|
Description:
|
This dissertation explores beta dose profile of microspheres packed in arteries , various source geometries of 142Pr that can be used for therapeutic purpose , and dose backscatter factors for selected beta sources .
A novel treatment method by injecting microspheres into feeding arteries of arteriovenous malformation (AVM ) is under pre -clinical 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 mm to 3 mm ; microsphere radii varied from 10 mm 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 rad . ) filled with large microspheres ( > 0 .03 cm rad . ) . Dose increase between small arteries (0 .03 cm rad . ) was less significant .
The dose profiles of prototype 142Pr 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 beta sources currently used indicating that 142Pr can substitute for current sources for certain cases and the DPK was closely matched with MCNP result .
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 potentially useful sources for therapeutic purpose . 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 distance from the surface of interface between water and scattering material . |