Basic And Clinical Researches On Microwave Ablation Of Renal Tumors

ObjectiveUsing the model of in vitro and in vivo porcine kidneys to clarify the characteristics of MWA of renal tissue under different conditions. Clinical follow-up was performed in the patients that received MWA therapy for renal tumors to evaluate its feasibility and clinical efficacy.MethodsWe used 2450 MHz water circulative-cooling microwave needle, length of the anterior pole was 1.1cm. The independent variables were power(50-70W), time(240s-600s) and ablated with different combination. We observed the ablation shape,zone and pathological characteristics.Six pigs were utilized for the experiment using Kang You 18-G water circulative-cooling microwave needles. The operating frequency was 2450 MHz, and the independent variables were power(50-60W) and time(300-600s). The kidneys were dissociated laparoscopically and ablated with a single or double needle at different power/time combinations and depths of puncture. Changes in the kidneys were carefully observed. Specimens of the ablated lesions were stained with H&E to evaluate the pathological features.From April 2013 to July 2014, seventeen patients(13 males and 4 females) accepted MWRTA in our department. The mean age was 59.4 years(range from 42 to 83years). According to indications, they were divided into three groups, the first group(contraindications of common operation or severity concomitant diseases) included six patients, the second group(to clarify the diagnosis and treated with MWRTA)included nine patients, the third group(to clarify the diagnosis and receiving palliative treatment of MWRTA) included two patients. All of the patients accepted needle biopsy associate with MWRTA.ResultIn vitro, the effective ablation shape was similar to a chestnut and the zone enlarged with the increasing of power and time. The data indicated that the largest transverse diameters of combination of 50W/480 s, 60W/300 s, 70W/240 s was close to 3cm and the length-diameter was about 3.3cm. The pathological characteristics were that renal tissue of carbonization zone was thoroughly necrotic.Coagulative necrosis was observed in coagulation area, though there were residual profile of glomerulus, renal tubular and vessels, they had lost activity. Most of the tissue in transition zone was normal, however, some cells were swelling because of thermal damage.In vivo, the kidney tissues of the ablated zone were dry, atrophied and hard. The effective ablation shape was similar to that of a chestnut. The ablated lesions could be divided into three zones: the carbonization zone, solidification zone, and inflammatory reaction zone. The ablation zone enlarged with increasing power and time. When combined with two needles, the maximum diameter of the ablated lesions significantly increased. The pathological results indicated that the renal tissues of the carbonization zone were thoroughly necrotic. Coagulative necrosis was observed in the coagulation zone, and the structure was disordered. No ‘skipping’ areas were noted in any ablation zone. The structure of the inflammatory reaction zone was integrated, and interstitial small blood vessels were highly expanded and congested with infiltrated inflammatory cells.In clinic, there were five clear cell RCC confirmed by pathologist in the first group and one case was not available. The mean follow-up was 11.5±3.8 months(range from 6 to 16 months). One case of urine leakage had been noted, the others had no complications, recurrence or metastasis. In the second group, three cases were clear cell RCC, one case was high-differentiated adenocarcinoma, five cases were angiomyolipomas. The mean follow-up was 5.6±4.2 months(range from 1 to 11months), there were no complications, no recurrence or metastasis. In the third group,two cases were clear cell RCC. The mean follow-up was 9.5±2.1 months(range from8 to 11 months). The VAS pain score of waist descended from 6-8 point of preoperation to 0-2 point of postoperation. One case had distant metastasis and tumor progression. The other occurred pathologic fracture due to metastasis, whereas the recurrent renal tumor was cured. The mean hospital stay of all the patients was4.0±1.0 days(range from 2 to 7 days).ConclusionThis study has provided the in vitro and in vivo ablation parameters for us. MWA is a safe and feasible thermotherapy for selected patients, for example, for patients with contraindications of common operation or severity concomitant diseases, for patients with small renal tumors and the pathology unknown, or for patients with advanced tumors. Combining needle biopsy during MWRTA could clarify the pathological diagnosis. However, the long-term efficacy is unclear and need further follow-up.