Dosimetry of Hepatic Transarterial Yttrium-90 Radioembolization: What Interventional Oncologists Need to Know

Purpose: Transarterial yttrium-90 radioembolization (Y-90 RE) is a safe and effective treatment modality for both primary and metastatic hepatic malignancies. The therapeutic effect is dependent on the appropriate dose delivered to the targeted tumor(s), which depends on the quantity and characteristics of the radioactive microspheres present within a given area. The purpose of this educational exhibit is to provide an understanding of (1) the physical properties of the Y90 isotope and its delivery platforms, (2) the dosimetry models for activity determination in Y-90 RE, (3) the important clinical and imaging factors that affect target dose, and (4) the technical considerations and recommendations needed to maximize the likelihood of an objective response in targeted tumor(s).

Materials and Methods: Tumor response, progression-free survival, overall survival, and incidence of postprocedure complications are directly correlated with dose delivered to the tumor(s). The understanding of various dosimetry models in conjunction with treatment objectives and patients clinical picture are critical factors in optimizing Y-90 RE therapeutic outcomes.

Results: The Y-90 isotope is a beta emitter with a half-life of 64.1 hours and a mean radiation penetration of 2.5 mm. Currently, two commercially available Y-90 RE microsphere platforms, glass and resin based, are approved for clinical use. The logistical, design, and technical specifications of the two platforms result in significantly different treatment profiles with their own strengths and benefits. To account for these differences, various dosimetry models are used with the goal of delivering tumoricidal dose to the tumor(s) while minimizing toxicity to nontumoral liver and lungs. These include the body surface area model, often used with resin microspheres, and the medical internal radiation dose model, often used with glass microspheres. The partition model, although less commonly used, offers the most personalized and versatile dose estimates. However, its labor-intensive nature often relegates its use for quality control and cases requiring special considerations. Additional clinical and imaging factors, such as liver function and tumor characteristics, can also affect the desired target dose and must be accounted for during dosimetry planning.

Conclusions: Successful and effective Y-90 RE requires optimal dosimetry planning, multidisciplinary collaboration, and clinical astuteness. Interventional oncologists should have an understanding of the technicalities of Y-90 RE dosimetry to play a central role in the pre-, intra-, and postprocedural steps of this novel and promising therapy.