Abstract
Radiation-induced polymerization in Polymethacrylamide Gels (PMAAGs) potentially used for 3D dose verification in radiotherapy has been studied using both Raman spectroscopy and Nuclear Magnetic Resonance (NMR) method. The dosimeters are composed of aqueous Methacrylamide (MAA) monomer and N, N’ methyelene-bis-acrylamide (BIS) crosslinker at various concentrations from 2 to 6% (w/w) and gelatin at 6% (w/w). The dosimeters were irradiated to doses up to 30 Gy using 60Co teletherapy ?-ray source at a constant dose rate. The formation of the polymer increases with increasing dose and was followed directly by Raman spectroscopic measurement for CH3 stretching mode assigned to polymethacrylamide and indirectly by the transverse spin-echo pulse NMR R2 relaxation rate of water protons within the polymer gel network. The half dose D1/2 values of both direct and indirect methods were used to evaluate the effects of initial concentrations of monomer and crosslinker to the dose required to produce 50% of the polymer in PMAAGs. The PMAAGs containing more crosslinker than monomer show larger D1/2 values, indicating that the crosslinker has a larger effect on the increase in dose required to produce 50% of the polymer. The D1/2 value of the direct method is consistently higher than that of the indirect method, indicating that the indirect method is more sensitive to the dose response, but fundamentally does not measure the amount of polymethacrylamide formed. There is a correlation between D1/2 value and concentrations of monomer and crosslinker. The correlation factor, kC of the crosslinker is always greater than kM of monomer, for both the direct and indirect methods, suggesting the crosslinker reacts more efficiently than monomer to produce 50% of the polymer of polymethacrylamide.
Highlights
Polymer gel dosimeter used in conjunction with magnetic resonance imaging (MRI) is the most popular dosimeter imaging modality as a potential tool for mapping complex dose distributions[1,2,3,4,5]
The proton relaxation rate increases with dose and the dose distribution of polymer gels may be constructed from the relaxation rate images obtained from MRI scans
The dose response of the polymer gel dosimeters is represented by the relative Raman intensity as a function of dose[10]
Summary
Polymer gel dosimeter used in conjunction with magnetic resonance imaging (MRI) is the most popular dosimeter imaging modality as a potential tool for mapping complex dose distributions[1,2,3,4,5]. The amount of polymer formed is related to absorbed dose received by the polymer gel These polymer aggregates are usually evaluated indirectly using nuclear magnetic resonance (NMR) technique, the principle of MRI, which measures the proton relaxation times of the surrounding water molecules. The sensitivity of a polymer gel dosimeter is dependent to some extent, on physical parameters such as radiant energy, temperature during MRI evaluation, the time between irradiation and NMR evaluation and magnetic strength[7]. Applied Sci., 2 (8): 1248-1255, 2005 observed the effect of pH during synthesis on the dose required to produce 50% of the polymer in response of a modifier polymer gel dosimeter. It is well polymethacrylamide gel (PMAAG) dosimeters.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
