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

Highlights: • Polymer gel contains N,N'-methylene-bis-acrylamide (BIS) without monomer is introduced as a new low toxic dosimeter. • The dose sensitivity increased from 0.07 to 0.33 Gy^-1s^-1 with the increase of MgCl₂ concentration from 0 to 0.9 M. • The dosimeter showed a good dose linearity up to 10 Gy with total uncertainty of 7.04% (2σ, 95% confidence level). • The dosimeter is independent of dose-rate (200 and 500 cGy/min) as well as radiation energy (6 and 15 MV). 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 dose-response 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% (2σ, 95% confidence level).