⁹⁰Y Radioembolization (SIRT)

Quick Answer

⁹⁰Y radioembolization (also called selective internal radiation therapy, SIRT, or transarterial radioembolization, TARE) delivers yttrium-90-loaded microspheres through the hepatic artery into the tumor's blood supply, where they lodge in the microvasculature and irradiate the tumor with short-range beta radiation. It treats hepatocellular carcinoma and hepatic metastases (notably colorectal and neuroendocrine). A mandatory pre-treatment ⁹⁹ᵐTc-MAA mapping study simulates microsphere distribution to measure lung-shunt fraction and detect extrahepatic deposition before therapy.

The essentials in one place

⁹⁰Y radioembolization (SIRT/TARE) delivers beta-emitting microspheres via the hepatic artery into a tumor's blood supply to treat HCC and hepatic metastases (colorectal, neuroendocrine). A mandatory pre-treatment ⁹⁹ᵐTc-MAA mapping study measures the lung-shunt fraction (high shunt risks radiation pneumonitis) and detects extrahepatic GI deposition (risk of ulceration) before therapy. Activity is individualized by dosimetry — personalized/partition dosimetry beat standard dosimetry in DOSISPHERE-01 (a ~120 Gy tumor threshold for glass drives response), and an ablative single-segment dose ("radiation segmentectomy") can be curative-intent for early HCC.

Clinical Importance

Radioembolization is a liver-directed therapy delivered jointly by nuclear medicine and interventional radiology. Because Y-90's beta range is only millimeters, very high tumor doses can be delivered with relative sparing of normal liver — enabling treatment of tumors unsuitable for resection or ablation, and increasingly used for downstaging and as a segmental "radiation segmentectomy."

Evidence & Indication

• Hepatocellular carcinoma: used across intermediate/advanced stages, for downstaging to transplant/resection, and as radiation segmentectomy for localized disease.
• Metastatic disease: hepatic metastases from colorectal cancer (chemorefractory/liver-dominant) and neuroendocrine tumors, among others.

Microsphere types

Patient Selection

• Liver-dominant, unresectable disease with adequate liver function and reserve.
• Pre-treatment ⁹⁹ᵐTc-MAA mapping to quantify lung-shunt fraction (excessive hepatopulmonary shunting risks radiation pneumonitis) and identify extrahepatic GI deposition requiring coil embolization.
• Preserved performance status; portal vein patency considerations depend on approach.

Preparation & Workflow

1. Planning angiogram with ⁹⁹ᵐTc-MAA injection into the intended arterial territory.
2. MAA SPECT/CT to calculate lung-shunt fraction and check for extrahepatic activity.
3. Dosimetry/activity planning (partition model or single-compartment methods) based on target volume, lung shunt, and microsphere type.
4. Treatment day: catheter-directed delivery of Y-90 microspheres into the tumor-feeding artery.
5. Post-treatment imaging: Y-90 bremsstrahlung SPECT or Y-90 PET (from the small internal pair-production branch) to confirm distribution.

Dose / Activity

Activity is individualized by dosimetry, target volume, lung-shunt fraction, and microsphere type — not a single fixed value. Lung dose limits guide maximum permissible shunt.

Monitoring

Liver function, post-embolization symptoms, and imaging follow-up for response and any non-target effects.

Radiation Safety

Y-90 is a pure beta emitter with minimal external exposure risk; precautions focus on handling during delivery and standard post-procedure guidance.

Expected Outcomes

Tumor response and local control; downstaging to curative therapy in selected HCC; disease control in liver-dominant metastatic disease.

Complications & Toxicities

• Post-embolization syndrome (fatigue, pain, nausea).
• Radiation-induced liver disease (REILD) with excessive normal-liver dose.
• Non-target deposition: radiation pneumonitis (high lung shunt), GI ulceration (extrahepatic GI deposition), cholecystitis.

Dosimetry approaches

Activity is individualized, and the dosimetry method matters for outcome:

• Single-compartment (MIRD/BSA) methods target a whole-liver or perfused-volume dose but do not account for tumor-versus-normal-liver distribution.
• Partition model separates tumor, normal liver, and lung compartments (using MAA distribution and volumes) to maximize tumor dose while capping normal-liver and lung dose.
• Personalized/multicompartment dosimetry improved response versus standard dosimetry in DOSISPHERE-01 — higher tumor-absorbed dose (often a ≥120 Gy tumor threshold for glass) drives response.
• Lung dose is constrained by the MAA lung-shunt fraction (commonly ≤30 Gy single / ≤50 Gy cumulative).

Radiation segmentectomy

Delivering an ablative dose to one or two Couinaud segments feeding a tumor ("radiation segmentectomy") can achieve very high local control for early HCC (supported by the LEGACY cohort) and functions as a curative-intent, parenchyma-sparing option analogous to ablation.

Response Assessment

Cross-sectional imaging with tumor-specific criteria (e.g. mRECIST for HCC — enhancement, not just size), tumor markers, and functional imaging where relevant. Post-treatment Y-90 PET or bremsstrahlung SPECT confirms distribution and supports delivered-dose verification.

Self-Check

Key References

• Salem R, et al. Radioembolization outcomes in hepatocellular carcinoma.
• SNMMI/EANM procedure guidance and joint interventional-radiology standards for ⁹⁰Y radioembolization.