Design of a fiber-phantom detector for quality assurance in Proton Therapy

Tese de mestrado, Engenharia Física , Universidade de Lisboa, Faculdade de Ciências, 2022The quality assurance of a beam is a key step in delivering a dose to a patient in a safe and accurate manner, with international recommendations for proton therapy being established by the American Association of Physicists in Medicine. This radiotherapy modality, in contrast to others, permits a greater accuracy by creating a high dose region, minimizing damage to the surrounding tissue. Depending on the delivery technique chosen there are several parameters that must be checked regularly, be it daily, weekly, monthly or annually. The detectors used in these procedures must be able to measure the in-depth energy distribution with very good spatial-resolution. In this project the prototype of a fiber-phantom for quality control in particle radiotherapy is to be designed using a detector currently constructed with scintillating plastic optical fibers juxtaposed in a frame. The dimensions of the fibers provide a high transversal spatial resolution and their composition allows them to be tissue equivalent. This phantom will be built with a modular structure consisting of a central module where the detector is embedded, to which additional volumes can be added to increase the size of the phantom, as well as changing the position of the detector, enabling it to measure the dose profile at different depths. Different designs will be tested in Monte Carlo simulations to ascertain the one most adequate one. As the fiber-phantom requires testing a 50 kV X-ray tube will be characterized through the use of other dosimeters (ionization chambers and radiochromic film) so it can be inserted into the simulations. A delay in the detector readout availability meant that practical results could not be achieved, nevertheless the photon source to be used was characterized and used in the study of the possible structures for the fiber-phantom through its inclusion in simulations. A proton source was also simulated to test the effectiveness of the detector setups, from which resulted the need to propose alternative configurations for the central module