Beta dose calculation in human arteries for various brachytherapy seed types

Abstract

This dissertation explores beta dose profiles of microspheres packed in arteries, various source geometries of [formula omitted] that can be used for therapeutic purposes, and dose backscatter factors for selected beta sources. A novel treatment method by injecting microspheres into feeding arteries of arteriovenous malformations (AVM) is under preclinical investigation. To optimize radiation dose to the clinically important area, i.e., arterial wall, preliminary dosimetric studies were needed. Monte Carlo calculations were performed for several geometries simulating arteries filled with microspheres packed by random packing methods. Arterial radii used in the simulation varied from 50 μm to 3 mm; microsphere radii varied from 10 μm to 0.7 mm. Dose varied significantly as a function of microsphere size, for constant arterial sizes. For the same sizes of arteries, significant dose increase was observed because of inter-artery exposure for large arteries (>0.1 cm radius) filled with large microspheres (>0.03 cm radius). Dose increase between small arteries (<0.03 cm radius) was less significant. The dose profiles of prototype [formula omitted] beta brachytherapy sources were calculated using MCNP 4C Monte Carlo code as well as dose point kernel (DPK) for selected cases. Dose profiles were similar to those for beta sources currently used indicating that [formula omitted] can substitute for current sources for certain cases. The DPK and MCNP results matched closely. Backscattering of electrons is a prominent secondary effect in beta dosimetry. The backscattering is closely correlated with factors such as geometry of source and scattering material, and composition of scattering material. The backscattering factors were calculated for selected beta sources that are currently used as well as for other potentially useful sources. The factors were calculated as a function of distance from the interface between water and scatterers. These factors were fit by a simple function for future incorporation into a DPK code. Backscattering effect was significant for short distances from interfaces between water and scattering material. © 2003, American Association of Physicists in Medicine. All rights reserved.