Flexible real-time skin dosimeter based on a thin-film copper indium gallium selenide solar cell for electron radiation therapy

PURPOSE

Various dosimeters have been proposed for skin dosimetry in electron radiotherapy. However, one main drawback of these skin dosimeters is their lack of flexibility, which could make accurate dose measurements challenging due to air gaps between a curved patient surface and dosimeter. Therefore, the purpose of this study is to suggest a novel flexible skin dosimeter based on a thin-film copper indium gallium selenide (CIGS) solar cell, and to evaluate its dosimetric characteristics.

METHODS

The CIGS solar cell dosimeter consisted of (a) a customized thin-film CIGS solar cell and (b) a data acquisition (DAQ) system. The CIGS solar cell with a thickness of 0.33 mm was customized to a size of 10 × 10 mm² . This customized solar cell plays a role in converting therapeutic electron radiation into electrical signals. The DAQ system was composed of a voltage amplifier with a gain of 1000, a voltage input module, a DAQ chassis, and an in-house software. This system converted the electrical analog signals (from solar cell) to digital signals with a sampling rate of ≤50 kHz and then quantified/visualized the digital signals in real time. We quantified the linearity/ sampling rate effect/dose rate dependence/energy dependence/field size output factor/reproducibility/curvature/bending recoverability/angular dependence of the CIGS solar cell dosimeter in therapeutic electron beams. To evaluate clinical feasibility, we measured the skin point doses by attaching the CIGS solar cell to an anthropomorphic phantom surface (for forehead, mouth, and thorax). The CIGS-measured doses were compared with calculated doses (by treatment planning system) and measured doses (by optically stimulated luminescent dosimeter).

RESULTS

The normalized signals of the solar cell dosimeter increased linearly as the delivered dose increased. The gradient of the linearly fitted line was 1.00 with an R-square of 0.9999. The sampling rates (2, 10, and 50 kHz) of the solar cell dosimeter showed good performance even at low doses (<50 cGy). The solar cell dosimeter exhibited dose rate independence within 1% and energy independence within 3% error margins. The signals of the solar cell dosimeter were similar (<1%) when penetrating the same side of the CIGS cell regardless of the rotation angle of the solar cell. The field size output factor measured by the solar cell dosimeter was comparable to that measured by the ion chamber. The solar cell signals were similar between the baseline (week 1) and the last time point (week 4). Our detector showed curvature independence within 1.8% (curvatures of <0.10 mm^- ) and bending recovery (curvature of 0.10 mm^-1 ). The differences between measured doses (CIGS solar cell dosimeter vs. optically stimulated luminescent dosimeter) were 7.1%, 9.6%, and 1.0% for forehead, mouth, and thorax, respectively.

CONCLUSION

We present the construction of a flexible skin dosimeter based on a CIGS solar cell. Our findings demonstrate that the CIGS solar cell has a potential to be a novel flexible skin dosimeter for electron radiotherapy. Moreover, this dosimeter is manufactured with low cost and can be easily customized to various size/shape, which represents advantages over other dosimeters.

Air-Stable Organic Radicals: New-Generation Materials for Flexible Electronics?

In the last few years, air-stable organic radicals and radical polymers have attracted tremendous attention due to their outstanding performance in flexible electronic devices, including transistors, batteries, light-emitting diodes, thermoelectric and photothermal conversion devices, and among many others. The main issue of radicals from laboratory studies to real-world applications is that the number of known air-stable radicals is very limited, and the radicals that have been used as materials are even less. Here, the known and newly developed air-stable organic radicals are summarized, generalizing the way of observing air-stable radicals. The special electric and photophysical properties of organic radicals and radical polymers are interpreted, which give radicals a wide scope for various of potential applications. Finally, the exciting applications of radicals that have been achieved in flexible electronic devices are summarized. The aim herein is to highlight the recent achievements in radicals in chemistry, materials science, and flexible electronics, and further bridge the gap between these three disciplines.