Image-Guided Ablation of Renal Tumors

Before the advent of tumor ablation, the curative treatment for primary renal cell cancer (RCC) was to perform laparoscopic or open nephrectomy or partial nephrectomy. Many patients are deemed unsuitable for potentially curative surgical techniques because of limited renal functional reserve, desire to avoid renal replacement therapy, and comorbid conditions.

The development of needle applicators for tumor ablation has provided selected patients who are unsuitable or unwilling to undergo renal surgery with less invasive nephron-sparing treatment options. This chapter focuses on percutaneous ablation procedures.

Methods of Ablation

There are multiple series published of RCC and benign tumor ablation in humans using percutaneous radiofrequency ablation (RFA) and cryoablation ( Box 26-1 ). Medium-term follow-up data exist for microwave ablation in RCC. Reports of in vivo use of laser interstitial thermal therapy and ultrasound ablation exist in normal animal kidney and RCC ( Table 26-1 ). There are first reports of irreversible electroporation in human and animal kidney.

Box 26-1

Renal Tumor Ablative Techniques

Thermal
- Radiofrequency ablation
- Cryoablation
- Microwave ablation
- Laser interstitial thermal therapy
- Ultrasound ablation
Irreversible electroporation

Table 26-1

Ablation Zone Diameter with Tumor Ablative Techniques

Modality	Mean Ablation Size (cm)	Generator Power (W)	Endpoint Determinant	Tissue Ablated
2-cm multitined expandable electrode (Starburst XL; Rita Medical Systems) with renal collecting system cooling	2.6	NS	Temperature	In vivo pig kidney
2-cm multitined expandable electrode (Starburst XL; Rita Medical Systems) without renal collecting system cooling	2.7	NS	Temperature	In vivo pig kidney
3-cm cooled electrode (Covidien)	2.5	200	12 minutes Impedance control	In vivo pig kidney
2.5-cm cooled cluster electrode (Covidien)	3.1	200	12 minutes Impedance control	In vivo pig kidney
Three 3-cm electrodes placed 1.5 cm apart using switching device (Covidien)	5.0	200	12 minutes Impedance control with switching controller	In vivo pig kidney
Three 3-cm electrodes placed 2 cm apart using switching device (Covidien)	4.4	200	12 minutes Impedance control with switching controller	In vivo pig kidney
Single interstitial laser fiber	1.8	NS	4 minutes	In vivo pig kidney

NS, not stated.

The method of action of each of the ablation techniques is similar in kidney and liver, discussed in Chapter 25 .

Indications and Outcome

Image-Guided Ablation for Renal Cell Cancer

RCC can be ablated for local control in patients who are unsuitable for renal resection, because of comorbidities, limited renal functional reserve, a single kidney, multiple RCCs, or a condition with an increased risk of RCC occurrence in residual renal tissue such as von Hippel-Lindau disease ( Box 26-2 ). Ablation is suitable for RCCs that are predominantly solid or cystic.

Box 26-2

Indications for Renal Ablation

Patient unsuitable for renal resection
Limited functional renal reserve
Single kidney
Multiple renal cell carcinomas
Von Hippel-Lindau disease

Effectiveness and Local Control

At a mean follow-up of less than 2 years, percutaneous computed tomography (CT)-guided RFA achieves successful local control in 93%-100% of patient series for a wide range of tumor sizes. The number of RFAs necessary for complete ablation increases with tumor size ( Table 26-2 ). RCCs smaller than 3 cm are more likely than larger tumors to be completely ablated in a single session. RCCs that are 3-5 cm in size are completely ablated in one or two ablation sessions. In one series, only 25% of RCCs of 5 cm or larger could be completely ablated by repeated ablation sessions. The upper limits of RCC size suitable for ablation vary among institutions and are not standardized. In general, RCCs that are 4 cm or less (stage T1a) are suitable for RFA, although with newer technology many completely ablated tumors exceed this size. At our institution we have successfully ablated 6- to 8-cm tumors.

Table 26-2

Achievement of Complete Necrosis (Imaging Definition) and Number of Radiofrequency Ablation Sessions to Achieve Complete Necrosis Based on Tumor Size

Tumor size (cm)	% of all Tumors That Will Achieve Complete Necrosis After Multiple Sessions	% of Adequately Treated Tumors That Will Achieve Complete Necrosis After 1 Ablation Session	% of Adequately Treated Tumors That Will Achieve Complete Necrosis After 2 Ablation Sessions	% of Adequately Treated Tumors That Will Achieve Complete Necrosis After 3 Ablation Sessions
<3	100	92	8	NA
3-5	92	53	44	3
>5	25	0	50	50

NA, Not applicable.

Percutaneous CT-guided cryotherapy for primary RCC has a local control rate of 92%-100% in patient series with a wide range of tumor sizes at a mean follow-up of less than 2 years. Overall, 95%-100% of small RCC can be completely ablated in a single ablation session ( Box 26-3 ).

Box 26-3

Local Effectiveness of Ablation

93%-100% for radiofrequency ablation
92%-100% for cryoablation
Renal cell carcinoma (RCC) less than 3 cm can be ablated with single session
RCC between 3 and 5 cm usually requires more than one session
Local control decreases for RCC greater than 5 cm

Ultrasound-guided microwave ablation of RCC has achieved 1-, 2-, and 3-year disease-free survival rates of 95.4%, 92.3%, and 92.3%, respectively.

Early data from phase 2 clinical trials regarding ultrasound ablation demonstrate pathologic response in 15%-35% of targeted tissue in resected RCCs treated with extracorporeal high-intensity focused ultrasound.

There are no published data yet regarding the effectiveness and rate of local control of RCC with laser interstitial thermal therapy or irreversible electroporation. Data are available for application in normal animal kidney. Further medium- and long-term follow-up is required to determine the efficacy of all forms of percutaneous ablation.

Quality of Life

A nonrandomized comparison of percutaneous RFA and laparoscopic radical nephrectomy for small renal cell carcinoma demonstrated there was a significant lower baseline quality of life and greater age in those patients who were selected for RFA. This difference in age demographic may reflect indications for RFA in the study which included coexisting morbidities and surgical or anesthetic risk. After treatment, the surgery group demonstrated a significant reduction in quality of life at 1 week, whereas patients who had RFA demonstrated no significant change in quality of life in the first week. There was a tendency toward improvement above baseline for age in quality of life in the RFA group up to 24 weeks after RFA.

Cost Effectiveness

In an analysis of the relative cost effectiveness of percutaneous RFA and nephron-sparing surgery in patients of 65 years of age with small renal cell carcinoma (<4 cm) performed at our institution in 2007, nephron-sparing surgery yielded a minimally greater average quality-adjusted life expectancy than RFA (2.5 days), but was more expensive (assuming a 10% higher incidence of tumor recurrence after RFA when compared with nephron-sparing surgery). For nephron-sparing surgery to be preferred over RFA, an estimated nephron-sparing surgery cost reduction of $7500, or RFA cost increase of $6229, was necessary. RFA was preferred even if the annual probability of post-RFA local recurrence was up to 48%.

Image-Guided Ablation of Benign Renal Masses

Image-guided ablation has been used for benign tumors such as oncocytomas, angiomyolipomas and renal arteriovenous malformation. Therapy is indicated for angiomyolipomas when there are symptoms such as pain or when the lesion is greater than 4 cm because of a risk of spontaneous hemorrhage; however, angiomyolipomas of this size are typically treated by transcatheter embolization, and the role of ablation is not well established. Further criteria for treatment of angiomyolipomas include growth of the lesion by 2 cm at annual CT or presentation with acute hemorrhage.

Some institutions consider oncocytomas for ablation as an alternative to imaging follow-up or resection. Case reports describe successful use of tumor ablation in patients with hypertension secondary to oncocytoma.

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