Enhancing Tumor Response in Hepatocellular Carcinoma: The Role of Voxel-Based Dosimetry in Yttrium-90 Glass Microsphere Radioembolization
The radiation activity delivered to a tumor via radiation segmentectomy (RS) greatly impacts resulting tumor cell death, measured as complete pathologic necrosis (CPN). Due to the tumor vasculature, microsphere deposition within tumors is heterogeneous, which persists even with an increased number of spheres. This results in some areas receiving a higher dose (ie, 'hotter' regions) and others receiving a lower dose (ie, 'colder' regions). One way to overcome tumor heterogeneity is to increase microsphere specific activity (SA), as more radiation per sphere ensures more radiation decay to achieve a dose that increases the likelihood of CPN. This is important for improving patient outcomes, as CPN is associated with improved overall survival and longer recurrence-free survival.
In a recent retrospective study, voxel-based dosimetry was used to calculate glass microsphere concentration in hepatocellular carcinoma (HCC) tumors, providing insight into sphere deposition and distribution. The single-center analysis evaluated tumors from 56 patients with solitary, treatment-naïve HCC treated with yttrium-90 (Y-90) RS with glass microspheres (TheraSphere; Boston Scientific, Marlborough, MA). All vessels feeding to the tumor areas were treated with target radiation doses during a single session. Posttreatment voxel-based dosimetry was evaluated using Mirada DBx Build 1.2.0 Simplicit90Y software (Boston Scientific) and used to calculate tumor sphere concentration. Dose-volume histogram curves were produced to identify the minimum absorbed dose to 70% (D70), 90% (D90), and 99% (D99) of the total tumor volume. The primary outcome—time-to-progression (TTP)—was the time from the first cycle of Y-90 until HCC progression.
The study demonstrated a median tumor absorbed dose of 732 Gy (median tumor diameter, 3.4 cm). The median SA at delivery was 1445 Bq. Voxel-based dosimetry revealed a median tumor sphere concentration of 12 868 microspheres/mL, while the median nontumoral concentration was 7893 microspheres/mL. Tumor sphere concentration was inversely correlated with perfused treatment volume, with lower perfusion volumes resulting in higher sphere concentrations in the tumor. Objective response was noted in 96% of tumors (complete response, 82%; partial response, 14%), and durable response at 2 years was observed in 97% of tumors. Median TTP was not reached, and the 2-year progression rate was 11%. In the 15 patients who received a liver transplant, median tumor necrosis was 99%, and CPN was significantly correlated with lower tumor volume and higher D99. No procedure-related adverse events were noted for up to 6 months.
The results of this study demonstrate that voxel-based dosimetry following Y-90 radioembolization can provide valuable information on sphere deposition and distribution in the tumor and surrounding tissue. Data showed that D70, D90, and D99 play a critical role in CPN, highlighting the importance of delivering high SA throughout the tumor. Moreover, ablative RS with high SA was well tolerated with limited AEs. Though the study included a relatively small sample size, these results likely have implications for improving patient outcomes in treating HCC.
Source:
Sandow T, Gimenez J, Nunez K, et al. Using voxel-based dosimetry to evaluate sphere concentration and tumor dose in hepatocellular carcinoma treated with yttrium-90 radiation segmentectomy with glass microspheres. J Vasc Interv Radiol. 2024;35(11):1602-1612.e1. doi:10.1016/j.jvir.2024.05.020
