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1755005 
Journal Article 
Monte Carlo model for a prototype CT-compatible, anatomically adaptive, shielded intracavitary brachytherapy applicator for the treatment of cervical cancer 
Price, MJ; Gifford, KA; Horton, JL, Jr; Eifel, PJ; Gillin, MT; Lawyer, A; Mourtada, F 
2009 
1 
Medical Physics
ISSN: 0094-2405 
36 
9 
4147-4155 
19810488 
WOS:000270086000032 
Purpose: Current, clinically applicable intracavitary
brachytherapy applicators that utilize shielded ovoids contain a pair of tungsten-alloy shields
which serve to reduce dose delivered to the rectum and bladder during source afterloading. After
applicator insertion, these fixed shields are not necessarily positioned to provide optimal
shielding of these critical structures due to variations in patient anatomies. The authors
present a dosimetric evaluation of a novel prototype intracavitary brachytherapy ovoid
[anatomically adaptive applicator (A(3))], featuring a single shield whose position can be
adjusted with two degrees of freedom: Rotation about and translation along the long axis of the
ovoid. Methods: The dosimetry of the device for a HDR (192)Ir was characterized using
radiochromic film measurements for various shield orientations. A MCNPX Monte Carlo model was
developed of the prototype ovoid and integrated with a previously validated model of a v2 mHDR
(192)Ir source (Nucletron Co.). The model was validated for three distinct shield orientations
using film measurements. Results: For the most complex case, 91% of the absolute simulated and
measured dose points agreed within 2% or 2 mm and 96% agreed within 10% or 2 mm. Conclusions:
Validation of the Monte Carlo model facilitates future investigations into any dosimetric
advantages the use of the A(3) may have over the current state of art with respect to
optimization and customization of dose delivery as a function of patient anatomical geometries.
(C) 2009 American Association of Physicists in Medicine. [DOI: 10.1118/1.3193682] 
brachytherapy; intracavitary applicators; Monte Carlo; adaptive shielding