The complexity of Intensity Modulated Radiation Therapy (IMRT) plans requires the definition of an accurate Quality Assurance (QA) programs to ensure the agreement between the calculated and delivered dose distribution. Different QA programs are in use such as those based on dose measurements performed with radiochromic film and ionization chambers 2D array. A lively debate is going on in the scientific community to establish if radiochromic film is a superior technique than ionization chambers array for IMRT quality assurance. In this paper, we calibrate GAFChromic EBT2 films and perform a comparison between their dosimetrical accuracy and that of ionizing chambers array on a prostate IMRT treatment plane. We find that GAFChromic EBT2 films do not give a linear response; the relation between doses and gray – levels is a 2° degree polynomial. Moreover, we obtain that their dosimetrical accuracy is comparable to that of ionizing chambers array. This result together with the consideration that 2D arrays are easier to use because they do not require an expensive calibration and delay between irradiation and read – out of the dosimeter, as it happens for radiochromic films, take us to prefer their use.