Cosolvent-free polymer gel dosimeters with improved dose sensitivity and resolution for x-ray CT dose response

This study reports new N-isopropylacrylamide (NIPAM) polymer gel recipes with increased dose sensitivity and improved dose resolution for x-ray CT readout. NIPAM can be used to increase the solubility of N, N'-methylenebisacrylamide (Bis) in aqueous solutions from approximately 3% to 5.5% by weight, enabling the manufacture of dosimeters containing up to 19.5%T, which is the total concentration of NIPAM and Bis by weight. Gelatin is shown to have a mild influence on dose sensitivity when gels are imaged using x-ray CT, and a stronger influence when gels are imaged optically. Phantoms that contain only 3% gelatin and 5 mM tetrakis hydroxymethyl phosphonium chloride are sufficiently stiff for dosimetry applications. The best cosolvent-free gel formulation has a dose sensitivity in the linear range (∼0.88 H Gy-1) that is a small improvement compared to the best NIPAM-based gels that incorporate isopropanol as a cosolvent (∼0.80 H Gy-1). This new gel formulation results in enhanced dose resolution (∼0.052 Gy) for x-ray CT readout, making clinical applications of this imaging modality more feasible.