Polymer gel containing N,N′-methylene-bis-acrylamide (BIS) as a single monomer for radiotherapy dosimetry

In this study, the first polymer gel that contains N,N' -methylene-bis-acrylamide (BIS) crosslinker without the need of adding another radiosensitive monomer has been introduced as a new low toxic polymer gel dosimeter. Various concentrations (0-0.9 M) of magnesium chloride (MgCl2) were added to BIS gel to improve the doseresponse of the gel dosimeter. The gel samples were irradiated in a water phantom to different doses using 6 MV Linac X-ray beams with 200 cGy/min dose rate. The samples were read out using nuclear magnetic resonance (NMR) spectroscopy to measure the relaxation rates (R2) of the scanned samples by a standard Multi-Spin-Echo sequence. The optimum formulation gels were irradiated to different dose-rates (200 and 500 cGy/min) with a fixed radiation-energy of 6 MV, while other samples were irradiated to different radiation-energy (6 and15 MV) with a fixed dose rate of 200 cGy/min to investigate the influence of these important parameters on the performance of gel dosimeters. The dose sensitivity of the composition containing BIS, gelatin and antioxidant agent (BISGAT) polymer gel was very small (0.07 Gy 1s 1) compared to the available normoxic polymer gels such as NIMPAGAT. A significant increase in dose sensitivity (0.33 Gy 1s 1) of BISGAT dosimeter was achieved after adding 0.9 M MgCl2 to the gel which is greater than the standard composition of NIPAMGAT (i.e. BIS and NIPAM monomer) polymer gel with dose sensitivity of 0.16 Gy 1 s 1. The temporal stability of irradiated samples to different doses changed insignificantly (0.07%) in the period up to 6 days. The BISGAT gel with MgCl2 was independent of dose-rate (200 and 500 cGy/min) as well as radiation energy (6 and 15 MV). Additionally, the gel is water equivalent and has theoretical energy-independent response from 0.1 to 20 MeV for the optimum composition. The gel dosimetry accuracy was evaluated in this study by calculating the overall uncertainty and found to be 7.04% (2s, 95% confidence level).

Automated summary

A new low toxic polymer gel dosimeter containing BIS crosslinker was introduced in this study, which showed improved dose response with the addition of various concentrations of MgCl2. The gel samples were irradiated and read out using NMR spectroscopy to measure relaxation rates, with the dose sensitivity significantly increased after adding MgCl2. The dosimeter showed temporal stability, independence of dose-rate and radiation energy, and water equivalence, with an evaluated dosimetry accuracy of 7.04% at 95% confidence level.