A Library of Experimentally Derived Microscale Blood and Lymphatic Vasculature Models for Applications to Radiopharmaceutical Dosimetry
Abstract
Purpose
To develop a library of 3D computational, tissue-representative models incorporating physiologically relevant microvascular network patterns for calculating local alpha particle and electron dosimetry effects. It is hypothesized that to compute scale-accurate doses for shorter range alpha particles and lower energy electrons, explicitly modeled blood and lymphatic microvasculature must be considered in radiation transport simulations.
Methods
To obtain relevant microvascular network patterns, eight adult rat mesenteric tissues labeled for PECAM (blood vessel marker) and Lyve-1 (lymphatic marker) were imaged – two of which were angiogenically stimulated to provide higher vascular density model variations. Representative images of network regions were then imported into the Creo Parametric software and manually converted to a 3D surface polygon mesh model. Conversion into the tetrahedral mesh format was completed using POLY2TET. The model was then incorporated into the Particle and Heavy Ion Transport code System (PHITS) and absorbed fractions were computed for the blood microvascular, lymphatic and interstitial regions. Simulations were performed for alpha particles of energies 1-12 MeV in increments of 0.5 MeV and for electrons on a logarithmic energy grid from 10 keV to 10 MeV, consisting of 25 energies.
Results
In the low energy simulations, absorbed fractions in non-source target regions were approximately zero due to minimal escape from the source regions. Absorbed fractions approached the volume fraction of the target region with increasing energy source particle. Variation of up to about 25% in absorbed fractions is observed across unstimulated regions of interest, primarily due to volume differentials, with slight changes in curve shapes due to varying vessel spatial distributions.
Conclusion
A library of eight microscale models inclusive of blood and lymphatic vasculature were developed with variation in vascular density and spatial pattern. A complete data set of absorbed fractions for alpha particles and electrons was generated.