Imaging Cerenkov emission as a quality assurance tool in electron radiotherapy

Abstract

A new potential quality assurance (QA) method is explored (including assessment of depth dose, dose linearity, dose rate linearity and beam profile) for clinical electron beams based on imaging Cerenkov light. The potential of using a standard commercial camera to image Cerenkov light generated from electrons in water for fast QA measurement of a clinical electron beam was explored and compared to ionization chamber measurements. The new method was found to be linear with dose and independent of dose rate (to within 3%). The uncorrected practical range measured in Cerenkov images was found to overestimate the actual value by 3 mm in the worst case. The field size measurements underestimated the dose at the edges by 5% without applying any correction factor. Still, the measured field size could be used to monitor relative changes in the beam profile. Finally, the beam-direction profile measurements were independent of the field size within 2%. A simulation was also performed of the deposited energy and of Cerenkov production in water using GEANT4. Monte Carlo simulation was used to predict the measured light distribution around the water phantom, to reproduce Cerenkov images and to find the relation between deposited energy and Cerenkov production. The camera was modelled as a pinhole camera in GEANT4, to attempt to reproduce Cerenkov images. Simulations of the deposited energy and the Cerenkov light production agreed with each other for a pencil beam of electrons, while for a realistic field size, Cerenkov production in the build-up region overestimated the dose by +8%.

Quality assurance in proton beam therapy using a plastic scintillator and a commercially available digital camera

“…However, nuclear decay and nonelastic nuclear interactions can still create some Cerenkov light emission. Previously, we used Geant4 to determine the average light production of scintillation and Cerenkov emission when the scintillator was irradiated by a 60 MeV proton beam 25, 26. We found the relative production of Cerenkov emission compared to scintillation light was of the order 10 −5 .…”

“…A 60 MeV proton beam is not capable of producing Cerenkov emission directly 25, 26. However, nuclear decay and nonelastic nuclear interactions can still create some Cerenkov light emission.…”

“…It is caused by geometrical effects within the lens 3, 25, 26. A vignetting correction was performed by acquiring a flat white image for a homogeneous light field supplied by a lightbox trans‐illuminating a homogeneous scattering medium.…”

“…Light generated near to the camera (i.e., +1.25 cm from the midline for a 2.5 cm field size) contributes a higher intensity than light generated from behind the midline. We adopted the method used by Helo et al 25, 26. to correct for this.…”

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.…”