The liver is a relatively radiosensitive organ, but shows a marked volume effect due to the serial nature of its functional sub-units. Hepatic lobules are typically considered as a hexagonal slab of tissue with a central lobular vein that drains to the hepatic veins. Branches of the portal vein, the hepatic artery and the biliary tree run in the corners of the hexagon. Hepatocytes lie in the space between the outer vessels and the central vein.
Radiation induced liver disease may present with signs of liver failure, including:
- Poor coagulation (due to reduction in coagulation factor production and platelet growth factors)
- Peripheral oedema (due to reduced production of albumin)
- Jaundice (due to reduced processing of bilirubin)
- Renal failure
- Hepatic encephalopathy
Patients with pre-existing liver disease are more susceptible to damage.
The defining lesion is thrombosis of the central lobular vein. This leads to obstruction of blood flow through the lobule, ischaemia of hepatocytes and eventual fibrosis of the region.
The dose recommendations are based on the type of liver lesion as well as the fractionation of the dose - stereotactic treatment of liver lesions is becoming more common. Mean doses are recommended given the volume effect seen in the liver.
- A mean dose of < 32 Gy is recommended for patients with normal liver function
- A mean dose of < 28 Gy is recommended for patients with compromised liver function, or who have hepatocellular carcinoma
- A mean dose of < 15 Gy is recommended for patients who have fractionated stereotactic radiotherapy