AbstractID: 9443 Title: Grid: A Location Dependent Intensity Modulated Radiotherapy
ABSTRACT
Recently, promising clinical results have been shown in the delivery of palliative
treatments using megavoltage photon grid radiation therapy1. However, these results were
limited to some fixed grid size and geometrical patterns. Experimental verification of
dose distributions in various grid size and patterns seems either impossible or very timeconsuming. In this project, dose distribution of modulated external beam grid therapy has
been investigated using MCNP Monte Carlo code. 2D and 3D dose distributions were
obtained in Solid WaterTM phantom. Simulations were performed for a commercially
available linear accelerator, with a lead grid block which was set to 60 cm from target,
using 10x10 cm2 fields. The tally cells were placed at various depths in the phantom with
100 cm SSD, to obtain 2-D and 3D matrix dose distribution. The results of the Monte
Carlo simulations were compared with the measured data using TLD and radiochromic
film, for the same geometrical setups. The preliminary results for 19-hole grid, for 6 MV
photon beams, have shown an excellent agreement with measured data. Both the
measurement and the Monte Carlo simulation show that there is about 24% background
between the grid holes, and the uniform external beam is modulated by the grid. These
results show that the Monte Carlo technique could be used to construct and optimize the
dose distribution of grid therapy.