Monte Carlo Dose Estimation of Absorbed Dose to the Hematopoietic Stem Cell Layer of the Bone Marrow Assuming Nonuniform Distribution Around the Vascular Endothelium of the Bone Marrow: Simulation and Analysis Study.

Abstract

Background: Recent studies have shown that hematopoietic stem cells (HSCs) are concentrated around the endothelium of the sinusoidal capillaries. However, the current dosimetry model proposed by the International Commission on Radiological Protection (ICRP) does not account for the heterogeneity of bone marrow tissue and stem cell distribution. If the location of the hematopoietic stem cell layer differs from previous assumptions, it is necessary to re-evaluate the dose. It is especially important for short-range alpha particles where the energy deposited in the target HSC layer can vary greatly depending on the distance from the source region.

Objective: The objective of this study is to evaluate the red bone marrow doses assuming that the hematopoietic stem cell layer of the bone marrow is localized in the vascular endothelium.

Methods: A model of the trabecular bone tissues in the cervical vertebrae was developed using the Particle and Heavy Ion Transport System code. Radiation transport simulations were performed for beta and alpha radionuclides as well as noble gases, and the absorbed doses to the stem cell layer within the perivascular HSC layer of the bone marrow from inhaled radionuclides were estimated. The estimated doses were then compared with the absorbed dose based on the ICRP 60 and ICRP 103 recommendations.

Results: The absorbed doses to the bone marrow obtained from the model calculations were not significantly different from ICRP 60 and ICRP 103 for beta-nuclides. However, for alpha-nuclides, the absorbed doses were much lower than previously estimated. In addition, the contribution of red bone marrow and blood sources was greater than that of trabecular bone for alpha-nuclides. Noble gases in the red bone marrow may also affect the bone marrow stem cell layer.

Conclusions: The bone marrow dose assessment for alpha nuclides and noble gases should be re-examined using a precise model based on computed tomography images from the perspective of occupational and public radiation protection.