Yttrium-90 Radioembolization Dosimetry: What Trainees Need to Know
Alexander Villalobos, Mohamed Mohamed Soliman, Bill S. Majdalany, David M. Schuster, James R. Galt, Zachary Bercu, Nima Kokabi
Abstract
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.