EXTERNAL BEAM RADIATION THERAPY (SBRT OR SABR)
External beam radiation therapy is used to treat localized metastases causing symptoms, most commonly painful bone metastases. Techniques that focus the radiation such as stereotactic radiotherapy (SBRT or SABR, sometimes called gamma knife or CyberKnife) and proton therapy can be used for localized tumors deeper in the body, most commonly paraganglionomas or pheochromocytoma, and for liver metastases not amenable to other forms of liver-directed therapy.
LIVER-DIRECTED THERAPY (LDT)
Ninety percent of NET patients with malignant disease will develop liver metastases. These metastases are a leading cause of eventual death due to liver failure. Therefore, LDTs are commonly used in the setting of liver dominant disease. Embolization is a liver-directed therapy where a catheter is placed into the hepatic artery to the liver, which is selectively embolized in the areas of metastatic deposit. This technique is based on the fact that tumors in the liver derive their blood supply from the hepatic arterial system, while the normal liver tissue receives most of its blood from the portal venous system.
cuts off the arterial supply to the tumors by the introduction of oil, gelatin, or tiny particles into the selected branch of the hepatic artery.
(transarterial chemoembolization, TACE) utilizes one or more chemotherapeutic drugs added to the embolic material, causing the drugs to be trapped in the tumors at a high concentration.
utilizes microscopic resin or glass particles with yttrium 90 (Y90), a beta-radioisotope which emits radiation that can travel only a few millimeters inside the body, radiating the tumors specifically.
Current guidelines recommend embolization therapy for liver metastases that are symptomatic or progressive despite octreotide or lanreotide therapy, without recommendation among the available embolization techniques. On average, embolization results in control of hormonal symptoms in 85% of patients, substantial reduction in tumor burden in 55%-60%, and prevents disease progression in the liver for one and a half years.