Introduction: The importance of evaluating interfractional movements in head and neck radiotherapy is crucial, since even small displacement can produce overdose of critical structures nearby or underdose the target volume. A solution to reduce set-up errors and safety margins is repeatable and certain immobilization, such as usage of individual headrest. Purpose: The purpose of this research was to evaluate the importance of individual headrest in head and neck radiotherapy, to calculate interfractional movements, systematic and random error and to compare optimum safety margin between group with individual and standard headrest. Methods: In present study we included 120 patients with head and neck cancer, radically treated with intensity modulated (IMRT) or volumetric modulated radiation therapy (VMAT). They were divided into 6 groups, considering linear accelerator and time period in which they were treated. Groups 1 and 2 represented patient with standard headrest, and the rest of them, ones with individual. Systematic population and random population errors were evaluated, based on interfractional movements, that were measured on daily pre-treatment electronic portal images (EPI). Also the optimum safety margins of clinical and planning target volume, according to van Herk, were calculated. Results: The substantial interfraction movements show in posterior and inferior direction. The major difference between individual and standard headrest is represented in anteroposterior (AP) direction and inconsiderable in mediolateral (ML) direction. Since the individual headrest have been in use, systematic and random errors have mostly reduced: for about 0,1 - 0,5 mm. Consequently narrower PTV-CTV margin is neeeded, to be specific - 3,3 mm in AP, 2,6 mm in SI and 3,2 mm in ML direction. Discussion and conclusion: Conclusion, based on the results, shows that imobilization with individual headrest reflects in minor interfractional movements and lower frequency of isocenter correction. Statistically significant differences (p<10-3) were found between individual and standard headrests. An extenstion, no greater than 4 mm, of clinical target volume margin ensures that 90% of patients will recieve a minimum cumulative dose greater than 95% of the prescribed dose.