Cherenkov excited luminescence imaging induced by megavolt X-ray beams in the second near-infrared window

The Cherenkov radiation induced by megavolt X-ray beams of a medical linear accelerator is highly intense in blue and ultraviolet lights. This poses a challenge for in vivo imaging, which favors longer wavelengths. However, using quantum dots with a large Stokes shift, we converted the Cherenkov photons to fluorescent photons in the second near-infrared (NIR-II) window. A system was designed to provide shielding for the NIR-II camera, and high quality NIR-II CELI signal was acquired. The NIR-II CELI of X-ray beams was shown at various depths, and the condition to trigger it was also studied. Animal experiments showed this technique could visualize the delivery of X-ray radiation in mice qualitatively. We concluded that CELI induced by megavolt X-ray beams in the NIR-II window possesses a great potential as a quality control tool in radiotherapy.