Cerenkov emission induced by external beam radiation stimulates molecular fluorescence.
Axelsson, Johan 1, a); Davis, Scott C. 1; Gladstone, David J. 2; Pogue, Brian W. 3
[Letter]
Medical Physics.
38(7):4127-4132, July 2011.
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Purpose: Cerenkov emission is induced when a charged particle moves faster than the speed of light in a given medium. Both x-ray photons and electrons produce optical Cerenkov photons in everyday radiation therapy of tissue; yet, this phenomenon has never been fully documented. This study quantifies the emissions and also demonstrates that the Cerenkov emission can excite a fluorophore, protoporphyrin IX (PpIX), embedded in biological phantoms.
Methods: In this study, Cerenkov emission induced by radiation from a clinical linear accelerator is investigated. Biological mimicking phantoms were irradiated with x-ray photons, with energies of 6 or 18 MV, or electrons at energies 6, 9, 12, 15, or 18 MeV. The Cerenkov emission and the induced molecular fluorescence were detected by a camera or a spectrometer equipped with a fiber optic cable.
Results: It is shown that both x-ray photons and electrons, at MeV energies, produce optical Cerenkov photons in tissue mimicking media. Furthermore, we demonstrate that the Cerenkov emission can excite a fluorophore, protoporphyrin IX (PpIX), embedded in biological phantoms.
Conclusions: The results here indicate that molecular fluorescence monitoring during external beam radiotherapy is possible.
(C) 2011 John Wiley & Sons, Ltd