Master thesis defense by Georgios Savvidis

Monte Carlo simulations with Geant4 for estimation of external radiation doses in nuclear medicine

The aim of this thesis is to create a scientific tool based on Monte Carlo simulations in order to estimate the external radiation doses of several radioisotopes used in typical Nuclear Medicine procedures. Our purpose is to build an environment which can be applicable for testing the dose rate at different distances from a radioactive source which can be easily adjust according to the user's desire. In this way we would like to provide a Monte-Carlo based model for estimating the radiation dose on persons in the vicinity of the patient who have been administered by a typical radioisotope and leaving the Nuclear Medicine department.

For the implementation of the project, the Monte Carlo simulations were performed by the Geant4 toolkit, a software which provide the propagation of particles through matter and have been used in several researches concerning Medical Physics field. In our simulations, three different isotopes were tested, ¹³¹I, ¹⁸F and ^99mTc while three different phantoms filled with the corresponding isotopes are created, a point source, a cylinder phantom and a simple human-like phantom. In this way we will examine the validity of our environment, comparing the cases relative to the implementation of the inverse square law of dosimetry while real measurements of radiation doses are taken in different positions at the hospital's lab also, in order to compare them with our Monte Carlo method. Lastly, several theoretical approaches have been established for calculation of external doses, such as the point source and line source model, and in this project, we will compare our results with these approximations as well.

It is important to mention that all the real measurements of the isotopes were taken in Hvidovre Hospital, Copenhagen, Denmark. In addition, all the Monte Carlo simulations were performed also in the hospital's computers.