Radioembolization of Colorectal Liver Metastases: Indications, Technique, and Outcomes

Abstract

Liver metastases are a major cause of death from colorectal cancer. Intraarterial therapy options for colorectal liver metastases include chemoinfusion via a hepatic arterial pump or port, irinotecan-loaded drug-eluting beads, and radioembolization using ⁹⁰Y microspheres. Intraarterial therapy allows the delivery of a high dose of chemotherapy or radiation into liver tumors while minimizing the impact on liver parenchyma and avoiding systemic effects. Specificity in intraarterial therapy can be achieved both through preferential arterial flow to the tumor and through selective catheter positioning. In this review, we discuss indications, contraindications, preprocedure evaluation, activity prescription, follow-up, outcomes, and complications of radioembolization of colorectal liver metastases. Methods for preventing off-target embolization, increasing the specificity of microsphere delivery, and reducing the lung-shunt fraction are discussed. There are 2 types of ⁹⁰Y microspheres: resin and glass. Because glass microspheres have a higher activity per particle, they can deliver a particular radiation dose with fewer particles, likely reducing embolic effects. Glass microspheres thus may be more suitable when early stasis or reflux is a concern, in the setting of hepatocellular carcinoma with portal vein invasion, and for radiation segmentectomy. Because resin microspheres have a lower activity per particle, more particles are needed to deliver a particular radiation dose. Resin microspheres thus may be preferable for larger tumors and those with high arterial flow. In addition, resin microspheres have been approved by the U.S. Food and Drug Administration for colorectal liver metastases, whereas institutional review board approval is required before glass microspheres can be used under a compassionate-use or research protocol. Finally, radiation segmentectomy involves delivering a calculated lobar activity of ⁹⁰Y microspheres selectively to treat a tumor involving 1 or 2 liver segments. This technique administers a very high radiation dose and effectively causes the ablation of tumors that are too large or are in a location considered unsafe for thermal ablation. The selective delivery spares surrounding normal liver, reducing the risk of liver failure.

Keywords: 90Y; colorectal cancer; irinotecan-loaded drug-eluting beads; liver metastases; microspheres; radioembolization.

FIGURE 1.

CRC liver metastases can be hypervascular on angiography, allowing selective intraarterial delivery of particles into tumor. (A) CRC liver metastases (arrow) are typically considered hypovascular because they do not enhance as much as background liver on contrast-enhanced CT. (B) However, on catheter angiogram (segment 4), which shows only arterial blood supply, this liver metastasis is actually hypervascular (greater hepatic artery supply than normal liver). (C) Hypervascularity is confirmed by enhancement of lesion on helical CT during injection of contrast material into segment 4 artery. (D) Bremsstrahlung SPECT/CT after injection of ⁹⁰Y microspheres into same artery shows preferential flow of microspheres into tumor.

FIGURE 2.

Radiation segmentectomy. (A) Patient with intrahepatic cholangiocarcinoma who developed a 3-cm recurrence at resection margin after left hepatectomy (arrow). (B) Entire right-lobe dose was delivered into tiny artery supplying tumor. This tiny artery (arrow) could not be selectively catheterized, so off-target vessels were protected with gelatin foam (Gelfoam; Pfizer) before dose was delivered into parent vessel. (C) Bremsstrahlung SPECT/CT after injection of ⁹⁰Y microspheres shows selective delivery of particles into tumor. (D) CT at 2 mo after procedure shows lack of enhancement, corresponding to tumor necrosis.