Yttrium-90 Radioembolization (Y-90 / TARE / SIRT)

Transarterial Radioembolization (TARE) — targeted treatment of liver tumors using the Yttrium-90 isotope, minimizing impact on healthy tissues.

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Biophysical and radiobiological mechanism of action

At the core of radioembolization (Selective Internal Radiation Therapy — SIRT) is a combination of endovascular microembolization and brachytherapy.

Plaintext

Hypervascular tumor blood flow (Hepatic artery)
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Selective insertion of microcatheter into the feeding vessel
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Infusion of Y-90 microspheres (Size: 20–40 µm, Glass/Resin)
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Entrapment in the microvascular bed (Arterioles) of the tumor
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Beta radiation (β-) of ultra-high local dose (up to 100–150+ Gy)
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Double-strand DNA breaks (DSB) ➔ Apoptosis and mitotic death

Characteristics of the Yttrium-90 isotope (⁹⁰Y):

Radiation type: Pure beta emitter (β⁻).
Half-life (T₁/₂): 64.1 hours (approximately 2.67 days).
Radiation energy: Mean energy is 0.935 MeV (maximum — 2.27 MeV).
Tissue penetration depth: Mean path length of beta particles in soft tissue is only 2.5 mm (maximum — up to 11 mm).

Occlusion and geometric distribution:

Microspheres (glass or resin) with a diameter of 20–40 µm are administered superselectively via a microcatheter into the terminal branches of the hepatic artery. They lodge in the capillary bed of the tumor. Due to the ultra-small range of beta particles, the entire absorbed radiation dose is focused strictly inside the tumor mass.

Radiobiological superiority over External Beam Radiation Therapy (EBRT):

Standard external beam radiation therapy (EBRT) is limited by the tolerance threshold of healthy liver parenchyma (risk of radiation-induced liver disease, RILD), which prevents delivering doses above 30–40 Gy. Y-90 radioembolization delivers a focal dose of 120 to 400+ Gy directly to the tumor node, completely destroying the malignant clone without damaging uninvolved segments.

Two-stage procedure protocol

The method requires precise radioisotope and angiographic planning:

STAGE 1: Diagnostic angiography and modeling (1–2 weeks prior to TARE)
- Occlusion (using coils) of branches feeding the GI tract (protection against ulcers).
- Administration of ⁹⁹ᵐTc-MAA (Macroaggregated Albumin) ➔ Assessment of Hepatopulmonary Shunt on SPECT/CT.
STAGE 2: Y-90 therapeutic infusion (Theranostics)
- Calculation of individual activity in Bq/MBq considering liver mass and tumor volume.
- Precise endovascular infusion of microspheres containing the Y-90 isotope.

Key clinical advantages

Ultra-local ultra-high dose. Ability to deliver sub-lethal radiation doses (>150 Gy) to the tumor, impossible with external radiation.
Minimal post-embolization syndrome. Unlike standard TACE, Y-90 microspheres do not cause massive ischemia of liver tissues due to their smaller quantity and size, which significantly improves tolerance and eliminates severe pain.
Feasibility of "Radiation Lobectomy". Allows atrophy of the affected liver lobe with concurrent compensatory hypertrophy of the healthy contralateral lobe, enabling subsequent surgical resection (conversion therapy).
Treatment in portal vein invasion. The method is safe and effective even in the presence of portal vein tumor thrombosis (PVTT), which is a contraindication for classic chemoembolization.

Clinical indications

Unresectable primary hepatocellular carcinoma (HCC) at any stage (including BCLC-B and BCLC-C with portal vein tumor thrombosis).
Intrahepatic cholangiocarcinoma.
Refractory colorectal cancer liver metastases (mCRC).
Neuroendocrine tumor (NET) metastases and breast cancer metastases to the liver.
Conversion therapy (Downstaging) to convert unresectable cancer into a surgically resectable status or preparation for liver transplantation.