• carcinoma
• hcc
• hepatocellular
• holmium-166
• intra-arterial
• liver
• liver
• metastases
• radioembolization
• sirt
• tare
• treatment
• tumors

Purpose
To retrospectively analyze early radiological tumor response to 166Holmium radioembolization (166Ho-RE) in a series of patients with primary or secondary liver tumors.
Materials and Methods
We retrospectively collected the data of all patients treated with 166Ho-RE between January 2018 and July 2021. Post-treatment dosimetry was assessed by SPECT-CT performed before patients’ discharge. Target and overall tumor responses were assessed on triphasic CT at 6 ± 2 weeks, based on Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 for all tumor types, and, additionally, modified RECIST (mRECIST) for hepatocellular carcinoma (HCC) and arterially enhancing metastases. In patients with disease control, subsequent response was analysed on cross-sectional images at 12 ± 2 weeks and the best radiological response was collected.
Results
Twenty-six patients were included (21 male; mean age 70.6 ± 8.7 years) with intrahepatic cholangiocarcinoma (ICC, n=5), hepatocellular carcinoma (HCC; n=12) and metastastic lesions (n=9). The median administered activity was 3.54 GBq and the median average tumor absorbed dose (TAD) was 107 Gy. Best target and overall OR rates were 50% and 42.3%, respectively, with corresponding DC rates of 76.9% and 57.7%. Early tumor shrinkage as to achieve PR by RECIST 1.1 was observed in 7/26 patients, allowing liver transplantation in one HCC case and resection in a ICC patient. Target response was significantly associated to TAD, with a minimum threshold of 118 Gy to achieve OR (AUC 0.77).
Conclusions
166Ho-RE is a safe and effective treatment option in primary and secondary liver tumors. Early reduction in tumor size may be evident in 25% of patients. Further studies are needed to implement personalized dosimetry.