Imaging of monochromatic beams by measuring secondary electron bremsstrahlung for carbon-ion therapy using a pinhole x-ray camera

Abstract

A feasibility study on the imaging of monochromatic carbon-ion beams for carbon-ion therapy was performed. The evaluation was based on Monte Carlo simulations and beam-irradiation experiments, using a pinhole x-ray camera, which measured secondary electron bremsstrahlung (SEB). The simulation results indicated that the trajectories of the carbon-ion beams with injection energies of 278, 249 and 218 MeV/u in a water phantom, were clearly imaged by measuring the SEB with energies from 30 to 60 keV, using a pinhole camera. The Bragg-peak positions for these three injection energies were located at the positions where the ratios of the counts of SEB acquisitions to the maximum counts were approximately 0.23, 0.26 and 0.29, respectively. Moreover, we experimentally demonstrated that it was possible to identify the Bragg-peak positons, at the positions where the ratios coincided with the simulation results. However, the estimated Bragg-peak positions for the injection energies of 278 and 249 MeV/u were slightly deeper than the expected positions. In conclusion, for both the simulations and experiments, we found that the 25 mm shifts in the Bragg-peak positions can be observed by this method.

Use of a Si/CdTe Compton Camera for In vivo Real-Time Monitoring of Annihilation Gamma Rays Generated by Carbon Ion Beam Irradiation

“…Moreover, the dead time of the Compton camera for gammaray detection in the on-beam condition is longer when compared to that in the off-beam condition. The projectile produces various secondary radiation, such as prompt gamma-rays and secondary-electron bremsstrahlungs (41)(42)(43)(44)(45). The detector deadtime caused by the measurement of the secondary radiations reduces the detection efficiency of the annihilation gammarays.…”

Deep learning-based in vivo dose verification from proton-induced secondary-electron-bremsstrahlung images with various count level

“…The calculated position signals were used to produce a 44 × 44 matrix image with a 0.45 mm pixel size. In order to acquire clear images of the beam shape, the energy window of the camera was set from 30 keV to 60 keV [19][20][21][22]. The acquired images of 44 pixel × 44 pixels were cropped to 40 × 40 pixels in the center of the image for the DL.…”

“…In addition, the SEB is relatively easier to detect by gamma cameras than higher energy prompt gamma photons emitted by positron annihilations or nuclear reactions. Dedicated low-energy x-ray cameras were developed and tested during particle-beam irradiations for detecting the SEB, and the cameras could be used to image the beam distributions [16][17][18][19][20][21][22].…”

“…Second, most of the SEB would be attenuated in human body because of their low energy in comparison to prompt gamma photons. In addition, the images measured by the current x-ray camera suffered from the limited spatial resolutions and high statistical noises because of the inevitable low count condition [16][17][18][19][20][21][22]. These issues deteriorated the performance of the estimation of the ranges and widths of the beams in the measured SEB images [16][17][18][19][20][21][22].…”

Dual-energy CT tissue segmentation methods for Monte Carlo dose calculations in proton therapy

“…Also for the purpose of in vivo range verification, other more exotic approaches are under development, such as measuring thermoacoustic waves created during particle 115 irradiation [44], and detecting bremsstrahlung photons and correlating them with the beam path [45][46][47].…”