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Red Spectral Shift of Cherenkov Emission with Applications in Image-Guided and Intensity-Modulated Radiation Therapy

Y Zlateva

Y Zlateva*, I El Naqa, N Quitoriano, McGill University, Montreal, QC

WE-G-500-5 Wednesday 4:30PM - 6:00PM Room: 500 Ballroom

Purpose: This work aims to validate the potential application of Cherenkov emission (CE) in radiotherapy by a spectral shift to the optical window of biological tissue in order to increase CE detection during radiotherapy.

Methods: 18 MeV and 18 MV clinical electron and photon beams are used for the experiments. The CE detector consists of a multi-mode fiber optic cable (numerical aperture = 0.22), positioned out of the beam and connected to a spectrometer incorporating a front-illuminated CCD array. In order to evaluate the dose versus CE correlation, depth and profile scans were acquired at the angle of maximum emission. A Monte Carlo CE simulator, designed with the Geant4 simulation toolkit, was used to validate the correlation. A spectral shift was achieved with CdSe/ZnS core/shell nanoparticles (NPs) emitting at 650 nm. Measurements were acquired with a water tank, in order to test the signal's capacity to stimulate NP photoluminescence, and at varying depths in a tissue-simulating phantom composed of water, Intralipid and bovine blood.

Results: A strong correlation between dose and CE is evident with a Spearman correlation coefficient of 0.99 or higher for simulated data. Water tank results confirm that CE by radiotherapy beams sufficiently stimulates NP photoluminescence. A considerable signal increase was observed near 650 nm with NPs placed at depths up to 1 cm in the tissue-simulating phantom.

Conclusion: These results indicate that development of spectral shifting techniques that enhance tissue transmission and detection of CE during radiotherapy will be beneficial for online tumor imaging and localization, since CE is intrinsic to the beam and non-ionizing, and for intensity modulation based on tumor microenvironment information, such as oxygenation, contained within the spectral distribution. This setup and methodology will be used to investigate different beam qualities and wavelength-shifting schemes, and fine-tune the phantom optical properties.

Funding Support, Disclosures, and Conflict of Interest: NSERC - Discovery Grant

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