Lithium formate EPR dosimetry : Properties and applications in radiotherapy

Abstract

Each year 10 000 Norwegian cancer patients are treated with radiation. According to the World Health Organization (WHO), more than half of all cancer patients should be offered radiation therapy during their period of illness. The precise radiation targeting of cancer cells with sufficient radiation dose, so that the cancer cells stop dividing while adverse effects are acceptable, is crucial for the outcome of radiation therapy. In this dissertation for the degree of Philosophiae doctor, Einar Waldeland has studied a method for measuring radiations doses, namely electron paramagnetic resonance (EPR) dosimetry. The radiation sensitive material employed is lithium formate monohydrate, which is a relatively new material for this application. To date, this method is not routinely used in Norway and to a limited extent elsewhere. The thesis covers some basic properties of this new dosimetry system and concludes with the feasibility of the method for high precision dosimetry of patient treatments. The work also compares this method with the most established EPR dosimetry system, alanine EPR dosimetry. 6 individual peer-reviewed papers are included in the thesis. They show basic qualitative properties of the EPR signal from lithium formate irradiated with neutrons, protons, nitrogen ions, electrons and photons, and how these properties may be utilized for dose measurements. The two first works outline how the signal may be used to characterize the radiation type used, when this is not known by the observer. The third work describes properties of the method when extremely high doses are used, such as industrial sterilization of food. The next two papers include correction factors necessary for standardized high precision dose measurements for radiation therapy of patients. The last work demonstrates the use of lithium formate EPR dosimetry in a realistic treatment of a humanlike phantom.