Luminescence Imaging Of Water Research Articles

Luminescence imaging of water irradiated by protons under FLASH radiation therapy conditions

Objective. FLASH radiation therapy with ultrahigh dose rates (UHDR) has the potential to reduce damage to normal tissue while maintaining anti-tumor efficacy. However, rapid and precise dose distribution measurements remain difficult for FLASH radiation therapy with proton beams. To solve this problem, we performed luminescence imaging of water following irradiation by a UHDR proton beam captured using a charge-coupled device camera. Approach. We used 60 MeV proton beams with dose rates of 0.03–837 Gy s−1 from a cyclotron. Therapeutic 139.3 MeV proton beams with dose rates of 0.45–4320 Gy s−1 delivered by a synchrotron-based proton therapy system were also tested. The luminescent light intensity induced by the UHDR beams was compared with that produced by conventional beams to compare the dose rate dependency of the light intensity and its profile. Main results. Luminescence images of water were clearly visualized under UHDR conditions, with significantly shorter exposure times than those with conventional beams. The light intensity was linearly proportional to the delivered dose, which is similar to that of conventional beams. No significant dose-rate dependency was observed for 0.03–837 Gy s−1. The light-intensity profiles of the UHDR beams agreed with those of conventional beams. The results did not differ between accelerators (synchrotron or cyclotron) and beam energies. Significance. Luminescence imaging of water is achievable with UHDR proton beams as well as with conventional beams. The proposed method should be suitable for rapid and easy quality assurance investigations for proton FLASH therapy, because it facilitates real-time, filmless measurements of dose distributions, and is useful for rapid feedback.

Simultaneous imaging of luminescence and prompt x-rays during irradiation with spot-scanning proton beams at clinical dose level

Prompt x-ray imaging is a promising method for observing the beam shape from outside a subject. However, its distribution is different from dose distribution, and thus a comparison with the dose is required. Meanwhile, luminescence imaging of water is a possible method for imaging the dose distribution. Consequently, we performed simultaneous imaging of luminescence and prompt x-rays during irradiation by proton beams to compare the distributions between these two different imaging methods. Optical imaging of water was conducted with spot-scanning proton beams at clinical dose level during irradiation to a fluorescein (FS) water phantom set in a black box. Prompt x-ray imaging was also conducted simultaneously from outside the black box using a developed x-ray camera during proton beam irradiation to the phantom. We measured images of the luminescence of FS water and prompt x-rays for various types of proton beams, including pencil beams, spread-out Bragg peak (SOBP) beams, and clinically used therapy beams. After the imaging, ranges were estimated from FS water and prompt x-rays and compared with those calculated with a treatment planning system (TPS). We could measure the prompt x-ray and FS water images simultaneously for all types of proton beams. The ranges estimated from the FS water and those calculated with the TPS closely matched, within a difference of several mm. Similar range difference was found between the results estimated from prompt x-ray images and those calculated with the TPS. We confirmed that the simultaneous imaging of luminescence and prompt x-rays were possible during irradiation with spot-scanning proton beams at a clinical dose level. This method can be applied to range estimation as well as comparison with the dose for prompt x-ray imaging or other imaging methods used in therapy with various types of proton beams at a clinical dose level.

Luminescence imaging of helium ions during irradiation to water and to an acrylic block

Although the luminescence images of water and an acrylic block during irradiation of proton and carbon ion beams were measured recently, they were not measured for helium ions. Because the mass of helium ions is four times that of protons and one-third that of carbon ions, different results from protons or carbon ions will be obtained by luminescence imaging. We measured the luminescence images of water and an acrylic block during irradiation of helium ion beams. Imaging was conducted using a cooled charge-coupled device (CCD) camera during the irradiation of helium ion pencil beams at three different energies to a water phantom and an acrylic block in addition to mini-beams of helium ions at four different energies. From the measured luminescence images during irradiation of helium ion pencil beams, we could estimate the ranges of the beams for water and the acrylic block. In the luminescence images of the acrylic block during irradiation of mini-beams of helium ions, we observed the luminescence of mini-beams with Bragg peaks in the images. Luminescence imaging of water and an acrylic block during the irradiation of helium ion beams was possible and could be used for range determination of the beams.

Imaging of fragment particles in water by nuclear spallation during carbon-ion irradiation

Recently we found that the luminescence imaging of water during carbon-ion irradiation was possible using a cooled charge-coupled device (CCD) camera and the method could be used for range estimation of the beam. In the luminescence image, we found luminescence from the fragment particles produced by the nuclear spallation reaction of carbon ions. The luminescence may be used for the estimation of the distribution of the fragment particles by the nuclear spallation. For this purpose, we irradiated carbon ions of 241.5 MeV u−1 to a water phantom and measured the luminescence image of water using a CCD camera. Then, we carefully observed the luminescence distribution after the Bragg peak to find the luminescence from the nuclear spallation reaction. In the luminescence image, we could clearly observe the luminescence from the fragment particles produced by the nuclear spallation reaction during irradiation of carbon ions. The beam widths of the luminescence image of the nuclear spallation were compared with those measured by the ionization chamber. The relative difference of the beam width at FWHM between luminescence image and ionization chamber was 23%. With these results, we conclude that the luminescence image of water during carbon-ion irradiation has a potential to be a new and efficient method for the width estimation of the fragment particles by the nuclear spallation reaction.

Luminescence imaging of water during uniform-field irradiation by spot scanning proton beams

Luminescence was found during pencil-beam proton irradiation to water phantom and range could be estimated from the luminescence images. However, it is not yet clear whether the luminescence imaging is applied to the uniform fields made of spot-scanning proton-beam irradiations. For this purpose, imaging was conducted for the uniform fields having spread out Bragg peak (SOBP) made by spot scanning proton beams. We designed six types of the uniform fields with different ranges, SOBP widths and irradiation fields. One of the designed fields was irradiated to water phantom and a cooled charge coupled device camera was used to measure the luminescence image during irradiations. We estimated the ranges, field widths, and luminescence intensities from the luminescence images and compared those with the dose distribution calculated by a treatment planning system. For all types of uniform fields, we could obtain clear images of the luminescence showing the SOBPs. The ranges and field widths evaluated from the luminescence were consistent with those of the dose distribution calculated by a treatment planning system within the differences of −4 mm and −11 mm, respectively. Luminescence intensities were almost proportional to the SOBP widths perpendicular to the beam direction. The luminescence imaging could be applied to uniform fields made of spot scanning proton beam irradiations. Ranges and widths of the uniform fields with SOBP could be estimated from the images. The luminescence imaging is promising for the range and field width estimations in proton therapy.

Luminescence Imaging of Water During Irradiation of Beta Particles With Energy Lower Than Cerenkov-Light Threshold

The luminescence imaging of water during irradiation of beta particles with energy lower than the Cerenkov-light threshold has widely been considered impossible because such particles do not emit Cerenkov light. Contrary to this consensus, we found that luminescence imaging of water is in fact possible with such relatively low-energy beta particles. Beta particles from a 500-kBq 45Ca beta source (maximum energy: 257 keV) were irradiated to pure water, and the source’s luminescence images were acquired with a high-sensitivity, cooled charge-coupled device camera. We also conducted image acquisition for an acrylic plate and a plastic scintillator. The water’s luminescence image during beta particle irradiation became visualized after a 1200-s acquisition time. The luminescence intensity with the beta irradiation of water was 0.54 photons/MeV, and the luminescence intensity with that of the acrylic plate was 3.3 photons/MeV. Consequently, we have shown that luminescence imaging of water using beta particles with energy lower than the Cerenkov-light threshold is a promising new method for beta particle detection and distribution measurements.

Luminescence imaging of water during irradiation of X-ray photons lower energy than Cerenkov- light threshold

Luminescence imaging of water using X-ray photon irradiation at energy lower than maximum energy of ~200keV is thought to be impossible because the secondary electrons produced in this energy range do not emit Cerenkov- light. Contrary to this consensus assumption, we show that the luminescence imaging of water can be achieved by X-ray irradiation at energy lower than 120keV. We placed water phantoms on a table with a conventional X-ray imaging system, and luminescence images of these phantoms were measured with a high-sensitivity, cooled charge coupled device (CCD) camera during X-ray photon irradiation at energy below 120keV. We also carried out such imaging of an acrylic block and plastic scintillator. The luminescence images of water phantoms taken during X-ray photon irradiation clearly showed X-ray photon distribution. The intensity of the X-ray photon images of the phantom increased almost proportionally to the number of X-ray irradiations. Lower-energy X-ray photon irradiation showed lower-intensity luminescence at the deeper parts of the phantom due to the higher X-ray absorption in the water phantom. Furthermore, lower-intensity luminescence also appeared at the deeper parts of the acrylic phantom due to its higher density than water. The intensity of the luminescence for water was 0.005% of that for plastic scintillator. Luminescence imaging of water during X-ray photon irradiation at energy lower than 120keV was possible. This luminescence imaging method is promising for dose estimation in X-ray imaging systems.

Luminescence imaging of water during alpha particle irradiation

The luminescence imaging of water using the alpha particle irradiation of several MeV energy range is thought to be impossible because this alpha particle energy is far below the Cerenkov-light threshold and the secondary electrons produced in this energy range do not emit Cerenkov-light. Contrary to this consensus, we found that the luminescence imaging of water was possible with 5.5MeV alpha particle irradiation. We placed a 2MBq of 241Am alpha source in water, and luminescence images of the source were conducted with a high-sensitivity, cooled charge-coupled device (CCD) camera. We also carried out such imaging of the alpha source in three different conditions to compare the photon productions with that of water, in air, with a plastic scintillator, and an acrylic plate. The luminescence imaging of water was observed from 10 to 20s acquisition, and the intensity was linearly increased with time. The intensity of the luminescence with the alpha irradiation of water was 0.05% of that with the plastic scintillator, 4% with air, and 15% with the acrylic plate. The resolution of the luminescence image of water was better than 0.25mm FWHM. Alpha particles of 5.5MeV energy emit luminescence in water. Although the intensity of the luminescence was smaller than that in air, it was clearly observable. The luminescence of water with alpha particles would be a new method for alpha particle detection and distribution measurements in water.