EANM dosimetry committee series on standard operational procedures: a unified methodology for 99mTc-MAA pre- and 90Y peri-therapy dosimetry in liver radioembolization with 90Y microspheres

The aim of this standard operational procedure is to standardize the methodology employed for the evaluation of pre- and post-treatment absorbed dose calculations in Y-90 microsphere liver radioembolization. Basic assumptions include the permanent trapping of microspheres, the local energy deposition method for voxel dosimetry, and the patient-relative calibration method for activity quantification.The identity of Tc-99m albumin macro-aggregates (MAA) and Y-90 microsphere biodistribution is also assumed. The large observed discrepancies in some patients between Tc-99m-MAA predictions and actual Y-90 microsphere distributions for lesions is discussed. Absorbed dose predictions to whole non-tumoural liver are considered more reliable and the basic predictors of toxicity. Treatment planning based on mean absorbed dose delivered to the whole non-tumoural liver is advised, except in super-selective treatments. Given the potential mismatch between MAA simulation and actual therapy, absorbed doses should be calculated both pre- and post-therapy. Distinct evaluation between target tumours and non-tumoural tissue, including lungs in cases of lung shunt, are vital for proper optimization of therapy. Dosimetry should be performed first according to a mean absorbed dose approach, with an optional, but important, voxel level evaluation. Fully corrected Tc-99m-MAA Single Photon Emission Computed Tomography (SPECT)/computed tomography (CT) and Y-90 TOF PET/CT are regarded as optimal acquisition methodologies, but, for institutes where SPECT/CT is not available, non-attenuation corrected Tc-99m-MAA SPECT may be used. This offers better planning quality than non dosimetric methods such as Body Surface Area (BSA) or mono-compartmental dosimetry. Quantitative Y-90 bremsstrahlung SPECT can be used if dedicated correction methods are available. The proposed methodology is feasible with standard camera software and a spreadsheet. Available commercial or free software can help facilitate the process and improve calculation time.

Automated summary

The standard operational procedure aims to standardize the evaluation methodology for absorbed dose calculations in Y-90 microsphere liver radioembolization. Treatment planning based on average absorbed dose is advised, with distinct evaluation between target tumors and non-tumoral tissue being vital for proper therapy optimization. Various imaging methodologies such as SPECT/CT and PET/CT are recommended for accurate dosimetry calculations.