One of our greatest challenges in treating cancer is destroying the tumor without damaging the healthy tissues that surround it. In interventional radiology, we use a variety of techniques that minimize this concern by specifically targeting only those cells that are cancerous.
by Ross A. Christensen, MD
Interventional radiology (IR) is an area of specialization within the field of radiology which uses various radiology techniques (such as X-rays, ultrasound or CT scans) to place devices inside the body that diagnose or treat disease. Newer IR treatments for cancer fall into two categories: ablative and embolization techniques, the newest of which is Selective Internal Radiation Therapy (SIRT). The type of technique used depends on the size, location and type of the tumor being treated.
Ablative therapies use heat or cold to kill cancerous cells. Using a needle guided by CT, ultrasound or X-rays, we deposit either heat, cold or electrical energy into the tumor, which enables us to attack the tumor while preserving surrounding tissues. The most commonly used ablative techniques include radiofrequency or cryotherapy; microwave and ultrasound are more recently introduced techniques. Cryotherapy (or “cold” therapy) freezes and kills the tumor cells, preserving the surrounding normal structures.
Ablative therapies have a wide variety of uses, including treatment of tumors in the abdomen, chest, lung, breast and extremities. They can be especially helpful in patients whose cancers have metastasized or spread to their bones. Bone cancer can be difficult to treat; often, the only treatment option these patients have is radiation therapy, and the amount of radiation they can undergo may be limited because of damage to surrounding normal tissue. Using ablative therapy, we can often kill the tumor without damaging normal tissue. If necessary, we also can place bone cement in the site to improve the strength and structure of the bone.
Whether or not ablation is an appropriate treatment depends on where the tumor is located and what other structures, such as nerves or blood vessels, might be affected by the needle passing through them on its way to the tumor. The key is knowing what we can do safely with a minimal amount of risk to surrounding normal tissues.
Selective Internal Radiation Therapy
Selective Internal Radiation Therapy (SIRT) uses advanced IR techniques to treat liver cancer. In the past, it has been extremely challenging to treat liver tumors with radiation without destroying healthy liver tissue, which then increases the risk of liver failure. SIRT delivers radiation directly to the tumor through millions of microscopic resin beads that are roughly one-third the diameter of a strand of human hair and contain a type of radiation called Yttrium-90. The radioactive beads are injected into the tumor from the artery to the liver through a small tube called a catheter. When the tumor absorbs the beads, the radiation goes to work destroying the cancer. Since the radiation from Yttrium- 90 does not travel more than a couple of millimeters away from the bead, it targets tumor cells without harming healthy liver tissue. Through SIRT, we can deliver hundreds of times the radiation to liver tumors than through conventional radiology treatments.
SIRT is especially suited to liver cancer because the liver has two sources of blood supply. A liver tumor gets 80 to 90 percent of its blood supply from the hepatic (liver) artery, whereas a normal liver gets most of its blood supply through the portal vein. This dual blood supply enables us to deliver the radioactive beads through the hepatic artery to both target the tumor and cut off the tumor’s blood supply, while the rest of the healthy liver continues to get the blood it needs through the portal vein.
We can also use the same technique to deliver chemotherapy to liver tumors in a process known as chemoembolization. Through this technique, we inject chemotherapy through the catheter directly into the liver tumor and cut off the blood supply to the tumor as in SIRT. Chemoembolization allows us to increase the amount of chemotherapy drugs in the liver by 40 to 100 times over standard delivery through a blood vein. Plus, we can do so without exposing the entire body to the effects of chemotherapy.
We are currently studying how to use IR to alter the genetic structure of tumors and organs to help treat or even prevent disease. For example, stem cell researchers are exploring the possibility of implanting stem cells inside the liver of people with diabetes; the stem cells would develop into pancreatic cells and produce more insulin. Researchers are also looking into ways to implant plastic stents that contain medication or gene therapy into tumors or organs; the stents would eventually dissolve, leaving the treatment in the tissue to continue to fight the disease over time.
Ross A. Christensen, M.D., is an interventional radiologist at Scripps Memorial Hospital La Jolla. For more information or to schedule an appointment, please call 1-800-SCRIPPS 1-800-727-4777.