Selective internal radiotherapy (SIRT)
Selective internal radiotherapy (SIRT)
SIRT stands for selective internal radiotherapy and is a procedure using a radioactive isotope for the targeted therapy of malignant tumors in the liver. It represents an important therapeutic option for patients, where other therapeutic procedures (surgery, radiofrequency ablation, chemotherapy etc.) are no longer possible or no longer effective.
SIRT involves the targeted introduction of radioactive Yttrium-90 (Y-90) microspheres (so-called glass microspheres) into the liver tumors. This is possible because liver tumors, in contrast to the healthy tissue, are primarily supplied via the hepatic artery. SIRT makes use of this difference in blood supply so that the radioactive glass microspheres are transported directly to the tumors in the liver via a catheter inserted into the groin. Due to their very small diameter, the microspheres can easily distribute themselves in the tumor-feeding vessels and release a high, locally-limited energy (of Y-90) over several days. In this way, it is finally possible to irradiate tumor cells in a targeted manner and to largely spare healthy tissue. SIRT does not provide a cure, but it is able to alleviate symptoms and possibly delay the progression of the tumor disease by local tumor control.
Selective internal radiotherapy is used in patients with neuroendocrine tumors in which the liver metastases are not operable.
In addition, the overall tumor burden should be limited to the liver. In exceptional cases, SIRT is also possible if other organ systems are affected, and the predominant disease load is in the liver, as a prognosis-relevant organ. The indication for SIRT is confirmed in the interdisciplinary tumor board comprising medical specialists from different disciplines (general and visceral surgery, internal medicine and gastroenterology, nuclear medicine, oncology and radiology), and also in cooperation with the local physicians of the patient. The current tumor status, previous treatments (surgery, chemotherapy, radiation, etc.) and imaging (CT, MRI, etc.) are taken into account. Decisions on therapy planning are taken by consensus, and appropriate recommendations are made. Prior to SIRT, a CT or MRI examination using contrast medium is indispensable in order to confirm the blood supply of liver tumors. Stronger the blood supply to liver tumors (so-called "hypervascularization"), better are the chances of success. In addition, certain laboratory parameters of liver function (bilirubin, albumin, transaminases etc.) and coagulation (INR) must be determined in advance.
A team of nuclear medicine physicians and radiologists performs the selective internal radiotherapy. Initially, an inpatient admission for about three days is planned to check the technical feasibility of SIRT. A low-radioactivity of therapeutically ineffective substance (Tc-99m HSA) is injected in a liver artery via a groin catheter in order to evaluate whether the microspheres would also reach other organs via small vessels during SIRT. If this were the case, these adjacent vessels would have to be sealed beforehand. In addition, the nuclear medicine physician also measures how much of this radioactive substance flows into the lungs. If the test procedure fulfills all criteria (including the fact that flow to the lung is insignificant), the patient is admitted again for SIRT about one to two weeks later. A catheter is again inserted into the groin reaching the liver artery and the radioactive Y-90 microspheres are applied. The procedure takes about 90 minutes. After a further inpatient stay of 2 days, the patient is discharged.
SIRT is generally well-tolerated, especially compared to external-beam radiation therapy or chemotherapy.
The most common symptoms immediately after SIRT are:
• Feeling of pressure in the upper abdomen
• Mild and short-term rise in body temperature, rarely fever
• Tiredness and loss of appetite (short-term)
However, these complaints can be well-treated with the help of medication. In exceptional cases, despite prior examination of the technical feasibility, microspheres can get into other organs and cause tissue damage there (e.g. intestine, gall bladder). In addition, radiation effect of the Y-90 microspheres can lead to a temporary or even permanent impairment of liver function.
Following SIRT, adequate follow-up care is essential. It is personalized, also in this case interdisciplinary, and in cooperation with the local oncologist of the patient.
CT and MRI examinations as well as PET/CT play an important role in assessing the response of liver tumors to selective internal radiotherapy. In addition, a close follow-up of laboratory parameters must be performed after therapy with determination of the blood count and liver parameters, giving a special consideration to bilirubin, ASAT, ALAT and albumin.
Registration form SIRT: Download (pdf)