hvl evaluation of orthovoltage x-ray machine using egsnrc code of simulation

background: making use of the orthovoltage machines in radiotherapy, is one of the routine methods for the treatment of the superficial lesions. in this study, an important determinant of x-ray quality, the hvl (half value layer), has been evaluated. materials and methods: the hvls of a orthovoltage x-ray machine in 120 and 180 kvp are measured, using an empirical method, in which the hvls are derived from the absorption curves. the measured hvls are compared with calculated (monte carlo simulation) hvls. using the beamdp code of simulation, the output spectra are obtained and employed for the measurement of the hvls. results: comparing the calculated and measured hvl values, the results show that the highest and lowest differences between the two are 4.96% and 2.27%, respectively, which are, in fairly good agreement with those obtained in the former studies. conclusion: this study shows that the egsnrc simulation code is capable of being used for the extraction of the quality indices for the superficial x-ray radiotherapy machines. it seems that, the mentioned code, with the mentioned experimental method, can be employed as a routine clinical test tool for every superficial radiotherapy department.