| Objective: To observe the shape and the volume of internally cooled microwave ablation lesions in porcine kidney, and investigate the effectiveness and protocol of the microwave ablation in kidney. To evaluate the feasibility, effectiveness and safety of implanted microwave ablation for renal tumors guided by ultrasonography on implanted renal VX2 tumors in rabbit and short-term local effectiveness in a small series patient.Material and methods:Part one: The experimental study of microwave ablation in porcine kidney The internally cooled microwave antenna was used in both vitro and in vivo porcine kidney ablation experiments. In vitro tissue coagulation, 12 experimental groups were created base on the coagulation power, duration and total energy. In vivo tissue coagulation, 6 experimental groups were created base on the coagulation power, duration in 6 adult pigs. The maximum longitudinal diameter, transverse diameter and width of the congestive reaction zone of the ablation lesions were measured. The ablation volume and the volume of the charred zone were determined using a special computer software base on the photos of the gross section. The changes of the temperature around the microwave antenna were recorded using an advanced temperature monitor system.Part two: The experimental study of microwave ablation in rabbit implanted renal VX-2 tumor Twenty-six rabbits with implanted renal VX-2 tumors were divided into three groups according to the type of therapy: nephrectomy, percutaneous ultrasound-guided microwave ablation, and no treatment (7, 12 and 7 respectively). The tumors were evaluated by two-dimensional ultrasonography for the changes of the size, shape and the echo pre-treatment, during the course of treatment and post-treatment (3d, 1 w, 2w and3w respectively) in microwave ablation and no- treatment groups. Vein blood was also taken at the same time point for to investigate creatinine and urea nitrogen in nephrectomy and microwave groups. CT scans were performed in 2 rabbits from microwave group random at pre-treatment and instantly following microwave ablation. Histological examinations were performed in 5 rabbits from microwave ablation group. These rabbits were sacrificed at post-treatment (instantly, 1 w, 2w, 3w and 4w respectively), and the other rabbits of microwave group died naturally. The survival time and complications were compared in three groups.Part three: The preliminary clinical experience of microwave ablation renal tumors We selected for treatment 9 tumors in 9 patients (1 with a solitary right kidney), 5 males and 4 females, aged between 39 and 83 years old. Five tumors were renal cell carcinoma; three were angioleiomyolipoma; one was oxyphilic adenoma. The size of the tumors was 0.5 - 5.7 cm. in diameter. CE-CT/MRI, CE-US were performed for each patient pre-treatment and post-treatment (1 month, 3 months, 6 months, 9 months, 1 year respectively). Blood routine test, urine routine test, blood urea nitrogen level, and serumcreatinine level were examined at the same time point. Results: Part one: The shapes of ablation lesions were all elliptical. Histologicalexamination reveal four zone from central to circumferential region of the microwave ablation lesion: carbonization, coagulation, congestive reaction and normal zone respectively in vivo porcine kidney. Histological examination revealed complete coagulation necrosis in ablation region. In congestive reaction region, hemorrhaging was scattered, and renal tubules were dilated. The ablation volume enlarged with the increase of power output and time, but there is not linear relationship between volume and power and time. The charred volume and longitudinal diameter significantly enlarged with the increase power output especially it exceeded 60W. The charred volume and longitudinal diameter in group 70W and 80W were significantly larger (p<0.05) than that in 60W group.An increase in ablation time correlated with an increase in the size of the induced lesions, and during 420s and 600s of the ablation procedure, the coagulation volume and transverse diameter grew fast. The maximum longitudinal diameter and transverse diameter enlarged with the increase of time, but the increase of the transverse diameter were larger than that of the longitudinal diameter in same time .The increase of the transverse diameter in 600s was the largest. The ablation volumes were lager in high power output than that in lower power output. But with increase in power output, the coagulation volume grew slow, and the maximum longitudinal diameter grew fast. The charred volume in group 70W and 80W were significantly larger (p<0.05) than that in 50W group. The ablation volume in vivo is significantly smaller (p<0.05) than in vitro.Part two: The survival time of the three groups were 37.67 ± 4.01d (microwave group), 31.20 ± 1.53 d(nephrectomy group) and 22.00 ± 2.03d(no-treatment group) respectively. The survival time in the microwave group was significantly higher than that in the no-treatment group (p<0.05), and was the same as that in the nephrectomy group. The serum creatinine level did not increase after microwave therapy. After microwave ablation, the growth velocity of tumor in the microwave group was slower than that in the no-treatment group. The volume of the tumor in microwave group was smaller than that in no-treatment group in same time (p<0.05). After microwave ablation, histological examination of the MWA-treated kidneys demonstrated marked coagulative necrosis in most of the tumor. Beyond this coagulative necrosis area, hemorrhage and inflammation can be seen in the adjacent tissue. After microwave ablation, enhanced CT scanning showed clear margin surrounding the tumor; ablation lesions exhibited as wedge-shaped non-enhancive area. The ablation area was larger than the size of the tumor.Part three: Eight patients were treated by US-guided percutaneous MWA and one patient with the largest lesion was treated by MWA during laparotomy. All patients follow-up ranged from 87 to 368 days. All patients treated byUS-guided percutaneous MWA were discharged home within 7 days after treatment. No serious complications recurrence occurred after US-guided MWA sessions. The Contrast-Enhanced Ultrasound and CT characteristics of successfully ablated renal tumors included clear margin, the absence of enhancement, larger ablation area than the size of the tumor, and minimal size reduction over time. Ablated lesions were characterized by high signal intensity on T1-weighted images, low signal intensity on T2-weighted images, and an absence of contrast enhancement in MRI scans. There were no significant changes in renal function after ablation.Conclusion: (1) The shapes of microwave ablation lesions are all elliptical in porcine kidney. (2) The ablation volume enlarge with the increase of power output and time, but there is not linear relationship between volume and power and time . Optimal microwave ablation lesions may be produce with the power of 50W to 60W and ablation time 600s in clinic. (3)The ablation volume in vivo is significantly smaller than in vitro. (4) Histological examination reveal four zone from central to circumferential region of the microwave ablation lesion: carbonization, coagulation, congestive reaction and normal zone, respectively. (5) Microwave can generate certain size of ablation lesion and result in coagulative necrosis in tumor model. (6) Microwave ablation renal tumor can inhibit tumor growth; prolong survival of tumor-loading anima. The clinical effectiveness of microwave ablation in renal tumor as same as that of radical nephrectomy.(7) Microwave ablation tumor guided by ultrasound is a safe, feasible and effective therapy in treatment of renal tumor.
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