Purpose: We developed a new type of multi-layered thin-film radiation detector employing fast electrons to generate self-powered signal in periodic micro-structures.
Methods: Low-Z (Al) and high-Z (Ta) electrodes of 10Î¼m thickness were deposited on 50Î¼m-thick polyimide aerogel (PA) films to obtain periodic N x (Al-PA-Ta-PA-Al) structures (N=1-10). Sensors were tested with X-rays with 40, 60, 80, 100, 120kVp and with 2.5MV, 6MV, 6MV-FFF linac beams (TrueBeam, Varian). Signal was collected from each electrode. Performance of PA sensors was compared to commercial A12 Farmer ionization chamber as well as to radiation transport simulations using CEPXS/ONEDANT with nanometer-to-micrometer spatial resolution.
Results: Combined signal from PA sensors was similar to that of the A12 ion chamber and to the simulated net leakage electron current averaged over the PA thickness. External bias voltage was not applied and yet the total charge collected was linear with dose and independent of dose rate. Detector responses to different X-ray sources showed higher quantum efficiency (QE) for kVp than MV beamlines, as expected based on theory and on computations of absorbed flux in each structure. Beam attenuation per unit element in the detector was 0.5%, 1%, 3% and 46% for 6MV, 6MV-FFF, 2.5MV and 120kVp, respectively, mainly due to absorption in the Ta electrodes. Simulations showed that the detector QE can be optimized for a specific beam quality by tuning the number and the thicknesses of layers (for N=10 the optimal thickness of each Ta is 3Î¼m/10Î¼m for 120kVp/6MV).
Conclusion: We demonstrated that nano-porous aerogel films achieve high transmission of fast electrons between high-Z / low-Z electrodes and furthermore that a periodic structure with thinner electrodes yields improved efficiency. Specific applications of this new technology remain to be investigated, e.g. for on-line flux/dose monitoring of kVp in interventional radiology and of MV beams in radiotherapy.
Funding Support, Disclosures, and Conflict of Interest: This research was partially sponsored by SBIR grant AF151-009.