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 (Y-90 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 (Tc-99m) MAA SPECT/CT, Yttrium-90 (Y-90) bremsstrahlung (BRS) SPECT/CT, and Y-90 PET/CT. Methods: Ten SIRTs of nine patients with unresectable hepatocellular carcinoma (HCC) were investigated. The Tc-99m SPECT/CT data, obtained from Tc-99m-MAA-based treatment simulation prior to Y-90 SIRT, were scaled with the administered Y-90 therapy activity. 3D absorbed dose images were generated by dose kernel convolution with scaled Tc-99m/90Y SPECT/CT, Y-90 BRS SPECT/CT, and Y-90 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 Y-90 PET/CT. Results: The percentage deviation of tumor absorbed dose estimates from Y-90 PET/CT values was on average-2 18% for scaled Tc-99m/90Y SPECT/CT, whereas estimates from Y-90 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 Y-90 SIRT tumor dosimetry, while healthy liver absorbed dose values were comparable for all investigated imaging data. When no Y-90 PET/CT image data are available, the proposed scaled Tc-99m/Y-90 SPECT/CT dosimetry method was found to be more appropriate for HCC tumor dosimetry than Y-90 BRS SPECT/CT based dosimetry.