| Summary: | Radionuclide therapy is an innovative treatment in nuclear medicine that uses unsealed sources to treat some specific tumours in the human body. With an increasing interest in this modality, some efforts have been done to improve this field in nuclear medicine, such as the radiopharmaceuticals administered or the components of the imaging equipment. Pure beta emitters are the radionuclides most used in radionuclide therapy. They are described to have extremely high potential in the treatment of malignant and non-malignant disorders. The energy of these radionuclides is absorbed close to the target site due to its low range (few mm in tissue). The problem is the impossibility of imaging their uptake in the interest places since there are no gamma rays emissions and the beta radiation is impossible to detect externally. As a result, the only radiation capable to be perceived by the gamma camera is the bremsstrahlung photons produced when an accelerate beta particle passes close to the atomic nucleus and is deflected towards it. The detection of these photons is relevant for dosimetric purposes, in order to detect the real uptake of the radionuclide and hence to know the absorbed dose in the patient. Thus, the current dissertation reports a study about bremsstrahlung characteristics by using a Monte Carlo simulation. The study attempts to realise in what way the bremsstrahlung photons are produced in different types of biological materials, using different beta particles energies. The simulator used was the EGSnrc (Electron Gamma Shower) system (V4 2.3.2), a package for Monte Carlo simulations. The programs were written in Mortran language and compiled to Fortran. With this study, an additional aim was to obtain a strong knowledge on EGSnrc system and to be able to modify and produce a wide range of different simulations in different physical conditions. In order to understand the bremsstrahlung photons several simulations were performed, in different media and with different energies of beta particles emissions. Future work should be necessary in order to relate the bremsstrahlung photons understanding with the gamma camera components. The aim will be to improve the bremsstrahlung imaging and hence gathering realistic dosimetric data for the pure beta emitters.
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