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