Depth dose of 6 and 18 MV photons in water measurement and calculation by the penelope MC code

In this study, we used PENELOPE Monte Carlo Code version 2011 which uses most update physical models for the interaction of 6 and 18 MV photons with water and calculated the depth dose, percent depth dose values and physical parameters such as energy distribution, angular distribution, interaction cross-sections, mass absorption coefficients, mean free path and range, stopping power. .YDD (percentage depth dose) values were obtained from PENELOPE depth dose values to compare with the experimental values of percentage depth dose(YDD). In the study, also, percentage depth dose values obtained experimentallyI For this, Varian Clinac DHX linear accelarator of Ondokuz Mayıs University, Faculty of Medicine, Depatment of Radiation Oncology was used.In the experimental work interactions of 6 and 18 MV photons with water phantom placed 100 cm from the accelerator head were examined and PDD values were measured as a function of depth (z). and avarage PDD values together with standart deviations (SD) were calculated. The results are in agreement with in one. The experimental results are also in good agreement with that of BJR 25 (The British Journal of Radiology (1996)):Best fit curves for 6 and 18 MV experimental results were obtained. The differences are found in the results because of the differences in the geometry of the experimental system. The differences mostly dissappered when we included the bremsstrahlung contribution coming from the head and water phantom.Key Words: 6 and 18 MV photon water percent depth dose values, PENELOPE Monte Carlo Simulation, depth dose, depth dose function.