Absorbed-dose calculation for treatment of liver neoplasms with ⁹⁰Y-microspheres

The aim of this review article is to present a state-of-the-art of the absorbed-dose calculation for the selective internal radiation therapy (SIRT) of liver neoplasms with ⁹⁰Y-microspheres. The review focuses on the following aspects: activity quantification, partition model, medical internal radiation dose (MIRD) formalism, three-dimensional dosimetry, micro-scale dosimetry, and radiobiological modeling. ^99mTc-macro-aggregated albumin (MAA) with single-photon emission tomography (SPECT) serves as a surrogate for ⁹⁰Y-microspheres for treatment planning and predictive dosimetry. Iterative reconstruction with physic modeling to compensate quantification biases is now a standard for activity quantification. For post-implantation dosimetry, direct ⁹⁰Y quantification with time of flight positron emission tomography has demonstrated good accuracy. The partition model is a simple and well-known approach for tumor, normal liver, and lung dosimetry measured from ^99mTc-MAA-SPECT, while the MIRD equations can provide more detailed schemes for pre- and post-implantation dosimetry. 3D dosimetry allows considering heterogeneous activity and material distribution thanks to voxel-based quantification and energy deposition modeling. For the latter, dose-kernel convolution or local energy deposition approaches are widespread. Micro-scale dosimetry studies have highlighted high-absorbed-dose heterogeneities at the microscopic level. Microscopic models were developed and can be incorporated into macro-scale dosimetry. More recently, radiobiological models have been applied to calculate the biological effective dose. ⁹⁰Y-microspheres dosimetry for SIRT is an active field of research in all its aspects. Its ease of implementation in a clinical setting along with the development of microscopic and radiobiological models should contribute to better handle treatment outcomes.