Effect of composition interactions on the dose response of an N-isopropylacrylamide gel dosimeter

Feasibility evaluation of N-Isopropyl Acrylamide 3D gel dosimeters for proton therapy

This study aimed to investigate the feasibility of applying 3D gel dosimeters for proton therapy. Two different formulations (5-5-3-5, 5-3-3-10) for the N-Isopropyl Acrylamide (NIPAM) polymer gel were used to find the best composition for the application of NIPAM polymer gels for proton therapy. The reaction of the gel under different physical conditions, including dependence on energy and dependence on the dose rate of the NIPAM gel under proton irradiation, was also explored. A NIPAM gel dosimeter was used to record the 3D dose distribution, and a self-developed parallel beam optical computed tomography scanner was used to obtain non-irradiated and post-irradiated gel phantom images. The NIPAM gel was filled into a cylindrical acrylic phantom. The results showed that the optical density of the irradiated NIPAM dosimeter was linear in the dose range of 0 to 6 Gy, and the linearity of the two NIPAM gel formulations at the depth of the dose point (2 cm) was 0.98 to 0.89. The dose depth curves showed different patterns with different gel sensitivities. This study demonstrated that the NIPAM gel dosimeter with the 5-3-3-10 formulation is suitable for verifying the dosimetry dose of proton beams.

Small-Field Measurements of 3D Polymer Gel Dosimeters through Optical Computed Tomography

With advances in therapeutic instruments and techniques, three-dimensional dose delivery has been widely used in radiotherapy. The verification of dose distribution in a small field becomes critical because of the obvious dose gradient within the field. The study investigates the dose distributions of various field sizes by using NIPAM polymer gel dosimeter. The dosimeter consists of 5% gelatin, 5% monomers, 3% cross linkers, and 5 mM THPC. After irradiation, a 24 to 96 hour delay was applied, and the gel dosimeters were read by a cone beam optical computed tomography (optical CT) scanner. The dose distributions measured by the NIPAM gel dosimeter were compared to the outputs of the treatment planning system using gamma evaluation. For the criteria of 3%/3 mm, the pass rates for 5 × 5, 3 × 3, 2 × 2, 1 × 1, and 0.5 × 0.5 cm² were as high as 91.7%, 90.7%, 88.2%, 74.8%, and 37.3%, respectively. For the criteria of 5%/5 mm, the gamma pass rates of the 5 × 5, 3 × 3, and 2 × 2 cm² fields were over 99%. The NIPAM gel dosimeter provides high chemical stability. With cone-beam optical CT readouts, the NIPAM polymer gel dosimeter has potential for clinical dose verification of small-field irradiation.