Characterization of a polymer gel dosimetry system based on Nisopropylacrylamide and N-N-methylenebisacrylamide

Diagnostic radiology and radiotherapy are the most used techniques to detect and treat several pathologies like tumor and cancer diseases. According to available evidence at least 52% of cancer patients should receive radiotherapy during their treatment. The process of radiotherapy is complex and involves understanding of the principles of medical physics, radiobiology, radiation safety, dosimetry, radiotherapy planning, simulation and interaction of radiation therapy with other treatment modalities. One of the key aspects of radiotherapy is to determine the real dose an organ or tissue is exposed. For that purpose, if the irradiation conditions are well defined and known in relation to the anatomy of the patient, Monte Carlo simulations of the energy deposition can be performed. However, if those conditions are not fulfilled, it is also possible to measure the organ dose directly with the use of suitable phantoms and dosimeters. Among the different types of dosimeters, polymeric ones are of great interest because of their capability to mimic soft-tissue while maintaining a specific shape presenting high dose sensitivity and the ability to retain 3D spatial dose distribution for long periods of time after being exposed. A typical polymer gel dosimeter is a complex aqueous composition of physical gel-forming agent, monomers, and oxygen scavengers. The concentration of each component affects the sensitivity and the response of the dosimeter to radiation. Therefore, an in depth study on the preparation methodology is essential for the development of new dosimeters. In this work the preparation and characterization of a polymeric dosimeter based on the monomers N-isopropylacrylamide (NIPAM), N-N-methylenebisacrylamide (Bis) and an aqueous gelatin matrix containing Tetrakis(hydroxymethyl)phosphonium chloride (THPC) as oxygen scavenger is studied. Different characterization techniques, such as X-ray Raman spectroscopy, con focal and scanning electronic microscopy, and absorbance/transmittance analysis of the different dosimeters after being irradiated are presented and analyzed from a physical and chemical point of view, in the interest of proposing new materials for specific treatment purposes