LD783NR
Area: Física Medica
Tipo de presentacion: Poster

Viviane Batista De Lacerda I¹, Wilson Vieira J², Liane De Oliveira M^3,1, Roberto De Andrade Lima F^4,1

¹Departamento de Energia Nuclear Universidade Federal de Pernambuco.
²Departamento de Radiologia Instituto Federal de Pernambuco.
³Divisão de Produção de Radiofármacos Comissão Nacional de Energia Nuclear.
⁴Divisão de Técnicas Analíticas e Nucleares Comissão Nacional de Energia Nuclear.

Numerical dosimetry uses programs that simulate the interaction of radiation with matter using Monte Carlo method. Among them, the EGSnrc is a general-purpose software toolkit that can be applied to build Monte Carlo simulations of coupled electron-photon transport. This software has 14 radioactive source algorithms, however, none is suitable to perform simulations of the Positron Emission Tomography (PET). This is an exam that has become an established nuclear imaging modality and has proved especially useful in oncology. In this work, an algorithm of the radioactive source used in the PET exam was developed for evaluation of the absorbed dose distribution in patients submitted to this exam. In order to make the EGSnrc able to perform simulations of PET exams, adaptations in an algorithm of general internal source were performed to simulate the positronic emission of 18F-FDG, the radiopharmaceutical most used in this exam. If-else conditionals were placed to separate cycles of photons (even order from odd order) to characterize the photons source. To draft opposite directions for each type of cycle, cosine directors were allocated to maintain the position and to reverse the emission directions of two consecutive 511 keV photons. The results are presented as absorbed dose/cumulated activity (mGy/MBq.s). With the purpose of testing the coupling of the developed algorithm, we simulated the administration of 310.8 MBq of 18FFDG in an adult, resulting 12.80, 6.73 and 5.83 mGy of absorbed dose, in the source organs brain, liver and lungs, respectively. This is similar to results reported by Kaushik et al. (2013) who estimated absorbed dose of 100 patients submitted to 18F-FDG PET/CT whole body studies. This suggests that the developed algorithm can be used for dosimetric evaluation of patients submitted to PET exam. From small modifications in this algorithm, other simulations can be performed for other positron emitting radiopharmaceuticals.