Abstract
We investigate Cherenkov emission (CE) by radiotherapy beams via radiation dose‐versus‐CE correlation analyses, CE detection optimization by means of a spectral shift towards the near‐infrared (NIR) window of biological tissue, and comparison of CE to on‐board MV imaging. Dose‐CE correlation was investigated via simulation and experiment. A Monte Carlo (MC) CE simulator was designed using Geant4. Experimental phantoms include: water; tissue‐simulating phantom composed of water, Intralipid®, and beef blood; plastic phantom with solid water insert. The detector system comprises an optical fiber and diffraction‐grating spectrometer incorporating a front/back‐illuminated CCD. The NIR shift was carried out with CdSe/ZnS quantum dots (QDs), emitting at (650±10) nm. CE and MV images were acquired with a CMOS camera and electronic portal imaging device.MC and experimental studies indicate a strong linear dose‐CE correlation (Pearson coefficient > 0.99). CE by an 18‐MeV beam was effectively NIR‐shifted in water and a tissue‐simulating phantom, exhibiting a significant increase at 650 nm for QD depths up to 10 mm. CE images exhibited relative contrast superior to MV images by a factor of 30. Our work supports the potential for application of CE in radiotherapy online imaging for patient setup and treatment verification, since CE is intrinsic to the beam and non‐ionizing and QDs can be used to improve CE detectability, potentially yielding image quality superior to MV imaging for the case of low‐density‐variability, low‐optical‐attenuation materials (ex: breast/oropharynx). Ongoing work involves microenvironment functionalization of QDs and application of multi‐channel spectrometry for simultaneous acquisition of dosimetric and tumor oxygenation signals.
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