Effect of Varying Phantom Size in Dosimetry of Iridium-192: A Comparison of Experimental Data with EGSnrc Monte Carlo Calculation

摘要

There have been increasing numbers of studies in high dose-rate (HDR) brachytherapy dosimetry, which have shown that the phantom size has significant effect on the dose delivered. The most frequently used methodology consisted of verifying the Monte Carlo calculations with the experimental measurements. This paper primarily reports the effects of varying scatter material thickness above an Iridium-192 (~(l92)Ir) HDR source by using a PTW Roos chamber (PTW, Germany) and the EGSnrc Monte Carlo code (National Research Council Canada, Canada). Virtual Water (Med-Cal, USA) was utilized as a scatter material. A microSelectron remote afterloader unit (Nucletron, Netherlands) was utilized to deliver ~(l92)lr source. The Roos chamber placed in the recess of a 20 mm thick Virtual Water slab was positioned above the backscatter material. A catheter attached to the treatment tube from the remote afterloader unit was fixed above the central axis of a Roos chamber. Secondly, the position dependence of a Roos chamber with respect to the source has been investigated. This was achieved by placing two different thick scatter materials between the planes of the source and a Roos chamber. The results from both experimental measurements and Monte Carlo calculations has shown increased dose with increasing scatter material thickness above ~(192)Ir source, with Monte Carlo calculated results showing less variation in dose. The dose output reduced considerably with increasing thickness of scatter materials between the chamber and the source.