Multi-Responsive Polysiloxane/Poly(N-isopropylacrylamide) Interpenetrating Networks Containing Urea and Thiourea Groups

Novel interpenetrating polymer networks (IPNs) were synthesized from N-isopropylacrylamide (NIPAM) and polysiloxanes containing a urea or thiourea side group, in addition to the silanol residue, through two reactions, such as the radical gelation of NIPAM and the condensation of silanols to form a siloxane linkage. The obtained IPNs showed a typical temperature-responsive volume change in water based on the constructed poly-NIPAM gel component. In addition, the characteristic color and volume changes responding to chemical stimuli, such as acetate and/or fluoride ions, based on the introduced urea and thiourea groups onto the polysiloxane gel were observed in N,N-dimethylformamide.

Dosimetric characteristics of intensity-modulated radiation therapy and RapidArc® therapy using a 3D N-isopropylacrylamide gel dosimeter

This study aimed to investigate the dosimetric characteristics of intensity-modulated radiation therapy (IMRT) and RapidArc therapy by using 3D N-isopropylacrylamide (NIPAM) polymer gel. Optical computed tomography, specifically OCTOPUSTM-10X fast optical computed tomography scanner, was used as a readout tool. Two cylindrical acrylic phantoms (10 cm in diameter, 10 cm in height, and 3 mm in thickness) were filled with NIPAM gel and used for IMRT and RapidArc irradiation by using the Clinac iX treatment machine. The irradiation energies for IMRT and RapidArc® were set as 6 MV photons, but their irradiation angles and dose rates differed during irradiation. The irradiation angles of IMRT were 120°, 155°, 180°, 215°, and 245°, and the dose rate was fixed at 400 cGy/min. RapidArc® rotated continuously during irradiation, and the dose rate varied from 330 cGy/min to 400 cGy/min. The pass rates were 98.02% and 97.48% for IMRT and RapidArc®, respectively, and the rejected area appeared at the edge of the irradiated region. The isodose lines of IMRT and RapidArc® were consistent with those of TPS in most regions. Scattering and edge enhancement effects are main factors that cause dose inaccuracy in the edge region and reduced pass rates. Considering dose rate dependence, we used variable dose rates during irradiation with RapidArc®. Results showed that the dose distribution of NIPAM gel was consistent with that of TPS. The pass rates were also the same for IMRT and RapidArc® irradiation. This study proposes a preliminary profile of dosimetric characteristics of IMRT and RapidArc® by using a NIPAM gel dosimeter.