Journal
EJNMMI PHYSICS
Volume 8, Issue 1, Pages -Publisher
SPRINGER
DOI: 10.1186/s40658-021-00394-3
Keywords
Radioembolization dosimetry; Tc-99m-MAA; Y-90 microspheres; Lung shunt; Liver dosimetry; Tumour dosimetry; Y-90 PET; Prospective; retrospective dosimetry
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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.
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.
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