E2864. Assessment of Response to Liver Directed Radiation-Based Therapies: Current Guidelines, Challenges, and Future Directions
  1. Anisha Banda; University of Washington
  2. Guilherme Cunha; University of Washington
Hepatocellular Carcinoma (HCC) treatment options are dictated by tumor burden. In patients with disease burden beyond surgically actionable early-stage disease, but not yet advanced enough to warrant palliative systemic therapy, local-regional (i.e., liver directed) options are the modalities of choice, either with curative, as a bridge to transplant, or downstaging intent. After treatment, it is important to assess tumor response to determine further management, patient prognosis, or as endpoint outcomes in clinical trials. To standardize imaging interpretation and reporting of HCC response to local-regional treatment, a few imaging-based response assessment systems exist. Two have emerged as the most commonly used in the United States; the Liver Imaging Reporting and Data System (LI-RADS) Treatment Response Algorithm (LR-TRA) and the modified Response Evaluation Criteria In Solid Tumors (mRECIST). These systems rely on contrast enhancement of any residual viable tumor to quantify the response, the former providing a per lesion-based assessment of response and the latter a per-patient assessment.

Educational Goals / Teaching Points
In this exhibit we will review local-regional treatment options for HCC with an emphasis in radiation-based options; summarize current imaging criteria for assessing HCC response to local-regional therapies; discuss practical limitations and gaps in knowledge when applying these response criteria to radiation-based treatment; and address future directions that may help to improve accuracy and outcomes when assessing response to radiation-based HCC treatment.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Recently, radiation-based local-regional therapies (e.g., transarterial radioembolization with Y-90, external beam radiation therapy) have gained wide acceptance due to promising rates of tumor response, survival, and safety profiles. While currently used response assessment systems have been validated for ablative and most transarterial locoregional therapy modalities, challenges remain when assessing response to liver directed radiation-based therapies. After radiation, hyperemic alterations in the treatment bed coupled with specific pattern of tumor necrosis can be confounding factors to reliably associate the presence of persistent contrast enhancement to the presence of viable tumors.

Radiation-based liver-directed therapies have emerged as effective and safe modalities for treatment for hepatocellular carcinoma. There are challenges associated with the assessment of these treated tumors. Research is still needed to address some limitations of current imaging criteria for assessing tumor response to these novel techniques.