Development and characterization of novel radiochromic dosimeters for X-rays and UV radiation

This thesis presents the development of two tissue equivalent and water equivalent chemical dosimeters for the measurement of the three-dimensional dose distribution in radiotherapy and the dose from UV sources. Current radiotherapy techniques implement treatment plans based on volumetric dose distributions with complex shapes and sharp gradients. To verify the agreement between these treatment plans and the dose that is actually delivered to the patient, a dosimetric system that is truly three dimensional, sensitive to radiation in each point and tissue equivalent is required. For this purpose, we developed a radio-chromic gel based on polyvinyl alcohol (PVA) chemically cross-linked with glutaraldehyde (GTA). This gel dosimeter has high sensitivity and stability of the signal, i.e. low diffusion of the iron complex. Furthermore, it is transparent and therefore can be imaged with optical techniques, as well as with NMR. The dosimetric characteristics of the PVA-GTA gel were compared to those of a Fricke gelatine gel and to other gel dosimeters previously studied by other investigators. Even though UVA and UVB rays are commonly adopted in many treatments for skin disease and tumors, a passive and water equivalent dosimeter for both this type of radiations does not exist. We developed an aqueous dosimeter that is sensitive to UVA, UVB and X-rays named Redox-Phen solution. This dosimeter is inexpensive and tissue equivalent, being made of 99% of water. It changes color in the visible region upon irradiation, thus it can be measured via simple optical method, and an evaluation of the exposition can be made also by naked eyes. We studied the influence of the main chemical parameters on the dose-response and storage stability of the dosimeter to select the best formulation and compare it with the performances of other UV passive dosimeters.