University of Wisconsin

Department of Biomedical Engineering

Department of Surgery

Department of Electrical and Computer Engineering

 
  
 
 
 


Introduction to Liver Ablation
 

Colorectal carcinoma remains a serious clinical problem despite recently intensified screening. In 2001, an estimated 135,400 new cases were anticipated with 56,700 deaths in the United States[1] . The majority of deaths associated with colorectal cancer are due, at least in part, to liver metastases. An additional 16,200 cases of primary liver cancer with 14,100 deaths are also predicted. The treatment options for liver tumors are limited. Long-term survivors are rare with systemic chemotherapy, and external beam radiation is associated with a high complication rate. The best curative option is hepatic resection with complete removal of metastatic tumors, resulting in a five-year survival of between 25 and 38%, compared to a 0% five-year survival without resection[2] .

Although hepatic resection remains the gold-standard in the treatment of liver tumors, a large number of patients have disease that is not amenable to surgical therapy[3] . This may be due to unfavorable anatomy, the presence of multiple tumors, or poor hepatic reserve[4] . Therefore, several treatment modalities have been developed for local control of liver tumors. These may be roughly broken into three categories: chemical (percutaneous ethanol injection or PEI[5] ), cold-based (cryotherapy[6, 7]), and heat-based (radiofrequency ablation[8] , microwave coagulation therapy[9] , and laser hyperthermia[10]).

In general, PEI has been useful in the treatment of hepatocellular carcinoma but not metastatic colorectal adenocarcinoma[5] . Cryotherapy and radiofrequency (RF) ablation are the most commonly used treatment modalities in the United States. There has been considerable debate between practitioners of the two techniques[11] . Cryotherapy offers several advantages, including the ability to drive multiple cryoprobes simultaneously. Cryotherapy is also easy to image by ultrasound, as the resultant iceball is highly echogenic. On the other hand, RF ablation is more amenable to percutaneous application and may have a lower complication rate, but is more difficult to visualize under ultrasound guidance.

Although rarely used outside of Asia, MW ablation offers many of the advantages of RF while possibly overcoming some of the limitations. RF ablation is fundamentally restricted by the need to conduct electrical energy into the body. As temperatures reach 100 degree C and boiling occurs, increased impedance limits further deposition of electricity into tissue[12] . This becomes even more pronounced if charring occurs; theresultant eschar forms a highly effective insulator around the RF electrode. Since MCT is based on creation of an electromagnetic field and does not rely on conduction of electricity into tissue, it is not limited by charring.

To date there have been relatively few studies comparing ablation modalities. In a non-randomized study, Bilchick et al found that RF and cryotherapy had comparable local recurrence rates for tumors under 3cm and that there was less blood loss, reduced thrombocytopenia, and shorter hospital stays with[13] . However, for tumors greater than 3cm local recurrence was 38% for RF and only 17% for cryotherapy. Large tumors also required four times the operative time under RF compared to cryotherapy (60 minutes vs. 15 minutes). In contrast, Pearson et al found in a non-randomized comparison that RF was significantly better than cryotherapy in both local recurrence (2.2% vs. 13.6%) and complication rate (3.3% vs. 40.7%)[14].

Research Goals:

Liver ablation (regardless of technology) has been an increasingly useful option in the treatment of both metastatic colorectal cancer and primary hepatocellular carcinoma. Ablation has also been used in palliative care of neuroendocrine tumors and in treatment of tumors in other locations, such as kidney, breast, lung, and bone. It has been limited by variably high recurrence rates, small lesion sizes, and difficult imaging of both tumors and ablation lesions. We have established a multidisciplinary working group of researchers interested in tumor ablation, including surgeons, radiologists, engineers, and medical physicists. Some of our current projects include:

Finite element analysis of RF and cryoablation
Characterization of microwave ablation
Improved performance of RF ablation near heat sink blood vessels
Multiple probe ablation
Elastographic and thermographic ultrasonography of ablation
Robot-assisted ablation

References:

  1. Greenlee, R.T., et al., Cancer statistics, 2001. CA Cancer J Clin, 2001. 51(1): p. 15-36.
  2. Yoon, S.S. and K.K. Tanabe, Multidisciplinary management of metastatic colorectal cancer. [Review] [94 refs]. Surgical Oncology, 1998. 7(3-4): p. 197-207.
  3. Cance, W.G., A.K. Stewart, and H.R. Menck, The National Cancer Data Base Report on treatment patterns for hepatocellular carcinomas: improved survival of surgically resected patients, 1985-1996. Cancer, 2000. 88(4): p. 912-920.
  4. Cha, C., et al., Rationale for the combination of cryoablation with surgical resection of hepatic tumors. Journal of Gastrointestinal Surgery, 2001. 5(2): p. 206-213.
  5. Bartolozzi, C. and R. Lencioni, Ethanol injection for the treatment of hepatic tumours. [Review] [99 refs]. European Radiology, 1996. 6(5): p. 682-696.
  6. Kane, R., et al., Five year survival in US-guided hepatic cryosurgery. Radiology, 1997. 205: p. 201.
  7. Lee, F.T., Jr., et al., Hepatic cryosurgery with intraoperative US guidance. Radiology, 1997. 202(3): p. 624-632.
  8. Curley, S.A., et al., Radiofrequency ablation of unresectable primary and metastatic hepatic malignancies: results in 123 patients. [see comments]. Annals of Surgery, 1999. 230(1): p. 1-8.
  9. Shibata, T., et al., Microwave coagulation therapy for multiple hepatic metastases from colorectal carcinoma. Cancer, 2000. 89(2): p. 276-284.
  10. Muralidharan, V. and C. Christophi, Interstitial laser thermotherapy in the treatment of colorectal liver metastases. [Review] [143 refs]. Journal of Surgical Oncology, 2001. 76(1): p. 73-81.
  11. Mahvi, D.M. and F.T. Lee, Jr., Radiofrequency ablation of hepatic malignancies: is heat better than cold? Ann.Surg., 1999. 230(1): p. 9-11.
  12. Goldberg, S.N., et al., Radiofrequency tissue ablation: increased lesion diameter with a perfusion electrode. Academic Radiology, 1996. 3(8): p. 636-644.
  13. Bilchik, A.J., et al., Cryosurgical ablation and radiofrequency ablation for unresectable hepatic malignant neoplasms: a proposed algorithm. Arch.Surg., 2000. 135(6): p. 657-662.
  14. Pearson, A.S., et al., Intraoperative radiofrequency ablation or cryoablation for hepatic malignancies. Am.J.Surg., 1999. 178(6): p. 592-599.