Selective internal radiation therapy

Selective internal radiation therapy (SIRT), also know as hepatic radioembolisation, is a relatively new and developing modality for treating non-resectable liver tumours. The procedure consists of a transcatheter injection of radioactive particles via hepatic artery. 

It generally considered efficacious in patients with hepatocellular cancer, neuroendocrine and colorectal liver metastases. It generally involves a single delivery of ⁹⁰yttrium micro-spheres into the hepatic artery. Preferential uptake is achieved into liver tumours, because of their predominant hepatic arterial blood supply. Average tumour doses of radiation in excess of 200 Gy are achieved.

Indications

Is a method of treating liver tumors (primary or secondary) in patients in whom surgery is not an option, such as:

• unresectable hepatic metastatic disease
• unresectable hepatocellular carcinoma (HCC)
• hepatic tumour progression despite treatment
• symptoms related to hepatic tumor bulk or hormonal excess (Neuroendocrine tumors)
• "bridge to transplant": stop tumor progression while awaiting liver transplant 
• life expectancy > 90 days
• liver-dominant tumor burden

Contraindications

• extensive or progressive extrahepatic disease
• poor baseline liver function
• Eastern Cooperative Oncology Group (ECOG) performance status > 3
• exaggerated hepatopulmonary shunting
• reflux into the arteries that supply the gastroduodenal region
• uncorrectable extrahepatic shunts
• portal venous thrombosis (while it is listed in the package insert as a contraindication to use of the resin microsphere device, treatment with the glass microsphere device has been successful in patients with this condition with superselective delivery ⁴
• life expectancy < 90 days
• total bilirubin >2.0 mg/dl
• contraindications to angiography:
  • contrast allergy causing anaphylaxis
  • renal insufficiency
  • peripheral vascular disease
  • uncorrectable bleeding diathesis

Pathophysiology

Primary and metastatic hepatic malignancies derive 80-100% of their blood supply from the hepatic artery unlike normal liver that receives only 20% from the arterial supply. This allows the use of higher doses or internal radiation or chemotherapy than the normal liver can tolerate. 

The transcatheter hepatic artery infusion of radioisotope delivers high doses local intratumoural radiation, while sparing the surrounding healthy liver parenchyma (or at least only a low, tolerable dose). 

It`s achieved by the intraarterial injection of Yttrium 90 (beta emitter) labelled glass or resin microspheres as an interventional radiology procedure. An alternative method is the used of I-131 labelled Lipiodol.

Procedure

• pre-procedure evaluation
• lab work to confirm bilirubin, coagulation profiles and platelets are adequate.
• Injection of 99mTc-MAA (macroaggregated albumin) into hepatic artery with followup nuclear medicine scan to determine degree of shunting to lungs and bowel.
• confirmation of portal vein patency.
• calculation of dose of Y-90 based on body surface area, % tumor volume in liver, liver function and % shunting of spheres to lung.

Procedure steps

• preliminary angiogram to determine vascular anatomy, confirm location of metastases, inject  99mTc-MAA for scan shortly after angiogram, determine extrahepatic arteries arising from the celiac axis that will need to be avoided or embolized including cystic artery if gall bladder is still present.
• left and Right lobes of liver usually done on two separate procedures at least 4 weeks apart to insure adequate liver function is maintained and any change in bilirubin, liver enzymes and platelets return to baseline levels.
• prior to actual infusion of Y-90 spheres, extrahepatic branches are embolized.
• meticulous procedure is used to minimize exposure to staff including confining and preparing spheres in an acrylic shielded box that absorbs beta radiation and minimizes Bremsstrahlung radiation production.
• after Y-90 infusion and catheter removal, gamma camera images are usually performed using the Bremsstrahlung radiation produced by the beta particles to produce images of where the spheres are located.

Post-procedure evaluation

• 99mTc-MAA scan after first angiogram to determine extrahepatic shunting.
• lab work just before and after two therapeutic procedures.
• followup CT or MRI of the liver 3-6 months after treatment. 

Potential Complicationscomplications

• nausea, vomiting, fever, diarrhea and abdominal pain
• transient lab abnormalities including liver function, hemoglobin and platelet levels.
• acute pancreatitis, radiation pneumonitis, radiation gastritis and hepatitis, acute cholecystitis.

See also

• liver and billiary interventional procedures
• radioembolisation