Equivalent phantom sizes and shapes for brachytherapy dosimetric studies of and

Abstract

The impact of phantom size and shape in brachytherapy dosimetry was assessed using Monte Carlo methods in liquid water for and point sources. This is needed since differences in published dosimetry data, both measurements and simulations, employ a variety of phantom sizes and shapes which can cause dose differences exceeding 30% near the phantom periphery. Spheres of radius, , were examined to determine the equivalent spherical phantom size to a variety of cylinder and cube sizes, and , respectively. These sizes ranged from . The equivalent for a given size cylinder or cube was determined using a figure of merit (FOM) function to minimize differences between radial dose functions, . Using the FOM approach, a linear fit was obtained for the equivalent for a given size cylinder or cube. The equivalent phantom for a cylinder, of diameter and length , is a sphere of in radius and the equivalent phantom for a cube of on each side is a sphere of 17.5 in radius. When normalizing all results to for comparisons of phantom shape, the absolute dose rates were equivalent within 0.1% for for both and . Correlation factors to permit comparisons of unbounded data for in 20 published datasets resulted in agreement generally within 2%. Residual differences with four datasets were attributed to methodological uncertainties in the published references.