Evaluation Of Patient Doses From Digital X-ray Photography

[Objective] In the area of diagnostic X-ray imaging, digital X-ray photography is gradually substituting the traditional screen-film X-ray imaging. The purpose of this research was to study the quantitative relationship between exposure indicator and radiation dose, such as patient entrance surface dose, organ dose and effective dose, developing a method for fast evaluation of patient’s dose undergoing digital X-ray photography, which could be a robust tool for medical radiation dose investigation and collective dose evaluation.[Methods] Based on the dose indicator in the digital X-ray system (CR), a theoretical model for patient entrance surface dose calculation was established. Moreover, the influence of tube potential, total filter and body part thickness thoroughly discussed, to quantify the relationship between exposure indicator and entrance surface dose. The determination of those parameters, such as thickness-attenuation-function and image-plate-energy-response-function, in this relationship was obtained through water phantom experiments and Monte Carlo simulation. The universal verification experiments of this model were conducted on three other different X-ray systems, using thermoluminescence detector to measure the entrance surface dose results of abdomen X-ray examination. In addition, the study did some comparison among the dose indicator method, the exposure parameter method and the dose-area-product method to see if there were any differences among them. Patient’s organ dose and effective dose calculation were carried out using the up-to-date MIRD phantom and Monte Carlo program MCNP5in order to get the entrance surface dose-organ dose conversion factors with various combinations of X-ray examination, tube potential and total filter. The conversion factors were verified by comparing with several previous results. Furthermore, the entrance surface dose-effective dose conversion factors were calculated on top of the organ dose conversion factors and the latest tissue weight coefficient. Finally, the calculation of effective dose based on exposure indicator was established based on the entrance surface dose evaluation model and the entrance surface dose-effective dose conversion factors. [Results] The estimation method for patient’s entrance surface dose and effective dose of digital X-ray examinations were set up in this study based on dose indicator. The verification experiment results showed that the relative differences between estimation results of patients’entrance surface dose using the method established in this study and the measured ones ranged from-16.9%to18.1%. Also, estimation results of this method were generally equivalent to other various estimation methods. The differences between entrance surface dose-organ dose conversion factors calculated in this study and previous ones ranged from-28.6%to24.8%for those organs located in the beam area. The relative differences of entrance surface dose-effective dose conversion factors calculated by this study and previous ones ranged from-12.5%to3.2%, when the tissue weight factors were set to be the same. The results fitted with each other quite well.[Conclusion] The estimation results of the method built in this study can basically satisfy the needs of evaluation in radiation protection dosimetry field. This model can be used to directly calculate patient’s entrance surface dose, main organ dose and effective dose of certain digital X-ray examination, dose indicator, tube potential and body part thickness. This method provided an effective and convenient way for up-to-date or retrospective analysis of patient doses undergoing digital X-ray examination.