ARRS 2022 Abstracts

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E1153. A Primer on the Imaging of Liver Treated with Radioembolization
Authors
  1. Surbhi Trivedi; University of Illinois Chicago
  2. Ana Gonzalez; University of Illinois Chicago
  3. Josi Herren; University of Illinois Chicago
  4. Alaa Elmaoued; Loyola University Medical Center
  5. Karen Xie; University of Illinois Chicago
Background
Transarterial radioembolization (TARE) is an endovascular procedure to treat unresectable primary and secondary hepatic tumors with yttrium-90 radioisotope-impregnated microspheres. This technique induces beta-decay via radioembolization by capitalizing on the tumor's primarily-arterial vascular supply. Compared to transarterial chemoembolization, TARE has higher time-to-progression, lower risk of post-embolization syndrome, and can be used despite portal vein thrombosis.

Educational Goals / Teaching Points
Characterizing post-treatment imaging findings is crucial to determining future treatment. This exhibit will discuss the optimal timeline for obtaining follow-up imaging as well as differences between a nonviable and viable tumor. We will detail the benign findings that can occur due to treatment effects, various classification systems of tumor treatment response, and emerging imaging modalities that may have added utility for radiologists in the future.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
There is no standard timeline for follow-up imaging; however, imaging at 3–6 months is considered the most appropriate time period for assessing tumor viability. Imaging earlier than this may overestimate enhancement that will eventually abate due to delayed necrosis. There are various classification systems for assessing tumor response, which characterize treated tumor changes as complete response, partial response, stable disease, or progressive disease. Earlier systems measured changes by tumor size, but newer functional systems including the European Association for the Study of the Liver (EASL) and the modified Response Evaluation Criteria in Solid Tumors (mRESIST) incorporate tumor enhancement pattern as well as size changes. EASL and mRESIST responses are associated with survival benefits in some hepatic tumors treated with certain therapies. Typical post-treatment changes include decrease or increase in tumor size, decreased or residual enhancement, and peritumoral ring enhancement due to granulation tissue. Devascularization may unmask new tumoral foci. The adjacent liver parenchyma may be affected as well, demonstrating new peritumoral edema, hepatic fibrosis, or capsular retraction. Future directions include emerging techniques in imaging such as volumetric functional analysis with DWI-MRI and ADC mapping to detect the percent of tumor that has responded to treatment. FDG-PET and yttrium-90-PET may have a role in determining tumor viability when compared to baseline uptake. Perfusion CT evaluates temporal changes in tissue contrast density and may have a role in assessing tumor vascularization. Conventional and dynamic contrast-enhanced MRI may have a role in detecting tumor vascularity, perfusion, and response to anti-angiogenic treatments.

Conclusion
As the application of radioembolization evolves and expands, it remains paramount for radiologists to accurately characterize tumor response to treatment, which includes being familiar with appropriate follow-up timeline, survival-associated guidelines for tumor response, benign and concerning treatment-related tumor changes, and the emerging modalities of tumor imaging.