Although GAFCHROMIC EBT3 (EBT3) as a radiochromic film shows only slight energy dependency errors in comparison with other radiochromic films, the influence of energy dependence in the diagnosis energy range (less than 100 keV) is larger in the high energy range (over 100 keV). Based on this characteristic, adaptation of the EBT3 dosimetry in the diagnosis range was investigated. The energy response of the EBT3 in the diagnosis range at 30, 40, 50, 60 keV was measured using the density-absorbed dose calibration curve of the absorbed dose versus film density for the EBT3. Various data (degree of leaning, coefficient of determination) of each effective energy were compared. The density - absorbed dose calibration curves were linearly correlated in each of the effective energies. There was an energy dependent error of approximately 0.2% from 30 to 60 keV. As a result, it can be seen that the EBT3 is available in the diagnosis energy range. However, the influence of the non-uniformity error caused by the repeatability of the scan method must be considered because EBT3 distortion has a serious influence on measurement precision.