Individual breast dosimetry for mammographic exams : a back-projection approach

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The aim of this project is to propose and validate a procedure for estimating a dose at the axial plane of the breast in patients under mammographic exposure by means of electronic portal imaging device (EPID) dosimetry. In vivo transit dosimetry consists of measuring the transmitted radiation through the breast with an EPID, and then back-projecting the fluence through the same volume in order to reconstruct the dose at a certain plane. The methodology relies on the fact that from individual beam attenuation information, is possible to estimate dose deposition in the mammary gland. Beam attenuation was calculated from the exit and entrance fluence. Monte Carlo simulation of the entrance fluence was computed for three beam qualities. Exit fluence is calculated for each case, by deconvolution of the EPID image with previously determined composite kernel. A complete model (i.e., X-ray tube, breast compression paddle, different breast thickness and detector) of the GE Senograph Essential with Tomosynthesis device, was simulated with EGSnrc. Specific codes as BEAMnrc and DOSXYZnrc were used for beam and detector simulations, respectively. Three different beam qualities were simulated (only for 2D conventional mammography image acquisition) and additionally, and in-house graphical user interphase MATLAB1 program “BreDose” was designed to estimate doses at an axial mid-plane of the breast from the EPID images.
Tesis (Magíster en Física Médica)--Pontificia Universidad Católica de Chile, 2017