Quantum Detective Efficiency (DQE) is referred in literature as the most robust object-independent parameter for characterization of radiation detectors efficiency. DQE evaluation is particularly important in digital X-ray detectors, where the efficiency loss implies in image quality degradation and increase of patient exposed radiation dose. However, DQE cannot be evaluated directly. Its evaluation is derived of four other measurements: the Modulation Transfer Function (MTF), the Noise Power Spectrum (NPS), the Gamma factor (γ) and the Photon fluency (φ). The Photon fluency has a not easy experimental evaluation, being calculated by the integral of the X-ray radiation emission spectrum, using spectrophotometers or X-ray tube mathematical modeling. These approaches may lead to errors. In this study, Photon fluency was extrapolated from the measurements of absorbed dose and of half value layer, using monochromatic radiation. Assuming this restriction, the Photon fluency can be evaluated using only a conventional dosimeter. Therefore, this technique is compatible with the investments allocated for regular services of preventive maintenance and image quality control. As an evaluation of the viability in using this methodology in clinical environment, a DQE evaluation routine was implemented for the Digora (Soredex, Helsink, Finland) dental digital X-ray system with very good results that agreed with those obtained with conventional techniques.4 30563059Workman, A., Brettle, D.S., Physical performance measures of radiographic imaging systems (1997) Dentomaxillofacial Radiology, 26, pp. 139-146Barret, H.H., Swindell, W., (1981) Radiological Imaging: The Theory of Image Formation, Detection and Processing, 1-2. , Academic Press, London, UKDaint, J.C., Shaw, R., (1976) Image Science - Principles, Analyses and Evaluation of Photographic-type Imaging Process, , Academic Press, London, UKAlbuquerque, J.A.G., (2001) Avaliação Automática de Parâmetros Fisicos de Qualidade de Imagem em Sistemas de Radiologia Digital Odontológica, , http://www.rau-tu.unicamp.br/nou-rau/sbu/, M.Sc. dissertation, Biomed. Eng. Program, Unicamp, Campinas, Brazil, in PortugueseAlbuquerque, J.A.G., Costa, E.T., Haiter Neto, F., Paganinni, G.A., Bóscolo, F.N., Oliveira, A.E.F., Evaluation of PSPL plate erasing time of a digital dental radiology system Proc. SPIE Medical Imaging 2001, 4320, pp. 227-239. , San Diego, CACosta, E.T., Albuquerque, J.A.G., Haiter Neto, F., Paganinni, G.A., Bóscolo, F.N., Oliveira, A.E.F., Environment influence on PSPL-based digital dental radiology systems Proc. SPIE Medical Imaging 2001, 4320, pp. 219-226. , San Diego, CAHanam, J., (1992) Quality Control of Gamma Cameras and Associated Computer Systems, , Institute of Physical Sciences in Medicine, Bradford, UKAttix, F.H., (1986) Introduction to Radiological Physics and Radiation Dosimetry, , Wiley-Interscience, New York, NYSeelentag, W.W., Panzer, W., Equivalent photon energy including Rayleigh (coherent) scattering (1979) Gesellschaft für StrahlenBrettle, D.S., Wokman, A., Ellwood, R., Launders, J.H., Horner, K., Davies, R.M., The imaging performance of a storage phosphor system for dental radiography (1996) The British Journal of Radiology, 69, pp. 256-261Granfords, P.R., Aufrichtig, R., DQE(f) of an amorphous silicon flat panel X-ray detector: Detector parameter influences and measurement methodology Proc. SPIE Medical Imaging 2000, 3977, pp. 2-13