Current guidelines consider thermal ablation as an alternative to nephron-sparing surgery (NSS) for patients who have renal dysfunction or have no surgical indication [6]. Recently, the long-term efficacy of ablative therapy has been reported to be comparable to the outcome of surgical resection, with the greatest retention of renal function and few major complications. Ablative therapy is a minimally invasive treatment that maximizes nephron retention and is usually appropriate for patients who are ineligible for surgical resection, have only a solitary functioning kidney or have combined renal dysfunction [7]. By using electric pulses to create nanopores in the cell membrane of tumor cells, IRE will eventually induce cell apoptosis. Since the scope of IRE is limited to the cell membrane, the other extracellular matrix structuresare not affected, which allows the rapid regeneration of normal tissues.

Compared with the decrease in renal function after thermal ablation for RCC [8], no significant changes in renal function or serious complications ofIRE treatment forRCC have been reported in the literature. Noah E. Canvasser et al. [9] chose 42 cT1a RCC lesions from 41 patients with IRE. The initial treatment success rate was 93%(39/42), and the 2-year local-recurrence-free survival (LRFS) was 83%.No major complications occurred. Steffen J. Diehl et al. [10] described a series of 5 patients with 7 potentially malignant renal lesions in a solitary kidney treated with IRE. The author reported no significant decrease in eGFR over 3 months, even though 1 patient’s eGFR decreased from >60 ml/min/1.73 m2 to 44 ml/min/1.73 m2. In our study,there were no significant changes in serum creatinine, serum urea nitrogen and eGFR after IRE therapy compared with the corresponding values before IRE in 15 patients, including 1 patient with nephrotic syndrome and 7 patients with a solitary kidney. Moreover, the normal renal function was completely preserved. No serious complications (Clavien-Dindo grade III or above) occurred.

The presence of a “heat sink effect” in thermal ablation, such as RFA and MWA,can affect the outcome of thermal ablation in lesions close to the vessel. There is also a “warming effect” of cryoablation [10, 11]. The incidence of postoperative hemorrhage, intraoperative area infection, urine leakage, ureteral injury and stricture, intestinal damage and other nontherapeutic target organs caused by ablation is relatively high (4%) [12, 13]. However, IRE does not have these limitations. For centrally located kidney tumors, IRE has advantages over surgical resection and thermal ablation techniques. At the same time, compared with thermal ablation and cryoablation, IRE requires no preoperative preparation for malignant renal tumors near important organs and tissues (such as pyelostomy, ureteral stent implantation, and artificial pneumoperitoneum and ascites, etc., to protect important tissues and organs). Transient gross hematuria occurred in 2 patients with centrally located lesions without any otherserious postoperative complications inour study.

The tumor maximal diameter of patient 10 was 4.5 cm. IRE was not recommended for this situation because the diameter exceeded the surgical indications. The guidelines also do not recommend ablation for tumors larger than 3 cm in diameter. At the same time, the related literature also pointed out that the risk of recurrence is higher [1, 14]. The patient 10 chose to try the IRE treatment and had a satisfactory curative effect. Regarding the complications and deficiencies caused by IRE, the latest literature has been explored in animal experiments to find improved methods. Timothy J. O’Brien et al. [15] tested the effects of using several pulse-timing paradigms on electrical current, tissue temperature, and tissue treatment size. They believe that cycled pulsing patterns may hold promise for enhancing the efficacy of IRE application in clinical practice and could lead to better overall outcomes for patients. N. Beitel-White et al. [16] found that larger overall changes in output current are correlated with larger decreases in T cell populations 24 h after treatment. Real-time decisions can be made regarding the optimal follow-up therapy based on the range of output current delivered during treatment. This approach will also maximize the immunomodulating effect of IRE in synergy with follow-up immunotherapy.

Safe and successful CT-guided percutaneous ablation of RCC by IRE begins with careful preprocedural evaluation of imaging to plan the appropriate patient position, needle approach, and trajectory. The kidney is surrounded by the liver, diaphragm, lower lobe of the lung, vertebral bodies, spleen, and bowel. Given the anatomical relationship of the kidney and its surrounding organs, a suitable approach should be used according to the location of the tumor to avoid major complications related to the puncture procedure, such as scarring with ureteropelvic junction obstruction, neuromuscular injury, and bowel wall perforation.

It has been reported in the relevant literature that thermal ablation of renal tumors via the anterior approach is considered to be a relative contraindication. The main reason is the risk of percutaneous ablation-related complications, such as damage to nontarget organs, including the small intestine, pancreas, colon,etc. [17, 18]. Hegg et al. [19] reported 18 patients (19 tumors) who underwent transhepatic renal RFA procedures by ultrasound guidance without the development of major complications during the procedures. Ginat et al. [20] described several bowel displacement and protection techniques during percutaneous renal tumor thermal ablation to avoid potential devastating consequences. In our treatment experience, CT guidance is the more suitable method for the IRE procedure because of its ability to reveal the detailed anatomy along the electrodeneedle pathway. The transhepatic approach is safe forthe treatment of tumors located anterolaterally in the right kidney. The left colon-spleen space is appropriate for tumors located at the anterior border of the left kidney. Most tumors located in the lateral and posterior part of the kidney are suitable for a posterior approach. Combined with other literatures and our experience, we can explain the ideal patient, candidate to IRE. First, it is reserved for patients who have not the surgical indication, or are prone to have postoperative complications and the patient who are not willing to accept surgical treatment. Second, IRE is suitable for the patients with higher risk of postoperative complications after thermal ablation (patients with tumor close to the urinary collection system, vital organs and great vessels, or with high R.E.N.A.L. score). Third, patients with renal insufficiency or patient who has a solitary kidney are also the ideal candidate for IRE treatment.

The current study is limited by its retrospective nature. There was no comparison arm of patients. The patient sample size wassmall, and the follow-up time was relatively short. In recent years, IRE technology for RCC has remained relatively less developed globally,and thus, the safety and efficacy of this treatment need to be further clarified through a prospective study design with a larger sample size.

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