SIMULATION OF PHOTON DOSE CALCULATION: PENCIL BEAM CONVOLUTION

• Main Author: YULIA RAHMA (NIM : 10213036), ANNISA
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/21151
• Institution: Institut Teknologi Bandung

Pencil beam convolution as a method of photon model-based dose calculation which is proposed by Ahnesjo (1992) has proven accurate result with error 0.6% -1.5% compared with measurement data. This method is based on analytical convolution of TERMA and pencil beam kernel function. Total dose consists of primary, secondary, contaminant particle, and head scatter component. This research is aimed to simulate photon dose calculation for 6 MV photon beams energy using PBC method. In this simulation, photon beam is regarded as a monoenergetic pencil beam. The calculations are carried out with the integral semianalytic approach of the kernel convolution for the primary, secondary, contaminant, and head-scatter components to the TERMA function, a Gaussian distribution function, and simulated using MATLAB software. Simulation is presented in homogenous cylindrical water phantom with field size 10x10 cm2. Dose distributions in depth and in radial were analyzed using the percentage depth dose (PDD) and dose profile. To test the accuracy of calculation, PDD and profiles were compared with Monte Carlo PDD and dose profiles. The zmax value has shifted about 14% in compare with MC simulation result. In PDD data, the total surface dose consists of 52.5% primary dose, 7.5% secondary dose, 5.7% dose of contaminant, and ~ 10-9% dose of head scatter. From PBC dose profile data obtained the beam edge point and treatment field size are 4.8 cm and 9.6x9.6 cm2 respectively with an error about 4% from MC simulation results. The dose in the penumbra area is greater 7.5% in compare with MC simulation results. In this monoenergetic photon beam simulation, PBC method show an error in calculations about 0.3-37.5% for dose in depth and 4-7.5% for dose in radial. Further studies are needed to consider the weight of photon beam in simulation based on photon energy spectrum used in order to improve the calculation accuracy.