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Percutaneous radiofrequency ablation of renal tumors: technique, limitations, and morbidity
RAPID COMMUNICATION
PERCUTANEOUS RADIOFREQUENCY ABLATION OF RENAL TUMORS: TECHNIQUE, LIMITATIONS, AND MORBIDITY KENNETH OGAN, LUCAS JACOMIDES, BART L. DOLMATCH, FRANK J. RIVERA, MARCO F. DELLARIA, SHELLIE C. JOSEPHS, AND JEFFREY A. CADEDDU
ABSTRACT Objectives. To evaluate our evolving experience with percutaneous radiofrequency (RF) renal tumor ablation and focus on our technique to ensure maximal treatment efficacy and reduce the possibility of complications. Methods. Fifteen patients with small (less than 4 cm) posterior or lateral contrast-enhancing (more than 10 Hounsfield units) renal tumors were candidates for RF treatment. Of these patients, 12 (13 tumors) received computed tomography-guided percutaneous RF ablation. General anesthesia was administered in all but our first 2 patients, who received intravenous sedation. After treatment, patients were closely followed up with computed tomography scans at 6 weeks and 3, 6, and 12 months, and every 6 months thereafter. Successful ablation was defined as a lesion along with a margin of normal parenchyma that no longer enhanced (less than 10 Hounsfield units) on follow-up contrast imaging. Results. The mean tumor size was 2.4 ⫾ 0.6 cm. The average procedure time was 95 minutes (range 60 to 150) and length of stay 0.9 days. All patients underwent the procedure without any major complications. At a mean follow-up of 4.9 months, 12 (93%) of 13 tumors were successfully ablated. In 3 patients, the procedure was not performed because of intervening bowel or lung parenchyma when positioned in the prone position before the procedure. Conclusions. Computed tomography-guided percutaneous RF ablation of small renal tumors is a viable minimally invasive treatment option with a high short-term success rate and low morbidity. This new technology must be uniformly applied to assess its long-term efficacy. UROLOGY 60: 954–958, 2002. © 2002, Elsevier Science Inc.
S
mall occult renal neoplasms are generally treated in a nephron-sparing manner. To decrease surgical morbidity, laparoscopic partial nephrectomy and in situ ablative therapies have been introduced as minimally invasive alternatives. Tumor ablation minimizes the morbidity associated with partial nephrectomy while still sparing the renal parenchyma. Investigators have used cryoablation,1,2 radiofrequency (RF),3,4 microwaves,5 and high-intensity ultrasonography6 as ablative modalities. We report on our experience with perFrom the Clinical Center for Minimally Invasive Urologic Cancer Treatment, Department of Urology and Division of Interventional Radiology, Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas Reprint requests: Jeffrey A. Cadeddu, M.D., Department of Urology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9110 Submitted: July 31, 2002, accepted (with revisions): August 27, 2002
954
© 2002, ELSEVIER SCIENCE INC. ALL RIGHTS RESERVED
cutaneous RF ablation (RFA) with emphasis on technique and patient selection. MATERIAL AND METHODS PATIENT SELECTION AND PREPARATION Patients with contrast-enhancing (greater than 10 Hounsfield units [HU]) renal tumors less than 4 cm in size were candidates for the procedure. Standard supine and prone computed tomography (CT) scans were obtained preoperatively. Exophytic, as well as endophytic, tumors were eligible for treatment. Those patients in whom the colon or small bowel was within 1 cm of the renal mass on prone CT imaging were excluded to minimize the risk of a thermal bowel injury. General anesthesia was administered in all but our first 2 patients, who received intravenous sedation. General anesthesia is advantageous for smaller tumors (less than 2 cm), because it is difficult to target the mass precisely if the patient is breathing spontaneously. Furthermore, with the patient positioned prone, our anesthesiologists prefer general anesthesia.
TECHNIQUE The patient was positioned prone and CT imaging performed. An 18-gauge core biopsy needle was directed into the 0090-4295/02/$22.00 PII S0090-4295(02)02096-4
repositioned for a second round of treatment. After ablation, the probe was withdrawn slowly in “track ablate” mode to prevent bleeding and the “theoretical” risk of tumor seeding. Immediately after ablation, contrast CT imaging provided indirect evidence of treatment, with success determined only with follow-up CT scans. The standard follow-up included CT scans at 6 weeks and 3, 6, and 12 months, and every 6 months thereafter. Ablation was successful if the lesion, along with a margin of normal parenchyma, no longer enhanced on CT (less than 10 HU). For treatment failures, our protocol was to repeat the treatment or perform surgical extirpation. This decision was based on the location of the failure, the response to the original treatment, and patient preference. Postablation biopsies were avoided because of their historically low sensitivity.
RESULTS
FIGURE 1. (A) RF probe with tines deployed just before ablation. (B) Follow-up CT scan at 3 months demonstrating no further contrast enhancement of tumor. peripheral margin of the tumor, and multiple biopsies were obtained. A 15-gauge RITA StarBurst probe (RITA Medical Systems, Mountain View, CA) was then advanced to just within the peripheral tumor margin. The tines of the RF probe were then deployed for a lesion ablation diameter of approximately 0.5 to 1.0 cm beyond the CT-measured tumor diameter. Repeated imaging should demonstrate coverage of the entire tumor by the tines so that a rim of normal parenchyma at the deep margin will confidently be ablated because the extent of the RF lesion extends several millimeters beyond the tip of each tine (Fig. 1). The RITA electrosurgical generator (Model 1500), set to deliver up to 150 W, was connected to the RF probe (target temperature 105°C). The tumors were heated until the average temperature measured from the tips of five of nine tines reached the target temperature. The tumor was then treated at 105°C for one or two 5 to 8-minute cycles (surgeon preference), depending on tumor size (5 minutes for tumors less than 2 cm, 7 minutes for those less than 3 cm, and 8 minutes for those less than 4 cm). If adequate tumor coverage was not accomplished because of tumor size or shape, the probe was UROLOGY 60 (6), 2002
Fifteen patients met the criteria for percutaneous RFA. Early in our experience, three tumors were inaccessible because of the proximity of overlying bowel or intervening lung parenchyma discovered at the time of prone imaging under anesthesia. These patients were instead treated with laparoscopic RFA so that the tumors could be directly visualized and the surrounding structures protected. Therefore, our preoperative protocol was amended to include prone CT to assess kidney mobility and any change in tumor location relative to the adjacent organs (Fig. 2). All but 1 patient had a single tumor treated. One patient had two tumors treated, for a total of 13 ablations. The mean tumor size was 2.4 ⫾ 0.6 cm (Table I). The mean tumor difference between the noncontrast and contrast images before treatment was 38.5 ⫾ 34.4 HU. The average procedure time was 95 minutes (range 60 to 150), with most of the time spent positioning the RF probe. No major complications occurred. One patient developed a small perinephric hematoma after the biopsy, which resolved uneventfully without intervention. Patients experienced minimal pain after the procedure (mean intravenous morphine 1.7 mg). Patients were discharged the same day or observed overnight (mean hospitalization 0.9 days). The mean follow-up to date was 4.9 months (range 1 to 13). Tumor biopsies were performed immediately before ablation on the most recent eight lesions. In the initial 5 patients, no biopsies were taken at the time of ablation. In the subsequent 2 patients, biopsies were performed after ablation. Neither specimen was adequate for pathologic analysis because of RF treatment artifact. Thereafter, all biopsies were performed before ablation. The pathologic findings of these biopsies demonstrated two renal cell carcinomas, three oncocytomas and one angiomyolipoma. Importantly, all specimens obtained before ablation were adequate for an accurate diagnosis. 955
COMMENT Several studies have reported percutaneous RFA of small renal tumors.3,4,8 Although the results of these early clinical series have been encouraging, a few have questioned the efficacy of RFA.7,9 We believe that the shortcomings attributable to RF energy are not due to a failure of the technology, but rather, are associated with the technique. Thus, we report our early experience with an emphasis on the technique to improve efficacy.
FIGURE 2. (A) Supine CT scan with black arrow pointing at the renal mass and white arrow pointing at the spleen. (B) Prone CT scan showing the kidney (black arrow) rotating anterolaterally adjacent to a loop of bowel (white arrow).
Of 13 tumors, 12 (93%) demonstrated complete ablation (Fig. 1) on the most recent CT scan. Success in our series was defined as the destruction of contrast-enhancing tumors, because we only have histologic evidence of malignancy from two of the tumors owing to the initial biopsy techniques. Only one tumor demonstrated a rim of persistent contrast enhancement along the deep margin of the tumor on the follow-up CT scans. This patient was retreated 6 months after the original procedure with no persistent enhancement at the 6-week follow-up CT scan. It is difficult to use decreasing size as a measure of success because a margin of normal parenchyma is clearly ablated. No patient has had evidence of persistent or new tumor enhancement if the first 6-week CT scan demonstrated complete ablation.7 956
PROBE CONFIGURATION AND PLACEMENT It is paramount that the tines of the RF probe are deployed to ablate 0.5 to 1.0 cm beyond the deepest margin of the tumor. This is critical, because one report found viable tumor cells at the periphery of the treated tumors.7 Equally important, in the same study, cell destruction in the central portion of the ablation zone was complete. Thus, the failure was a result of inadequate targeting and insufficient deployment, rather than the technology. We prefer the RITA probe and generator system because the StarBurst electrode configuration permits visual (CT) confirmation that the entire tumor is “covered” (Fig. 1A). This temperaturebased system also allows direct measurement of the temperature within the tumor and permits adjustment of the power delivery so that the entire tumor reaches a lethal temperature (more than 70°C). The target temperature is set at 105°C to ensure adequate ablation at the periphery, because laboratory studies have demonstrated a rapid drop in temperature away from the tips of each electrode. TUMOR SIZE AND LOCATION The probe can be deployed to a maximal diameter of 5 cm, but our size limit is 4 cm because the intended ablation should exceed the tumor diameter by 0.5 to 1.0 cm. Even with this size cutoff,3 inhomogeneous tumor shapes make it difficult to ablate some tumors with the RF probe in only one position (Table I). Therefore, tumors that cannot be adequately targeted with one deployment are treated again at a second location in the tumor. The treatment failure in our series and those reported by others3,4 were more commonly associated with larger centrally located tumors. Central tumor ablation likely fails more frequently because of a “heat-sink” effect in which regional vascular flow reduces the extent of the thermally induced coagulation.9 Selective arterial embolization of centrally located tumors before ablation may minimize the “heat-sink”10 effect but complete renal vascular occlusion is not recommended.11 UROLOGY 60 (6),
TABLE I. Patient characteristics Pt. No./ Age (yr)/ Sex
Tumor Side/Pole/Location
1/79/M 2/63/M 3/58/M 4/62/M 5/56/F 6/55/M 7/70/M 8/75/M 9/70/F 10/72/M 10/72/M 11/39/F 12/63/F
R/upper/posterior R/lower/posterior R/lower/posterior R/upper/posterior R/mid/posterior R/mid/posterior R/upper/posterior L/lower/lateral R/mid/posterior L/lower/posterior L/lower/posterior R/lower/posterior L/mid/posterior
Tumor Type
Tumor Size (cm)
Treatment Cycles (n)/Total Ablation Time (min)
Treatment Success (<10 HU Difference)
Pathologic Finding
Exophytic Exophytic Exophytic Exophytic Endophytic Endophytic Exophytic Exophytic Exophytic Exophytic Exophytic Exophytic Mixed
2.3 1.6 3.6 2.3 2.5 3.2 2.4 3.1 2.3 1.6 2.5 2.5 1.4
1/10 1/5.5 2/12 2/14 2/14 2/16 4/20 2/14 3/15 2/10 3/15 3/19 2/10
Y Y Y Y No, ⫹ peripheral rim Y Y Y Y Y Y Y Y
None None None None None Nondiagnostic Nondiagnostic Oncocytoma RCC Oncocytoma Oncocytoma AML RCC
KEY: Pt. No. ⫽ patient number; HU ⫽ Hounsfield unit; M ⫽ male; R ⫽ right; Y ⫽ yes; F ⫽ female; L ⫽ left; RCC ⫽ renal cell carcinoma; AML ⫽ angiomyolipoma.
AVOIDING INJURY TO BOWEL, LUNG, AND RENAL COLLECTING SYSTEM Supine CT scans do not reliably predict whether overlying bowel will preclude percutaneous RFA. In 2 patients on the day of treatment in the full and modified (30°) prone position, the bowel moved to within a few millimeters of the renal tumor (Fig. 2). As a result, to determine which patients are true candidates for percutaneous RFA, we now perform prone CT scans before the day of treatment as a part of our standard preoperative evaluation. If the bowel anatomy is unfavorable, the patient is rescheduled for laparoscopic RFA. In equivocal situations, several maneuvers are available to facilitate ablation and protect adjacent bowel. If elevating the ipsilateral flank does not suffice, Rendon et al.12 reported hydro-dissection and gas dissection techniques during porcine renal RFA to protect the surrounding structures. They surmised that the major complication in their series would have been avoided if hydro-dissection had been used.7 If these maneuvers fail to produce a safe margin (5 to 10 mm) between the tumor and bowel, the procedure should be aborted, because a bowel injury can be catastrophic. The second situation that prevented us from performing percutaneous RFA was in a patient with chronic obstructive pulmonary disease and an upper pole renal mass. Although the supine preoperative CT scan was normal, at the axial level, where the probe was to be inserted in the prone position, intervening lung parenchyma within the pleural cavity was present. The situation would have been avoided if a preprocedure prone CT had been obtained. Finally, in the case of tumors adjacent to the collecting system, no studies have reported urinary UROLOGY 60 (6), 2002
extravasation or fistula formation after treatment.3,4,8 However, Gervais et al.4 reported on several patients with gross hematuria, clot formation, and eventual blood transfusion after RFA. In our series, no patient reported hematuria, most likely because the treated tumors did not grossly involve the pelvicaliceal system. PATHOLOGIC DIAGNOSIS A criticism of ablative therapy is the lack of a specimen for pathologic analysis. We have found that multiple core biopsies immediately before ablation provide sufficient tissue for diagnosis. The postablation biopsy specimens were too small and demonstrated significant RF-treatment artifact. As a result, we recommend that multiple biopsies be performed just before the procedure. CONCLUSIONS RFA is a new procedure for the treatment of small renal tumors. Its success for the treatment of tumors in other organs is well documented. However, as with any new technology, success is predicated on the correct application of the technology and appropriate follow-up. The measures noted should allow for a more uniform delivery of RFA for renal tumors. Only when longer term results are available can its efficacy be compared with other nephron-sparing treatments. REFERENCES 1. Gill IS, Novick AC, Meraney AM, et al: Laparoscopic renal cryoablation in 32 patients. Urology 56: 748 –753, 2000. 2. Shingleton WB, and Sewell PE Jr: Percutaneous renal tumor cryoablation with magnetic resonance imaging guidance. J Urol 165: 773–776, 2001. 3. Pavlovich CP, Walther MM, Choyke PL, et al: Percuta957
neous radio frequency ablation of small renal tumors: initial results. J Urol 167: 10 –15, 2002. 4. Gervais DA, McGovern FJ, Wood BJ, et al: Radio-frequency ablation of renal cell carcinoma: early clinical experience. Radiology 217: 665–672, 2000. 5. Yoshimura K, Okubo K, Ichioka K, et al: Laparoscopic partial nephrectomy with a microwave tissue coagulator for small renal tumor. J Urol 165: 1893–1896, 2001. 6. Vallancien G, Chartier-Kastler E, Bataille N, et al: Focused extracorporeal pyrotherapy. Eur Urol 23(suppl 1): 48 – 52, 1993. 7. Rendon RA, Kachura JR, Sweet JM, et al: The uncertainty of radio frequency treatment of renal cell carcinoma: findings at immediate and delayed nephrectomy. J Urol 167: 1587–1592, 2002. 8. de Baere T, Kuoch V, Smayra T, et al: Radio frequency
958
ablation of renal cell carcinoma: preliminary clinical experience. J Urol 167: 1961–1964, 2002. 9. Goldberg SN, Gazelle GS, and Mueller PR: Thermal ablation therapy for focal malignancy: a unified approach to underlying principles, techniques, and diagnostic imaging guidance. AJR Am J Roentgenol 174: 323–331, 2000. 10. Hall WH, McGahan JP, Link DP, et al: Combined embolization and percutaneous radiofrequency ablation of a solid renal tumor. AJR Am J Roentgenol 174: 1592–1594, 2000. 11. Corwin TS, Lindberg G, Traxer O, et al: Laparoscopic radiofrequency thermal ablation of renal tissue with and without hilar occlusion. J Urol 166: 281–284, 2001. 12. Rendon RA, Gertner MR, Sherar MD, et al: Development of a radiofrequency based thermal therapy technique in an in vivo porcine model for the treatment of small renal masses. J Urol 166: 292–298, 2001.
UROLOGY 60 (6), 2002
PERCUTANEOUS RADIOFREQUENCY ABLATION OF RENAL TUMORS: TECHNIQUE, LIMITATIONS, AND MORBIDITY KENNETH OGAN, LUCAS JACOMIDES, BART L. DOLMATCH, FRANK J. RIVERA, MARCO F. DELLARIA, SHELLIE C. JOSEPHS, AND JEFFREY A. CADEDDU
ABSTRACT Objectives. To evaluate our evolving experience with percutaneous radiofrequency (RF) renal tumor ablation and focus on our technique to ensure maximal treatment efficacy and reduce the possibility of complications. Methods. Fifteen patients with small (less than 4 cm) posterior or lateral contrast-enhancing (more than 10 Hounsfield units) renal tumors were candidates for RF treatment. Of these patients, 12 (13 tumors) received computed tomography-guided percutaneous RF ablation. General anesthesia was administered in all but our first 2 patients, who received intravenous sedation. After treatment, patients were closely followed up with computed tomography scans at 6 weeks and 3, 6, and 12 months, and every 6 months thereafter. Successful ablation was defined as a lesion along with a margin of normal parenchyma that no longer enhanced (less than 10 Hounsfield units) on follow-up contrast imaging. Results. The mean tumor size was 2.4 ⫾ 0.6 cm. The average procedure time was 95 minutes (range 60 to 150) and length of stay 0.9 days. All patients underwent the procedure without any major complications. At a mean follow-up of 4.9 months, 12 (93%) of 13 tumors were successfully ablated. In 3 patients, the procedure was not performed because of intervening bowel or lung parenchyma when positioned in the prone position before the procedure. Conclusions. Computed tomography-guided percutaneous RF ablation of small renal tumors is a viable minimally invasive treatment option with a high short-term success rate and low morbidity. This new technology must be uniformly applied to assess its long-term efficacy. UROLOGY 60: 954–958, 2002. © 2002, Elsevier Science Inc.
S
mall occult renal neoplasms are generally treated in a nephron-sparing manner. To decrease surgical morbidity, laparoscopic partial nephrectomy and in situ ablative therapies have been introduced as minimally invasive alternatives. Tumor ablation minimizes the morbidity associated with partial nephrectomy while still sparing the renal parenchyma. Investigators have used cryoablation,1,2 radiofrequency (RF),3,4 microwaves,5 and high-intensity ultrasonography6 as ablative modalities. We report on our experience with perFrom the Clinical Center for Minimally Invasive Urologic Cancer Treatment, Department of Urology and Division of Interventional Radiology, Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas Reprint requests: Jeffrey A. Cadeddu, M.D., Department of Urology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9110 Submitted: July 31, 2002, accepted (with revisions): August 27, 2002
954
© 2002, ELSEVIER SCIENCE INC. ALL RIGHTS RESERVED
cutaneous RF ablation (RFA) with emphasis on technique and patient selection. MATERIAL AND METHODS PATIENT SELECTION AND PREPARATION Patients with contrast-enhancing (greater than 10 Hounsfield units [HU]) renal tumors less than 4 cm in size were candidates for the procedure. Standard supine and prone computed tomography (CT) scans were obtained preoperatively. Exophytic, as well as endophytic, tumors were eligible for treatment. Those patients in whom the colon or small bowel was within 1 cm of the renal mass on prone CT imaging were excluded to minimize the risk of a thermal bowel injury. General anesthesia was administered in all but our first 2 patients, who received intravenous sedation. General anesthesia is advantageous for smaller tumors (less than 2 cm), because it is difficult to target the mass precisely if the patient is breathing spontaneously. Furthermore, with the patient positioned prone, our anesthesiologists prefer general anesthesia.
TECHNIQUE The patient was positioned prone and CT imaging performed. An 18-gauge core biopsy needle was directed into the 0090-4295/02/$22.00 PII S0090-4295(02)02096-4
repositioned for a second round of treatment. After ablation, the probe was withdrawn slowly in “track ablate” mode to prevent bleeding and the “theoretical” risk of tumor seeding. Immediately after ablation, contrast CT imaging provided indirect evidence of treatment, with success determined only with follow-up CT scans. The standard follow-up included CT scans at 6 weeks and 3, 6, and 12 months, and every 6 months thereafter. Ablation was successful if the lesion, along with a margin of normal parenchyma, no longer enhanced on CT (less than 10 HU). For treatment failures, our protocol was to repeat the treatment or perform surgical extirpation. This decision was based on the location of the failure, the response to the original treatment, and patient preference. Postablation biopsies were avoided because of their historically low sensitivity.
RESULTS
FIGURE 1. (A) RF probe with tines deployed just before ablation. (B) Follow-up CT scan at 3 months demonstrating no further contrast enhancement of tumor. peripheral margin of the tumor, and multiple biopsies were obtained. A 15-gauge RITA StarBurst probe (RITA Medical Systems, Mountain View, CA) was then advanced to just within the peripheral tumor margin. The tines of the RF probe were then deployed for a lesion ablation diameter of approximately 0.5 to 1.0 cm beyond the CT-measured tumor diameter. Repeated imaging should demonstrate coverage of the entire tumor by the tines so that a rim of normal parenchyma at the deep margin will confidently be ablated because the extent of the RF lesion extends several millimeters beyond the tip of each tine (Fig. 1). The RITA electrosurgical generator (Model 1500), set to deliver up to 150 W, was connected to the RF probe (target temperature 105°C). The tumors were heated until the average temperature measured from the tips of five of nine tines reached the target temperature. The tumor was then treated at 105°C for one or two 5 to 8-minute cycles (surgeon preference), depending on tumor size (5 minutes for tumors less than 2 cm, 7 minutes for those less than 3 cm, and 8 minutes for those less than 4 cm). If adequate tumor coverage was not accomplished because of tumor size or shape, the probe was UROLOGY 60 (6), 2002
Fifteen patients met the criteria for percutaneous RFA. Early in our experience, three tumors were inaccessible because of the proximity of overlying bowel or intervening lung parenchyma discovered at the time of prone imaging under anesthesia. These patients were instead treated with laparoscopic RFA so that the tumors could be directly visualized and the surrounding structures protected. Therefore, our preoperative protocol was amended to include prone CT to assess kidney mobility and any change in tumor location relative to the adjacent organs (Fig. 2). All but 1 patient had a single tumor treated. One patient had two tumors treated, for a total of 13 ablations. The mean tumor size was 2.4 ⫾ 0.6 cm (Table I). The mean tumor difference between the noncontrast and contrast images before treatment was 38.5 ⫾ 34.4 HU. The average procedure time was 95 minutes (range 60 to 150), with most of the time spent positioning the RF probe. No major complications occurred. One patient developed a small perinephric hematoma after the biopsy, which resolved uneventfully without intervention. Patients experienced minimal pain after the procedure (mean intravenous morphine 1.7 mg). Patients were discharged the same day or observed overnight (mean hospitalization 0.9 days). The mean follow-up to date was 4.9 months (range 1 to 13). Tumor biopsies were performed immediately before ablation on the most recent eight lesions. In the initial 5 patients, no biopsies were taken at the time of ablation. In the subsequent 2 patients, biopsies were performed after ablation. Neither specimen was adequate for pathologic analysis because of RF treatment artifact. Thereafter, all biopsies were performed before ablation. The pathologic findings of these biopsies demonstrated two renal cell carcinomas, three oncocytomas and one angiomyolipoma. Importantly, all specimens obtained before ablation were adequate for an accurate diagnosis. 955
COMMENT Several studies have reported percutaneous RFA of small renal tumors.3,4,8 Although the results of these early clinical series have been encouraging, a few have questioned the efficacy of RFA.7,9 We believe that the shortcomings attributable to RF energy are not due to a failure of the technology, but rather, are associated with the technique. Thus, we report our early experience with an emphasis on the technique to improve efficacy.
FIGURE 2. (A) Supine CT scan with black arrow pointing at the renal mass and white arrow pointing at the spleen. (B) Prone CT scan showing the kidney (black arrow) rotating anterolaterally adjacent to a loop of bowel (white arrow).
Of 13 tumors, 12 (93%) demonstrated complete ablation (Fig. 1) on the most recent CT scan. Success in our series was defined as the destruction of contrast-enhancing tumors, because we only have histologic evidence of malignancy from two of the tumors owing to the initial biopsy techniques. Only one tumor demonstrated a rim of persistent contrast enhancement along the deep margin of the tumor on the follow-up CT scans. This patient was retreated 6 months after the original procedure with no persistent enhancement at the 6-week follow-up CT scan. It is difficult to use decreasing size as a measure of success because a margin of normal parenchyma is clearly ablated. No patient has had evidence of persistent or new tumor enhancement if the first 6-week CT scan demonstrated complete ablation.7 956
PROBE CONFIGURATION AND PLACEMENT It is paramount that the tines of the RF probe are deployed to ablate 0.5 to 1.0 cm beyond the deepest margin of the tumor. This is critical, because one report found viable tumor cells at the periphery of the treated tumors.7 Equally important, in the same study, cell destruction in the central portion of the ablation zone was complete. Thus, the failure was a result of inadequate targeting and insufficient deployment, rather than the technology. We prefer the RITA probe and generator system because the StarBurst electrode configuration permits visual (CT) confirmation that the entire tumor is “covered” (Fig. 1A). This temperaturebased system also allows direct measurement of the temperature within the tumor and permits adjustment of the power delivery so that the entire tumor reaches a lethal temperature (more than 70°C). The target temperature is set at 105°C to ensure adequate ablation at the periphery, because laboratory studies have demonstrated a rapid drop in temperature away from the tips of each electrode. TUMOR SIZE AND LOCATION The probe can be deployed to a maximal diameter of 5 cm, but our size limit is 4 cm because the intended ablation should exceed the tumor diameter by 0.5 to 1.0 cm. Even with this size cutoff,3 inhomogeneous tumor shapes make it difficult to ablate some tumors with the RF probe in only one position (Table I). Therefore, tumors that cannot be adequately targeted with one deployment are treated again at a second location in the tumor. The treatment failure in our series and those reported by others3,4 were more commonly associated with larger centrally located tumors. Central tumor ablation likely fails more frequently because of a “heat-sink” effect in which regional vascular flow reduces the extent of the thermally induced coagulation.9 Selective arterial embolization of centrally located tumors before ablation may minimize the “heat-sink”10 effect but complete renal vascular occlusion is not recommended.11 UROLOGY 60 (6),
TABLE I. Patient characteristics Pt. No./ Age (yr)/ Sex
Tumor Side/Pole/Location
1/79/M 2/63/M 3/58/M 4/62/M 5/56/F 6/55/M 7/70/M 8/75/M 9/70/F 10/72/M 10/72/M 11/39/F 12/63/F
R/upper/posterior R/lower/posterior R/lower/posterior R/upper/posterior R/mid/posterior R/mid/posterior R/upper/posterior L/lower/lateral R/mid/posterior L/lower/posterior L/lower/posterior R/lower/posterior L/mid/posterior
Tumor Type
Tumor Size (cm)
Treatment Cycles (n)/Total Ablation Time (min)
Treatment Success (<10 HU Difference)
Pathologic Finding
Exophytic Exophytic Exophytic Exophytic Endophytic Endophytic Exophytic Exophytic Exophytic Exophytic Exophytic Exophytic Mixed
2.3 1.6 3.6 2.3 2.5 3.2 2.4 3.1 2.3 1.6 2.5 2.5 1.4
1/10 1/5.5 2/12 2/14 2/14 2/16 4/20 2/14 3/15 2/10 3/15 3/19 2/10
Y Y Y Y No, ⫹ peripheral rim Y Y Y Y Y Y Y Y
None None None None None Nondiagnostic Nondiagnostic Oncocytoma RCC Oncocytoma Oncocytoma AML RCC
KEY: Pt. No. ⫽ patient number; HU ⫽ Hounsfield unit; M ⫽ male; R ⫽ right; Y ⫽ yes; F ⫽ female; L ⫽ left; RCC ⫽ renal cell carcinoma; AML ⫽ angiomyolipoma.
AVOIDING INJURY TO BOWEL, LUNG, AND RENAL COLLECTING SYSTEM Supine CT scans do not reliably predict whether overlying bowel will preclude percutaneous RFA. In 2 patients on the day of treatment in the full and modified (30°) prone position, the bowel moved to within a few millimeters of the renal tumor (Fig. 2). As a result, to determine which patients are true candidates for percutaneous RFA, we now perform prone CT scans before the day of treatment as a part of our standard preoperative evaluation. If the bowel anatomy is unfavorable, the patient is rescheduled for laparoscopic RFA. In equivocal situations, several maneuvers are available to facilitate ablation and protect adjacent bowel. If elevating the ipsilateral flank does not suffice, Rendon et al.12 reported hydro-dissection and gas dissection techniques during porcine renal RFA to protect the surrounding structures. They surmised that the major complication in their series would have been avoided if hydro-dissection had been used.7 If these maneuvers fail to produce a safe margin (5 to 10 mm) between the tumor and bowel, the procedure should be aborted, because a bowel injury can be catastrophic. The second situation that prevented us from performing percutaneous RFA was in a patient with chronic obstructive pulmonary disease and an upper pole renal mass. Although the supine preoperative CT scan was normal, at the axial level, where the probe was to be inserted in the prone position, intervening lung parenchyma within the pleural cavity was present. The situation would have been avoided if a preprocedure prone CT had been obtained. Finally, in the case of tumors adjacent to the collecting system, no studies have reported urinary UROLOGY 60 (6), 2002
extravasation or fistula formation after treatment.3,4,8 However, Gervais et al.4 reported on several patients with gross hematuria, clot formation, and eventual blood transfusion after RFA. In our series, no patient reported hematuria, most likely because the treated tumors did not grossly involve the pelvicaliceal system. PATHOLOGIC DIAGNOSIS A criticism of ablative therapy is the lack of a specimen for pathologic analysis. We have found that multiple core biopsies immediately before ablation provide sufficient tissue for diagnosis. The postablation biopsy specimens were too small and demonstrated significant RF-treatment artifact. As a result, we recommend that multiple biopsies be performed just before the procedure. CONCLUSIONS RFA is a new procedure for the treatment of small renal tumors. Its success for the treatment of tumors in other organs is well documented. However, as with any new technology, success is predicated on the correct application of the technology and appropriate follow-up. The measures noted should allow for a more uniform delivery of RFA for renal tumors. Only when longer term results are available can its efficacy be compared with other nephron-sparing treatments. REFERENCES 1. Gill IS, Novick AC, Meraney AM, et al: Laparoscopic renal cryoablation in 32 patients. Urology 56: 748 –753, 2000. 2. Shingleton WB, and Sewell PE Jr: Percutaneous renal tumor cryoablation with magnetic resonance imaging guidance. J Urol 165: 773–776, 2001. 3. Pavlovich CP, Walther MM, Choyke PL, et al: Percuta957
neous radio frequency ablation of small renal tumors: initial results. J Urol 167: 10 –15, 2002. 4. Gervais DA, McGovern FJ, Wood BJ, et al: Radio-frequency ablation of renal cell carcinoma: early clinical experience. Radiology 217: 665–672, 2000. 5. Yoshimura K, Okubo K, Ichioka K, et al: Laparoscopic partial nephrectomy with a microwave tissue coagulator for small renal tumor. J Urol 165: 1893–1896, 2001. 6. Vallancien G, Chartier-Kastler E, Bataille N, et al: Focused extracorporeal pyrotherapy. Eur Urol 23(suppl 1): 48 – 52, 1993. 7. Rendon RA, Kachura JR, Sweet JM, et al: The uncertainty of radio frequency treatment of renal cell carcinoma: findings at immediate and delayed nephrectomy. J Urol 167: 1587–1592, 2002. 8. de Baere T, Kuoch V, Smayra T, et al: Radio frequency
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