title: Mathematical and Ex Vivo Thermal Modeling for Renal Tumor Radiofrequency Ablation with Pyeloperfusion.
abstract: OBJECTIVE
  Radiofrequency ablation (RFA) is an effective technique for the treatment of patients with small renal tumors, although it is often limited to tumors at least 2 cm from the renal pelvis or ureter. Retrograde pyeloperfusion (PPF) of the pelvis with cold saline during RFA may protect the pelvis and ureter. We designed a mathematical and ex vivo model of RFA to investigate the effects of PPF.
  
  
  METHODS
  Our theoretical model uses heat transfer principles simplifying the RFA probe to a heat-emitting cylinder within a material. In the ex vivo model, an RFA probe was placed 18 mm from the pelvis in porcine kidneys and with temperature probes on either side of the RFA probe. Control trials with no PPF were compared with either cold saline (2°C), warm saline (38°C), or antifreeze (-20°C) pumped into the renal calix at a rate of 60 mL/min. Ablated volumes were measured and confirmed histologically.
  
  
  RESULTS
  The average steady state temperatures at each probe were highest with no PPF, followed by warm saline, cold saline, then antifreeze. Compared with no PPF, temperatures were significantly (P<0.05) colder with warm saline (-8.4°C), cold saline (-18°C), and significantly colder at the calix (warm -14°C, cold -27°C). While RFA output a constant voltage, significantly lower resistances in warm (171Ω) and cold (124Ω) PPF vs no PPF (363Ω) translated to significantly greater power outputs in warm (40 W) and cold (42 W) vs no PPF (14 W). The ablated volumes were significantly higher in warm saline (2.3 cm(3)) vs cold saline (0.84 cm(3)) and no PPF (1.1 cm(3)). Mathematical modeling produced a predictive temperature curve with R2=0.44.
  
  
  CONCLUSIONS
  PPF lowers temperatures throughout the entire kidney during RFA, most notably near the collecting system and is dependent on the temperature of the liquid used. In addition, PPF may cause less charring of the tissue around the probe resulting in lower resistance and higher power outputs.
authors: 1 Department of Urology, Florida International University , Miami, Florida.
authors: Michael
authors: M
authors: Glamore
authors: 2 Department of Urology, University of Miami , Miami, Florida.
authors: Thomas
authors: T
authors: Masterson
authors: 3 Department of Urology, University of Miami Miller School of Medicine , Miami, Florida.
authors: Karli J
authors: KJ
authors: Pease
authors: 3 Department of Urology, University of Miami Miller School of Medicine , Miami, Florida.
authors: Gideon
authors: G
authors: Lorber
authors: 4 Department of Engineering, University of Miami , Miami, Florida.
authors: Kevin
authors: K
authors: Nella
authors: 3 Department of Urology, University of Miami Miller School of Medicine , Miami, Florida.
authors: Nelson
authors: N
authors: Salas
authors: 1 Department of Urology, Florida International University , Miami, Florida.
authors: Raymond J
authors: RJ
authors: Leveillee
mesh_terms: D000818:Animals; D002292:Carcinoma, Renal Cell / Q000601:surgery*; D017115:Catheter Ablation / Q000379:methods*; D003080:Cold Temperature; D004195:Disease Models, Animal; D006801:Humans; D007680:Kidney Neoplasms / Q000601:surgery*; D008954:Models, Biological; D008962:Models, Theoretical; D010388:Pelvis; D012965:Sodium Chloride / Q000008:administration & dosage; D013552:Swine
chemical_list: D012965:Sodium Chloride