Estudo da interação de pósitrons com alvos de interesse biológico

Abstract

Understanding the interaction of particles with matter is fundamental for their application. Fast charged particles have been used in cancer treatment and diagnosis since the 19th century. Cancer is the second leading cause of death worldwide, and not all available treatments are sufficient to cure it. Therefore, studies aimed at developing potential new technologies and treatments are of great importance. Among the types, breast cancer has the highest incidence and mortality rate among women in Brazil and worldwide. Brain cancer, particularly gliomas, although among the least frequent, has a mortality rate of approximately 90% of cases. The positron, the electron’s antiparticle, is widely used in medical imaging through Positron Emission Tomography (PET). However, its potential for therapies remains largely unexplored. Studies have indicated that positrons may offer advantages over electrons in cancer treatment. This work investigates the behavior of positrons interacting with biological targets, particularly brain and breast tissue, using a theoretical and computational approach. This behavior is analyzed through stopping power and CSDA range, based on the phenomenological model of Gümüş, comparing the results with simulations performed in the TOPAS program, which employs the Monte Carlo method to simulate radiation transport. Furthermore, due to the scarcity of comparative data on absorbed dose in biological tissues between positrons and electrons within radiotherapy energy ranges, the dose distribution is obtained for water, brain tissue, and a tumor within the brain for electrons and positrons interacting with the medium. This provides the percentage depth dose for the three simulated media and the total absorbed dose in the tumor. The results obtained in this study allowed for the verification of the accuracy of the theoretical model used for stopping power and CSDA range calculations in biological tissues, as well as providing a comparative analysis of the absorbed dose between positrons and electrons.