Post-TARE (transarterial radioembolization) assessment of hepatocellular carcinomas is essential for evaluating the success of the therapy.
Hepatocellular carcinomas that are not amenable to definitive therapy with thermal ablation or resection can be treated with trans-arterial radioembolization (TARE). The end goal may be palliation or downstaging to meet liver transplantation criteria, depending on the situation.
The imaging follow up schedule varies between institutions, but a 1 month follow up exam with follow up exams every three months afterward has been adopted by most centers. The short interval follow up studies allow for temporal evaluation of the treatment cavity, which is important to evaluate the response to therapy.
Radiographic features
MRI
Expected evolution of the treatment zone
Post-TARE evaluation is typically performed with MRI. Notable, the evolution of the treatment cavity is different than that with TACE, which can be confusing for radiologists who are unfamiliar with a liver-directed therapy that has less of an embolic component and relies on the relatively slow effects of radiation.
Sometimes on the initial (1 month) follow up scan, the treated lesion is completely non-enhancing (although the adjacent liver often shows post-radiation arterial phase enhancement) and this is compatible with a successful treatment response. This is a less common appearance after therapy.
It is often the case that on the 1 and 3 month follow up exams, the treated lesion is unchanged in size (or even slightly increased in size) and peripheral irregular (or even nodular) enhancement may persist for months (pseudoprogression). Typically the treatment cavity slowly decreases in size over time. Often, 1 and 3 month follow ups have an "equivocal" appearance and only at around 6 months can one make a more confident assessment whether the therapy has been effective.
Findings suspicious for new or recurrent tumor in the treatment zone
Findings are equivocal <6 months after therapy:
- increase in size of the treatment cavity
- new or increasing areas of peripheral enhancement
- new or increasing DWI hyperintensity and ADC hypointensity in a suspicious area can be helpful to confirm.
A hepatobiliary-specific contrast agent is not typically used for post-TARE assessment.
Radiology report
In the LI-RADS system, treated lesions fall into three categories for treatment response (TR) 1:
- LR-TR nonviable: expected post-treatment chance with no arterial phase enhancement or other finding to suggest residual or recurrent tumor
- LR-TR equivocal
- LR-TR viable: nodular or masslike enhancement in the treatment zone with arterial phase hyperenhancement, wash out on the portal venous phase, or enhancement similar to the pre-treatment lesion
Often a post-TARE treatment zone has an "equivocal" appearance <6 months and only >6 months does the treatment effect become more apparent.
EASL and mRECIST measurements may be misleading for evaluating post-TARE change and are not typically used.
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