An Optimized Methodology for Patient-Specific Therapeutic Activity Administration in Liver Radioembolization

Radioembolization (RE) with glass microspheres (MS) loaded with Yttrium-90 (Y-90) has been used to treat tumors in the liver with some reported success. However, assessing absorbed doses (AD) in the planning tumor volume (PTV) and normal liver volume (NLV) is a key problem to address in RE. In clinical practice, the computation of Y-90 activity to be administered follows the manufacturer's recommendations, which do not consider the specific characteristics of MS deposition in each patient's liver. Our main aim is to develop a methodology to estimate the optimal activity for each patient treatment. It uses the absorbed dose distribution (ADD) derived from the Technetium-99m (Tc-99m)-labeled macroaggregated albumin (MAA) obtained from pre-treatment planning single-photon emission computed tomography (SPECT) images. Post-treatment positron emission tomography (PET) images of the Y-90-MS distribution were used to estimate the ADD for treatment verification. Sixteen RE treatments were retrospectively selected. The agreement between the estimated mean AD based on the planning imaging and real post-treatment mean AD was good in PTV with an intraclass correlation coefficient (ICC) of 0.79 and excellent in NLV (ICC = 0.97). The optimization of Y-90 activity using pre-defined clinical AD thresholds (<70 Gy in NLV and >80 Gy in PTV) imposed on the PTV and NLV voxels showed remarkably high agreement (ICC = 0.96, p < 0.001) in eleven out of the sixteen RE treatments between SPECT-MAA-based and PET-MS-based optimal activity estimates. In conclusion, under well-controlled conditions, pre-treatment SPECT-MAA imaging predicts well the treatment of ADD. In addition, SPECT-MAA imaging can be used to optimize the Y-90-MS activity to be administered to the liver.