Phantom study for ⁹⁰Y liver radioembolization dosimetry with a long axial field-of-view PET/CT

The physical properties of yttrium-90 (⁹⁰Y) allow for imaging with positron emission tomography/computed tomography (PET/CT). The increased sensitivity of long axial field-of-view (LAFOV) PET/CT scanners possibly allows to overcome the small branching ratio for positron production from ⁹⁰Y decays and to improve for the post-treatment dosimetry of ⁹⁰Y of selective internal radiation therapy.

For the challenging case of an image quality body phantom, we compare a full Monte Carlo (MC) dose calculation with the results from the two commercial software packages Simplicit90Y and Hermes. The voxel dosimetry module of Hermes relies on the ⁹⁰Y images taken with a LAFOV PET/CT, while the MC and Simplicit90Y dose calculations are image independent.

The resulting doses from the MC calculation and Simplicit90Y agree well within the error margins. The image-based dose calculation with Hermes, however, consistently underestimates the dose. This is due to the mismatch of the activity distribution in the PET images and the size of the volume of interest. We found that only for the smallest phantom sphere there is a statistically significant dependence of the Hermes dose on the image reconstruction parameters and scan time.

Our study shows that Simplicit90Y's local deposition model can provide a reliable dose estimate. On the other hand, the image based dose calculation suffers from the suboptimal reconstruction of the ⁹⁰Y distribution in small structures.