EXPERIMENTAL DETERMINATION OF THE MEAN GLANDULAR DOSE DISTRIBUTION IN DIFFERENT MAMMOGRAPHIC BEAM QUALITIES

Abstract

Estimates of mean glandular dose are made from external breast measuring and, in practical situations, externally to a phantom representing a typical breast. The estimate of the mean glandular dose is obtained from results of the Monte Carlo method, which considers specific measuring architectures and that must be reproduced by the measuring process in question. Correlations between this quantity and specific properties of breast type to be evaluated were established. This involves the glandularity and compressed breast thickness as well as the properties of the X-ray spectrum used to produce the image, such as the combination anode/filter and the voltage applied to the X-ray tube, which modifies the half value layer (HVL) of the beam. The characterization of the X-ray beam through the direct measurement of its spectrum is a procedure of high complexity and difficult to implement in clinical systems due to the architecture of the equipment and the impossibility of adequate controls of the fluency of photons produced by these devices. Due to the strong dependence of the mean glandular dose to the quality of the radiation beam, it is expected that there is a correlation between the measured spectrum shape and glandular dose. These empirical limitations motivate the proposal of this project, which work plan the following steps: (i) Development of an experimental setup for measuring of the X-ray spectra in clinical mammography systems; (ii) Measurement of X-ray spectra and correlation with estimates of mean glandular dose using technical specifications widely used in mammographic examinations adopted in Brazil; (iii) Measurement of dose distributions at different depths of the breast using optically stimulated luminescence dosimetry; (iv) Analysis of the correlation between the measured spectra and distributions of corresponding doses at different depths considering breasts with different granularity and simulated results found in the literature. Thus, it is expected to produce information that can contribute to a better understanding of the behavior of the dose distribution in the typical breast diagnostic procedures and overcome, at least partially, the limitations currently found for empirical approach to determining the radiation spectra produced by clinical mammography equipment. For this, the work program was targeted leverage the experience gained by the candidate in his Master's program, with FAPESP scholarship (Experimental study of the relationship between air kerma and ambient dose equivalent for the calculation of barriers in primary classrooms radiological) in the field of X-ray spectrometry.