en Radiation Biology Radiation Biology تحقيق بديع Original Research <p><strong>Background:</strong> 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.<strong> Materials and Methods:</strong> 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. <strong>Results:</strong> 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. <strong>Conclusion:</strong> 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.</p> HVL, EGSnrc, MC simulation, orthovoltage machine 325 330 http://ijrr.com/browse.php?a_code=A-10-1-523&slc_lang=en&sid=1 A. Shabestani Monfared 790031947532846009425 790031947532846009425 No Biochemistry and Biophysics Deptartment, Babol University of Medical Sciences, Shahid Rajaee Oncology Hospital, Babolsar, Iran T. Allahverdi Pourfallah tpourfallah@mazums.ac.ir 790031947532846009426 790031947532846009426 Yes Biochemistry and Biophysics Department, Faculty of Medicine, Mazandaran University of Medical Sciences, Sari, Iran H. Babapour 790031947532846009427 790031947532846009427 No Nuclear Engineering Department, Azad Islamic University- Sciences and Researches Branch, Tehran, Iran A.R. Shirazi 790031947532846009428 790031947532846009428 No Medical Physics Department, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran