Projection imaging of photon beams by the Čerenkov effect

Glaser, Adam K.; Davis, Scott C.; McClatchy, David M.; Zhang, Rongxiao; Pogue, Brian W.; Gladstone, David J.

doi:10.1118/1.4770286

Cited by 102 publications

(142 citation statements)

References 53 publications

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“…Many of these dosimeters make use of the concept of tomography to reconstruct a 3D scintillation volume from many different perspectives (or projections). [15][16][17] While these techniques have shown potential to perform accurate dosimetry on a whole 3D volume, their application to dynamic, modulated radiation delivery is not straightforward, since components of the dosimeter need to rotate during acquisition, a fact which limits their real-time capability. Some other approaches use only fixed components to image and reconstruct a scintillating volume in real-time.…”

Section: Introductionmentioning

confidence: 99%

Novel, full 3D scintillation dosimetry using a static plenoptic camera

et al. 2014

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Purpose: Patient-specific quality assurance (QA) of dynamic radiotherapy delivery would gain from being performed using a 3D dosimeter. However, 3D dosimeters, such as gels, have many disadvantages limiting to quality assurance, such as tedious read-out procedures and poor reproducibility. The purpose of this work is to develop and validate a novel type of high resolution 3D dosimeter based on the real-time light acquisition of a plastic scintillator volume using a plenoptic camera. This dosimeter would allow for the QA of dynamic radiation therapy techniques such as intensity-modulated radiation therapy (IMRT) or volumetric-modulated arc therapy (VMAT). Methods: A Raytrix R5 plenoptic camera was used to image a 10 × 10 × 10 cm 3 EJ-260 plastic scintillator embedded inside an acrylic phantom at a rate of one acquisition per second. The scintillator volume was irradiated with both an IMRT and VMAT treatment plan on a Clinac iX linear accelerator. The 3D light distribution emitted by the scintillator volume was reconstructed at a 2 mm resolution in all dimensions by back-projecting the light collected by each pixel of the light-field camera using an iterative reconstruction algorithm. The latter was constrained by a beam's eye view projection of the incident dose acquired using the portal imager integrated with the linac and by physical consideration of the dose behavior as a function of depth in the phantom. Results: The absolute dose difference between the reconstructed 3D dose and the expected dose calculated using the treatment planning software Pinnacle 3 was on average below 1.5% of the maximum dose for both integrated IMRT and VMAT deliveries, and below 3% for each individual IMRT incidences. Dose agreement between the reconstructed 3D dose and a radiochromic film acquisition in the same experimental phantom was on average within 2.1% and 1.2% of the maximum recorded dose for the IMRT and VMAT delivery, respectively. Conclusions: Using plenoptic camera technology, the authors were able to perform millimeter resolution, water-equivalent dosimetry of an IMRT and VMAT plan over a whole 3D volume. Since no moving parts are required in the dosimeter, the incident dose distribution can be acquired as a function of time, thus enabling the validation of static and dynamic radiation delivery with photons, electrons, and heavier ions.

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Section: Introductionmentioning

confidence: 99%

Novel, full 3D scintillation dosimetry using a static plenoptic camera

et al. 2014

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“…In air, given the low index of refraction, electrons must have energy greater than 20.3 MeV to produce Cherenkov radiation, which is beyond the range of most medical linear accelerators (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Several studies have however utilized Cherenkov radiation generated in water and tissue for dosimetry [22][23][24][25] and molecular imaging. [26][27][28][29][30] While much weaker than Cherenkov radiation, air scintillation can probe and monitor the characteristics of a beam before it enters a patient, in a minimally perturbing manner (perturbation of the beam by air always occurs, independent of our measurement).…”

Section: Introductionmentioning

confidence: 99%

Seeing the invisible: Direct visualization of therapeutic radiation beams using air scintillation

et al. 2013

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Purpose: To assess whether air scintillation produced during standard radiation treatments can be visualized and used to monitor a beam in a nonperturbing manner. Methods: Air scintillation is caused by the excitation of nitrogen gas by ionizing radiation. This weak emission occurs predominantly in the 300-430 nm range. An electron-multiplication chargecoupled device camera, outfitted with an f/0.95 lens, was used to capture air scintillation produced by kilovoltage photon beams and megavoltage electron beams used in radiation therapy. The treatment rooms were prepared to block background light and a short-pass filter was utilized to block light above 440 nm. Results: Air scintillation from an orthovoltage unit (50 kVp, 30 mA) was visualized with a relatively short exposure time (10 s) and showed an inverse falloff (r 2 = 0.89). Electron beams were also imaged. For a fixed exposure time (100 s), air scintillation was proportional to dose rate (r 2 = 0.9998). As energy increased, the divergence of the electron beam decreased and the penumbra improved. By irradiating a transparent phantom, the authors also showed that Cherenkov luminescence did not interfere with the detection of air scintillation. In a final illustration of the capabilities of this new technique, the authors visualized air scintillation produced during a total skin irradiation treatment. Conclusions: Air scintillation can be measured to monitor a radiation beam in an inexpensive and nonperturbing manner. This physical phenomenon could be useful for dosimetry of therapeutic radiation beams or for online detection of gross errors during fractionated treatments.

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“…[31][32][33] It has been shown that, above the threshold energy forČerenkov radiation (approximately 220 KeV in biological tissue), under the approximation of charged particle equilibrium, the dose deposited by megavoltage radiotherapy radiation, and the number ofČerenkov photons released locally are directly proportional; therefore, beam profiling and superficial dosimetry imaging based onČerenkov radiation is feasible. [34][35][36] Radiation dose is calculated by D = E max 0…”

Section: Introductionmentioning

confidence: 99%

Superficial dosimetry imaging based on Čerenkov emission for external beam radiotherapy with megavoltage x‐ray beam

et al. 2013

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Purpose:Čerenkov radiation emission occurs in all tissue, when charged particles (either primary or secondary) travel at velocity above the threshold for theČerenkov effect (about 220 KeV in tissue for electrons). This study presents the first examination of opticalČerenkov emission as a surrogate for the absorbed superficial dose for MV x-ray beams. Methods: In this study, Monte Carlo simulations of flat and curved surfaces were studied to analyze the energy spectra of charged particles produced in different regions near the surfaces when irradiated by MV x-ray beams.Čerenkov emission intensity and radiation dose were directly simulated in voxelized flat and cylindrical phantoms. The sampling region of superficial dosimetry based oň Cerenkov radiation was simulated in layered skin models. Angular distributions of optical emission from the surfaces were investigated. Tissue mimicking phantoms with flat and curved surfaces were imaged with a time domain gating system. The beam field sizes (50 × 50-200 × 200 mm 2 ), incident angles (0• -70 • ) and imaging regions were all varied. Results: The entrance or exit region of the tissue has nearly homogeneous energy spectra across the beam, such that theirČerenkov emission is proportional to dose. Directly simulated local intensity ofČerenkov and radiation dose in voxelized flat and cylindrical phantoms further validate that this signal is proportional to radiation dose with absolute average discrepancy within 2%, and the largest within 5% typically at the beam edges. The effective sampling depth could be tuned from near 0 up to 6 mm by spectral filtering. The angular profiles near the theoretical Lambertian emission distribution for a perfect diffusive medium, suggesting that angular correction of Cerenkov images may not be required even for curved surface. The acquisition speed and signal to noise ratio of the time domain gating system were investigated for different acquisition procedures, and the results show there is good potential for real-time superficial dose monitoring. Dose imaging under normal ambient room lighting was validated, using gated detection and a breast phantom. Conclusions

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Projection imaging of photon beams by the Čerenkov effect

Cited by 102 publications

References 53 publications

Novel, full 3D scintillation dosimetry using a static plenoptic camera

Novel, full 3D scintillation dosimetry using a static plenoptic camera

Seeing the invisible: Direct visualization of therapeutic radiation beams using air scintillation

Superficial dosimetry imaging based on Čerenkov emission for external beam radiotherapy with megavoltage x‐ray beam

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