**2.4.2 Selective Internal Radiation Treatment (SIRT)**

Selective internal radiation treatment (SIRT) is the delivery of radiation treatment via intrahepatic arterial administration of yttrium 90 (Y-90) microspheres. This technique involved the administration of Y-90 microspheres into the hepatic arterial via the transfemoral route. The administered Y-90 microspheres are then entrapped within the microvasculature and release irradiation. The high tumor concentration of Y-90 microspheres results in an effective tumoricidal radiation-absorbed level while the radiation injury to the normal liver parenchyma is limited.

Its role as a safe and effective therapeutic option for patients with unresectable hepatocellular carcinoma is increasingly recognized. Recently, Lau et al (Lau et al, 2011) reviewed the role of SIRT with Y-90 microspheres for hepatocellular carcinoma, including recurrent unresectable HCC. SIRT is a recommended option of palliative therapy for large or multifocal HCC without major portal vein invasion or extrahepatic spread. It can be used as a bridging therapy before liver transplantation or as a tumor downstaging treatment, or as a curative treatment for patients who are not fit for surgery. However, the evidence was limited to cohort studies and comparative studies with historical control and was mainly targeted on primary HCC. Future research may yield more information on its role on recurrent HCC and the efficacy when compared to chemoembolization or target therapy.

In contrary to chemoembolization, optimal perfusion is required to enhance the free radicaldependent cell death in SIRT. In order to minimize the treatment-related toxicity, hepatic scintigraphy with technetium Tc 99m (99mTc) macro-aggregate albumin (MAA) should be performed to determine the arterial anatomy and to calculate the shunt fraction delivered to the lungs before subjecting the patient to SIRT. Pulmonary shunt fraction greater than 15% on 99mTc-MAA scan predisposes to radiation pneumonitis and is therefore a contraindication for SIRT. In addition to radiation pneumonitis, other serious complication associated with SIRT include gastric or duodenal ulcers or perforation as a result of reflux of Y-90 microspheres into the gastrointestinal vascular bed and radiation hepatitis resulting from a radiation dose higher than the tolerable level. Nevertheless, most patients only reported mild symptoms like abdominal pain, lethargy or nausea, which may require symptomatic treatment. (Rossi et al, 2010) In most cases, it is a well-tolerated minimally invasive therapy.
