Real-time in vivo Cherenkoscopy imaging during external beam radiation therapy

Abstract

Cherenkov radiation is induced when charged particles travel through dielectric media (such as biological tissue) faster than the speed of light through that medium. Detection of this radiation or excited luminescence during megavoltage external beam radiotherapy (EBRT) can allow emergence of a new approach to superficial dose estimation, functional imaging, and quality assurance for radiation therapy dosimetry. In this letter, the first in vivo Cherenkov images of a real-time Cherenkoscopy during EBRT are presented. The imaging system consisted of a time-gated intensified charge coupled device (ICCD) coupled with a commercial lens. The ICCD was synchronized to the linear accelerator to detect Cherenkov photons only during the 3.25-μs radiation bursts. Images of a tissue phantom under irradiation show that the intensity of Cherenkov emission is directly proportional to radiation dose, and images can be acquired at 4.7 frames/s with SNR>30. Cherenkoscopy was obtained from the superficial regions of a canine oral tumor during planned, Institutional Animal Care and Use Committee approved, conventional (therapeutically appropriate) EBRT irradiation. Coregistration between photography and Cherenkoscopy validated that Cherenkov photons were detected from the planned treatment region. Real-time images correctly monitored the beam field changes corresponding to the planned dynamic wedge movement, with accurate extent of overall beam field, and expected cold and hot regions.

Cherenkov radiation fluence estimates in tissue for molecular imaging and therapy applications

“…Imaging of these optical signals is achievable by using highly sensitive cameras, or long exposure times. In the case of radionuclides, this weak signal requires exposure times on the order of minutes, whereas this signal from radiotherapy beams can be captured in near real-time (Zhang et al, 2013b). So it is important to recognize that using these signals for molecular imaging is feasible, but typically would require some of the most sensitive measurements systems or cameras available.…”

“…To date, these applications have included small animal imaging and tomography of radionuclide distributions and kinetics (Robertson et al, 2009, Hu et al, 2010, Li et al, 2010, Spinelli et al, 2010, Mitchell et al, 2011, Boschi et al, 2011), clinical imaging of 18 F-FDG in human patients (Holland et al, 2011, Thorek et al, 2014), intraoperative imaging (Holland et al, 2011, Thorek et al, 2012, Liu et al, 2012, Carpenter et al, 2014), as well as dosimetric imaging during external beam radiation therapy and brachytherapy (Glaser et al, 2013a, Glaser et al, 2013b, Glaser et al, 2013d, Glaser et al, 2014, Zhang et al, 2013a, Zhang et al, 2013c, Zhang et al, 2013b, Jarvis et al, 2014, Lohrmann et al, 2015). While all of these studies have appreciated the inherently weak intensity of this form of light emission, there have been limited attempts at absolute quantification of the light fluence of Cherenkov radiation for each of these applications.…”

Cherenkov-excited luminescence scanned imaging

“…Such radiation can be induced by MV radiation beams in water [7,8] and in biological tissues [9,10]. The spectrum of Cherenkov emission is weighted toward ultraviolet and blue frequencies [6].…”

Online Combination of EPID & Cherenkov Imaging for 3-D Dosimetry in a Liquid Phantom

“…Additionally, fully reconstructed 3D images can be acquired [10], but require many angles of view for accurate filtered back-projection reconstruction. So while Cherenkov beam imaging has the strengths of real time acquisition [11][12] and a clear view of the depth dose profile, it is limited by the single 2D view of a 3D dose distribution.…”