Selective internal radiotherapy (SIRT, or radioembolization) fights liver cancer that cannot be operated on, or can no longer be operated on. In this procedure, several million tiny spheres containing the radioactive nuclide yttrium-90 are sent directly into tumor cells. To get the beta radiation there, a catheter is placed from the inguinal artery to the hepatic artery. The beta emitters flow with the blood into the diseased organ and usually get stuck in the small capillary vessels of the liver. There they destroy the tumor from the inside with radiation and at the same time block further blood transport to the liver. In this way, the affected area can be starved. The radiation only has a very short range of a maximum of around eleven millimeters, so healthy liver tissue is spared.
What is selective internal radiotherapy?
The therapy is most often used for advanced primary liver tumors as well as liver metastases resulting from cancers of other internal organs. The beads average one-third the diameter of hair. They are biodegradable and have only a marginal effect on liver tissue. The beta emitter yttrium-90 has a half-life of 64 hours. After eleven days, the material has delivered 94 percent of its radiation dose and decays into the stable isotope zirconium-90. SIRT can significantly reduce the size and number of liver tumors. The effectiveness of the therapy depends on the extent to which the cancer is concentrated in the liver, because only there can the beta radiation achieve the desired effect. In addition, the organ should not yet be seriously impaired in its ability to function and the patient should have a life expectancy of at least three months. If these conditions are met, selective internal radiotherapy can prolong the survival time of patients with the disease. The aim is also to improve the quality of life of those affected. SIRT is often used at an early stage of liver cancer in combination with chemotherapy. Primarily, radiotherapy is also suitable for downgrading an inoperable liver tumor to an operable one. This means a significant reduction in the size of the affected tissue. For classical surgery, at least a quarter of the functional liver epithelium must be preserved. This status may be achievable with SIRT. In some cases, the malignant tissue has even been completely eliminated with the help of radiotherapy. As a treatment method, it directly intervenes in the main blood supply of tumors to the liver. In most cases, this occurs via the hepatic artery, through which the beta emitters travel. This irradiation from the inside is much more effective than from the outside, as in conventional radiotherapy, for example. In addition, a higher dose of radiation can be used directly against cancer cells from the inside than from the outside.
Function, effect, and goals
Selective internal radiotherapy is performed and monitored by an interdisciplinary team of physicians. Liver specialists and oncologists first thoroughly familiarize themselves with the patient’s medical history. The patient must be free of previous diseases to the extent that he or she can withstand partial occlusion of blood vessels without any problems. This initial procedure is necessary to ensure that the radioactive beads actually travel only to the liver and not to other internal organs as well. Here, direct blood routes to the lungs as well as detours via small side vessels to the stomach, gall bladder and pancreas are possible, but must be safely excluded. However, these complications have occurred extremely rarely to date. The next step is to determine the appropriate dose of microspheres, which is then finally administered to the patient. Placing the catheter up to the liver usually takes around 90 minutes. It is done under local anesthesia with a comparatively small incision. Afterwards, however, measurements must be taken for a longer period of time to determine the extent to which radioactive radiation may penetrate to the lungs. After a rest period of two to four days at the most, the patient is allowed to leave the clinic. SIRT is a comparatively well-tolerated form of treatment. After insertion of the tube, patients may experience pain in the upper abdomen, nausea and a slight fever. Over a few days or a few weeks, the patient may be affected by fatigue, poor appetite and listlessness.
Risks, side effects and dangers
Immediately after administration of the radioactive beads, it is imperative that the patient be on bed rest for five to six hours to prevent any secondary bleeding in the groin area from causing secondary damage. If necessary, prophylactic medication is used to counteract possible swelling of the liver. The same applies to so-called radiation hepatitis, which can affect healthy liver tissue in rare cases. On the day of catheterization, the patient is also given a saline solution via the vein. If nausea and vomiting occur beyond the normal level, special medications and also painkillers are available. However, the side effects after the minor procedure usually subside three to four days later. According to current knowledge, selective internal radiotherapy cannot completely cure a tumor, but it can contain the cancer to such an extent that it can no longer be detected by standard examination methods. In any case, regular follow-up measures under the responsibility of an oncologist are advisable after the intervention. As a rule, these take place at intervals of three months. The specialist can also initiate appropriate therapeutic measures at any time or, if necessary, proceed to a repeat SIRT.
