Radiofrequency Ablation

Transcription

1 September 2001 Radiofrequency Ablation Jay W. Patti Harvard Medical School Gillian Lieberman, M.D.

2 But first, 2 unknown quiz cases

3 Unknown #1Diagnosis? Gallbladder Spleen Liver

4 Situs inversus viscerum 1 in 10,000 to 15,000 adults in the United States levocardia in the presence of situs inversus. Can be associated with a single ventricle, pulmonary stenosis, arterial transposition, VSDs, ASDs, atrioventricular septal defect, anomalous pulmonary venous return, tricuspid atresia, and pulmonary arterial hypoplasia or atresia. 50% of people with Primary Ciliary Dyskinesia (PCD) have Kartegener's syndrome: situs inversus, chronic sinusitis and otitis, and airways disease leading to bronchiectasis 25% of people with situs inversus have PCD If none of the above associated abnormalities are present then it is usually asymtomatic

5 Unknown #2 Diagnosis?

6 Unknown #2

7 Diagnosis: THE PATIENT TOOK A BREATH which moved the kidneys superior and created an artifact that appears as though there is a mass above the left kidney. It is very important to keep a wide angle when looking at an area of suspected pathology. (It is tempting to narrow ones field to the area of interest.)

8 Radiofrequency Ablation Is the process by which discrete quantities of energy in the form of radiofrequency are deposited in specific tissues in an attempt to cause coagulative necrosis in a predetermined area. (Cooking tumors in vivo)

9 Patient History The 66 year old male patient was diagnosed with colon cancer metastatic to the liver and received one treatment of radiofrequency ablation with recurrence prior to being referred to the interventional radiology team at BIDMC.

10 Indication Radiofrequency ablation was first used in the treatment of unresectable hepatocellular carcinoma. This patient population provided a means to show that radiofrequency is safe, useful, technically straightforward and inexpensive. Currently radiofrequency ablation is used to treat hepatocellular carcinoma, colon metastases to the liver, renal cell carcinoma, chordomas, osteoid osteomas, fibroids, cutaneous metastases, and other tumors are under investigation. It is currently FDA cleared for the treatment of soft tissue masses Size and proximity to adjacent organs limits the use of radiofrequency ablation.

11 The Procedure Radiofrequency ablation can be preformed either percutaneously or intraoperatively. The procedure is preformed under ultrasound or CT guidance. The skin over the area of interest is cleaned with iodine and draped. It is important to maintain sterile conditions as the resultant necrotic tissue in the burned lesion is a nutrient rich broth for bacterial growth. The patient is provided with conscious sedation (benzodiazipine and narcotic). Some patients experience severe pain during the procedure which subsides after the treatment. Post-procedure patients may experience a dull ache or may be pain free. It is also important to prevent collateral damage of adjacent organs. Appropriate planning and intraprocedural monitoring of adjacent structures is necessary. Ablation of the needle tract is believed to reduce seeding the tract.

12 The Equipment THE BASICS: A RF probe is a metal needle that is covered by a plastic material on all but the tip of the probe. The tip makes direct contact with the tissue in the treatment area. There are many different types of RF probes in use but the two most common types are: RITA probe - Has three, four or six umbrella shaped prongs which can be deployed from with in the tumor. Cool-tip - Single or multiple parallel probes that are internally cooled during the procedure by a closed circuit cold water pump. Multiple grounding pads are used to complete the circuit.

13 The Equipment RITA Probe Radionics

14 Pathophysiology of Tissue Damage The exposed tip of the probe emits radiofrequency in the range of 500 khz. This energy excites the ions in the surrounding tissue which through friction raises the temperature of the tissue. At temperatures above 50 degrees centigrade the tissue literally cooks in vivo. The temperature is measured throughout the procedure by thermometers on the exposed tips of the probe. Current methods of RFA have increased the area of tissue necrosis from 1.6 cm diameter to 4-5 cm diameter. Temperature of 105 degrees centigrade for 10 minutes creates the ideal sphere. Time to return to body temperature indicates quality of treatment sphere. Treatment area should include a rim (margin) of healthy tissue to reduce recurrence.

15 Limitations Char-Broil: The impedance of the tissue rises as the cellular framework becomes disrupted and the tissues begin to char. The increased impedance acts as an insulation and hence isolates the energy producing tip from more distant tissues. Heat Sink: Tissue is continuously cooled by the relatively cool blood supply passing the cooking tissue. This too prevents the heating of tissues distant from the site of treatment Variable Heat Conduction: Some tumors conduct heat better than others, presumably due to vascularity and ionic density although never specifically shown. Neighboring Structures: Structures such as blood vessels use the heat sink effect as an internal protection. Structures such as the gallbladder and loops of bowel do not have such internal defenses and are particularly vulnerable to the increased temperatures.

16 Working Around Limitations Char-Broil: Most probes currently in use have internal safety mechanisms to limit both the increase in impedance and temperature. The turn off or pulse (much like a microwave oven in defrost mode) when they reach a defined level. Heat Sink: The pringle maneuver is often used to reduce the heat sink effect while ablating a tumor in the liver. Variable Heat Conduction: Some tumors are better conductors of heat. This phenomenon can be beneficial in that the tumor acts as vector for transferring heat to more tumor. Healthy tissue is hence protected from the increased heat transferred to other malignant tissue. A cirrhotic liver can also act as an insulator for the treatment area which aids in ablation (oven effect). Neighboring Structures: Extra thermometers are often placed between the treatment area and the threatened organ the local temperature can be monitored and treatment can be pulsed accordingly.

17 Lost to Follow-up (8 cm ) The patient was lost to follow up for five months and returned with the following CT scan

18 The Sphere of Ablation Around every burn area is an area of tissue that has been heated but not killed. This area is where most malignant cells evade ablation. Damaged Killed

19 Expanding the Sphere Current research is concentrating on creating larger yet predictable spheres of ablation. Injection of hypertonic fluids Aimed at increasing tonicity of tissues and decreasing impedance within tumor Multiple Probes Multiple treatment areas within the same treatment session. This is commonly used. Chemoembolization Two strike concept making the RF area more succeptable to chemo or vise versa. Heat Activated Liposomes Liposomes that carry chemotherapy across membranes can be activated by heat.

20 Pretreatment with Doxorubicin This particular patient was chosen for a new protocol which involved pretreatment with systemic doxorubicin. Patient was in the 48 hour Pre-treatment group. Optimal timing of treatments is currently under investigation. Recent studies by Goldberg et. al. (2001) in mice have showed the ability to increase treatment area by possibly increasing the tumor cell sensitivity to RFA. Diameter of treatment area has been shown to double with combined treatment.

21 CT Guidance

22 Post Ablation Imaging Immediate post ablation imaging has been shown to have limited ability to correctly differentiate kill area and residual tumor. The kill area will appear hypodense and non enhancing The Damaged Area enhances as there is vascular permeability and inflammatory response. CT imaging is recommended after 2 weeks and is usually done at 6 weeks post ablation.

23 CT with contrast post procedure shows area of hypointesity consistent with coagulative Jay Patti necrosis. Some mild enhancement can be seen in the periphery which may represent residual tumor of inflammatory response

24 Summary Indication hepatocellular carcinoma, colon metastases to the liver, renal cell carcinoma, chordomas, osteoid osteomas, fibroids, cutaneous metastases, and other tumors are under investigation. Procedure Using an insulated probe with the tip exposed, Radiofrequency is administered at a specific site guided by CT or US. Pathophysiology of Tissue Damage Ionic agitation to ideal temperature coagulative necrosis Limitations and Working Around Them Char Broil, Heat Sink, Tissue Conduction, Collateral Damage Current RFA Research Hypertonic Fluids, Chemoembolization, Multiple Probes, Liposomes

25 References 1. Goldberg SN, Saldinger PF, Gazelle GS, Huertas JC, Stuart KE, Jacobs T, Kruskal JB. Percutaneous Tumor Ablation Increases Necrosis with Combined Radiofrequency Ablation and Intratumoral Doxorubicin Injection in the Rat Breast Tumor Model. Radiology 2001;220(2) Gazelle GS, Goldberg SN, Solbiati L, Livraghi T. Tumor Ablation with Radiofrequency Energy. Radiology 2000;217: Livraghi T, Goldberg SN, Lazzaroni S, Meloni F, Solbiati L, Gazelle GS. Small Hepatocellular Carcinoma: Treatment with Radiofrequency Ablation versus Ethanol Ablation. Radiology 1999;210: MDConsult.com Surgery Text Book. and many more

26 Acknowledgements Special thanks to Larry Barbaras and Cara Lyn D amour, our Webmasters Dr. Gillian Lieberman Pamela Lepkowski