Dosimetric Analysis of a Laser Accelerated Electron Beam and Optimization of FBX Chemical Dosimeter

Abstract

Cancer is the second leading cause of death worldwide, and it has become a global social and economic problem due to the continuous rise in incidence and mortality. Traditionally, there are three major treatment modalities for cancer diseases: surgery, radiotherapy and systematic therapy (chemo-, hormon-, immunotherapy).Radiation therapy is applied during the course of disease management in 70 % of cancer cases and the number of radiation treatments have been growing due to increasingly efficient treatment methods, precise and homogenous dose delivery. In fact, we may claim that the number of treated cases is limited by the quantity of available radiotherapy equipment and/or the relative costs of treatment.Beside the classical particle acceleration techniques, laser wakefield acceleration (LWFA) offers a promising compact solution for the production of high and very high energy electron (VHEE) beams, which have an ultrashort pulse duration with a high instantaneous dose rate and small source size. These unique properties are of radiobiological as well as clinical interest.This thesis is focused on the potential application of high repetition rate LWFA electron beams for radiotherapy. On the basis of particle-in-cell and Monte Carlo simulations it is expected that using a commercially available 1 kHz laser system we can generate electron beams with 35.7 MeV mean energy and 3 pC electron bunch charge at 1 kHz repetition rate to deliver a dose rate of 18 Gy/min.This electron beam could be extremely useful for real radiotherapy applications. Thanks to the high repetition rate, dose delivery can be performed with high precision making this system a reliable alternative to conventional clinical electron accelerators.The success of radiation therapy crucially depends on the accuracy of dose delivery to the target volume. For this reason radiation dosimetry plays an important role in the successful and safe use of radiotherapy procedures. The consistency and accuracy of the applied dosimetry methods pre-define the outcomes of these applications.This thesis presents a version of the well-known ferrous sulfate -benzoic acid -xylenol orange (FBX) chemical dosimeter with improved sensitivity, accuracy and precision. Sensitivity is increased due to a slight modification in composition and the preparation procedures. We use stock solutions for the preparation of the dosimeter solution, which consists of 1 mM ferrous sulphate and 16 mM benzoic acid with 0.25 mM xylenol orange added post-irradiation. The nonlinear response to the absorbed dose of this system is eliminated by the increased ferrous sulphate concentration, permitting the calculation of the absorbed dose by a linear relationship between the absorbed dose and the optical absorbance of the solution.The measured chemical yield of our dosimeter is 9.08 • 10 −6 mol/J for 6 MV photon beams and 6.42 • 10 −6 mol/J for 250 kVp x-rays. This is a 24 % enhancement over the original FBX solution, which permits a finer dose resolution.