Background: The dose rate distribution
delivered by a low dose rate 137Cs pellet source, a
spherical source used within the source trains of the
Selectron gynecological brachytherapy system, was
investigated using the MCNP4C Monte Carlo code.
Materials and Methods: The calculations were
performed in both water and Plexiglas and the
absolute dose rate distribution for a single pellet
source and the AAPM TG-43 parameters were
computed. A spherical phantom with dimensions
large enough (60 cm) was used to provide full
scattering conditions. In order to score dose at
different distances from the source centre, this
sphere was divided into a set of 600 concentric
spherical shells of 0.05 cm thickness. The
calculations were performed up to a distance of 10
cm from the source centre. To calculate the effect of
the applicator and dummy pellets on dose rate
constant and radial dose function, a single pellet
source was simulated inside the vaginal applicator,
and spherical tally cells with radius of 0.05 cm were
used in the simulations. The F6 tally was used to
score the absolute dose rate at a given point in the
phantom. Results: The dose rate constant for a single
active pellet was found to be 1.102±0.007 cGyh-1U-1,
and the dose rate constant for an active pellet inside
the applicator was 1.095±0.009 cGyh-1U-1. The
tabulated data and 5th order polynomial fit
coefficients for the radial dose function along with the
dose rate constant are provided for both cases. The
effect of applicator and dummy pellets on anisotropy
function of the source was also investigated.
Conclusion: The error resulting from ignoring the
applicator was reduced using the data of a single
pellet. The results indicate that F(r, θ) decreases
towards the applicator. Iran. J. Radiat. Res., 2009 7
(3): 135-140
Sina S, Faghihi R, Meigooni A, Mehdizadeh S, Zehtabian M, Mosleh-Shirazi M. Simulation of the shielding effects of an applicator on the AAPM TG-43 parameters of CS-137 Selectron LDR brachytherapy sources. Int J Radiat Res 2009; 7 (3) :135-140 URL: http://ijrr.com/article-1-565-en.html