Optimization of Personal Dosimetry of Medical Staff Wearing Radioprotective Garments

Personal dosimetry plays a very important role in the dose monitoring of medical staff working in interventional radiology and cardiology. In order to shield the radiation scattered in the patient during the examination, medical staff have to wear radiation protection garments like lead aprons and thyroid collars. The effective dose received by the physician and the dose absorbed by the personal whole-body dosimeters worn by her/him are altered by the presence of lead. Some personal dosimetry methodologies (single and double dosimetry) exist for the evaluation of the effective dose when radioprotective garments are worn. Single dosimetry consists in the use of only one dosimeter worn over or under the apron and the effective dose is evaluated through the division or multiplication of the dose by correction factors. Double dosimetry proposes the combination of the dose received by two dosimeters, one worn over and one under the apron and combines the two doses through an algorithm. Both of these methods are characterized by high uncertainties that can lead to strong overestimations and underestimations. This master thesis study focuses on the design of a whole-body personal dosimeter for the estimation of the effective dose when wearing radioprotective garments made of lead. The innovative feature is that only one dosimeter (worn over the lead apron) is needed to provide a good estimate of the effective dose. In particular, this analysis regards the optimization of dosimeter based on radiophotoluminescent (RPL) detectors. The project consists in the design of a new dosimeter starting from an existent dosimeter used to estimate the effective dose without lead garments. Filters are inserted and adapted to obtain an estimation of the effective dose as close as possible to the reference values of effective dose with lead garments already calculated. The dose of the dosimeter is estimated from the dose of two detectors that represent all the parts of the body exposed to radiation: the first dose is read in a detecting volume surrounded by low Z material filters and represents tissues and organs which are not covered by radioprotective garments, while the second one is read in a detecting volume surrounded by high Z material filters and represents the parts covered by lead garments. The objective is to determine a configuration that allows to minimize overestimations and underestimations of the effective dose in all the exposure conditions considered: parallel photon beams with energies between 20 and 120 keV and angles of incidence between 0° and 60°. The new design and its optimization are performed through Monte Carlo simulations using the radiation transport code MCNPX. The first part of this thesis focuses on the design of a simplified dosimeter, in which two detectors with different filtrations are studied separately and then combined in terms of dose. The second and third parts focus on the design of a realistic dosimeter with its real structure, dimensions and characteristics.