3D image-based dosimetry for Yttrium-90 radioembolization of hepatocellular carcinoma: Impact of imaging method on absorbed dose estimates.

Background: To improve therapy outcome of Yttrium-90 selective internal radiation therapy ( ⁹⁰ Y SIRT), patient-specific post-therapeutic dosimetry is required. For this purpose, various dosimetric approaches based on different available imaging data have been reported. The aim of this work was to compare post-therapeutic 3D absorbed dose images using Technetium-99m ( ^99m Tc) MAA SPECT/CT, Yttrium-90 ( ⁹⁰ Y) bremsstrahlung (BRS) SPECT/CT, and ⁹⁰ Y PET/CT.
Methods: Ten SIRTs of nine patients with unresectable hepatocellular carcinoma (HCC) were investigated. The ^99m Tc SPECT/CT data, obtained from ^99m Tc-MAA-based treatment simulation prior to ⁹⁰ Y SIRT, were scaled with the administered ⁹⁰ Y therapy activity. 3D absorbed dose images were generated by dose kernel convolution with scaled ^99m Tc/ ⁹⁰ Y SPECT/CT, ⁹⁰ Y BRS SPECT/CT, and ⁹⁰ Y PET/CT data of each patient. Absorbed dose estimates in tumor and healthy liver tissue obtained using the two SPECT/CT methods were compared against ⁹⁰ Y PET/CT.
Results: The percentage deviation of tumor absorbed dose estimates from ⁹⁰ Y PET/CT values was on average -2 ± 18% for scaled ^99m Tc/ ⁹⁰ Y SPECT/CT, whereas estimates from ⁹⁰ Y BRS SPECT/CT differed on average by -50 ± 13%. For healthy liver absorbed dose estimates, all three imaging methods revealed comparable values.
Conclusion: The quantification capabilities of the imaging data influence ⁹⁰ Y SIRT tumor dosimetry, while healthy liver absorbed dose values were comparable for all investigated imaging data. When no ⁹⁰ Y PET/CT image data are available, the proposed scaled ^99m Tc/ ⁹⁰ Y SPECT/CT dosimetry method was found to be more appropriate for HCC tumor dosimetry than ⁹⁰ Y BRS SPECT/CT based dosimetry.
(Copyright © 2020 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)