Superficial dosimetry imaging of Čerenkov emission in electron beam radiotherapy of phantoms

Zhang, Rongxiao; Fox, Colleen; Glaser, Adam K.; Gladstone, David J.; Pogue, Brian W.

doi:10.1088/0031-9155/58/16/5477

Cited by 65 publications

(88 citation statements)

References 56 publications

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“…Imaging approaches based on air scintillation 20 or Cherenkov radiation 29 also offer the ability to visualize the beam. These techniques enjoy the advantage of not perturbing the treatment beam but generally require much more advanced imaging setups and image processing.…”

Section: Discussionmentioning

confidence: 99%

Monitoring external beam radiotherapy using real‐time beam visualization

Jenkins

Naczynski

et al. 2015

Medical Physics

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Purpose: To characterize the performance of a novel radiation therapy monitoring technique that utilizes a flexible scintillating film, common optical detectors, and image processing algorithms for real-time beam visualization (RT-BV). Methods: Scintillating films were formed by mixing Gd 2 O 2 S:Tb (GOS) with silicone and casting the mixture at room temperature. The films were placed in the path of therapeutic beams generated by medical linear accelerators (LINAC). The emitted light was subsequently captured using a CMOS digital camera. Image processing algorithms were used to extract the intensity, shape, and location of the radiation field at various beam energies, dose rates, and collimator locations. The measurement results were compared with known collimator settings to validate the performance of the imaging system. Results: The RT-BV system achieved a sufficient contrast-to-noise ratio to enable real-time monitoring of the LINAC beam at 20 fps with normal ambient lighting in the LINAC room. The RT-BV system successfully identified collimator movements with sub-millimeter resolution. Conclusions: The RT-BV system is capable of localizing radiation therapy beams with sub-millimeter precision and tracking beam movement at video-rate exposure. C 2015 American Association of Physicists in Medicine. [http://dx

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Section: Discussionmentioning

confidence: 99%

Monitoring external beam radiotherapy using real‐time beam visualization

Jenkins

Naczynski

et al. 2015

Medical Physics

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“…The depth of all theČerenkov photons escaping the entrance surface was logged in a histogram and was fitted by a single exponential decay. 44 The effective sampling depth (depth where the detection sensitivity drops to 1/e) was calculated. Sampling depth tuning based on spectral filtering can be discerned from the results of this simulation.…”

Section: C Simulation: Sampling Region In Layered Skin Modelsmentioning

confidence: 99%

“…45 Affine transformation was implemented based on chosen points on the image to correct the perspective distortion. 44 Finally, each image was smoothed by bilateral filtering and self-normalized by the maximum to the range of [0, 1]. Acquisition speed and signal to noise ratio for different acquisition procedure were investigated.…”

Section: E1 Flat Phantommentioning

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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“…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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Superficial dosimetry imaging of Čerenkov emission in electron beam radiotherapy of phantoms

Cited by 65 publications

References 56 publications

Monitoring external beam radiotherapy using real‐time beam visualization

Monitoring external beam radiotherapy using real‐time beam visualization

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

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

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