Poster — Wed Eve—25: Comparison of Dose Calculation Algorithms with Monte Carlo Simulation for Surface Dosimetry

Abstract

The aim of this study is to compare the surface dosimetry calculated by the analytical anisotropic algorithm (AAA) and collapsed cone convolution (CCC) algorithm with Monte Carlo (MC) simulation. The MC simulations are verified by measurements. In this study, tangential photon beams (6 and 15 MV; 4 × 4 and ), produced by a Varian 21 EX linear accelerator, with central beam axis (CAX) parallel to the water phantom surface were used. In addition, the photon beam was tilted clockwise 3 and 5 degrees around the isocenter located at a distance of 2 mm from the phantom surface to represent the skin thickness. Relative dose profiles (2 mm from the phantom surface) corresponding to the above experimental configuration were calculated using the AAA, CCC and MC methods based on the Eclipse, Pinnacle3 treatment planning system and the EGSnrc code. It is found that both the AAA and CCC methods agreed with uncertainty < ±3% compared to the MC, in calculating the relative surface dose profiles, when the CAXs of the photon beams were overlapped along the profiles. However, when the photon beams (6 and 15 MV; 4 × 4 and ) were tilted clockwise, the AAA and CCC methods underestimated the dose in the relative surface profile as compared to the MC. The deviation of the calculated relative surface dose profile among the AAA, CCC and MC methods depends on the energy, angle and field size of the photon beam.