Assessing the Validity of Image-Based DVH Metrics for Y-90 Tare Dosimetry
Abstract
Purpose
Dose–volume histograms (DVHs) are widely used in external beam radiation therapy, but their applicability to Y-90 transarterial radioembolization (TARE) remains uncertain. In Y-90 TARE, absorbed dose maps are derived from post-therapy PET or bremsstrahlung SPECT imaging, which are limited by spatial resolution and noise. Despite these limitations, DVH metrics such as D80 and D90 are increasingly used without systematic validation. This study evaluates when image-based DVH metrics provide information beyond mean absorbed dose in Y-90 TARE dosimetry.
Methods
A pilot feasibility study was performed using a 3D digital phantom (1-mm³ voxel) consisting of a uniform cylindrical background containing a spherical tumor. Tumors included off-center cold necrotic cores (0–30 mm radius) with a 20:1 tumor-to-background activity ratio. Dose maps were generated by convolving activity distributions with Gaussian kernels of FWHM 3, 10, and 20 mm and normalized to a maximum dose of 400 Gy. The 3-mm kernel modeled the reference Y-90 dose map, while 10 and 20-mm kernels simulated PET-like and SPECT-like dose maps. Multiple configurations were evaluated.
Results
Higher-threshold DVH metrics (e.g., D80) captured tumor dose heterogeneity under favorable imaging conditions. As necrotic core size increased, D80/Dmean decreased substantially in reference Y-90 dose maps (100% to 45%), modestly in PET-like maps (83% to 73%), and minimally in SPECT-like maps (~75%), demonstrating reduced DVH sensitivity with decreasing spatial resolution.
Conclusion
These preliminary results show that the utility of DVH metrics in Y-90 TARE dosimetry depends on imaging resolution and tumor heterogeneity. As resolution degrades, DVH metrics converge toward mean dose and become largely redundant under SPECT-like conditions. At PET-like resolution, DVH metrics retain sensitivity to dose heterogeneity and may provide added value. This feasibility study establishes a framework for evaluating DVH performance in Y-90 TARE, with future work planned to define thresholds for DVH reliability.