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Equivalent phantom sizes and shapes for brachytherapy dosimetric studies of Ir 192 and Cs 137
Author(s) -
Granero Domingo,
PerezCalatayud Jose,
PujadesClaumarchirant MCarmen,
Ballester Facundo,
Melhus Christopher S.,
Rivard Mark J.
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2982140
Subject(s) - imaging phantom , dosimetry , brachytherapy , medical physics , medical imaging , nuclear medicine , radiation therapy , medicine , radiology
The impact of phantom size and shape in brachytherapy dosimetry was assessed using Monte Carlo methods in liquid water for Ir192 and Cs137 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, R sph , 10 – 40 cm were examined to determine the equivalent spherical phantom size to a variety of cylinder and cube sizes, R cyl and R cube , respectively. These sizes ranged from 10 to 30 cm . The equivalent R sph for a given size cylinder or cube was determined using a figure of merit (FOM) function to minimize differences between radial dose functions, g ( r ) . Using the FOM approach, a linear fit ( R 2 > 0.99 ) was obtained for the equivalent R sph for a given size cylinder or cube. The equivalent phantom for a cylinder, of 40 cm diameter and length 40 cm , is a sphere of 21 cm in radius and the equivalent phantom for a cube of 30 cm on each side is a sphere of 17.5 in radius. When normalizing all results to r = 1 cm for g ( r )comparisons of phantom shape, the absolute dose rates were equivalent within 0.1% forR sph ⩾ 10 cm for both Ir192 and Cs137 . Correlation factors to permit comparisons of unbounded g ( r )data for r ⩽ 15 cm in 20 published datasets resulted in agreement generally within 2%. Residual differences with four datasets were attributed to methodological uncertainties in the published references.