Monte Carlo Simulation and Experimental Determination of Tissue Phantom Ratio for Photon Beams delivered from Medical Linear Accelerator

Abstract

For an external radiotherapy procedure, the tissue phantom ratio (TPR20,10) is used as a photon beam quality index. This work presents an estimate of TPR20,10 using two cylindrical ionization chambers (NE2571 Farmer and PTW30013) in three high-energy photon modes (6, 10 and 15 MV) using both the Monte Carlo simulation and the experimental setup. The MCNPX (version 2.6.0) was used for the simulation of photon beams delivered by Varian-2300CD linac for the determination of TPR20,10 according to technical report series (TRS) 398. Again, applying the same protocol TPR20,10 values were measured experimentally with NE2571 Farmer and PTW30013 chambers for the same medical linear accelerator (LINAC). The differences of TPR20, 10 between MCNPX and experimental values were found for NE2571 Farmer chamber within 4.17 percent, 2.9 percent and 2.5 percent and similarly, these were within 3.89 percent, 2.71 percent and 1.98 percent at 6, 10 and 15 MV respectively for PTW30013. The TPR20,10 values simulated by MCNPX demonstrated close agreement with our experimental results.