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AJR 2005; 185:84-85
© American Roentgen Ray Society

Technical Innovation

Pediatric Return Electrodes for Radiofrequency Ablation in Children

Paul R. Morrison1, Stephen D. Brown2 and Eric vanSonnenberg3

1 Radiology, Brigham and Women's Hospital, Boston, MA 02115.
2 The Children's Hospital, Boston, MA.
3 Dana-Farber Cancer Institute, Boston, MA.

Received August 20, 2004; accepted after revision November 2, 2004.

 
Address correspondence to P. R. Morrison (pmorrison{at}partners.org).


Introduction
Top
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
Radiofrequency energy can be delivered interstitially to destroy tissues thermally in situ for a therapeutic effect. This process is generally referred to as radiofrequency ablation. Although percutaneous radiofrequency ablation has been applied extensively in adults to a range of pathologic conditions [1-5], its use to treat tumors percutaneously in children has been limited primarily to treating osteoid osteomas [6]. Considering the increasing interest and breadth of use in adults, percutaneous radiofrequency ablation will likely be used for a range of applications in children as well. Radiofrequency ablation in small children, however, raises technical concerns because procedures typically involve the deposition of radiofrequency energy at relatively high powers and currents (> 100 W; ~ 1.5 A) for extended periods (several minutes); this raises technical concerns in small children. One such concern is the safe return of the applied current and the potential hazard of skin burns at the return electrodes (grounding pads). In this report, we describe the use of pediatric return electrodes for radiofrequency ablation in the kidney of a young patient for whom standard adult pads could not be used in a manner consistent with the manufacturer's instructions for use.


Subjects and Methods
Top
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 
The procedure was performed on a 16-kg, 5-year-old girl with a 1.8-cm central tumor (nephroblastoma) in her solitary right kidney. The radiofrequency ablation procedure was approved by our institutional review board under an innovative therapy mechanism.

Radiofrequency ablation was performed with a 2.0-cm-diameter array-style electrode (LeVeen, Boston Scientific) connected to a radiofrequency generator (RF 3000, Boston Scientific) capable of providing up to 200 W of power at a frequency of 460 kHz. The electrode was placed percutaneously into the tumor under CT guidance. Four rectangular, 12.1 x 9.5 cm infant return electrodes (Infant REM PolyHesive II, ValleyLab) were applied; two pads were placed on each thigh, one anterior and one posterior, with the long axis of each parallel to the femur (Fig. 1). These are marketed for use in monopolar electrosurgery.



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  		Fig. 1 —Photograph of return electrodes, or grounding pads, for radiofrequency ablation: 18.3 x 11.4 cm adult pad (left) and 12.1 x 9.5 cm infant pad (right). Smaller pad has 55% of area of larger adult version; four such infant pads were used in case discussed.

 
Radiofrequency energy was delivered with the power adjusted incrementally from an initial power setting of 10 W. The power was increased 5 W/min up to a maximum of 60 W. Subsequently, a second phase of treatment at the same site was applied at 40-45 W for 6.5 min and concluded the treatment. During ablation, the grounding pads were manually assessed for excessive warmth, and the skin around their edges was visually inspected for erythema.


Results
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 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
From a technical standpoint, the ablation was executed without incident. After a total of 19 min in the first phase of treatment, tissue impedance rose rapidly from an average value of approximately 70 ohms to several hundred ohms. This increase in impedance, indicative of tissue coagulation, is the clinical end point for the therapy using this particular ablation device. No operational problems with the radiofrequency generator occurred from using the pediatric return electrodes. The return electrodes did not get hot to the touch, and no burns on the skin were observed either during the procedure or at the end, when the pads were removed. Postprocedural imaging at 24 hr showed evidence of complete ablation of the tumor.


Discussion
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 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
Because of the small circumference of each of the child's thighs, standard large adult pads would not fit without considerable overlap, regardless of pad orientation. The use of four adult pads (two on each thigh) is the standard recommended in the instructions for use (Boston Scientific), which were written for use in adults. Uneven or skewed alignment, uneven skin contact, overlap, or an insufficient number of pads (and thus an inadequate surface area for returning current) add to the possibility of an excessive concentration of return current on the pad and therefore the risk of skin burns [7, 8]. Furthermore, the radiofrequency generator electronically monitors current to maintain an even distribution throughout the pads and will interrupt transmission if excessive current is detected. Thus, using substantially overlapping adult pads or only two adult pads could have presented device error messages that may have been hard to resolve, interrupting the procedure.

By using the smaller infant pads, we were able to have four well-placed, properly applied pads with no overlap. The total surface area provided was 460.0 cm2 (55% of the 834.5 cm2 provided by four adult pads [Adult REM PolyHesive II, ValleyLab]). In this procedure, the maximum power applied was 60 W with a current of approximately 0.9 A, and the treatment time was several minutes. Despite the reduced surface area and the potential for increased heating at the return pads, the device operated as expected in this procedure and the skin was not burned.

Ideally, the location and orientation of the pad should be in accordance with the manufacturer's instructions. In this case, we opted for the use of an alternative pad to get good placement on the thighs for the best electric conduction. For future cases, if the circumference of each thigh allows, we would recommend placing each pad with the long axis perpendicular to the femur to maximize the leading edge of the pad for the return current [9]. Separately, caution should be exercised in the use of electrode arrays larger than 2 cm that may necessitate higher applied powers or extended durations of energy deposition, since these parameters add to the risk of untoward tissue heating. The sites of the grounding pads should be checked manually and visually throughout the procedure.

Although an application in a single case is not definitive, we suggest that the judicious use of these pads is safe and advisable for radiofrequency ablation in pediatric patients. Two technical safety concerns were addressed successfully in this case by the use of the infant grounding pads: The skin was not burned despite the reduced total surface area for the return current, and the operation of the radiofrequency generator itself presented no problems.


Acknowledgments
 
We acknowledge the assistance and advice of Chris Pearson and Thom Lawson.


References
Top
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

  1. Livraghi T, Solbiati L, Meloni F, Ierace T, Goldberg SN, Gazelle GS. Percutaneous radiofrequency ablation of liver metastases in potential candidates for resection: the "test of time approach." Cancer 2003;97:3027 -3035[CrossRef][Medline]
  2. Curley SA, Marra P, Beaty K, et al. Early and late complications after radiofrequency ablation of malignant liver tumors in 608 patients. Ann Surg 2004;239:450 -458[CrossRef][Medline]
  3. Zagoria RJ. Percutaneous image-guided radiofrequency ablation of renal malignancies. Radiol Clin North Am2003; 41:1067 -1075[CrossRef][Medline]
  4. Steinke K, Sewell PE, Dupuy D, et al. Pulmonary radiofrequency ablation: an international study survey. Anticancer Res 2004;24:339 -343[Abstract/Free Full Text]
  5. Wood BJ, Ramkaransingh JR, Fojo T, Wather MM, Libutti SK. Percutaneous tumor ablation with radiofrequency. Cancer 2002;94:443 -451[CrossRef][Medline]
  6. Torriani M, Rosenthal DI. Percutaneous radiofrequency treatment of osteoid osteoma. Pediatr Radiol2002; 32:615 -618[CrossRef][Medline]
  7. de Baere T, Risse O, Kuoch V, et al. Adverse events during radiofrequency treatment of 582 hepatic tumors. AJR2003; 181:695 -700[Abstract/Free Full Text]
  8. Steinke K, Gananadha S, King J, Zhao J, Morris DL. Dispersive pad site burns with modern radiofrequency ablation equipment. Surg Laparosc Endosc Percutan Tech2003; 13:366 -371[Medline]
  9. Goldberg SN, Solbiati L, Halpern EF, Gazelle GS. Variables affecting proper system grounding for radiofrequency ablation in an animal model. J Vasc Interv Radiol2000; 11:1069 -1075[Medline]

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Home page
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S. D. Brown and E. vanSonnenberg
Issues in Imaging-Guided Tumor Ablation in Children Versus Adults
Am. J. Roentgenol., September 1, 2007; 189(3): 626 - 632.
[Abstract] [Full Text] [PDF]

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