DETERMINATION OF CHARACTERISTICS OF BRAGG CURVE FOR PROTON BEAM ON WATER PHANTOM USING MONTE CARLO SIMULATION (TOPAS)

• Main Author: Alifa Nadya, Elma
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/67924
• Institution: Institut Teknologi Bandung

Variations in the energy of the charged particle radiation beam will change the characteristics of the PDD (Percentage Depth-Dose) curve. This study will examine the effect of variations in proton beam energy on changes in the haracteristics of the Bragg curve in water phantoms using a Monte Carlo simulation, namely the Tool for Particle Simulation (TOPAS). The variation of the proton beam energy used is the energy range commonly used for proton therapy, which is 60-250 MeV and the proton beam energy distribution meets the Gaussian distribution. The homogeneous water phantom used was in the form of a block measuring 8 cm × 8 cm × 40 cm which was divided into 800 voxels as the measurement point for the dose at medium. Analysis was carried out on changes in the characteristics of the Bragg curve for each variation of the proton beam energy, namely the height of the Bragg peak, the position of the Bragg peak, and the FWHM of the Bragg peak. The position of the Bragg curve and FWHM increases quadratic to the energy of the proton beam, while the height of the Bragg peak increases to 160 MeV and then decreases. There are artifacts in the simulations, the appearance of secondary Bragg peaks in areas that should be relatively low and flat (plateaus) on the Bragg curve with energy variations of 140-250 MeV. Changes in the characteristics of the secondary Bragg peak were also observed as well as changes in the characteristics of the main Bragg peak. The cause of the emergence of simulation artifacts in the form of secondary peaks was found out using simulations of voxel size variations with a fixed proton beam energy. The thickness of the z-axis voxel which was previously 0.5 mm and has 800 measurement points, was varied to 1 mm, 2 mm, 5 mm, and 10 mm. The Bragg curve of variation in voxel thickness still produces secondary peaks. So that further simulations were carried out in the form of variations in the xy-plane surface area which previously measured 8 cm × 8 cm to 12 cm × 12 cm, 4 cm × 4 cm, 2 cm × 2 cm, and 1 cm × 1 cm. Surface variation of 2 cm x 2 cm and 1 cm × 1 cm did not give rise to simulation artifacts in the form of secondary peaks.