Room: AAPM ePoster Library
Purpose: Current treatment planning systems for Vaginal Cylinder Brachytherapy (VCB) take advantage of TG43 formalism for dose calculations, considering all the environment as water. This approach does not take the inhomogeneity of the cylinder into account. In this work, we used Monte Carlo simulation in order to assess the effect of inhomogeneity for a typical plan based on TG43.
Methods: A Varian 192Ir Gamma Med Plus source was simulated using GEANT4 Monte Carlo simulation code. First, the source was placed in various positions in a 30x30x30 cc water phantom based on clinical template plans’ dwell positions. In order to consider the effect of inhomogeneity of the vaginal cylinder applicator, at the second step, the source was positioned in the same condition in a simulated single lumen Varian’s vaginal cylinder made of PPSU plastic with a range of 20-35 mm diameter cylinder, a density of 1.29 g/cc, and a 3 mm dead space at the apex. The MATLAB software was used for data analysis.
Results: The comparison between the results from TG43 and those from a 30 mm dimeter cylinder showed a shrinkage of about 2 mm in dose coverage at periphery for the cylinder. However, there was no noticeable difference between the two at the apex.
Conclusion: Taking the inhomogeneity into account can be really important, in particular, for treatment of the patients with the thicker cylinders. There is a subset of patients who have recurring of the disease at the vaginal periphery. This could be related to underdosing of the periphery due to ignoring the correction for the cylinders’ inhomogeneity.