Fall 2012 - 09 Resized.pdf 629Vol. 9 | No. 4 | Fall 2012 |U R O LO G Y J O U R N A L Purpose: To provide key evidence-based strategies to improve outcomes of radiofrequency ablation and limit recurrences of small renal tumors. Materials and Methods: The literature was searched via OvidSP MEDLINE from 1997 to current using MeSH terms. All levels of evidence and types of reports were reviewed. Results: We comprehensively reviewed technical issues, mechanisms, imaging criteria, abla- rates, and follow-up strategies. Conclusion: The technique is safe and effective. Tumors < 2.5 cm are statistically most likely to remain disease-free. Anterior tumors are contraindicated. Strict follow-up is needed to detect failures, most of which occur within 3 months and can be easily salvaged with repeat radiofre- quency ablation. Homogeneous enhancement within 1 month is not necessarily a failure, and tends to disappear after 4 to 6 weeks. Multi-disciplinary meetings must occur to discuss each case prior to treatment. Keywords: percutaneous, radiofrequency ablation, renal cell carcinoma, computed tomogra- phy 1Division of Urology & Robot- ics, McGill University Health Centre, Canada 2Montreal General Hospital, Montreal QC, Canada 3Jewish General Hospital, Montreal QC, Canada 4Royal Australasian College of Surgeons & Urological Society of Australia and New Zealand, Australia 5Westmead Private Hospital, Westmead, Australia Richard L Haddad,1,2,3,4 Manish I Patel,4 Philip Vladica,5 Wassim Kassouf,1,2 Frank Bladou,1,3 Maurice Anidjar1,3 REVIEW Percutaneous Radiofrequency Ablation of Small Renal Tumors Using CT-Guidance A Review and Its Current Role Corresponding Author: Richard L Haddad, MD Division of Urology, McGill Uni- versity Health Centre, 687 Pine Avenue, West S6.88, Montreal Quebec, Canada H3A 1A1 Tel: +1 514 561 2803 E-mail: rlhad01@gmail.com Received July 2012 Accepted August 2012 630 | Review INTRODUCTION Small renal tumors (SRT) are increasingly detected as abdominal imaging, such as computed tomography (CT) and ultrasonography (US). An enhancing SRT may be either benign or malignant. The patient and physician have many treatment options avail- able, including active surveillance, open or minimally-inva- sive surgery, or ablative techniques, such as radiofrequency ablation (RFA) and cryoablation (CA). Percutaneous RFA plays a role in clinical T1a renal cell carcinoma (RCC) in - bidity, and in those with hereditary multiple RCC syndromes or those with a high risk of chronic kidney disease in whom nephron-sparing surgery (NSS) is favored. Renal cell carcinoma comprises 2% to 3% of human adult cancers, with an incidence that has risen from 7.4 to 17.6 per 100 000 from 1975 to 2006 in the United States, cor- responding to a mean annual increase in incidence of 3%.(1) There are 50 000 new cases of RCC per year in the United States.(2) As is the case with other urological malignancies, the treatment of a SRT suspected of being RCC depends on stage, grade, and patient’s factors. The metastatic potential of SRT rises with increasing tumor size from 1.2% of 2 to 3 cm RCC metastasizing to 3.9% of 3 to 4 cm RCC metastasizing.(3,4) The histological grade Although biopsy can help, it may lead to false-negative re- of 499 nephrectomies over 15 years and discovered that Fuhrman grade 3 RCC and the papillary RCC subtype were increasingly seen over time,(5) and that benign tumors were - sible treatment modality for a SRT.(6) The treatment options for a clinical stage T1a RCC depend on patient choice af- ter the treatment options have been discussed.(7) Surgical is the gold standard for a healthy patient who is keen on intervention. Oncological outcomes have been shown to be equivalent comparing radical nephrectomy versus partial surgery (NSS).(8,9) also relies on a strict imaging follow-up protocol involv- ing either CT, US, or magnetic resonance imaging (MRI). may complicate such an approach. Radiofrequency ablation major surgery, or when NSS is preferable, as in hereditary or multiple RCC syndromes, chronic kidney disease, and a solitary kidney. The percutaneous technique is minimally invasive and can be performed as an outpatient procedure. Computed tomog- raphy guidance allows for accurate tumor localization and immediate assessment of tumor response to treatment, and Level 4 evidence case series of percutaneous-RFA have reported complete ablation rates of above 90% at 3 to 27 months follow-up.(10-17) In a survey of trends of the treat- ment of SRT in academic American centers using ablative technology, 55% used RFA while 79% used CA.(18) MATERIALS AND METHODS A literature search was performed using OvidSP MEDLINE from 1997 to current, using the keywords of “radiofrequen- cy ablation, percutaneous, computed tomography-guided, relevancy to percutaneous CT-guided RFA of renal tumors to include review articles, any available level 1 to 4 evi- dence series, reports of technique, and morbidity. Cryoabla- use of RFA in open or minimally-invasive surgery. Onco- RFA PROCEDURE TECHNIQUE A combined urology and interventional radiology approach is required to decide on appropriate cases. Coagulation pro- - tion is used for the most part, otherwise general anesthesia positioning. The patient position depends on tumor location and the relationship of adjacent viscera to the kidney. immediately preceding RFA. The electrode is inserted 631Vol. 9 | No. 4 | Fall 2012 |U R O LO G Y J O U R N A L along the same tract, and the tract ablated at the comple- tion of the procedure to reduce the risk of seeding.(15) The diameter of the probe tines is matched to the diameter of the tumor. Therefore, the probe tines cover an additional 5 to 10 mm margin of renal tissue beyond the circumferential mar- the probe’s position and accounts for motion. The number of probe tines that are deployed depends on the diameter or size of the lesion. Deploying more tines allows for in- creased coverage and enhanced ablative effect. Dependent upon the tumor size and density and the number of probe tines being used, the impedance and temperature settings can be adjusted by the operator. Larger lesions may require overlapping or repeated RFA sessions to achieve a complete ablative response. An immediate post-RFA CT scan is performed to assess ad- - dure-related complications. After an observation period of 4 hours, the patient is discharged. The follow-up CT scan protocol is 6 weeks, then at 3, 6, 12, and 18 months, and then annually.(11) MECHANISM OF TUMOR DESTRUCTION Radiofrequency ablation produces thermal injury on tu- mor cells. The thermal energy produces ionic agitation and frictional heating. A minimum critical temperature of 48 to 50 ºC is required for cellular damage. Temperatures reach- ing 80 to 100 ºC produce irreversible protein denaturation, cell membrane damage, and coagulation necrosis.(19) The - ion.(20) Radiofrequency delivers a high frequency (460 to 500 kHz) alternating current into the tumor via the elec- trode (also called a tine), delivered from a power generator (250 W).(21,22) The energy is transferred via electrodes that cm tip. The tumor core is vaporized at temperatures nearing 100 ºC, whereas the surrounding concentric zones of tumor are ablated by convective heating. One single electrode will generally ablate a tumor less than 3 cm in diameter; how- ever, this depends upon the variability in tissue density. Larger and denser tumors require overlapping ablations with repositioning of the electrode tines and longer treat- ment sessions. Radiofrequency is limited by tissue charring and carbonization, which increases impedance to the RFA current.(19,23) TECHNICAL CONSIDERATIONS There are different types of RFA energy delivery systems. (21) The ‘Impedance Based’ system delivers energy based on a predetermined level of tissue impedance. The problem with this method is that even if a preset level of imped- ance is reached, this may not correlate with what is needed to reach adequate levels of tissue coagulative necrosis, and treatment may fail. The ‘Heat Based’ system delivers energy based on a preset temperature level. Usually the temperature is set to 70 to 100 ºC for a duration of 5 to 12 minutes. The problem with this method is that the temperature at the tip of the electrode may be higher than the actual temperature within the tumor tissue, again accounting for treatment failure. This reiter- ates the importance of the post-treatment CT scan to assess tissue destruction and then the long-term follow-up imag- ing to rule out tumor recurrence. Electrode tips can be either ‘wet’ or ‘dry’. A wet electrode tip is one which is cooled by infusing a saline solution into the peri-tumor tissue before and during the RFA session. (21,23) This decreases tissue resistance and allows for larger tumors to be treated. The problem with a wet electrode tech- nique is that it may cause CT imaging artifact and compro- mise the accuracy of the immediate post-RFA CT scan. A dry electrode is more prone to cause peri-electrode charring that increases resistance, which in turn limits the energy transfer from the central tumor zone to the peripheral zone. Another consideration is the protection of adjacent viscera during treatment, including the colon, spleen, duodenum, inferior vena cava, ureter, body wall muscle, pancreas, and pleura. One reported technique is the instillation of water or 5% away from the treatment zone.(24-27) A separate puncture is made between the tumor and the viscera, and the solution is instilled into the peri-nephric space. Renal CT-Guided RFA | Haddad et al 632 | Review at 1 atmosphere pressure) within the peri-nephric space to push the at risk structure aside.(28) The urinary collecting system is also at risk of thermal damage, which may lead to urinoma, ureteral perforation, or stricture. - ing up the ureter into the collecting system via a retrograde ureteral catheter has been described.(28,29) mL per minute is suggested. CT-GUIDANCE Computed tomography guidance is the preferred method - ing renal tumors of 100% and 90%, respectively.(30) A pre- treatment CT scan is performed to assess tumor size and location and the surrounding viscera, and to plan the path of electrode insertion. Intermittent ‘real-time’ CT can be per- formed to assess tumor response, seen on CT imaging as change. Computed tomography gives accurate information about electrode position and movement during treatment. - Computed tomography may however be contraindicated in certain populations, such as young women, pregnancy, and iodinated contrast allergy. Here there is a role for US or MRI. Ultrasonography may not be as accurate as CT because gas bubbles, which form during RFA, appear hy- perechoic and distort the US image. Magnetic resonance imaging with gadolinium is well-suited for RFA because it - ic planes. In addition, the T2-weighted acquisition times of 2 seconds allows for real-time monitoring of RFA.(19,31) Furthermore, MRI provides an accurate account of ablative success, seen as a signal loss in T2-weighted images. Mag- netic resonance imaging can be used during pregnancy and iodinated contrast allergy. DEFINING COMPLETE ABLATIVE SUCCESS success. In the immediate term, success is divided into tech- recurrence-free survival (RFS). Immediate technical suc- cess requires (i) ‘impedance roll-off’, which suggests that an adequate level of tissue ablation has taken place during treatment, and (ii) immediate CT evidence of tissue change, including CT evidence of loss of tissue density, tumor vacu- olation, and cavitation.(32,33) At the earliest follow-up CT, at the 6 week mark, there should be no appreciable contrast enhancement of the treat- ed tumor, which is no increase in HU density greater than 10 HU between the non-contrast and contrast scans.(14,34) There should also be no enlargement of the tumor bed or RFA treatment zone at long-term follow-up (after several months).(10,11) Earlier than 4 to 6 weeks, there may be post- treatment effect visualized on a contrast-enhanced CT that may be confused with failure. These changes eventually disappear and should not be evident at a 1-month scan.(35) Furthermore, another study has shown that the post ablation beds of SRT < 3 cm can show a slight increase in volume on However, this eventually scars down and the post ablation bed becomes smaller at long-term follow-up.(36) - ment of the tumor using the 10 HU cut-off and/or enlarge- ment of the tumor bed after RFA treatment beyond the 1 month point. It is not infrequent that a repeat treatment ses- sion is required after the 1 month mark, within the follow- up period, generally for persistent contrast enhancement, and this should be considered a failed RFA treatment. It is possible to visualize scar tissue within the treatment bed on follow-up scans, which is not to be confused with true treatment failure. Scar tissue will have a differing HU den- sity than surrounding renal tissue; however, it should not (19) - in the ablation zone immediately after the RFA session (day 0), and compared this to CT scans 1 and 6 months post- treatment. At day 0, 78% of tumors (28 of 36) showed a - ment (> 10 HU) within the ablation zone.(35) However, at contrast enhancement. This means that early enhancement (< 1 month) post-RFA will eventually disappear at follow- 633Vol. 9 | No. 4 | Fall 2012 |U R O LO G Y J O U R N A L up (usually after 1 month), and does not mean RFA has failed. Post-RFA biopsy of the ablation zone, as a method of con- - appear like there is cancer still present. However, when a are in fact dead.(37) In summary, the interventional radi- ologist and urologist need to follow the post-ablation bed months post-RFA. There are predictable imaging patterns that guide the interpretation of successful RFA. INDICATIONS AND CONTRAINDICATIONS FOR RFA Indications can be divided into patient’s and tumor’s fac- tors.(13,18,22,32) It is important to choose a suitably sized and - cessful RFA session. This is particularly relevant when a urology unit begins to offer RFA to patients, and undergoes - id neoplasm, without cystic component; and 4) Favorable peri-renal anatomy. It has been shown that size > 3 cm is prognostic of recur- rence.(38,39) This suggests that especially during the learning phase, the urologist and radiologist should choose smaller 2 patients who recurred had tumor sizes of 3.2 cm and 4 cm (40) RFA for cystic RCC (total of 9 patients). However, it is gen- erally felt that a cystic RCC does not respond to RFA well - tive thermal energy transfer from the central to peripheral zone of the tumor.(41) Unfavorable tumor’s factors therefore include: 1) Size > 2.5 cm; 2) Anterior location; 3) Endo- phytic; 4) Close to the collecting system; and 5) Cystic RCC. The patient’s factors that make RFA a preferred treatment kidney disease, or solitary kidney; and 3) Multiple RCC syndrome, or high risk of developing RCC in the future. The patient’s factors that preclude RFA include a coagu- lation disorder, gross obesity (precluding electrode place- ment), or noncompliance with follow-up protocol. ONCOLOGICAL EFFICACY Several series, as listed in Table, have shown an overall recurrence-free rate of > 90%, at median follow-up periods greater than 24 months.(17,38,41-43) Radiofrequency ablation has become a popular treatment alternative in elderly or co- morbid patients. Such a patient cohort may not tolerate a partial nephrectomy, and particularly may not tolerate the morbidity of a partial nephrectomy. The RFA series listed in Table are CT-guided renal RFA series. Radiofrequency ablation can also be used via a laparoscop- ic technique. In one large series of 208 patients receiving either percutaneous or laparoscopic RFA, the percutaneous approach was used for posterior or laterally positioned tu- mors, whereas tumors located anteriorly or medially, or in RFA.(17) It is not uncommon for certain tumors to recur either early on in follow-up (within 3 to 6 months) or later (after 24 months). Recurrence occurrs in less than 10% of the time. Recurrence is dealt with differently, either by additional RFA sessions, with success, or by radical nephrectomy or partial nephrectomy in other cases. Most RFA recurrences can be salvaged by repeat RFA, and this is one advantage of RFA over CA. Tumor size and location have been shown to be independ- ent predictors of success.(13,38,49) Anterior tumors are in bad locations and tend to recur, and are linked to a higher rate of adjacent organ damage.(51) Tumors smaller than 2.5 cm are - - relation (P = .001) between higher 3 and 5-year disease-free survival and tumor size < 3 cm. Their difference in 5-year disease-free survival rates for tumors that were < 3 cm com- pared to > 3 cm was 91% and 79%, respectively.(52) For tumors > 3 cm, the recurrence rate was 20%. Peripheral tumors are surrounded by peri-nephric fat, which Renal CT-Guided RFA | Haddad et al 634 | is insulating and tends to enhance the coagulative effects of RFA current. Central tumors suffer from a ‘heat-sink’ effect. This is when the RFA energy is dispersed because of - ing system. Vessels and the collecting system do not have the same insulating properties as fat, and RFA heat energy is lost to these structures. Furthermore, it has been suggested that benign lesions, such as oncocytoma, may have better from less heat-sink effect.(53) Most patients require one RFA session; however, a minority requires an additional RFA session to salvage early failures. (38) The indication is for those tumors with persistent en- hancement after 4 to 6 weeks. The treatment times within one RFA session depends on tumor size, with larger lesions requiring several overlapping RFA sessions in order to completely cover the entire tumor area. - possible to determine, and at times the biopsy is inconclu- sive. Certain authors use biopsy only if they are uncertain of - static lesion to the kidney.(41) of viable cancer cells within the ablation zone at one year post-RFA by performing a biopsy of the tumor bed using an 18-gauge Tru-Cut needle, with 4 passes into each tumor. (43) cases. One author reported on RFA of 9 patients with cystic RCC, either Bosniak III or IV lesions, with 100% RFS at 8 months median follow-up.(45) In general, cystic RCC is seen as a contraindication to RFA. One earlier series described a mean age of 39 years, where- in 21 patients with either von Hippel-Lindau or hereditary papillary RCC were treated with RFA.(16) One study com- pared either laparoscopic or percutaneous RFA with either open or laparoscopic partial nephrectomy for clinical T1a Review Oncological results of percutaneous CT-guided renal RFA series.* First Author Year n Size (mean), cm Age (mean), y FU (mean), mon RFS, % Pre-RFA biopsy Nitta(44) 2012 22 2.4 73 18 85 NA Kim(41) 2011 49 2.4 58.6 31.7 94 13/49 Tracy(17) 2010 172 2.4 64 27 97 172/172 Ferakis(38) 2010 31 3.9 61 61 90 NA Hiraoka(39) 2009 40 2.4 73 16 85 34/40 Levinson(42) 2008 31 2.1 71.7 61.6 90 31/31 Park(45) 2008 9 2.5 50 8 100 NA Raman(43) 2008 19 2.3 62 27 100 19/19 Watkins(10) 2007 11 3.5 74 8 82 8/11 Sabharwal(11) 2006 11 1.95 72 11 78 11/11 Hegarty(46) 2006 72 2.5 67 12 100 72/72 Arzola(33) 2006 23 2.7 74 24 90 23/23 Park(47) 2006 46 2.4 63.5 25 96.8 41/46 Ahrar(48) 2005 29 3.5 65 10 96 29/29 Matsumoto(34) 2005 63 2.5 62 19 98 63/63 Gervais(49) 2005 85 3.2 70 27 90 85/85 Mayo-Smith(15) 2003 32 2.6 76 9 81 18/32 Pavlovich(16) 2002 21 2.4 39 2 79 NA McGovern(50) 1999 1 3.5 84 3 100 1/1 Zlotta(6) 1997 3 2 to 5 NA NA NA 3/3 *CT indicates computed tomography, RFA, radio frequency ablation; FU, follow-up; and NA, not available. 635Vol. 9 | No. 4 | Fall 2012 |U R O LO G Y J O U R N A L RCC. Of 40 RFA and 37 partial nephrectomy, there were local recurrences in 2 RFA and 1 partial nephrectomy (mean follow-up of 30 and 47 months, respectively).(54) There is reproducible level 4 evidence (Table) that RFA is effective in rendering the patient disease-free. Ongoing reporting of longer term outcomes is required to monitor a durable RFS. Radiofrequency ablation is also safe with minimal morbidity. MORBIDITY Reported morbidity rates are between 0 to 11%.(17,39,41,46,49) There is no standardized reporting of morbidity among se- ries. However, morbidity can be divided into major that requires intervention and minor, which resolves with con- - cal complications should be used to standardize morbidity reporting.(55) It is conceivable that any structure adjacent to the RFA zone may be injured. Mortality is very rare; however, it has been reported.(56) The cause of death is aspiration pneumonia post procedure. Any form of adverse cardiorespiratory or cerebrovascular outcome is possible, especially since the patient cohort is elderly and comorbid. The more frequent minor complications include hematoma (peri-nephric or retroperitoneal) not requiring transfusion (5%), hematoma requiring transfusion (1%), neuromuscu- (< 2%), and wound infection.(57,58) Other more problematic complications include urinoma (< 1%), ureteral stricture (< 1%), thermal injury to the duodenum (< 1%), reno-duode- splenic or liver injury, pancreatic injury, hilar vascular in- jury or dissection, and colonic or bowel perforation (all < 1%).(59) and appendicular perforation are reported. Post-procedure pneumonia can occur. Also delayed ureteropelvic junc- tion obstruction is seen. Chronic pain or paresthesia at the skin site or in the distribution of the genitofemoral nerve is seen. Skin tract metastasis has been reported.(15) Damage to a segmental arterial branch can cause segmental renal infarction.(60) With these morbidities in mind, the operative morbidity is higher after partial nephrectomy, ranging from 14% to 26%.(60) RECOMMENDATIONS an option for treating an SRT. Its role is in comorbid pa- post-RFA CT imaging follow-up protocol is required to identify recurrences, most of which can be salvaged with repeat RFA. Risk factors for recurrence include tumor size > 2.5 cm and anterior tumors. Ideal tumors are < 2.5 cm, - evidence, we rely on series which report long-term disease- free survival rates. curve of units, which begin to offer renal RFA. Strong col- laboration between the urologist and interventional radiolo- gist through a multi-disciplinary meeting is mandatory to discuss each case and decide whether the tumor meets suit- ability selection criteria. This will help reduce morbidity CONFLICT OF INTEREST None declared. REFERENCES 1. Chow WH, Devesa SS, Warren JL, Fraumeni JF, Jr. Rising incidence of renal cell cancer in the United States. JAMA. 1999;281:1628-31. 2. Nepple K, Strope S. 961 Population-Based Analysis Of The Rising Incidence Of Renal Cancer: Evaluation Of Age-Specif- ic Trends (1975-2006). J Urol. 2011;185:e387-e. 3. 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;175:425-31. 4. 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;170:2217-20. 5. Doeuk N, Guo DY, Haddad R, et al. Renal cell carcinoma: stage, grade and histology migration over the last 15 years in a large Australian surgical series. BJU Int. 2011;107:1381- 5. Renal CT-Guided RFA | Haddad et al 636 | 18. Bandi G, Hedican SP, Nakada SY. Current practice patterns in the use of ablation technology for the management of small renal masses at academic centers in the United States. Urology. 2008;71:113-7. 19. Boss A, Clasen S, Kuczyk M, Schick F, Pereira PL. Image- guided radiofrequency ablation of renal cell carcinoma. Eur Radiol. 2007;17:725-33. 20. Sapareto SA, Dewey WC. Thermal dose determination in cancer therapy. Int J Radiat Oncol Biol Phys. 1984;10:787- 800. 21. Zelkovic PF, Resnick MI. Renal radiofrequency ablation: clinical status 2003. Curr Opin Urol. 2003;13:199-202. 22. McDougal WS. Radiofrequency ablation of renal cell carci- noma. BJU Int. 2007;99:1271-2. 23. McAchran SE, Lesani OA, Resnick MI. Radiofrequency abla- tion of renal tumors: past, present, and future. Urology. 2005;66:15-22. 24. Farrell MA, Charboneau JW, Callstrom MR, Reading CC, Engen DE, Blute ML. Paranephric water instillation: a technique to prevent bowel injury during percutane- ous renal radiofrequency ablation. AJR Am J Roentgenol. 2003;181:1315-7. 25. Arellano RS, Garcia RG, Gervais DA, Mueller PR. Percuta- neous CT-guided radiofrequency ablation of renal cell carcinoma: efficacy of organ displacement by injection of 5% dextrose in water into the retroperitoneum. AJR Am J Roentgenol 2009;193:1686-90. 26. Ginat DT, Saad W, Davies M, Walman D, Erturk E. Bowel displacement for CT-guided tumor radiofrequency abla- tion: techniques and anatomic considerations. J Endourol. 2009;23:1259-64. 27. Ginat DT, Saad WE. Bowel displacement and protection techniques during percutaneous renal tumor thermal abla- tion. Tech Vasc Interv Radiol. 2010;13:66-74. 28. Kam AW, Littrup PJ, Walther MM, Hvizda J, Wood BJ. Ther- mal protection during percutaneous thermal ablation of renal cell carcinoma. J Vasc Interv Radiol. 2004;15:753-8. 29. Wah TM, Koenig P, Irving HC, Gervais DA, Mueller PR. Radi- ofrequency ablation of a central renal tumor: protection of the collecting system with a retrograde cold dextrose pye- loperfusion technique. J Vasc Interv Radiol. 2005;16:1551-5. 30. Schreyer HH, Uggowitzer MM, Ruppert-Kohlmayr A. Helical CT of the urinary organs. Eur Radiol. 2002;12:575-91. Review 6. Zlotta AR, Wildschutz T, Raviv G, et al. Radiofrequency inter- stitial tumor ablation (RITA) is a possible new modality for treatment of renal cancer: ex vivo and in vivo experience. J Endourol. 1997;11:251-8. 7. Moch H, Artibani W, Delahunt B, et al. Reassessing the cur- rent UICC/AJCC TNM staging for renal cell carcinoma. Eur Urol. 2009;56:636-43. 8. Lee CT, Katz J, Shi W, Thaler HT, Reuter VE, Russo P. Surgical management of renal tumors 4 cm. or less in a contempo- rary cohort. J Urol. 2000;163:730-6. 9. Lerner SE, Hawkins CA, Blute ML, et al. Disease outcome in patients with low stage renal cell carcinoma treated with nephron sparing or radical surgery 1996. J Urol. 2002;167:884-9; discussion 9-90. 10. Watkins TW, Parkinson R. Percutaneous radiofrequency ablation of renal tumours: case series of 11 tumours and review of published work. Australas Radiol. 2007;51:412-9. 11. Sabharwal R, Vladica P. Renal tumors: technical success and early clinical experience with radiofrequency ablation of 18 tumors. Cardiovasc Intervent Radiol. 2006;29:202-9. 12. Wah TM, Arellano RS, Gervais DA, et al. Image-guided percutaneous radiofrequency ablation and incidence of post-radiofrequency ablation syndrome: prospective survey. Radiology. 2005;237:1097-102. 13. Gervais DA, Arellano RS, McGovern FJ, McDougal WS, Muel- ler PR. Radiofrequency ablation of renal cell carcinoma: part 2, Lessons learned with ablation of 100 tumors. AJR Am J Roentgenol. 2005;185:72-80. 14. Farrell MA, Charboneau WJ, DiMarco DS, et al. Imaging- guided radiofrequency ablation of solid renal tumors. AJR Am J Roentgenol. 2003;180:1509-13. 15. Mayo-Smith WW, Dupuy DE, Parikh PM, Pezzullo JA, Cronan JJ. Imaging-guided percutaneous radiofrequency abla- tion of solid renal masses: techniques and outcomes of 38 treatment sessions in 32 consecutive patients. AJR Am J Roentgenol. 2003;180:1503-8. 16. Pavlovich CP, Walther MM, Choyke PL, et al. Percutane- ous radio frequency ablation of small renal tumors: initial results. J Urol. 2002;167:10-5. 17. Tracy CR, Raman JD, Donnally C, Trimmer CK, Cadeddu JA. Durable oncologic outcomes after radiofrequency abla- tion: experience from treating 243 small renal masses over 7.5 years. Cancer. 2010;116:3135-42. 637Vol. 9 | No. 4 | Fall 2012 |U R O LO G Y J O U R N A L Renal CT-Guided RFA | Haddad et al 31. Lewin JS, Nour SG, Connell CF, et al. Phase II clinical trial of interactive MR imaging-guided interstitial radiofrequency thermal ablation of primary kidney tumors: initial experi- ence. Radiology. 2004;232:835-45. 32. Zagoria RJ, Hawkins AD, Clark PE, et al. Percutaneous CT- guided radiofrequency ablation of renal neoplasms: factors influencing success. AJR Am J Roentgenol. 2004;183:201-7. 33. Arzola J, Baughman SM, Hernandez J, Bishoff JT. Computed tomography-guided, resistance-based, percutaneous radi- ofrequency ablation of renal malignancies under conscious sedation at two years of follow-up. Urology. 2006;68:983-7. 34. Matsumoto ED, Johnson DB, Ogan K, et al. Short-term efficacy of temperature-based radiofrequency ablation of small renal tumors. Urology. 2005;65:877-81. 35. Javadi S, Ahrar JU, Ninan E, Gupta S, Matin SF, Ahrar K. Char- acterization of contrast enhancement in the ablation zone immediately after radiofrequency ablation of renal tumors. J Vasc Interv Radiol. 2010;21:690-5. 36. Davenport MS, Caoili EM, Cohan RH, et al. MRI and CT characteristics of successfully ablated renal masses: Imag- ing surveillance after radiofrequency ablation. AJR Am J Roentgenol. 2009;192:1571-8. 37. Marcovich R, Aldana JP, Morgenstern N, Jacobson AI, Smith AD, Lee BR. Optimal lesion assessment following acute radio frequency ablation of porcine kidney: cellular viability or histopathology? J Urol. 2003;170:1370-4. 38. Ferakis N, Bouropoulos C, Granitsas T, Mylona S, Poulias I. Long-term results after computed-tomography-guided percutaneous radiofrequency ablation for small renal tumors. J Endourol. 2010;24:1909-13. 39. Hiraoka K, Kawauchi A, Nakamura T, Soh J, Mikami K, Miki T. Radiofrequency ablation for renal tumors: our experience. Int J Urol. 2009;16:869-73. 40. Watanabe F, Kawasaki T, Hotaka Y, et al. Radiofrequency ablation for the treatment of renal cell carcinoma: initial experience. Radiat Med. 2008;26:1-5. 41. Kim JH, Kim TH, Kim SD, Lee KS, Sung GT. Radiofrequency ablation of renal tumors: our experience. Korean J Urol. 2011;52:531-7. 42. Levinson AW, Su LM, Agarwal D, et al. Long-term oncological and overall outcomes of percutaneous radio frequency abla- tion in high risk surgical patients with a solitary small renal mass. J Urol. 2008;180:499-504; discussion. 43. Raman JD, Stern JM, Zeltser I, Kabbani W, Cadeddu JA. Ab- sence of viable renal carcinoma in biopsies performed more than 1 year following radio frequency ablation confirms reliability of axial imaging. J Urol. 2008;179:2142-5. 44. Nitta Y, Tanaka T, Morimoto K, et al. Intermediate oncological outcomes of percutaneous radiofrequency ablation for small renal tumors: initial experience. Anticancer Res. 2012;32:615- 8. 45. Park BK, Kim CK, Lee HM. Image-guided radiofrequency ab- lation of Bosniak category III or IV cystic renal tumors: initial clinical experience. Eur Radiol. 2008;18:1519-25. 46. Hegarty NJ, Gill IS, Desai MM, Remer EM, O'Malley CM, Kaouk JH. Probe-ablative nephron-sparing surgery: cryoablation versus radiofrequency ablation. Urology. 2006;68:7-13. 47. Park S, Anderson JK, Matsumoto ED, Lotan Y, Josephs S, Cadeddu JA. Radiofrequency ablation of renal tumors: intermediate-term results. J Endourol. 2006;20:569-73. 48. Ahrar K, Matin S, Wood CG, et al. Percutaneous radiofre- quency ablation of renal tumors: technique, complications, and outcomes. J Vasc Interv Radiol. 2005;16:679-88. 49. Gervais DA, McGovern FJ, Arellano RS, McDougal WS, Muel- ler 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 Am J Roentgenol. 2005;185:64-71. 50. McGovern FJ, Wood BJ, Goldberg SN, Mueller PR. Radio fre- quency ablation of renal cell carcinoma via image guided needle electrodes. J Urol. 1999;161:599-600. 51. Rane A, Stein R, Cadeddu J. Focal therapy for renal mass le- sions: where do we stand in 2012? BJU Int. 2012;109:491-2. 52. Best SL, Park SK, Yaacoub RF, et al. Long-term outcomes of renal tumor radio frequency ablation stratified by tumor diameter: size matters. J Urol. 2012;187:1183-9. 53. Tan YK, Best SL, Olweny E, Park S, Trimmer C, Cadeddu JA. Radiofrequency ablation of incidental benign small renal mass: outcomes and follow-up protocol. Urology. 2012;79:827-30. 54. Stern JM, Svatek R, Park S, et al. Intermediate comparison of partial nephrectomy and radiofrequency ablation for clini- cal T1a renal tumours. BJU Int. 2007;100:287-90. 55. Dindo D, Demartines N, Clavien PA. Classification of surgi- cal complications: a new proposal with evaluation in a cohort of 6336 patients and results of a survey. Ann Surg. 2004;240:205-13. 56. 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;174:456-60; discussion 60. 57. Kimura M, Baba S, Polascik TJ. Minimally invasive surgery using ablative modalities for the localized renal mass. Int J Urol. 2010;17:215-27. 638 | 58. Igor Pinkhasov G, Raman JD. Management and preven- tion of renal ablative therapy complications. World J Urol. 2010;28:559-64. 59. Weizer AZ, Raj GV, O'Connell M, Robertson CN, Nelson RC, Polascik TJ. Complications after percutaneous radiofre- quency ablation of renal tumors. Urology. 2005;66:1176-80. 60. Park BK, Kim CK, Lim HK. Renal infarction resulting from segmental arterial injury during radiofrequency ablation of renal tumor in patient with a single kidney. Urology. 2009;73:442 e9-11. Review