Applied Radiology

Dr. Hanson has just completed his interventional radiology fellowship at the Hospital of the University of Pennsylvania in Philadelphia, PA. He received his MD from the University of Iowa in Iowa City in 1995 and completed his diagnostic radiology residency at the University of Utah in Salt Lake City in 2000. Dr. Hanson will be joining Medical X-Ray Consultants in Eau Claire, WI, in July 2001.

Dr. Michael Soulen is an Associate Professor of Radiology and Surgery at the Hospital of the University of Pennsylvania, Philadelphia, PA. He has a special interest in chemoembolization and other loco-regional cancer therapies.

A variety of ablative techniques have been developed to complement the traditional surgical and oncologic approaches used in treating tumors. These techniques include transarterial chemoembolization, percutaneous ablation with chemicals such as alcohol or acetic acid, or percutaneous treatment with radiofrequency ablation or cryotherapy. The clinical management of primary and metastatic hepatic tumors can be especially challenging. Therefore, regional and local ablative techniques used in the treatment of hepatic tumors have been studied extensively. More recently, these techniques have been used in treating a variety of other tumors, including renal and osseous tumors.

Hepatic malignancies

Hepatocellular carcinoma (HCC) has a worldwide annual incidence of more than 1 million people, making it one of the most common fatal malignancies. Colorectal carcinoma is the third leading cause of death due to cancer in the United States and is frequently metastatic to the liver. Surgical excision is the ideal treatment for these tumors, but only 5% to 15% of patients are candidates, and the 5-year survival is 20% to 40%. ^1-4 Systemic chemotherapy and external beam radiation therapy have limitations due to poor tumor response and hepatic toxicity. Regional and local ablative techniques continue to be refined in an attempt to achieve better outcomes for the large number of patients who are not operative candidates.

Regional ablation of hepatic malignancies

Chemoembolization

The intra-arterial administration of chemotherapeutic and embolic agents has many potential advantages, including increased concentration and dwell time of the chemotherapeutic agents within the liver, decreased systemic toxicity, the development of tumor ischemia, and ischemia-induced failure of cell membrane pumps leading to increased intracellular drug levels. ⁵

Patient selection --Candidates for chemoembolization must have their tumor confined to the liver, or the tumor must be liver-dominant and a significant source of morbidity and mortality. This generally includes patients with HCC and liver metastases from colorectal carcinoma, ocular melanoma, islet cell tumors, carcinoid tumor, and sarcomas. Occasionally, patients with liver metastases from other sites also are candidates. Assessment of portal venous flow is necessary, and if it is diminished the presence of collateral hepatopedal flow must be demonstrated. ⁶ Poor hepatopedal flow may necessitate more selective chemoembolization. Biliary obstruction increases the risk of biliary necrosis. Jaundice and hepatic encephalopathy are absolute contraindications. Patients with >50% liver volume replaced by tumor, lactate dehydrogenase (LDH) >425 IU/L, aspartate aminotransferase (AST) >100 IU/L, and total bilirubin >= 2 mg/dL are at increased risk for acute hepatic failure. ⁷

Procedure -- The procedure for chemoembolization at the University of Pennsylvania has been well described. ⁵ Three chemotherapeutic drugs are dissolved in contrast and emulsified with iodized oil. Polyvinyl alcohol (PVA) particles measuring 150 to 250 µm are added toward the end of the procedure. Embolization is performed until there is peripheral arterial pruning but not complete stasis of flow (figure 1). Standard orders for patients are listed in figure 2. Some institutions use different chemotherapeutic and embolic agents. Some institutions do not use iodized oil. The potential advantages of iodized oil include its drug-carrying ability, tumor-seeking ability, and embolic properties. ⁸ However, the dose of iodized oil should be <0.2 mg/kg to avoid liver and pulmonary toxicity. The final angiographic images help determine the need for repeat treatment, which usually is performed at 3- to 4-week intervals. Typically, 2 to 4 treatments are performed in a lobar or segmental distribution. Response is assessed using tumor markers and cross-sectional imaging. Distinguishing residual or recurrent disease from anatomic changes caused by the ablative procedure itself can be challenging. Murphy et al ⁹ proposed a window/level setting of 110/75 Hounsfield units to improve lesion detection on post-chemoembolization computed tomography (CT). Iman et al ¹⁰ used diffusion-weighted magnetic resonance imaging (MRI) to evaluate tumor necrosis post-chemoembolization and have found it especially useful with HCC. Fluoro-deoxyglucose-positron emission tomography (FDG-PET) has been found to be more accurate than CT in evaluating the efficacy of chemoembolization of HCC and colorectal metastases. ¹¹

Complications -- Major complications occur in 3% to 4% of cases and include hepatic insufficiency or infarction, hepatic abscess, tumor rupture, surgical cholecystitis, and nontarget embolization. Geschwind et al ¹² describe no significant deterioration in liver function following chemoembolization in 33 patients with Childs class A and 22 patients with Childs class B. The formation of liver abscesses has been associated with prior bilioenteric anastomosis despite standard antibiotic prophylaxis (figure 3). Liver abscesses occurred in 7 of 157 patients (8 of 397 procedures) with 6 of these patients having had a prior Whipple procedure. ¹³ Additional antibiotic prophylaxis and bowel preparation may be of benefit in this patient group.

Results --For HCC treated palliatively in a combined series of 800 patients from the United States, Europe, and Asia there was a 60% to 83% response rate characterized by decreasing serum alpha-fetoprotein and tumor volume. Probability of survival was 54% to 88%, 33% to 64%, and 18% to 51% at 1, 2, and 3 years, respectively. ^14-20 A European multicenter trial of 100 patients (90% Stage I) showed survival rates of 62% and 38% at 1 and 2 years compared with survivals in nontreated patients of 43% and 26%. ²¹ A French multicenter trial showed similar results in more advanced disease (62% Stage II or III) with treated survival of 64% and 38% compared with nontreated survival of 18% and 6% at 1 and 2 years, respectively. ²² Prognostic factors include tumor size and type, staging, Childs class, and the degree of oil uptake by the tumor. ^14-24 Uraki et al ²³ reported a 23-month mean survival for patients with nodular-type HCC (11 patients) compared with a 10-month mean survival for patients with diffuse-type HCC (39 patients). Portal vein invasion was not found to be a significant prognostic factor. Balzano et al ²⁵ have shown a 100% 12-month survival (43% at 2 years, 29% at 3 years) in 7 patients receiving chemoembolization (cisplatin and gelfoam) for recurrent HCC following liver transplantation. Patients received 4 to 12 cycles of chemoembolization repeated every 6 to 8 weeks.

Several Phase II studies have been performed for metastatic colorectal carcinoma demonstrating a 60% to 70% response rate and a 2-year median survival. ^26-29 The American College of Radiology Imaging Network (ACRIN) is funding a randomized multicenter trial of systemic chemotherapy, with or without chemoembolization, to prospectively evaluate the survival benefit of chemoembolization for metastatic colon carcinoma.

With traditional therapy, median survival of metastatic ocular melanoma is 2 to 6 months. Median survival for 30 patients treated with chemoembolization for ocular melanoma (cisplatin and polyvinyl alcohol particles) at M.D. Anderson Cancer center was 11 months. ³⁰ Mean survival for 28 patients treated with chemoembolization for ocular melanoma (BCNU [Carmustine, Bristol-Myers Squibb Oncology/Immunology Division, Princeton, NJ], Ethiodol [Savage Laboratories, Melville, NY], and gelatin sponge) at Thomas Jefferson University Hospital was 208 days (range 4 to 82 days). Tumor burden significantly influenced survival. Patients having <20%, 20% to 50%, and >50% liver replacement by tumor survived a mean of 471, 199, 107 days, respectively ( P = 0.0018). ³¹ Chemoembolization of hepatic metastases from breast carcinoma has been shown to decrease or stabilize the hepatic tumor burden in 7 of 8 patients treated at the University of Pennsylvania with the potential to palliate symptoms. However, mean survival following the first embolization is only 6 months due to development or progression of extrahepatic metastatic disease. ³²

Results in neuroendocrine tumors-- Bland embolization of neuroendocrine tumors, especially carcinoid tumors, can lead to cessation of symptoms for 5 to 10 months in 90% to 100% of patients. Chemoembolization can increase the cessation of symptoms to nearly 2 years, but there is a concern for increased complications compared with bland embolization. ^5,33-35 The release of vasoactive factors can lead to hypertensive crises as well as hypotension. Nowakowski et al ³⁶ retrospectively evaluated 159 hepatic chemoembolization procedures in 80 patients with metastatic carcinoid tumor. Hypertensive or hypotensive events occurred in 4.4% of cases and were all controlled periprocedurally. Patients were premedicated with octreotide (100 to 500 mg every 8 hours), hydrocortisone (100 mg every 6 hours), and ondansetron. An anesthesiologist administered conscious sedation. There was 1 periprocedural death due to hepatorenal syndrome, but no deaths were reported due to the release of vasoactive factors. At the University of Pennsylvania, 24 patients were treated for hepatic metastases of neuroendocrine tumors with a major complication rate of 6.4% and 1 patient death due to liver failure. There was morphologic tumor regression in all 19 patients for whom follow-up imaging was available. Survival was roughly estimated in this small sample size as 71% and 58% at 1 and 2 years, respectively. ³⁷

Newer therapies

The treatment of HCC with doxorubicin hydrochloride adsorbed to magnetic targeted carriers is being evaluated by Goodwin et al ³⁸ at UCLA. An external magnet positioned over the tumor was activated during infusion of the agent into the hepatic artery. Patients were evaluated with MRI immediately following the procedure to assess the location of the magnetic targeted carriers. Tumor size was evaluated with CT at baseline and at 28 days. Targeting of the agent within the tumor was achieved in 19 of the 21 patients. No drug was detected in the systemic circulation. Preliminary data in 10 patients showed tumor progression in only 1 patient, stabilization in 5 patients, and minor or partial responses in 4 patients. Dosing of the agent based on size of the tumor is being investigated. Coldwell et al ³⁹ are evaluating the treatment of primary and secondary hepatic tumors using intra-arterial embolization with Yttrium-90 glass microspheres. Patients received an average radiation dose of 146 Gray. Complications reported in 13 patients include 1 case of intrabdominal hemorrhage and 1 case of stroke 3 days following embolization. Additional outcomes have yet to be reported.

Percutaneous ablation of hepatic malignancies

Ablation of hepatic malignancies using a direct percutaneous approach involves chemical and thermal techniques. Chemical ablation includes absolute alcohol or acetic acid injection, and thermal techniques consist of radiofrequency, cryo-, microwave, laser, or high-intensity ultrasound ablation. Chemical ablation causes coagulative necrosis due to cytoplasmic dehydration, denaturation of cellular proteins, and small vessel thrombosis. Thermal ablation creates a focal area of tissue coagulation dependent on the local temperature produced by the specific device.

Patient selection

Patients with unresectable, small, intrahepatic tumors that can be localized with ultrasound or CT imaging are the best candidates for direct percutaneous techniques. Patients with resectable tumors who are poor operative candidates may also be considered. Patients with tumors >3 cm in size or >3 in number have a poorer response to these techniques. ⁵

Percutaneous ethanol injection

Percutaneous ethanol injection (PEI) has been shown to be safe, effective, and inexpensive in treating small (<3 cm), unifocal hepatocellular carcinomas. ^40,41

Procedure -- The procedure for PEI involves conscious sedation and can be done on an outpatient basis. Using sterile technique, following local anesthesia with Lidocaine, a 20-gauge needle (for example, a diamond tip, multi-sidehole Bernadino needle) is advanced under ultrasound or CT guidance to the far wall of the tumor and then slowly withdrawn as the ethanol is injected. Injection is discontinued if flow into adjacent structures is noted. Ethanol is brightly echogenic on ultrasound, likely due to microbubbles injected with the ethanol. Ethanol is hypodense on CT. The needle is left in place for 1 to 2 minutes and then withdrawn while aspirating. The total volume is calculated using the radius of the tumor and the formula for the volume of a sphere (4/3¼ [r+0.5] ³ ). The addition of 0.5 cm to the radius allows for a "tumor-free" margin. A 3-cm lesion therefore requires a total volume of 33 mL (Table 1). Lesions >4 cm usually require additional sessions due to alcohol toxicity (1 mL/kg). Follow-up evaluation is performed with CT, MRI, or PET and tumor markers.

Complications -- Pain and nausea during the procedure as well as fever and elevated liver enzymes in the subsequent few days are not uncommon. More significant complications occur in 1% to 4% of patients.

Results -- Complete necrosis occurs in 60% to 80% of patients, but 64% to 98% of patients develop new tumors in 5 years with a 5-year survival of 30% to 50%. ⁴² Patients with Childs class C have not demonstrated improved survival. ⁴³ Use of ethanol following chemoembolization can improve ethanol diffusion. One study showed patients with tumors 3 to 8 cm in size having improved survival with ethanol following chemoembolization versus chemoembolization alone. ⁴⁴ However, there are disadvantages to PEI. Multiple sessions are usually required, and treatment of multifocal disease is limited. PEI is less effective in treating metastatic disease, such as colorectal carcinoma, due to limited diffusion through this relatively firm tumor. ^40,41,45 Because of these limitations, PEI is being replaced by other techniques in many centers.

Acetic acid ablation

Acetic acid has been shown by Ohnishi et al ⁴⁶ to have superior cell kill at lower volumes compared with ethanol. Acetic acid has a higher degree of necrosis, more homogeneous diffusion, and is able to infiltrate tumor septae and capsules unlike ethanol.

Procedure -- Acetic acid is administered in a similar fashion to ethanol. Because of the increased diffusion, the dose is reduced by 1/3 compared with ethanol (Table 1) and the injection is performed very slowly. An injection >20 mL has the potential risk of renal toxicity and metabolic acidosis. As with alcohol, multiple sessions can be performed if necessary.

Results -- In a prospective randomized trial, Ohnishi et al ⁴⁶ demonstrated a need for fewer treatment sessions and decreased volume with injections of acetic acid (31 patients) compared with ethanol (29 patients) for treatment of small, HCC (<3 cm). Cancer-free survival at 1 and 2 years was 83% and 63% with acetic acid, compared with 59% and 33% with ethanol. There were no major complications. Liang et al ⁴⁷ treated 22 HCC nodules with a single acetic acid injection. Seventeen of 21 nodules evaluated on follow-up CT (at 6 to 29 months) showed complete necrosis. Injection was terminated prematurely in the other four nodules due to pain or intravasation of acetic acid. Three of these nodules showed complete necrosis following a second injection. Recently, acetic acid has been shown in vivo to produce significantly increased parenchymal diffusion and larger zones of necrosis in porcine liver. ⁴⁸ The diffusion characteristics of acetic acid may make it a useful agent in treating metastatic disease to the liver.

Radiofrequency ablation

The use of radiofrequency ablation (RFA) for treating hepatic neoplasms has received much attention. The devices used in RFA produce alternating current in the radiofrequency range. This leads to ionic agitation and frictional heat extending into the tissues adjacent to the device with subsequent development of coagulative necrosis. Three radiofrequency devices are available in the United States (figure 4). The devices have received approval for treatment of surgically unresectable hepatic neoplasms by the Food and Drug Administration. Each system has differences in electrode and generator design. The RITA system (RITA Medical Systems, Mountain View, CA) uses 4 to 9 retractable needles housed in a 14- or 15-gauge outer needle. Temperature is monitored at the tips of the electrodes and wattage is adjusted up to a maximum of 150 W to maintain a target temperature for a set period of time. The ablation diameter is reported as 3 to 5 cm with the RITA Starburst XL. The RadioTherapeutics LeVeen Needle Electrode (RadioTherapeutics Corp., Sunnyvale, CA; distributed by Boston Scientific Corp., Burlington, MA) has 10 to 12 retractable needles housed in a 14- to 15-gauge outer needle with a deployed diameter of 2, 3.5, or 4 cm. A 200-W generator has recently been released. Instead of using tissue temperature, the device uses an ablation algorithm based on tissue impedance that increases with tissue desiccation. An anticipated maximum ablation diameter of 4 cm is reported by the manufacturer. The Radionics device (Tyco Healthcare, Burlington, MA) uses a hollow-tip 17-gauge needle as a single cooled or noncooled electrode or as a Cool-Tip cluster of three parallel electrodes. Cooling is performed using a saline pump and is thought to help reduce tissue impedance adjacent to the electrode tip. The power is supplied by a 200-W generator and is adjusted according to tissue impedance. Tissue temperature can be measured with a thermocouple at the electrode tip. A maximum ablation diameter of 4 to 5 cm is reported.

Procedure -- Radiofrequency ablation can be performed percutaneously, laparoscopically, or with laparotomy. Evaluation of the number of tumors and their size is important. Patients with fewer than 5 tumors <5 cm diameter, and with no extrahepatic tumors are good candidates. ^49-52 Tumors numbering fewer than 2 and approaching 5 cm in size become difficult to fully ablate. ⁵³ For a device producing approximately a 3-cm ablation, the largest tumor treated with a single ablation should be 2 cm, allowing for a tumor-free margin of 5 mm. Most devices produce approximately a 3-cm ablation, so the largest tumor treated with a single ablation should be 2 cm, allowing for a tumor-free margin of 5 mm. Larger tumors require overlapping ablations. One method involves creating overlapping spheres, which yields only 25% more ablation margin using two spheres in each plane (6 spheres total). Another method involves creating overlapping cylinders. ⁵⁴ Each ablation can last 10 to 30 minutes. Careful preprocedural evaluation of the tumor is important to assess the best approach, identify the location of adjacent structures that may increase the complication risk, and determine the presence of vascular structures acting as potential heat sinks diminishing the thermal effect. Patients with Childs class C, active infection, or uncorrectable coagulopathy are not considered good candidates. Hepatocellular carcinoma and metastatic colon carcinoma are the most common neoplasms treated. Metastatic tumors from breast, pancreas, stomach, and neck as well as neuroendocrine tumors also have been treated. ⁵³ The choice of approach is debated in the literature. A percutaneous approach with ultrasound or CT guidance can be performed on an outpatient basis with conscious sedation and with minimum morbidity (figure 5). Laparoscopy allows direct imaging of the liver with a high-frequency ultrasonic transducer. This improves detection and visualization of small tumors and affords more accurate staging. ^53,55-57 In addition, a Pringle maneuver can be performed (occlusion of the hepatic artery and portal vein at the porta hepatis during treatment), which can increase the ablation margins. ⁵² However, laparoscopy is more invasive, and the approach is somewhat limited, depending on the sites chosen for the laparoscopic ports on the abdominal wall. Laparotomy has advantages similar to laparoscopy and improves access to the tumor, allowing possible resection or cryoablation, with the disadvantage of performing an open procedure. ⁵⁸ The RITA and Radionics systems allow cauterization of the percutaneous tract. A shortened 6F or 7F sheath can be placed on the RadioTherapeutics electrode prior to insertion and later can be used for tract embolization using gelfoam pledgets (figure 5). The RadioTherapeutics system soon will have a coaxial needle electrode system with an introducer sheath (CoAccess, RadioTherapeutics Corporation, Sunnyvale, CA) to allow the introduction of a biopsy gun, gelfoam, or other device. ⁵⁹ Follow-up evaluation usually is performed with CT (3-phase for HCC and 2-phase for colorectal metastases) and tumor markers. Newer imaging methods, as discussed with chemoembolization, may afford earlier detection of recurrence or new malignancy.

Complications -- Increased pain can occur with ablation of tumors near the liver capsule, gallbladder, main portal vessels, or diaphragm. Ablation of tumors near the gallbladder can cause cholecystitis. Ablation of tumors near the portal venous confluence increases the risk of biliary damage. Thermal necrosis in bowel loops adjacent to treated subcapsular lesions also can occur. Preventing thermal injury to the skin adjacent to the grounding pads requires appropriate placement of the pads on the thighs. ^53,60,61 The overall complication rate is <5%.

Results -- Complete tumor necrosis rates of 50% to 95% have been reported. However, rates as low as 25% have been reported for tumors >5 cm in size. ^53,62 The best local recurrence rate reported is 1.8% for primary and metastatic tumors following laparotomy and the use of a Pringle maneuver for 3 minutes. ⁵² Recurrence rates are higher with metastatic disease, most likely due to difficulty in detecting small lesions at the time of treatment. At the University of Pennsylvania, the cumulative risk of local recurrence is 15%, and the risk of new lesions is 64% at 1 year.

The use of modified Pringle maneuvers has been studied, including balloon occlusion of the hepatic artery or gelatin sponge embolization of hepatic arterial branches. For nodules with diameters 3.5 to 8.5 cm treated with RFA and a modified Pringle maneuver, Rossi et al ⁶³ reported a local recurrence rate of 19%, and an overall intrahepatic recurrence rate of 45% at 1 year. These results may reflect preserved portal venous flow to the tumor, preventing formation of an adequate tumor-free margin. Curley et al ⁵² treated 169 hepatic tumors with RFA performed percutaneously (31 patients) or with laparotomy using a Pringle maneuver (92 patients). Median tumor size was 2.4 cm in the patients treated percutaneously and 3.8 cm in those patients treated surgically. Local recurrence was 1.8% at 15 months, and 72% of patients were free of tumor. Wood et al ⁶⁴ treated 231 patients with unresectable hepatic tumors with RFA performed via percutaneous approach (25 patients), laparoscopy (27 patients), or laparotomy (39 patients). Intrahepatic ultrasound detected additional disease not evident with other imaging in 38% of cases. Resection and/or cryoablation were used in 38 of 84 patients. Median tumor size was 2 cm. The complication rate was 8%. Local recurrence was 18% at 9 months, and 43% of patients were free of tumor.

RFA has been shown to be more efficacious and to require fewer treatment sessions compared with PEI in treating HCC. Livraghi et al ⁶² demonstrated a higher rate of complete necrosis in small HCC treated with RFA (90%) versis PEI (80%). In addition, RFA required an average of 1.2 treatment sessions per tumor, compared with 4.8 sessions for PEI. RFA had a slightly higher complication rate, often related to tumor location and heating of adjacent organs. In these cases, the use of PEI may be more appropriate. As mentioned, PEI is not useful in treating metastatic disease. RFA has been shown to be cost-effective compared with palliative care in the treatment of HCC and metastatic colorectal carcinoma. ⁶⁵ Radiofrequency ablation has been used as salvage therapy for refractory carcinoid metastases with promising results reported in 3 patients. ⁶⁶

Other ablation techniques

Cryosurgical ablation has higher morbidity than RFA but still is used to treat larger unresectable hepatic neoplasms. ⁵⁸ In a prospective, nonrandomized trial, Pearson et al ⁶⁷ demonstrated a 40.7% complication rate, including 1 postoperative death, with intraoperative cryoablation compared with a 3.3% complication rate and no deaths with intraoperative RFA. Tumor recurrence was 13.6% for cryoablation and 2.2% for RFA at 15 months.

Microwave coagulation therapy and laser photocoagulation are being used to treat hepatic malignancies in Europe and Japan. Shibata et al ⁶⁸ recently reported that microwave coagulation therapy was as effective as surgery in the treatment of metastatic colorectal carcinoma. Thirty patients were randomized to microwave coagulation therapy or surgery. Mean survival for patients receiving microwave coagulation therapy during laparotomy was 27 months compared with a mean survival of 25 months for patients receiving hepatic resection. (Three-year survival rates were 14% and 23% for microwave versus surgery, P = nonsignificant.) The average tumor size was 2.7 cm. Complication rates were not significantly different, but patients receiving microwave coagulation therapy had decreased blood loss. Microwave coagulation therapy is most ideal in tumors <2 cm in size. It has been shown to be effective in HCC in a previous study. ⁶⁹ Laser photocoagulation therapy has been described as effective, but much more interest centers on RFA in this country. ⁷⁰

Combination therapy of hepatic malignancies

Accurately ablating the tumor and achieving adequate margins are crucial. Effective tumor detection also is important. Since hepatocellular carcinomas are supplied by the hepatic artery, a combined approach of hepatic arterial occlusion followed by radiofrequency ablation may prove to be beneficial. Occlusion of the hepatic artery can be performed with a modified Pringle maneuver using an occlusion balloon or gelfoam, or a course of chemoembolization can be administered prior to RFA. Using a Pringle maneuver during RFA performed during laparoscopy or laparotomy also has shown potential, as both the hepatic artery and portal vein can be occluded. As discussed, the latter methods also can have improved tumor detection in metastatic disease. Ultimately, combination therapy will have to be modified for each case based on tumor type, size, and number, as well as patient risk factors. A team approach to tumor management by oncologists, surgeons, and radiologists can provide the best care for these difficult cases.

Therapy of other tumors

Chemoembolization or RFA is also being used to treat malignancies elsewhere in the body.

Osseous tumors

RFA of both benign and malignant osseous tumors is being performed. Specifically, RFA is being used to treat osteoid osteomas. The conventional therapy for these benign, painful tumors is medical therapy with aspirin or nonsteroidal anti-inflammatory drugs or surgical or percutaneous resection. RFA of these tumors offers a less invasive approach and can be performed on an outpatient basis using CT guidance and general anesthesia or conscious sedation. Penetration of the cortex with a core bone biopsy needle and placement of the radiofrequency probe directly into the nidus are important. Both single and multi-electrode devices have been used. The procedure has been found to be safe and effective with pain relief reported in the literature in 83% to 91% of cases. ^71-73 The use of RFA in primary and metastatic malignant tumors alone and in combination with radiation therapy is also being evaluated at many centers. There may be a role for RFA in local tumor control and management of pain.

Renal tumors

Intra-arterial embolization of renal angiomyolipomas for the prevention of hemorrhage is safe and effective. ⁷⁴ Angiomyolipomas >= 4 cm are symptomatic in 82% to 94% of cases and hemorrhage spontaneously in 50% to 60% of cases. A variety of embolic agents have been used, including absolute alcohol, iodized oil, particles, and coils. The first two agents have the theoretical advantage of penetrating to the capillary level, causing effective tumor necrosis and avoiding repeat therapy due to the development of collaterals. The disadvantage of ethanol is the potential for reflux and non-target embolization and thrombosis. High quality, digital subtraction angiography performed prior to embolization is important in evaluating for the presence of aberrant anatomy and possible capsular collateral vessels communicating with lumbar and mesenteric vessels. An occlusion balloon can be used to prevent the reflux of ethanol. However, care must be taken, as aneurysm rupture has been reported as a complication with this technique. In smaller arteries, superselective catheters can be used to deliver the combination of ethanol with iodized oil in a 3:7 ratio (figure 6). Both methods have been performed at the University of Pennsylvania and have been found to be 90% effective in 5 patients over a mean follow-up period of 21 months. ⁷⁵ Clinical symptoms disappeared in 13 of 14 patients treated by Han et al ⁷⁴ over a mean follow-up period of 33 months. Han et al ⁷⁴ also demonstrated a decrease in the angiomyogenic components of the tumors on follow-up CT. The treatment of renal cell carcinoma with radiofrequency ablation is being evaluated. This may prove to be useful in those patients who are not operative candidates or for the treatment of small, localized carcinomas. ^76,77

Other tumors

Coldwell et al ⁷⁸ are evaluating the use of intra-arterial platinol in the treatment of radioresistant head and neck squamous cell carcinomas. A dose of 75 mg/m ² platinol was delivered every 2 weeks following superselective arterial catheterization. Follow-up CT was performed. Fourteen patients received an average of two infusions with complete response in 7 (50%), partial response in 3 (21%), stabilization in 2 (14%), and progression in 2 (14%). The treatment of desmoid tumors with percutaneous acetic acid injection is being performed at the University of Pennsylvania.

Conclusion

The role of the interventional radiologist in oncologic therapy is expanding. The treatment of hepatic tumors with regional and local ablative techniques continues to be refined, and similar techniques are being developed for the treatment of a variety of other tumors in the body. A combination of the available techniques most likely will offer the best therapy. The interventional radiologist has the opportunity to be an important member of the oncologic team, offering insight and assistance in the management of a variety of challenging cases. *