Dosimetry and prescription in liver radioembolization with⁹⁰Y microspheres: 3D calculation of tumor-to-liver ratio from global^99mTc-MAA SPECT information

Abstract

Dosimetry in liver radioembolization with Y microspheres is a fundamental tool, both for the optimization of each treatment and for improving knowledge of the treatment effects in the tissues. Different options are available for estimating the administered activity and the tumor/organ dose, among them the so-called partition method. The key factor in the partition method is the tumor/normal tissue activity uptake ratio (T/N), which is obtained by a single-photon emission computed tomography (SPECT) scan during a pre-treatment simulation. The less clear the distinction between healthy and tumor parenchyma within the liver, the more difficult it becomes to estimate the T/N ratio; therefore the use of the method is limited. This study presents a methodology to calculate the T/N ratio using global information from the SPECT. The T/N ratio is estimated by establishing uptake thresholds consistent with previously performed volumetry. This dose calculation method was validated against 3D voxel dosimetry, and was also compared with the standard partition method based on freehand regions of interest (ROI) outlining on SPECT slices. Both comparisons were done on a sample of 20 actual cases of hepatocellular carcinoma treated with resin microspheres. The proposed method and the voxel dosimetry method yield similar results, while the ROI-based method tends to over-estimate the dose to normal tissues. In addition, the variability associated with the ROI-based method is more extreme than the other methods. The proposed method is simpler than either the ROI or voxel dosimetry approaches and avoids the subjectivity associated with the manual selection of regions.

Optimización de la dosimetría en la planificación de los tratamientos de radioembolización hepática con microesferas de 90Y

“…Tanto la magnitud como la dispersión de las diferencias encontradas es superior a la observada por Mañeru et al (2017) [123]. Este grupo propone un método para calcular el índice TN a partir de la umbralización de la imagen SPECT y lo comparan con el método basado en ROIs, en una serie de 20 pacientes.…”