Semin intervent Radiol 2020; 37(05): 543-554
DOI: 10.1055/s-0040-1720954
Trainee Corner

Yttrium-90 Radioembolization Dosimetry: What Trainees Need to Know

Alexander Villalobos
1   Division of Interventional Radiology and Image Guided Medicine, Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, Georgia
,
Mohamed M. Soliman
2   Weill Cornell Medicine – Qatar School of Medicine, Education City, Al Luqta St, Ar-Rayyan, Qatar
,
Bill S. Majdalany
1   Division of Interventional Radiology and Image Guided Medicine, Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, Georgia
,
David M. Schuster
3   Division of Nuclear and Molecular Imaging, Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, Georgia
,
James Galt
3   Division of Nuclear and Molecular Imaging, Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, Georgia
,
Zachary L. Bercu
1   Division of Interventional Radiology and Image Guided Medicine, Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, Georgia
,
Nima Kokabi
1   Division of Interventional Radiology and Image Guided Medicine, Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, Georgia
› Institutsangaben

Funding/Support No funding was received to prepare this manuscript.
Preview

Erratum: Yttrium-90 Radioembolization Dosimetry: What Trainees Need to Know

Yttrium-90 radioembolization (Y90-RE), also known as transarterial radioembolization (TARE) or selective internal radiation therapy (SIRT), is a form of brachytherapy that has become an established liver-directed therapy for primary and secondary hepatic malignancies.[1] [2] [3] [4] [5] [6] [7] While a degree of embolization and ischemia may occur, the dominant mechanism of action for Y90-RE is radiation-induced necrosis from targeted transarterial administration of millions of Y90-labeled microspheres. The Y90 within these microspheres exert their effects primarily by undergoing β-decay to stable zirconium-90, which is not known to have any clinical effects.[8] [9] [10] The β-decay of Y90 results in the release of high-energy β-particles (i.e., electrons or β−) with an average energy of 0.9267 MeV (maximum of 2.28 MeV) and a half-life of 64.04 hours (2.67 days), which translates to 94% of the Y90 radiation being delivered within 11 days. These β-particles penetrate nearby tissues an average of 2.5 mm (maximum of 11 mm), resulting in the sought-after effect of radiation damage to nearby structures.[11] Additional types of radiation also occur as a result of Y90 decay. Although these are summarized in [Fig. 1], an in-depth discussion of them is beyond the scope of this article.

Zoom
Fig. 1 Yttrium-90 decay products and their clinical applications. Yttrium-90 predominantly undergoes β-decay to emit high-energy β-particles that are used clinically for targeted radiotherapy—which include direct injection of Y90 into a body cavity or space, conjugation of Y90 to an antibody for radioimmunotherapy (RIT), conjugation of Y90 to a peptide for peptide receptor radionuclide therapy (PRRT), or incorporation of Y90 to resin or glass microspheres for Y90 radioembolization (Y90-RE) therapy. As a result of the high-energy β-particle emission, a continuous spectrum of bremsstrahlung radiation occurs—which can be imaged using conventional nuclear medicine imaging systems (i.e., SPECT, SPECT/CT, planar gamma cameras). High-energy β-radiation also partakes in a phenomenon called Cherenkov radiation, which produces a continuous spectrum of ultraviolet and visible light photons (i.e., Cherenkov luminescence) which can be imaged using Cherenkov luminescence imaging (CLI). While β-decay is the predominant decay mechanism of Y90, every 32 per million Y90 decays result in an internal pair production (gamma-decay) that produces annihilation radiation that can be imaged using conventional PET/CT or PET/MRI systems.

Currently, there are two commercially available and Food and Drug Administration (FDA)-approved radioembolization microspheres in the United States: resin microspheres (SIR-Spheres; Sirtex Medical Inc, Woburn, MA), whose original formulations were developed in the mid-20th century, and glass microspheres (TheraSphere; Boston Scientific, Marlborough, MA), which were developed in the early 1980s.[9] Properties of these biocompatible and nonbiodegradable microspheres, at the time of calibration, are outlined in [Table 1].[9] [12] [13] Resin microspheres are FDA approved only for the treatment of unresectable metastatic liver tumors (MLTs) from primary colorectal cancer with adjuvant intrahepatic artery chemotherapy (IHAC) of FUDR (Floxuridine).[14] Glass microspheres are FDA approved, under a humanitarian drug exemption, only for the sole or neoadjuvant treatment of unresectable hepatocellular carcinoma (HCC).[15] Nevertheless, both types of microspheres are frequently used off-label for the treatment of various primary or secondary hepatic malignancies.[16] [17]

Table 1

Properties of the commercially available glass and resin Y90 microspheres at the time of calibration

Glass

Resin

Isotope attachment

Incorporated into glass matrix

Attached to resin surface

Mean diameters (μm)

25

32.5 ± 2.5

Diameter range (μm)

20–30

20–60

Microspheres per vial

1.2 million for 3 GBq; 8 mil for 20 GBq

40–80 million

Available standard doses (GBq)

3, 5, 7, 10, 15, and 20

3

Specific activity (Bq per microsphere)

2,500

50

Specific gravity (g/dL)

3.6

1.6

Notes: Please check the latest package insert for updated information, including availability of customizable doses. For reference, the specific gravity of blood is 1.05 g/dL.


As a result of the mounting evidence for a clear dose–effect relationship,[10] the goal of Y90-RE has evolved to reflect a classical principle of oncology—which is to deliver the maximum tolerated dose. Achieving this goal requires understanding of the multiple steps in the pre-, peri-, and posttherapy phases of Y90-RE. Several articles have sought to comprehensively explain the rationale and technical challenges found in each of these steps.[18] [19] However, a paucity of literature comprehensively describing the technical strengths and challenges of the commonly used Y90-RE dosimetry models remains. As an integral part of the team and an authorized user of Y90-RE devices, the interventional radiologist must have a fundamental understanding of the involved dosimetry. Therefore, the aim of this article is to provide a fundamental background of the rationale, limitations, and strengths involved in Y90-RE dosimetry planning, and the strategies employed in clinical practice when treating patients with Y90-RE.



Publikationsverlauf

Artikel online veröffentlicht:
11. Dezember 2020

© 2020. Thieme. All rights reserved.

Thieme Medical Publishers, Inc.
333 Seventh Avenue, 18th Floor, New York, NY 10001, USA