Optical dosimetry of radiotherapy beams using Cherenkov radiation: the relationship between light emission and dose

Abstract

Recent studies have proposed that light emitted by the Cherenkov effect may be used for a number of radiation therapy dosimetry applications. There is a correlation between the captured light and expected dose under certain conditions, yet discrepancies have also been observed and a complete examination of the theoretical differences has not been done. In this study, a fundamental comparison between the Cherenkov emission and absorbed dose was explored for x-ray photons, electrons, and protons using both a theoretical and Monte Carlo-based analysis. Based on the findings of where dose correlates with Cherenkov emission, it was concluded that for x-ray photons the light emission would be optimally suited for narrow beam stereotactic radiation therapy and surgery validation studies, for verification of dynamic intensity-modulated and volumetric modulated arc therapy treatment plans in water tanks, near monoenergetic sources (e.g., Co-60 and brachy therapy sources) and also for entrance and exit surface imaging dosimetry of both narrow and broad beams. For electron use, Cherenkov emission was found to be only suitable for surface dosimetry applications. Finally, for proton dosimetry, there exists a fundamental lack of Cherenkov emission at the Bragg peak, making the technique of little use, although post-irradiation detection of light emission from radioisotopes could prove to be useful.

Camera selection for real‐time in vivo radiation treatment verification systems using Cherenkov imaging

“…The Cherenkov spectrum plotted in the graph shown in (h) was generated using geant4-based simulations of a 6 MV x-ray beam irradiating a light-skinned tissue volume. 21 The QE curves were plotted from data supplied by the camera manufacturer.…”

“…18 In addition to quality assurance, 19 Cherenkov imaging is being examined for in vivo surface dosimetry and beam tracking for real-time treatment verification. 20,21 As a passive monitoring modality, Cherenkov imaging would neither require any further dose to the patient nor interfere with typical treatment protocols. Initial studies on the applications of Cherenkov imaging have shown feasibility of imaging repeatedly, and studies of the potential medical value are ongoing.…”

Cherenkov imaging in the potential roles of radiotherapy QA and delivery

“…The dose distribution is largely dictated by energetic electrons above the threshold value for Cherenkov emission. Indeed this is well known, as Monte Carlo simulations of dose often do not track secondary photons <200 keV because they contribute so little to the overall dose [4]. A Dose/Cherenkov comparison has been systematically examined in water, using the geometry of Figure 3, and showing measured data from depth dose and profile curves in Figure 4.…”

“…The emission is dominant in the blue range (Fig 1(b)) and falls off significantly with increasing wavelength, yet most of the light emitted from tissue is highly attenuated in the UV-blue-green, due to hemoglobin absorption, and so most of the detected light is above 600 nm when imaging tissue. The intensity of emission is a strong function of particle energy (Fig 1(c)) [4], however, it is relatively constant in the megavoltage energy range used in radiation therapy. Attenuation within tissue is due to scattering as well as high absorption in the UV-blue-green wavelengths, and so the detected Cherenkov light from animals originates from superficial interactions.…”

Cherenkov radiation from electrons passing through human tissue

“…[5][6][7][8][9][10] It was concluded that the Cherenkov emission is suitable for surface dosimetry applications. 7 In the present paper, we suggest the use of Cherenkov radiation produced by relativistic electrons for investigation of optical properties of human tissues. Since the features of Cherenkov radiation are well known, use of the Cherenkov radiation as a source of visible photons for the investigation of human tissue has several advantages:…”