Abstract
Currently, advanced dosimeters like polymer gels are capable of obtaining reliable and accurate 3D dose distributions from correlations with the different polymerization degrees induced by incident radiation. Samples of polymer gel dosimeters are commonly read out using magnetic resonance imaging or optical methods like visible light transmission or laser computed tomography. Alternatively, this work proposes and evaluates the implementation of Raman spectroscopy to provide direct information on the effect of oxygen permeating through the walls of phantoms on the polymerization initiated by irradiation in three types of polymer gel dosimeters, namely NIPAM, ITABIS and PAGAT. The aim of the present study is to provide better and complete interpretations using three different containers, adequate for integral, 2D and 3D dose mapping. Moreover, Raman spectroscopy has been used to analyze the well-known effect of oxygen inhibition on the different polymer gel dosimeters remarking the importance of avoiding air exposition during sample storage and readout. Dose-response curves for different polymer gels were obtained in terms of measurements with a calibrated ionization chamber. Additionally, dedicated Monte Carlo simulations were performed aimed at characterizing dose for different X-ray irradiation setups, providing also suitable information to evaluate oxygen diffusion through the sample wall. The obtained results were contrasted with optical transmission readout as well as Monte Carlo simulations attaining very good agreements for all dosimeter types.
Highlights
Dosimetry plays an essential role in most clinical applications of ionizing radiation like radiotherapy or radiology, and it’s the main method to provide a reliable verification of the dose delivered to a patient
The main goal of this study is to use Raman spectroscopy to assess the effect of oxygen on the polymerization induced by the radiation on different normoxic polymer dosimetry systems, based on polyacrylamide (PAGAT), N-isopropylacrylamide (NIPAM), and itaconic acid (ITABIS), and in particular the inhibition caused by oxygen entering to the dosimeter after its manufacturing through the walls of their container or phantom
Raman spectroscopy was used to evaluate the effect of oxygen on polymer gel dosimetry for three different materials based on acrylamide (PAGAT), N-isopropylacrylamide (NIPAM) and itaconic acid (ITABIS) and compared to optical transmission imaging results
Summary
Dosimetry plays an essential role in most clinical applications of ionizing radiation like radiotherapy or radiology, and it’s the main method to provide a reliable verification of the dose delivered to a patient. There are still concerns on the optimal composition of these materials, their stability, spatial integrity, temperature sensitivity, dose and energy dependence, tissue equivalence, and on which is the best readout method to retrieve the proper information once irradiated. These issues have limited the applicability of PGDs for routine clinical dose verification (Sedaghat et al, 2012; Baldock et al, 2010)
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