Fluorescent Nanogel Sensors for X-ray Dosimetry.

X-ray dosimeters are of significance for detecting the levels of ionizing radiation exposure in cells and phantoms; thus, they can further optimize X-ray radiotherapy in the clinic. In this paper, we designed a polyacrylamide-based nanogel sensor that is capable of measuring X-ray doses. The dosimeters were prepared by anchoring an X-ray-responsive probe (aminophenyl fluorescein, APF) to poly(acrylamide---(3-aminopropyl) methyl acrylamide) nanogels. The premise behind the dose measurement is the transition of APF to fluorescence in the presence of hydroxyl radicals that are caused by the radiolysis of water molecules under X-rays. Therefore, the dose of X-rays can be readily detected by measuring the fluorescence intensity of the resultant nanogel immediately after irradiation using fluorescence spectroscopy principles. Using an RS2000 X-ray biological irradiator, our dosimeters showed good linearity responsivity at X-ray doses ranging from 0 to 15 Gy, with a limit of detection (LOD) of 0.5 Gy. Additionally, the signals showed temperature stability (25-65 °C), durability (5 weeks), and dose-rate (1.177 and 6 Gy/min) and energy independence (160 kVp and 6 MV). As a proof-of-concept, we used our sensors to fluorescently detect X-ray doses in A549 tumor cells and 3D-printed eye phantoms. The results showed that our dosimeters were able to accurately predict doses similar to those used by treatment plan systems.