance-based RFA for the Cool-tip applicator, and double-freeze cycle when using cryoablation. After ablation, the applicators were removed. With RFA, tract ablation was not routinely performed. Patients were admitted to the urology service for overnight observation to monitor for complications. Follow-Up Imaging Imaging was performed within 24 hours of the ablation procedure to document technical success, assess for complications, and provide a baseline for future imaging. Additional follow-up imaging with contrast-enhanced CT or MRI was performed at 3, 6, and 12 months after ablation, and yearly thereafter. Efficacy was defined as technical success and lack of local tumor recurrence. As adapted from the International Working Group on Image-Guided Tumor Ablation [11], technical success was defined within 3 months of ablation by the absence of new enhancement and absence of tumor enlargement. Local tumor recurrence was defined as persistent or recurrent tumor evident by new nodular enhancement within the ablation zone or enlargement of the ablated tumor 3 months or later after ablation or compared with prior immediate postablation imaging (if obtained beyond 3 months). Complications Major complications were defined as those meeting or exceeding grade 2 classification according to Clavien-Dindo criteria [12]. Statistical Analysis Continuous features were summarized with means, SDs, medians, and ranges, whereas categoric features were summarized with frequency counts and percentages. Comparisons of features, technical outcome, and complications between tumors treated with RFA and cryoablation were evaluated using Wilcoxon rank sum, chi-square, and Fisher exact tests. Recurrence-free survival was estimated using the Kaplan-Meier method and was compared between tumors treated with RFA and cryoablation using a log-rank test. Statistical analyses were performed using the SAS software package (SAS Institute). All tests were two-sided, and p values less than 0.05 were considered statistically significant. Results The 256 tumors treated with RFA were obtained from 222 patients with a mean age at RFA of 68.8 years (SD, 11.6 years; median, 70 years; range, years), including 141 (64%) men and 81 (36%) women. Sixty-four (29%) patients had been previously treated for renal cell carcinoma (RCC), either in the same kidney or in the contralateral kidney; the remaining 158 (71%) patients had no history of renal cancer. All tumors underwent a single treatment session. One hundred fifty-two of the 256 tumors (59%) were biopsied, and 82 of those 152 tumors (54%) were found to be RCC. The 189 tumors treated with cryoablation were obtained from 163 patients with a mean age at the first cryoablation of 68.2 years (SD, 11.3 years; median, 69 years; range, years), including 107 (66%) men and 56 (34%) women. Sixty-three (39%) patients had been previously treated for RCC, and the remaining 100 (61%) patients were without a history of renal cancer. As with RFA, all tumors were treated during a single treatment session. One hundred forty of the 189 tumors (74%) were biopsied, and 79 of those 140 tumors (56%) were found to be RCC. There was not a statistically significant difference in age (p = 0.55) or sex (p = 0.67) between patients whose first treatment was RFA and patients whose first treatment was cryoablation. However, there was evidence that patients treated with RFA were more likely to be without a history of renal cancer (p = 0.043). Notably, 13 patients had multiple tumors that were treated with both RFA and cryoablation, either on the same date or on different dates. A comparison of the features studied and technical outcome between tumors treated with RFA and those treated with cryoablation is shown in Table 1. The mean tumor size for patients treated with cryoablation was larger than that for patients treated with RFA (2.3 ± 0.5 vs 1.9 ± 0.5 cm; p < 0.001). For centrally located tumors, cryoablation was performed more often than RFA (41% vs 7%; p < 0.001). The results of the biopsies did not differ significantly between the two groups. There were only five (1.1%) technical failures observed, including one (0.4%) among tumors treated with RFA and four (2.1%) among tumors treated with cryoablation (p = 0.17). The features of the tumors that resulted in technical failures are summarized in Table 2. Major complications were evaluated for each procedure (Table 3). Among the 232 RFA procedures performed, 10 (4.3%) resulted in a major complication, including three with grade 2 and seven with grade 3 complications. Among the 176 cryoablation procedures, nine major complications (5.1%) occurred related to eight (4.5%) procedures, including two patients with grade 2, five patients with grade 3, and one patient with two distinct grade 2 complications. There was not a statistically significant difference in the occurrence of a major complication between the RFA and cryoablation procedures (p = 0.91). Overall Local Tumor Recurrence Time to local tumor recurrence was assessed for the subset of 363 tumors that were followed for at least 3 months, which included 218 (60%) tumors treated with RFA and 145 (40%) tumors treated with cryoablation. Tumors treated with cryoablation were significantly less likely to be followed for at least 3 months compared with tumors treated with RFA (145/189 [77%] vs 218/256 [85%]; p = 0.023). Among the 218 tumors treated with RFA, seven (3.2%) showed local recurrence, at a mean of 2.8 years after the procedure (median, 2.8 years; range, years). The mean duration of follow-up for the 211 tumors treated with RFA that did not recur was 3.2 years (median, 2.8 years; range, years). Among the 145 tumors treated with cryoablation, four (2.8%) recurred locally, at a mean of 0.9 years after the procedure (median, 1.0 years; range, years). The mean duration of follow-up for the 141 tumors treated with cryoablation that did not recur was 1.8 years (median, 1.4 years; range, years). Estimated local recurrence-free survival rates at 1, 3, and 5 years for tumors treated with RFA were 100% (95% CI, %; 182 patients still at risk), 97.2% (95% CI, %; 100 patients still at risk), and 93.2% (95% CI, %; 44 patients still at risk), respectively, compared with 98.3% (95% CI, %; 89 patients still at risk), 95.6% (95% CI, %; 30 patients still at risk), and 95.6% (95% CI, %; four patients still at risk), respectively, for tumors treated with cryoablation (p = 0.48; Fig. 1). The features of the tumors that recurred are summarized in Table 2. Of the 16 tumors with either technical failure or local recurrence, 11 were retreated with ablation. Local Recurrence Based on Location Central tumors Estimated local recurrence-free survival rates at 1, 3, and 5 years for central tumors treated with RFA were 100% (95% CI, %; 12 patients still AJR:200, February

4 Atwell et al. TABLE 2: Characteristics of Renal Tumors With Treatment Failure Type of Failure, Procedure Year Size (cm) Location Position Biopsy Time to Recurrence (y) Technical failure RFA Left Exophytic None Cryoablation Right Central RCC Cryoablation Right Intraparenchymal RCC Cryoablation Right Central RCC Cryoablation Left Central None Local recurrence RFA Right Central None 2.8 RFA Left Intraparenchymal None 3.9 RFA Left Central None 4.1 RFA Left Intraparenchymal None 4.1 RFA Right Central None 1.2 RFA Right Exophytic RCC 1.5 RFA Right Exophytic None 2.0 Cryoablation Left Exophytic RCC 1.6 Cryoablation Left Central RCC 0.9 Cryoablation Left Intraparenchymal None 0.3 Cryoablation Left Intraparenchymal RCC 1.1 Note Dashes indicate at time of procedure. RFA = radiofrequency ablation, RCC = renal cell carcinoma. at risk), 77.9% (95% CI, %; five patients still at risk), and 62.3% (95% CI, %; four patients still at risk), respectively, compared with 97.8% (95% CI, %; 40 patients still at risk), 97.8% (95% CI, %; 11 patients still at risk), and not available (no patients left at risk at 5 years), respectively, for central tumors treated with cryoablation (p = 0.08). Exophytic tumors Estimated local recurrence-free survival rates at 1, 3, and 5 years for exophytic tumors treated with RFA were 100% (95% CI, %; 102 patients still at risk), 97.7% (95% CI, %; 58 patients still at risk), and 97.7% (95% CI, %; 27 patients still at risk), respectively, compared with 100% (95% CI, %; 21 patients still at risk), 93.8% (95% CI, %; eight patients still at risk), and 93.8% (95% CI, %; two patients still at risk), respectively, for exophytic tumors treated with cryoablation (p = 0.35). Intraparenchymal tumors Estimated local recurrence-free survival rates at 1, 3, and 5 years for intraparenchymal tumors treated with RFA were 100% (95% CI, %; 68 patients still at risk), 100% (95% CI, %; 37 patients still at risk), and 92.8% (95% CI, %; 13 patients still at risk), respectively, compared with 97.7% (95% CI, %; 28 patients still at risk), 94.2% (95% CI, %; 11 patients still at risk), and 94.2% (95% CI, %; two patients still at risk), respectively, for intraparenchymal tumors treated with cryoablation (p = 0.26). Local Recurrence of RCC Among the 363 tumors that were followed for at least 3 months, 136 were found to be RCC at biopsy (recognizing that some tumors were not biopsied). This includes 75 of 218 (34%) tumors treated with RFA and 61 of 145 (42%) tumors treated with cryoablation. One (1.3%) of the RCC tumors treated with RFA has shown local tumor recurrence, and three (4.9%) of the RCC tumors treated with cryoablation have shown local tumor recurrence. Among this subset of tumors that proved to be RCC at biopsy, the mean duration of followup for the 74 tumors treated with RFA that did not recur was 2.9 years (median, 2.5 years; range, years). The mean duration of follow-up for the 58 tumors treated with cryoablation that did not recur was 1.7 years (median, 1.1 years; range, years). Estimated recurrence-free survival rates at 1, 3, and 5 years for RCC tumors treated with RFA were 100% (95% CI, %; 62 patients still at risk), 98.1% (95% CI, %; 31 patients still at risk), and 98.1% (95% CI, %; 12 patients still at risk), respectively, compared with 97.3% (95% CI, %; 33 patients still at risk), 90.6% (95% CI, %; 13 patients still at risk), and 90.6% (95% CI, %; one patient still at risk), respectively, for tumors treated with cryoablation (p = 0.09). Progression of Disease Elsewhere Of the 158 patients without a history of RCC and treated with RFA, three patients have developed metastatic disease (without local recurrence). Two of these three patients have died, one because of RCC and one as the result of another cause. None of the 100 patients without a history of RCC and treated with cryoablation have developed metastatic disease. A total of 56 of 385 (15%) patients have died, 11 (3%) because of RCC. Of these 11 patients, two were treated with RFA for sporadic tumors (i.e., did not have a history of RCC), and the remaining nine had undergone prior nonablative treatment of RCC. Discussion The treatment strategy for small renal masses is in evolution. Of renal masses measuring 3 cm or smaller, about 25% will be benign, 464 AJR:200, February 2013

5 Radiofrequency Ablation and Cryoablation of Small Renal Masses TABLE 3: Major Complications of Radiofrequency Ablation (RFA) and Cryoablation Procedure, Complication No. (%) of Complications RFA (n = 232) Ureteropelvic stricture 3 (1.3) Ablation site abscess 1 (0.4) Arteriovenous fistula 1 (0.4) Urine leak 1 (0.4) Hematoma 1 (0.4) Nerve injury 1 (0.4) Hypertension 1 (0.4) Atrial fibrillation 1 (0.4) Overall 10 (4.3) Cryoablation (n = 176) Hemorrhage 1 (0.6) Hematuria requiring stent 2 (1.1) Pulmonary embolus 1 (0.6) Pulmonary edema 1 (0.6) Urosepsis 1 (0.6) Abscess 1 (0.6) Systemic inflammatory response 1 (0.6) Pneumothorax 1 (0.6) Overall 9 (5.1) Local Recurrence-Free Survival (%) No. of Patients at Risk 0 0 p = Years Cryoablation RFA Cryoablation RFA Fig. 1 Local recurrence-free survival for tumors treated with radiofrequency ablation (RFA) and cryoablation, including patients at risk. and of those that are malignant, most will be of low grade [13]. Given these features of small renal masses and the recognized slow growth of such masses under surveillance [14], the role of traditional surgical management for elderly or infirm patients is being reassessed. In addition to simple surveillance, interest in percutaneous thermal ablation of small renal masses has expanded and is now included in the American Urological Association guidelines for the management of the clinical T1 renal masses [9]. Formal published studies comparing renal RFA and cryoablation at the same institution are lacking. Thus, landmark meta-analyses were published in 2008 [5, 6], comparing mostly single institutional series of either RFA or cryoablation, suggesting that RFA is inferior to cryoablation in the treatment of renal masses. In the current series, we compare the outcome of patients treated with RFA and cryoablation at our institution over the last decade. The results of this current study of patients with a renal mass 3 cm or smaller suggest that major complications, technical success, and local recurrence rates were similar between the two treatment modalities. These results, if validated by others, should have important implications regarding treatment options for patients with a small renal mass and planning ablation. Specifically, for tumors 3 cm or smaller, both RFA and cryoablation are reasonable treatment options for patients planning an ablative procedure, although cryoablation may be more efficacious for central tumors near the renal hilum. Secondary generalizations about the effectiveness of RFA as presented in earlier publications, which primarily studied heterogeneous patient cohorts, can undermine its known efficacy in the treatment of small renal tumors [5, 6]. In fact, recently published American Urological Association guidelines for the management of clinical T1 renal masses quotes a local tumor control rate of 87.0% for RFA, in contrast to 90.6% for cryoablation [9]. We think that the known size- and location-based limitations of RFA need to be taken into consideration when evaluating these retrospective data. For example, the outcomes in this present study and those offered by others have shown the efficacy of RFA in the treatment of renal masses measuring 3 cm and smaller, with recognized difficulties in treating larger masses. Gervais et al. [7] found RFA to be 100% effective in the treatment of renal tumors 3 cm or smaller, in contrast to 81% effective in treating tumors larger than 3 cm. Similarly, Zagoria et al. [8] achieved 100% local control in the RFA of 95 RCCs measuring 3.5 cm or smaller but only 47% effectiveness in treating 30 RCCs measuring 3.6 cm or larger. This group observed a twofold risk of treatment failure for every 1-cm increase in tumor size. Meanwhile, in a large multicenter study by Gupta et al. [15], five initial treatment failures were identified after RFA of 163 masses, and four of five of these tumors measured 3 cm or larger. As opposed to RFA, cryoablation has been shown to be effective in the treatment of larger renal tumors as well, specifically those measuring greater than 3 cm in greatest dimension [16]. This can be attributed to the synergy of cryoprobes in generating ice balls large enough to encompass tumors as large as 8 cm in size, as well as the ability to AJR:200, February

6 Atwell et al. effectively monitor the ice ball as it encompasses the tumor. In the current cohort of patients, we showed a potential limitation of RFA in the treatment of central renal masses. RFA has known limitations in the treatment of such centrally located tumors because of thermal sink effects originating in the highly vascular renal hilum. Specifically, conductive relative cooling occurs at the central ablation margin as a result of 37 C blood flow, which contrasts with the desired 60 C or higher lethal temperatures [17]. Such an association of RFA failure with central tumors has been noted as well by Gervais et al. [7], for whom local failures occurred in a third of such masses. This contrasted with 100% effectiveness of RFA in treating exophytic tumors. Similarly, Gupta et al. [15] found that centrally located tumors were four times more likely to be incompletely treated compared with noncentral tumors. Takaki et al. [3] also reported the limitations of RFA in the treatment of central tumors, with a significantly lower rate of local control in the treatment of 16 of 24 (67%) central tumors compared with 26 of 27 (96%) noncentral tumors. On the other hand, cryoablation can be used to safely and successfully treat centrally located tumors [18, 19]. In part, this may be due to a limited thermal sink effect [20, 21]. In addition, one can recognize the relative safety in freezing the central renal collecting system [22 24] and be more aggressive in the treatment of these centrally located renal masses. There are important limitations to our study. This was a nonrandomized retrospective study. Triage of tumors to RFA or cryoablation was at the discretion of the physicians treating the patient, with some variation of the characteristics of tumors treated with RFA versus cryoablation. Particularly later in our experience, central tumors were primarily treated with cryoablation. We also acknowledge the use of two different RFA devices, which introduces some variation in treatment technique. In addition, early in our practice, we did not routinely biopsy renal masses at the time of treatment. Thus, many of the tumors treated, particularly with RFA, do not have a pathologic diagnosis. In conclusion, both RFA and cryoablation are effective in the treatment of renal masses measuring 3 cm or smaller. For tumors that extend centrally to the renal sinus, cryoablation may be the preferred treatment option. References 1. Atwell TD, Callstrom MR, Schmit GD, et al. Percutaneous renal cryoablation: local control at mean 26 months of followup. J Urol 2010; 184: McDougal WS, Gervais DA, McGovern FJ, Mueller PR. Long-term followup of patients with renal cell carcinoma treated with radio frequency ablation with curative intent. J Urol 2005; 174: Takaki H, Yamakado K, Soga N, et al. Midterm results of radiofrequency ablation versus nephrectomy for T1a renal cell carcinoma. Jpn J Radiol 2010; 28: Varkarakis IM, Allaf ME, Inagaki T, et al. Percutaneous radio frequency ablation of renal masses: results at a 2-year mean followup. J Urol 2005; 174: ; discussion, Kunkle DA, Egleston BL, Uzzo RG. Excise, ablate or observe: the small renal mass dilemma a meta-analysis and review. J Urol 2008; 179: ; discussion, Kunkle DA, Uzzo RG. Cryoablation or radiofrequency ablation of the small renal mass: a metaanalysis. Cancer 2008; 113: Gervais DA, McGovern FJ, Arellano RS, McDougal WS, Mueller PR. 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. AJR 2005; 185: Zagoria RJ, Traver MA, Werle DM, Perini M, Hayasaka S, Clark PE. Oncologic efficacy of CTguided percutaneous radiofrequency ablation of renal cell carcinomas. AJR 2007; 189: Campbell SC, Novick AC, Belldegrun A, et al. Guideline for management of the clinical T1 renal mass. J Urol 2009; 182: Atwell TD, Farrell MA, Callstrom MR, et al. Percutaneous cryoablation of 40 solid renal tumors with US guidance and CT monitoring: initial experience. Radiology 2007; 243: Goldberg SN, Grassi CJ, Cardella JF, et al. Imageguided tumor ablation: standardization of terminology and reporting criteria. Radiology 2005; 235: Dindo D, Demartines N, Clavien PA. Classification of surgical complications: a new proposal with evaluation in a cohort of 6336 patients and results of a survey. Ann Surg 2004; 240: Frank I, Blute ML, Cheville JC, Lohse CM, Weaver AL, Zincke H. Solid renal tumors: an analysis of pathological features related to tumor size. J Urol 2003; 170: Chawla SN, Crispen PL, Hanlon AL, Greenberg RE, Chen DY, Uzzo RG. The natural history of observed enhancing renal masses: meta-analysis and review of the world literature. J Urol 2006; 175: Gupta A, Raman JD, Leveillee RJ, et al. General anesthesia and contrast-enhanced computed tomography to optimize renal percutaneous radiofrequency ablation: multi-institutional intermediate-term results. J Endourol 2009; 23: Atwell TD, Farrell MA, Callstrom MR, et al. Percutaneous cryoablation of large renal masses: technical feasibility and short-term outcome. AJR 2007; 188: Goldberg SN, Gazelle GS, Mueller PR. Thermal ablation therapy for focal malignancy: a unified approach to underlying principles, techniques, and diagnostic imaging guidance. AJR 2000; 174: Rosenberg MD, Kim CY, Tsivian M, et al. Percutaneous cryoablation of renal lesions with radiographic ice ball involvement of the renal sinus: analysis of hemorrhagic and collecting system complications. AJR 2011; 196: Warlick CA, Lima GC, Allaf ME, et al. Clinical sequelae of radiographic iceball involvement of collecting system during computed tomographyguided percutaneous renal tumor cryoablation. Urology 2006; 67: Weld KJ, Hruby G, Humphrey PA, Ames CD, Landman J. Precise characterization of renal parenchymal response to single and multiple cryoablation probes. J Urol 2006; 176: Bishoff JT, Chen RB, Lee BR, et al. Laparoscopic renal cryoablation: acute and long-term clinical, radiographic, and pathologic effects in an animal model and application in a clinical trial. J Endourol 1999; 13: Sung GT, Gill IS, Hsu TH, et al. Effect of intentional cryo-injury to the renal collecting system. J Urol 2003; 170: Brashears JH 3rd, Raj GV, Crisci A, et al. Renal cryoablation and radio frequency ablation: an evaluation of worst case scenarios in a porcine model. J Urol 2005; 173: Janzen NK, Perry KT, Han KR, et al. The effects of intentional cryoablation and radio frequency ablation of renal tissue involving the collecting system in a porcine model. J Urol 2005; 173: AJR:200, February 2013