Large deflection angle, high-power adaptive fiber optics collimator with preserved near-diffraction-limited beam quality.

PubMed

Zhi, Dong; Ma, Yanxing; Chen, Zilun; Wang, Xiaolin; Zhou, Pu; Si, Lei

2016-05-15

We report on the development of a monolithic adaptive fiber optics collimator, with a large deflection angle and preserved near-diffraction-limited beam quality, that has been tested at a maximal output power at the 300 W level. Additionally, a new measurement method of beam quality (M² factor) is developed. Experimental results show that the deflection angle of the collimated beam is in the range of 0-0.27 mrad in the X direction and 0-0.19 mrad in the Y direction. The effective working frequency of the device is about 710 Hz. By employing the new measurement method of the M² factor, we calculate that the beam quality is Mx2=1.35 and My2=1.24, which is in agreement with the result from the beam propagation analyzer and is preserved well with the increasing output power.

Complex amplitude reconstruction for dynamic beam quality M² factor measurement with self-referencing interferometer wavefront sensor.

PubMed

Du, Yongzhao; Fu, Yuqing; Zheng, Lixin

2016-12-20

A real-time complex amplitude reconstruction method for determining the dynamic beam quality M² factor based on a Mach-Zehnder self-referencing interferometer wavefront sensor is developed. By using the proposed complex amplitude reconstruction method, full characterization of the laser beam, including amplitude (intensity profile) and phase information, can be reconstructed from a single interference pattern with the Fourier fringe pattern analysis method in a one-shot measurement. With the reconstructed complex amplitude, the beam fields at any position z along its propagation direction can be obtained by first utilizing the diffraction integral theory. Then the beam quality M² factor of the dynamic beam is calculated according to the specified method of the Standard ISO11146. The feasibility of the proposed method is demonstrated with the theoretical analysis and experiment, including the static and dynamic beam process. The experimental method is simple, fast, and operates without movable parts and is allowed in order to investigate the laser beam in inaccessible conditions using existing methods.

Influence of fundamental mode fill factor on disk laser output power and laser beam quality

NASA Astrophysics Data System (ADS)

Cheng, Zhiyong; Yang, Zhuo; Shao, Xichun; Li, Wei; Zhu, Mengzhen

2017-11-01

An three-dimensional numerical model based on finite element method and Fox-Li method with angular spectrum diffraction theoy is developed to calculate the output power and power density distribution of Yb:YAG disk laser. We invest the influence of fundamental mode fill factor(the ratio of fundamental mode size and pump spot size) on the output power and laser beam quality. Due to aspherical aberration and soft aperture effect in laser disk, high beam quality can be achieve with relative lower efficiency. The highest output power of fundamental laser mode is influenced by the fundamental mode fill factor. Besides we find that optimal mode fill factor increase with pump spot size.

Tunable Q-Factor RF Cavity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balcazar, Mario D.; Yonehara, Katsuya; Moretti, Alfred

Intense neutrino beam is a unique probe for researching beyond the standard model. Fermilab is the main institution to produce the most powerful and widespectrum neutrino beam. From that respective, a radiation robust beam diagnostic system is a critical element in order to maintain the quality of the neutrino beam. Within this context, a novel radiation-resistive beam profile monitor based on a gasfilled RF cavity is proposed. The goal of this measurement is to study a tunable Qfactor RF cavity to determine the accuracy of the RF signal as a function of the quality factor. Specifically, measurement error of themore » Q-factor in the RF calibration is investigated. Then, the RF system will be improved to minimize signal error.« less

Monte Carlo calculations of electron beam quality conversion factors for several ion chamber types.

PubMed

Muir, B R; Rogers, D W O

2014-11-01

To provide a comprehensive investigation of electron beam reference dosimetry using Monte Carlo simulations of the response of 10 plane-parallel and 18 cylindrical ion chamber types. Specific emphasis is placed on the determination of the optimal shift of the chambers' effective point of measurement (EPOM) and beam quality conversion factors. The EGSnrc system is used for calculations of the absorbed dose to gas in ion chamber models and the absorbed dose to water as a function of depth in a water phantom on which cobalt-60 and several electron beam source models are incident. The optimal EPOM shifts of the ion chambers are determined by comparing calculations of R50 converted from I50 (calculated using ion chamber simulations in phantom) to R50 calculated using simulations of the absorbed dose to water vs depth in water. Beam quality conversion factors are determined as the calculated ratio of the absorbed dose to water to the absorbed dose to air in the ion chamber at the reference depth in a cobalt-60 beam to that in electron beams. For most plane-parallel chambers, the optimal EPOM shift is inside of the active cavity but different from the shift determined with water-equivalent scaling of the front window of the chamber. These optimal shifts for plane-parallel chambers also reduce the scatter of beam quality conversion factors, kQ, as a function of R50. The optimal shift of cylindrical chambers is found to be less than the 0.5 rcav recommended by current dosimetry protocols. In most cases, the values of the optimal shift are close to 0.3 rcav. Values of kecal are calculated and compared to those from the TG-51 protocol and differences are explained using accurate individual correction factors for a subset of ion chambers investigated. High-precision fits to beam quality conversion factors normalized to unity in a beam with R50 = 7.5 cm (kQ (')) are provided. These factors avoid the use of gradient correction factors as used in the TG-51 protocol although a chamber dependent optimal shift in the EPOM is required when using plane-parallel chambers while no shift is needed with cylindrical chambers. The sensitivity of these results to parameters used to model the ion chambers is discussed and the uncertainty related to the practical use of these results is evaluated. These results will prove useful as electron beam reference dosimetry protocols are being updated. The analysis of this work indicates that cylindrical ion chambers may be appropriate for use in low-energy electron beams but measurements are required to characterize their use in these beams.

Sensitivity of the diagnostic radiological index of protection to procedural factors in fluoroscopy.

PubMed

Jones, A Kyle; Pasciak, Alexander S; Wagner, Louis K

2016-07-01

To evaluate the sensitivity of the diagnostic radiological index of protection (DRIP), used to quantify the protective value of radioprotective garments, to procedural factors in fluoroscopy in an effort to determine an appropriate set of scatter-mimicking primary beams to be used in measuring the DRIP. Monte Carlo simulations were performed to determine the shape of the scattered x-ray spectra incident on the operator in different clinical fluoroscopy scenarios, including interventional radiology and interventional cardiology (IC). Two clinical simulations studied the sensitivity of the scattered spectrum to gantry angle and patient size, while technical factors were varied according to measured automatic dose rate control (ADRC) data. Factorial simulations studied the sensitivity of the scattered spectrum to gantry angle, field of view, patient size, and beam quality for constant technical factors. Average energy (Eavg) was the figure of merit used to condense fluence in each energy bin to a single numerical index. Beam quality had the strongest influence on the scattered spectrum in fluoroscopy. Many procedural factors affect the scattered spectrum indirectly through their effect on primary beam quality through ADRC, e.g., gantry angle and patient size. Lateral C-arm rotation, common in IC, increased the energy of the scattered spectrum, regardless of the direction of rotation. The effect of patient size on scattered radiation depended on ADRC characteristics, patient size, and procedure type. The scattered spectrum striking the operator in fluoroscopy is most strongly influenced by primary beam quality, particularly kV. Use cases for protective garments should be classified by typical procedural primary beam qualities, which are governed by the ADRC according to the impacts of patient size, anatomical location, and gantry angle.

SU-E-T-204: Comparison of Absorbed-Dose to Water in High-Energy Photon Beams Based On Addendum AAPM TG-51, IAEA TRS-398, and JSMP 12

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kinoshita, N; Kita, A; Yoshioka, C

Purpose: Several clinical reference dosimetry protocols for absorbed-dose to water have recently been published: The American Association of Physicists in Medicine (AAPM) published an Addendum to the AAPM’s TG-51 (Addendum TG-51) in April 2014, and the Japan Society of Medical Physics (JSMP) published the Japan Society of Medical Physics 12 (JSMP12), a clinical reference dosimetry protocol, in September 2012. This investigation compared and evaluated the absorbed-dose to water of high-energy photon beams according to Addendum TG-51, International Atomic Energy Agency Technical Report Series No. 398 (TRS-398), and JSMP12. Methods: Differences in the respective beam quality conversion factors with Addendum TG-51,more » TRS-398, and JSMP12 were analyzed and the absorbed-dose to water using 6- and 10-MV photon beams was measured according to the protocols recommended in Addendum TG-51, TRS-398, and JSMP12. The measurements were conducted using two Farmer-type ionization chambers, Exradin A12 and PTW 30013. Results: The beam quality conversion factors for both the 6- and 10-MV photon beams with Addendum TG-51 were within 0.6%, in agreement with the beam quality conversion factors with TRS-398 and JSMP12. The Exradin A12 provided an absorbed-dose to water ratio from 1.003 to 1.006 with TRS-398 / Addendum TG-51 and from 1.004 to 1.005 with JSMP 12 / Addendum TG-51, whereas the PTW 30013 provided a ratio of 1.001 with TRS-398 / Addendum TG-51 and a range from 0.997 to 0.999 with JSMP 12 / Addendum TG-51. Conclusion: Despite differences in the beam quality conversion factor, no major differences were seen in the absorbed-dose to water with Addendum TG-51, TRS-398, and JSMP12. However, Addendum TG-51 provides the most recent data for beam quality conversion factors based on Monte Carlo simulation and greater detail for the measurement protocol. Therefore, the absorbed-dose to water measured with Addendum TG-51 is an estimate with less uncertainty.« less

Sci-Thur PM: YIS - 07: Monte Carlo simulations to obtain several parameters required for electron beam dosimetry.

PubMed

Muir, B; Rogers, D; McEwen, M

2012-07-01

When current dosimetry protocols were written, electron beam data were limited and had uncertainties that were unacceptable for reference dosimetry. Protocols for high-energy reference dosimetry are currently being updated leading to considerable interest in accurate electron beam data. To this end, Monte Carlo simulations using the EGSnrc user-code egs_chamber are performed to extract relevant data for reference beam dosimetry. Calculations of the absorbed dose to water and the absorbed dose to the gas in realistic ion chamber models are performed as a function of depth in water for cobalt-60 and high-energy electron beams between 4 and 22 MeV. These calculations are used to extract several of the parameters required for electron beam dosimetry - the beam quality specifier, R 50 , beam quality conversion factors, k Q and k R50 , the electron quality conversion factor, k' R50 , the photon-electron conversion factor, k ecal , and ion chamber perturbation factors, P Q . The method used has the advantage that many important parameters can be extracted as a function of depth instead of determination at only the reference depth as has typically been done. Results obtained here are in good agreement with measured and other calculated results. The photon-electron conversion factors obtained for a Farmer-type NE2571 and plane-parallel PTW Roos, IBA NACP-02 and Exradin A11 chambers are 0.903, 0.896, 0.894 and 0.906, respectively. These typically differ by less than 0.7% from the contentious TG-51 values but have much smaller systematic uncertainties. These results are valuable for reference dosimetry of high-energy electron beams. © 2012 American Association of Physicists in Medicine.

Binary phase plates cannot improve laser beam quality.

PubMed

Siegman, A E

1993-05-01

Binary phase plates are often suggested as a means for improving the far-field brightness of beams coming from antiphased laser arrays or waveguide lasers operating in higher-order modes. Somewhat surprisingly, however, binary phase plates actually cannot improve at all the second-moment-based beam quality factor M(2) as usually defined for such beams. Even from a power-in-the-bucket viewpoint, their usefulness is debatable.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mackenzie, Alistair, E-mail: alistairmackenzie@nhs.net; Dance, David R.; Young, Kenneth C.

Purpose: The aim of this work is to create a model to predict the noise power spectra (NPS) for a range of mammographic radiographic factors. The noise model was necessary to degrade images acquired on one system to match the image quality of different systems for a range of beam qualities. Methods: Five detectors and x-ray systems [Hologic Selenia (ASEh), Carestream computed radiography CR900 (CRc), GE Essential (CSI), Carestream NIP (NIPc), and Siemens Inspiration (ASEs)] were characterized for this study. The signal transfer property was measured as the pixel value against absorbed energy per unit area (E) at a referencemore » beam quality of 28 kV, Mo/Mo or 29 kV, W/Rh with 45 mm polymethyl methacrylate (PMMA) at the tube head. The contributions of the three noise sources (electronic, quantum, and structure) to the NPS were calculated by fitting a quadratic at each spatial frequency of the NPS against E. A quantum noise correction factor which was dependent on beam quality was quantified using a set of images acquired over a range of radiographic factors with different thicknesses of PMMA. The noise model was tested for images acquired at 26 kV, Mo/Mo with 20 mm PMMA and 34 kV, Mo/Rh with 70 mm PMMA for three detectors (ASEh, CRc, and CSI) over a range of exposures. The NPS were modeled with and without the noise correction factor and compared with the measured NPS. A previous method for adapting an image to appear as if acquired on a different system was modified to allow the reference beam quality to be different from the beam quality of the image. The method was validated by adapting the ASEh flat field images with two thicknesses of PMMA (20 and 70 mm) to appear with the imaging characteristics of the CSI and CRc systems. Results: The quantum noise correction factor rises with higher beam qualities, except for CR systems at high spatial frequencies, where a flat response was found against mean photon energy. This is due to the dominance of secondary quantum noise in CR. The use of the quantum noise correction factor reduced the difference from the model to the real NPS to generally within 4%. The use of the quantum noise correction improved the conversion of ASEh image to CRc image but had no difference for the conversion to CSI images. Conclusions: A practical method for estimating the NPS at any dose and over a range of beam qualities for mammography has been demonstrated. The noise model was incorporated into a methodology for converting an image to appear as if acquired on a different detector. The method can now be extended to work for a wide range of beam qualities and can be applied to the conversion of mammograms.« less

High beam quality and high energy short-pulse laser with MOPA

NASA Astrophysics Data System (ADS)

Jin, Quanwei; Pang, Yu; Jiang, JianFeng; Tan, Liang; Cui, Lingling; Wei, Bin; Sun, Yinhong; Tang, Chun

2018-03-01

A high energy, high beam quality short-pulse diode-pumped Nd:YAG master oscillator power-amplifier (MOPA) laser with two amplifier stages is demonstrated. The two-rod birefringence compensation was used as beam quality controlling methods, which presents a short-pulse energy of 40 mJ with a beam quality value of M2 = 1.2 at a repetition rate of 400Hz. The MOPA system delivers a short-pulse energy of 712.5 mJ with a pulse width of 12.4 ns.The method of spherical aberration compensation is improved the beam quality, a M2 factor of 2.3 and an optical-to-optical efficiency of 27.7% is obtained at the maximum laser out power.The laser obtained 1.4J out energy with polarization integration.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, A. Kyle, E-mail: kyle.jones@mdanderson.org

Purpose: To evaluate the sensitivity of the diagnostic radiological index of protection (DRIP), used to quantify the protective value of radioprotective garments, to procedural factors in fluoroscopy in an effort to determine an appropriate set of scatter-mimicking primary beams to be used in measuring the DRIP. Methods: Monte Carlo simulations were performed to determine the shape of the scattered x-ray spectra incident on the operator in different clinical fluoroscopy scenarios, including interventional radiology and interventional cardiology (IC). Two clinical simulations studied the sensitivity of the scattered spectrum to gantry angle and patient size, while technical factors were varied according tomore » measured automatic dose rate control (ADRC) data. Factorial simulations studied the sensitivity of the scattered spectrum to gantry angle, field of view, patient size, and beam quality for constant technical factors. Average energy (E{sub avg}) was the figure of merit used to condense fluence in each energy bin to a single numerical index. Results: Beam quality had the strongest influence on the scattered spectrum in fluoroscopy. Many procedural factors affect the scattered spectrum indirectly through their effect on primary beam quality through ADRC, e.g., gantry angle and patient size. Lateral C-arm rotation, common in IC, increased the energy of the scattered spectrum, regardless of the direction of rotation. The effect of patient size on scattered radiation depended on ADRC characteristics, patient size, and procedure type. Conclusions: The scattered spectrum striking the operator in fluoroscopy is most strongly influenced by primary beam quality, particularly kV. Use cases for protective garments should be classified by typical procedural primary beam qualities, which are governed by the ADRC according to the impacts of patient size, anatomical location, and gantry angle.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, A; Pasciak, A; Wagner, L

Purpose: To evaluate the sensitivity of the Diagnostic Radiological Index of Protection (DRIP) to procedural factors in fluoroscopy in an effort to determine an appropriate set of scatter-mimicking primary beams (SMPB) to be used in measuring the DRIP. Methods: A series of clinical and factorial Monte Carlo simulations were conducted to determine the shape of the scattered X-ray spectra incident on the operator in different clinical fluoroscopy scenarios. Two clinical evaluations studied the sensitivity of the scattered spectrum to gantry angle and patient size while technical factors were varied according to measured automatic dose rate control (ADRC) data. Factorial evaluationsmore » studied the sensitivity of the scattered spectrum to gantry angle, field of view, patient size and beam quality for constant technical factors. Average energy was the figure of merit used to condense fluence in each energy bin to a single numerical index. Results: Beam quality had the strongest influence on the scattered spectrum in fluoroscopy. Many procedural factors affected the scattered spectrum indirectly through their effects on primary beam quality through ADRC, e.g., gantry angle and patient size. Lateral C-arm rotation, common in interventional cardiology, increased the energy of the scattered spectrum, regardless of the direction of rotation. The effect of patient size on scattered radiation depended on ADRC characteristics, patient size, and procedure type. Conclusion: The scattered spectrum striking the operator in fluoroscopy, and therefore the DRIP, is most strongly influenced by primary beam quality, particularly kV. Use cases for protective garments should be classified by typical procedural primary beam qualities, which are governed by the ADRC according to the impacts of patient size, anatomical location, and gantry angle. These results will help determine an appropriate set of SMPB to be used for measuring the DRIP.« less

Numerical investigation of output beam quality in efficient broadband optical parametric chirped pulse amplification

NASA Astrophysics Data System (ADS)

Liu, Xiao-Di; Xu, Lu; Liang, Xiao-Yan

2017-01-01

We theoretically analyzed output beam quality of broad bandwidth non-collinear optical parametric chirped pulse amplification (NOPCPA) in LiB3O5 (LBO) centered at 800 nm. With a three-dimensional numerical model, the influence of the pump intensity, pump and signal spatial modulations, and the walk-off effect on the OPCPA output beam quality are presented, together with conversion efficiency and the gain spectrum. The pump modulation is a dominant factor that affects the output beam quality. Comparatively, the influence of signal modulation is insignificant. For a low-energy system with small beam sizes, walk-off effect has to be considered. Pump modulation and walk-off effect lead to asymmetric output beam profile with increased modulation. A special pump modulation type is found to optimize output beam quality and efficiency. For a high-energy system with large beam sizes, the walk-off effect can be neglected, certain back conversion is beneficial to reduce the output modulation. A trade-off must be made between the output beam quality and the conversion efficiency, especially when the pump modulation is large since. A relatively high conversion efficiency and a low output modulation are both achievable by controlling the pump modulation and intensity.

Quality correction factors of composite IMRT beam deliveries: theoretical considerations.

PubMed

Bouchard, Hugo

2012-11-01

In the scope of intensity modulated radiation therapy (IMRT) dosimetry using ionization chambers, quality correction factors of plan-class-specific reference (PCSR) fields are theoretically investigated. The symmetry of the problem is studied to provide recommendable criteria for composite beam deliveries where correction factors are minimal and also to establish a theoretical limit for PCSR delivery k(Q) factors. The concept of virtual symmetric collapsed (VSC) beam, being associated to a given modulated composite delivery, is defined in the scope of this investigation. Under symmetrical measurement conditions, any composite delivery has the property of having a k(Q) factor identical to its associated VSC beam. Using this concept of VSC, a fundamental property of IMRT k(Q) factors is demonstrated in the form of a theorem. The sensitivity to the conditions required by the theorem is thoroughly examined. The theorem states that if a composite modulated beam delivery produces a uniform dose distribution in a volume V(cyl) which is symmetric with the cylindrical delivery and all beams fulfills two conditions in V(cyl): (1) the dose modulation function is unchanged along the beam axis, and (2) the dose gradient in the beam direction is constant for a given lateral position; then its associated VSC beam produces no lateral dose gradient in V(cyl), no matter what beam modulation or gantry angles are being used. The examination of the conditions required by the theorem lead to the following results. The effect of the depth-dose gradient not being perfectly constant with depth on the VSC beam lateral dose gradient is found negligible. The effect of the dose modulation function being degraded with depth on the VSC beam lateral dose gradient is found to be only related to scatter and beam hardening, as the theorem holds also for diverging beams. The use of the symmetry of the problem in the present paper leads to a valuable theorem showing that k(Q) factors of composite IMRT beam deliveries are close to unity under specific conditions. The theoretical limit k(Q(pcsr),Q(msr) ) (f(pcsr),f(msr) )=1 is determined based on the property of PCSR deliveries to provide a uniform dose in the target volume. The present approach explains recent experimental observations and proposes ideal conditions for IMRT reference dosimetry. The result of this study could potentially serve as a theoretical basis for reference dosimetry of composite IMRT beam deliveries or for routine IMRT quality assurance.

A Monte Carlo study of the quality dependence factors of common TLD materials in photon and electron beams.

PubMed

Mobit, P N; Nahum, A E; Mayles, P

1998-08-01

A Monte Carlo simulation of the quality dependence of different TL materials, in the form of discs 3.61 mm in diameter and 0.9 mm thick, in radiotherapy photon beams relative to 60Co gamma-rays has been performed. The beam qualities ranged from 50 kV to 25 MV x-rays. The TL materials were: CaF2, CaSO4, LiF and Li2B4O7. The effects of the dopants on energy deposition in the TL material have also been determined for the highly sensitive LiF:Mg:Cu:P (TLD-100H) and for CaF2:Mn. It was found that there was a significant difference in the quality dependence factor derived from Monte Carlo simulations between LiF and LiF:Mg:Cu:P but not between CaF2 and CaF2:Mn. The quality dependence factors for Li2B4O7 varied from 0.990 +/- 0.008 (1 sd) for 25 MV x-rays to 0.940 +/- 0.009 (1 sd) for 50 kV x-rays relative to 60Co gamma-rays; Monte Carlo simulations were also performed for Li2B4O7 in megavoltage electron beams. For CaF2, the quality dependence factor varied from 0.927 +/- 0.008 (1 sd) for 25 MV x-rays to 10.561 +/- 0.008 (1 sd) for 50 kV x-rays. The figure for CaSO4 ranged from 0.943 +/- 0.008 (1 sd) for 25 MV x-rays to 9.010 +/- 0.008 (1 sd) for 50 kV x-rays. The quality dependence factor for CaF2 increases by up to 5% with depth and by up to 15% with field size for the kilovoltage x-ray beams. For LiF-TLD, however, there was no significant dependence on the field size or depth of irradiation in the kilovoltage energy range.

[Uncertainty of cross calibration-applied beam quality conversion factor for the Japan Society of Medical Physics 12].

PubMed

Kinoshita, Naoki; Kita, Akinobu; Takemura, Akihiro; Nishimoto, Yasuhiro; Adachi, Toshiki

2014-09-01

The uncertainty of the beam quality conversion factor (k(Q,Q0)) of standard dosimetry of absorbed dose to water in external beam radiotherapy 12 (JSMP12) is determined by combining the uncertainty of each beam quality conversion factor calculated for each type of ionization chamber. However, there is no guarantee that ionization chambers of the same type have the same structure and thickness, so there may be individual variations. We evaluated the uncertainty of k(Q,Q0) for JSMP12 using an ionization chamber dosimeter and linear accelerator without a specific device or technique in consideration of the individual variation of ionization chambers and in clinical radiation field. The cross calibration formula was modified and the beam quality conversion factor for the experimental values [(k(Q,Q0))field] determined using the modified formula. It's uncertainty was calculated to be 1.9%. The differences between (k(Q,Q0))field of experimental values and k(Q,Q0) for Japan Society of Medical Physics 12 (JSMP12) were 0.73% and 0.88% for 6- and 10-MV photon beams, respectively, remaining within ± 1.9%. This showed k(Q,Q0) for JSMP12 to be consistent with (k(Q,Q0))field of experimental values within the estimated uncertainty range. Although inter-individual differences may be generated, even when the same type of ionized chamber is used, k(Q,Q0) for JSMP12 appears to be consistent within the estimated uncertainty range of (k(Q,Q0)field.

Direct determination of k Q factors for cylindrical and plane-parallel ionization chambers in high-energy electron beams from 6 MeV to 20 MeV.

PubMed

Krauss, A; Kapsch, R-P

2018-02-06

For the ionometric determination of the absorbed dose to water, D w , in high-energy electron beams from a clinical accelerator, beam quality dependent correction factors, k Q , are required. By using a water calorimeter, these factors can be determined experimentally and potentially with lower standard uncertainties than those of the calculated k Q factors, which are tabulated in various dosimetry protocols. However, one of the challenges of water calorimetry in electron beams is the small measurement depths in water, together with the steep dose gradients present especially at lower energies. In this investigation, water calorimetry was implemented in electron beams to determine k Q factors for different types of cylindrical and plane-parallel ionization chambers (NE2561, NE2571, FC65-G, TM34001) in 10 cm  ×  10 cm electron beams from 6 MeV to 20 MeV (corresponding beam quality index R 50 ranging from 1.9 cm to 7.5 cm). The measurements were carried out using the linear accelerator facility of the Physikalisch-Technische Bundesanstalt. Relative standard uncertainties for the k Q factors between 0.50% for the 20 MeV beam and 0.75% for the 6 MeV beam were achieved. For electron energies above 8 MeV, general agreement was found between the relative electron energy dependencies of the k Q factors measured and those derived from the AAPM TG-51 protocol and recent Monte Carlo-based studies, as well as those from other experimental investigations. However, towards lower energies, discrepancies of up to 2.0% occurred for the k Q factors of the TM34001 and the NE2571 chamber.

Direct determination of k Q factors for cylindrical and plane-parallel ionization chambers in high-energy electron beams from 6 MeV to 20 MeV

NASA Astrophysics Data System (ADS)

Krauss, A.; Kapsch, R.-P.

2018-02-01

For the ionometric determination of the absorbed dose to water, D w, in high-energy electron beams from a clinical accelerator, beam quality dependent correction factors, k Q, are required. By using a water calorimeter, these factors can be determined experimentally and potentially with lower standard uncertainties than those of the calculated k Q factors, which are tabulated in various dosimetry protocols. However, one of the challenges of water calorimetry in electron beams is the small measurement depths in water, together with the steep dose gradients present especially at lower energies. In this investigation, water calorimetry was implemented in electron beams to determine k Q factors for different types of cylindrical and plane-parallel ionization chambers (NE2561, NE2571, FC65-G, TM34001) in 10 cm  ×  10 cm electron beams from 6 MeV to 20 MeV (corresponding beam quality index R 50 ranging from 1.9 cm to 7.5 cm). The measurements were carried out using the linear accelerator facility of the Physikalisch-Technische Bundesanstalt. Relative standard uncertainties for the k Q factors between 0.50% for the 20 MeV beam and 0.75% for the 6 MeV beam were achieved. For electron energies above 8 MeV, general agreement was found between the relative electron energy dependencies of the k Q factors measured and those derived from the AAPM TG-51 protocol and recent Monte Carlo-based studies, as well as those from other experimental investigations. However, towards lower energies, discrepancies of up to 2.0% occurred for the k Q factors of the TM34001 and the NE2571 chamber.

Measurement of in-phantom neutron flux and gamma dose in Tehran research reactor boron neutron capture therapy beam line.

PubMed

Bavarnegin, Elham; Sadremomtaz, Alireza; Khalafi, Hossein; Kasesaz, Yaser

2016-01-01

Determination of in-phantom quality factors of Tehran research reactor (TRR) boron neutron capture therapy (BNCT) beam. The doses from thermal neutron reactions with 14N and 10B are calculated by kinetic energy released per unit mass approach, after measuring thermal neutron flux using neutron activation technique. Gamma dose is measured using TLD-700 dosimeter. Different dose components have been measured in a head phantom which has been designed and constructed for BNCT purpose in TRR. Different in-phantom beam quality factors have also been determined. This study demonstrates that the TRR BNCT beam line has potential for treatment of superficial tumors.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Renaud, James, E-mail: james.renaud@mail.mcgill.ca; Seuntjens, Jan; Sarfehnia, Arman

Purpose: In this work, the authors describe an electron sealed water calorimeter (ESWcal) designed to directly measure absorbed dose to water in clinical electron beams and its use to derive electron beam quality conversion factors for two ionization chamber types. Methods: A functioning calorimeter prototype was constructed in-house and used to obtain reproducible measurements in clinical accelerator-based 6, 9, 12, 16, and 20 MeV electron beams. Corrections for the radiation field perturbation due to the presence of the glass calorimeter vessel were calculated using Monte Carlo (MC) simulations. The conductive heat transfer due to dose gradients and nonwater materials wasmore » also accounted for using a commercial finite element method software package. Results: The relative combined standard uncertainty on the ESWcal dose was estimated to be 0.50% for the 9–20 MeV beams and 1.00% for the 6 MeV beam, demonstrating that the development of a water calorimeter-based standard for electron beams over such a wide range of clinically relevant energies is feasible. The largest contributor to the uncertainty was the positioning (Type A, 0.10%–0.40%) and its influence on the perturbation correction (Type B, 0.10%–0.60%). As a preliminary validation, measurements performed with the ESWcal in a 6 MV photon beam were directly compared to results derived from the National Research Council of Canada (NRC) photon beam standard water calorimeter. These two independent devices were shown to agree well within the 0.43% combined relative uncertainty of the ESWcal for this beam type and quality. Absorbed dose electron beam quality conversion factors were measured using the ESWcal for the Exradin A12 and PTW Roos ionization chambers. The photon-electron conversion factor, k{sub ecal}, for the A12 was also experimentally determined. Nonstatistically significant differences of up to 0.7% were found when compared to the calculation-based factors listed in the AAPM’s TG-51 protocol. General agreement between the relative electron energy dependence of the PTW Roos data measured in this work and a recent MC-based study are also shown. Conclusions: This is the first time that water calorimetry has been successfully used to measure electron beam quality conversion factors for energies as low as 6 MeV (R{sub 50} = 2.25 cm)« less

The central electrode correction factor for high-Z electrodes in small ionization chambers.

PubMed

Muir, B R; Rogers, D W O

2011-02-01

Recent Monte Carlo calculations of beam quality conversion factors for ion chambers that use high-Z electrodes [B. R. Muir and D. W. O. Rogers, Med. Phys. 37, 5939-5950 (2010)] have shown large deviations of kQ values from values calculated using the same techniques as the TG-51 and TRS-398 protocols. This report investigates the central electrode correction factor, Pcel, for these chambers. Ionization chambers are modeled and Pcel is calculated using the EGSnrc user code egs_chamber for three cases: in photon and electron beams under reference conditions; as a function of distance from an iridium-192 point source in a water phantom; and as a function of depth in a water phantom on which a 200 kVp x-ray source or 6 MV beam is incident. In photon beams, differences of up to 3% between Pcel calculations for a chamber with a high-Z electrode and those used by TG-51 for a 1 mm diameter aluminum electrode are observed. The central electrode correction factor for a given value of the beam quality specifier is different depending on the amount of filtration of the photon beam. However, in an unfiltered 6 MV beam, Pcel, varies by only 0.3% for a chamber with a high-Z electrode as the depth is varied from 1 to 20 cm in water. The difference between Pcel calculations for chambers with high-Z electrodes and TG-51 values for a chamber with an aluminum electrode is up to 0.45% in electron beams. The central electrode correction, which is roughly proportional to the chambers absorbed dose sensitivity, is found to be large and variable as a function of distance for chambers with high-Z and aluminum electrodes in low-energy photon fields. In this work, ionization chambers that employ high-Z electrodes have been shown to be problematic in various situations. For beam quality conversion factors, the ratio of Pcel in a beam quality Q to that in a Co-60 beam is required; for some chambers, kQ is significantly different from current dosimetry protocol values because of central electrode effects. It would be best for manufacturers to avoid producing ion chambers that use high-Z electrodes.

Beam quality corrections for parallel-plate ion chambers in electron reference dosimetry

NASA Astrophysics Data System (ADS)

Zink, K.; Wulff, J.

2012-04-01

Current dosimetry protocols (AAPM, IAEA, IPEM, DIN) recommend parallel-plate ionization chambers for dose measurements in clinical electron beams. This study presents detailed Monte Carlo simulations of beam quality correction factors for four different types of parallel-plate chambers: NACP-02, Markus, Advanced Markus and Roos. These chambers differ in constructive details which should have notable impact on the resulting perturbation corrections, hence on the beam quality corrections. The results reveal deviations to the recommended beam quality corrections given in the IAEA TRS-398 protocol in the range of 0%-2% depending on energy and chamber type. For well-guarded chambers, these deviations could be traced back to a non-unity and energy-dependent wall perturbation correction. In the case of the guardless Markus chamber, a nearly energy-independent beam quality correction is resulting as the effects of wall and cavity perturbation compensate each other. For this chamber, the deviations to the recommended values are the largest and may exceed 2%. From calculations of type-B uncertainties including effects due to uncertainties of the underlying cross-sectional data as well as uncertainties due to the chamber material composition and chamber geometry, the overall uncertainty of calculated beam quality correction factors was estimated to be <0.7%. Due to different chamber positioning recommendations given in the national and international dosimetry protocols, an additional uncertainty in the range of 0.2%-0.6% is present. According to the IAEA TRS-398 protocol, the uncertainty in clinical electron dosimetry using parallel-plate ion chambers is 1.7%. This study may help to reduce this uncertainty significantly.

Quality correction factors of composite IMRT beam deliveries: Theoretical considerations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bouchard, Hugo

2012-11-15

Purpose: In the scope of intensity modulated radiation therapy (IMRT) dosimetry using ionization chambers, quality correction factors of plan-class-specific reference (PCSR) fields are theoretically investigated. The symmetry of the problem is studied to provide recommendable criteria for composite beam deliveries where correction factors are minimal and also to establish a theoretical limit for PCSR delivery k{sub Q} factors. Methods: The concept of virtual symmetric collapsed (VSC) beam, being associated to a given modulated composite delivery, is defined in the scope of this investigation. Under symmetrical measurement conditions, any composite delivery has the property of having a k{sub Q} factor identicalmore » to its associated VSC beam. Using this concept of VSC, a fundamental property of IMRT k{sub Q} factors is demonstrated in the form of a theorem. The sensitivity to the conditions required by the theorem is thoroughly examined. Results: The theorem states that if a composite modulated beam delivery produces a uniform dose distribution in a volume V{sub cyl} which is symmetric with the cylindrical delivery and all beams fulfills two conditions in V{sub cyl}: (1) the dose modulation function is unchanged along the beam axis, and (2) the dose gradient in the beam direction is constant for a given lateral position; then its associated VSC beam produces no lateral dose gradient in V{sub cyl}, no matter what beam modulation or gantry angles are being used. The examination of the conditions required by the theorem lead to the following results. The effect of the depth-dose gradient not being perfectly constant with depth on the VSC beam lateral dose gradient is found negligible. The effect of the dose modulation function being degraded with depth on the VSC beam lateral dose gradient is found to be only related to scatter and beam hardening, as the theorem holds also for diverging beams. Conclusions: The use of the symmetry of the problem in the present paper leads to a valuable theorem showing that k{sub Q} factors of composite IMRT beam deliveries are close to unity under specific conditions. The theoretical limit k{sub Q{sub p{sub c{sub s{sub r,Q{sub m{sub s{sub r}{sup f{sub p}{sub c}{sub s}{sub r},f{sub m}{sub s}{sub r}}}}}}}}}=1 is determined based on the property of PCSR deliveries to provide a uniform dose in the target volume. The present approach explains recent experimental observations and proposes ideal conditions for IMRT reference dosimetry. The result of this study could potentially serve as a theoretical basis for reference dosimetry of composite IMRT beam deliveries or for routine IMRT quality assurance.« less

On the impact of ICRU report 90 recommendations on kQ factors for high-energy photon beams.

PubMed

Mainegra-Hing, Ernesto; Muir, Bryan R

2018-06-03

To assess the impact of the ICRU report 90 recommendations on the beam-quality conversion factor, k Q , used for clinical reference dosimetry of megavoltage linac photon beams. The absorbed dose to water and the absorbed dose to the air in ionization chambers representative of those typically used for linac photon reference dosimetry are calculated at the reference depth in a water phantom using Monte Carlo simulations. Depth-dose calculations in water are also performed to investigate changes in beam quality specifiers. The calculations are performed in a cobalt-60 beam and MV photon beams with nominal energy between 6 MV and 25 MV using the EGSnrc simulation toolkit. Inputs to the calculations use stopping-power data for graphite and water from the original ICRU-37 report and the new proposed values from the recently published ICRU-90 report. Calculated k Q factors are compared using the two different recommendations for key dosimetry data and measured k Q factors. Less than about 0.1% effects from ICRU-90 recommendations on the beam quality specifiers, the photon component of the percentage depth-dose at 10 cm, %dd(10) x , and the tissue-phantom ratio at 20 cm and 10 cm, TPR1020, are observed. Although using different recommendations for key dosimetric data impact water-to-air stopping-power ratios and ion chamber perturbation corrections by up to 0.54% and 0.40%, respectively, we observe little difference (≤0.14%) in calculated k Q factors. This is contradictory to the predictions in ICRU-90 that suggest differences up to 0.5% in high-energy photon beams. A slightly better agreement with experimental values is obtained when using ICRU-90 recommendations. Users of the addendum to the TG-51 protocol for reference dosimetry of high-energy photon beams, which recommends Monte Carlo calculated k Q factors, can rest assured that the recommendations of ICRU report 90 on basic data have little impact on this central dosimetric parameter. © Her Majesty the Queen in Right of Canada 2018. Reproduced with the permission of the Minister of Science.

Automated beam monitoring and diagnosis for CO2 lasers

NASA Astrophysics Data System (ADS)

Mann, Stefan; Boeske, Lars; Kaierle, Stefan; Kreutz, Ernst-Wolfgang; Poprawe, Reinhart

2002-06-01

The usage of a quality management, in combination with a standard certification, is nearly inevitable for today's industrial manufacturing. In laser materials processing, a periodical beam diagnosis is to be executed as a quality-maintaining measure with any change of the workpiece geometry to guarantee an unambiguous allocation of the beam quality factors. Otherwise changes in the beam quality, caused by pollution, aging or defect of the optical components, remain unidentified for a long time, leading to impairments of the treatment quality or even costly down-times. As a solution a diagnosis system is integrated into a laser system. Data sources like measuring instruments, sensors and laser control transmit the diagnosis data to a diagnosis PC. A user-friendly software, based on Fuzzy algorithms, enables the operator to retrace changes in the beam quality to failures of the laser system. All diagnosis data are getting archived in a databank. The access to the archived data through the World Wide Web allows remote diagnoses. With the help of the beam diagnosis system failures can be discovered in advance, and losses of production can be avoided. The gained transparency of the beam characteristic values facilitates the integration of the laser system in the quality management. A prototype installation has been realized and latest results will be demonstrated.

SU-G-TeP1-03: Beam Quality Correction Factors for Linear Accelerator with and Without Flattening Filter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Czarnecki, D; Voigts-Rhetz, P von; Zink, K

2016-06-15

Purpose: The impact of removing the flattening filter on absolute dosimetry based on IAEA’s TPR-398 and AAPM’s TG-51 was investigated in this study using Monte Carlo simulations. Methods: The EGSnrc software package was used for all Monte Carlo simulations performed in this work. Five different ionization chambers and nine linear accelerator heads have been modeled according to technical drawings. To generate a flattening filter free radiation field the flattening filter was replaced by a 2 mm thick aluminum layer. Dose calculation in a water phantom were performed to calculate the beam quality correction factor k{sub Q} as a function ofmore » the beam quality specifiers %dd(10){sub x}, TPR{sub 20,10} and mean photon and electron energies at the point of measurement in photon fields with (WFF) and without flattening filter (FFF). Results: The beam quality correction factor as a function of %dd(10){sub x} differs systematically between FFF and WFF beams for all investigated ionization chambers. The largest difference of 1.8% was observed for the largest investigated Farmer-type ionization chamber with a sensitive volume of 0.69 cm{sup 3}. For ionization chambers with a smaller nominal sensitive volume (0.015 – 0.3 cm{sup 3}) the deviation was less than 0.4% between WFF and FFF beams for %dd(10){sub x} > 62%. The specifier TPR{sub 20,10} revealed only a good correlation between WFF and FFF beams (< 0.3%) for low energies. Conclusion: The results confirm that %dd(10){sub x} is a suitable beam quality specifier for FFF beams with an acceptable bias. The deviation depends on the volume of the ionization chamber. Using %dd(10){sub x} to predict k{sub Q} for a large volume chamber in a FFF photon field may lead to not acceptable errors according to the results of this study. This bias may be caused by the volume effect due to the inhomogeneous photon fields of FFF linear accelerators.« less

Correction factor for ablation algorithms used in corneal refractive surgery with gaussian-profile beams

NASA Astrophysics Data System (ADS)

Jimenez, Jose Ramón; González Anera, Rosario; Jiménez del Barco, Luis; Hita, Enrique; Pérez-Ocón, Francisco

2005-01-01

We provide a correction factor to be added in ablation algorithms when a Gaussian beam is used in photorefractive laser surgery. This factor, which quantifies the effect of pulse overlapping, depends on beam radius and spot size. We also deduce the expected post-surgical corneal radius and asphericity when considering this factor. Data on 141 eyes operated on LASIK (laser in situ keratomileusis) with a Gaussian profile show that the discrepancy between experimental and expected data on corneal power is significantly lower when using the correction factor. For an effective improvement of post-surgical visual quality, this factor should be applied in ablation algorithms that do not consider the effects of pulse overlapping with a Gaussian beam.

Measurement system with high accuracy for laser beam quality.

PubMed

Ke, Yi; Zeng, Ciling; Xie, Peiyuan; Jiang, Qingshan; Liang, Ke; Yang, Zhenyu; Zhao, Ming

2015-05-20

Presently, most of the laser beam quality measurement system collimates the optical path manually with low efficiency and low repeatability. To solve these problems, this paper proposed a new collimated method to improve the reliability and accuracy of the measurement results. The system accuracy controlled the position of the mirror to change laser beam propagation direction, which can realize the beam perpendicularly incident to the photosurface of camera. The experiment results show that the proposed system has good repeatability and the measuring deviation of M² factor is less than 0.6%.

Megavoltage planar and cone-beam imaging with low-Z targets: dependence of image quality improvement on beam energy and patient separation.

PubMed

Robar, James L; Connell, Tanner; Huang, Weihong; Kelly, Robin G

2009-09-01

The purpose of this study is to investigate the improvement of megavoltage planar and cone-beam CT (CBCT) image quality with the use of low atomic number (Z) external targets in the linear accelerator. In this investigation, two experimental megavoltage imaging beams were generated by using either 3.5 or 7.0 MeV electrons incident on aluminum targets installed above the level of the carousel in a linear accelerator (2100EX, Varian Medical, Inc., Palo Alto, CA). Images were acquired using an amorphous silicon detector panel. Contrast-to-noise ratio (CNR) in planar and CBCT images was measured as a function of dose and a comparison was made between the imaging beams and the standard 6 MV therapy beam. Phantoms of variable diameter were used to examine the loss of contrast due to beam hardening. Porcine imaging was conducted to examine qualitatively the advantages of the low-Z target approach in CBCT. In CBCT imaging CNR increases by factors as high as 2.4 and 4.3 for the 7.0 and 3.5 MeV/Al beams, respectively, compared to images acquired with 6 MV. Similar factors of improvement are observed in planar imaging. For the imaging beams, beam hardening causes a significant loss of the contrast advantage with increasing phantom diameter; however, for the 3.5 MeV/Al beam and a phantom diameter of 25 cm, a contrast advantage remains, with increases of contrast by factors of 1.5 and 3.4 over 6 MV for bone and lung inhale regions, respectively. The spatial resolution is improved slightly in CBCT images for the imaging beams. CBCT images of a porcine cranium demonstrate qualitatively the advantages of the low-Z target approach, showing greater contrast between tissues and improved visibility of fine detail. The use of low-Z external targets in the linear accelerator improves megavoltage planar and CBCT image quality significantly. CNR may be increased by a factor of 4 or greater. Improvement of the spatial resolution is also apparent.

Beam-beam interaction study of medium energy eRHIC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hao,Y.; Litvinenko, V. N.; Ptitsyn, V.

Medium Energy eRHIC (MeRHIC), the first stage design of eRHIC, includes a multi-pass ERL that provides 4GeV high quality electron beam to collide with the ion beam of RHIC. It delivers a minimum luminosity of 10{sup 32} cm{sup -2}s{sup -1}. Beam-beam effects present one of major factors limiting the luminosity of colliders. In this paper, both beam-beam effects on the electron beam and the proton beam in MeRHIC are investigated. The beam-beam interaction can induce a head-tail type instability of the proton beam referred to as the kink instability. Thus, beam stability conditions should be established to avoid proton beammore » loss. Also, the electron beam transverse disruption by collisions has to be evaluated to ensure that the beam quality is good enough for the energy recovery pass. The relation of proton beam stability, electron disruption and consequential luminosity are carried out after thorough discussion.« less

Experimental validation of beam quality correction factors for proton beams

NASA Astrophysics Data System (ADS)

Gomà, Carles; Hofstetter-Boillat, Bénédicte; Safai, Sairos; Vörös, Sándor

2015-04-01

This paper presents a method to experimentally validate the beam quality correction factors (kQ) tabulated in IAEA TRS-398 for proton beams and to determine the kQ of non-tabulated ionization chambers (based on the already tabulated values). The method is based exclusively on ionometry and it consists in comparing the reading of two ionization chambers under the same reference conditions in a proton beam quality Q and a reference beam quality 60Co. This allows one to experimentally determine the ratio between the kQ of the two ionization chambers. In this work, 7 different ionization chamber models were irradiated under the IAEA TRS-398 reference conditions for 60Co beams and proton beams. For the latter, the reference conditions for both modulated beams (spread-out Bragg peak field) and monoenergetic beams (pseudo-monoenergetic field) were studied. For monoenergetic beams, it was found that the experimental kQ values obtained for plane-parallel chambers are consistent with the values tabulated in IAEA TRS-398; whereas the kQ values obtained for cylindrical chambers are not consistent—being higher than the tabulated values. These results support the suggestion (of previous publications) that the IAEA TRS-398 reference conditions for monoenergetic proton beams should be revised so that the effective point of measurement of cylindrical ionization chambers is taken into account when positioning the reference point of the chamber at the reference depth. For modulated proton beams, the tabulated kQ values of all the ionization chambers studied in this work were found to be consistent with each other—except for the IBA FC65-G, whose experimental kQ value was found to be 0.6% lower than the tabulated one. The kQ of the PTW Advanced Markus chamber, which is not tabulated in IAEA TRS-398, was found to be 0.997 ± 0.042 (k = 2), based on the tabulated value of the PTW Markus chamber.

Analytical & Experimental Study of Radio Frequency Cavity Beam Profile Monitor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balcazar, Mario D.; Yonehara, Katsuya

The purpose of this analytical and experimental study is multifold: 1) To explore a new, radiation-robust, hadron beam profile monitor for intense neutrino beam applications; 2) To test, demonstrate, and develop a novel gas-filled Radio-Frequency (RF) cavity to use in this monitoring system. Within this context, the first section of the study analyzes the beam distribution across the hadron monitor as well as the ion-production rate inside the RF cavity. Furthermore a more effecient pixel configuration across the hadron monitor is proposed to provide higher sensitivity to changes in beam displacement. Finally, the results of a benchtop test of themore » tunable quality factor RF cavity will be presented. The proposed hadron monitor configuration consists of a circular array of RF cavities located at a radial distance of 7cm { corresponding to the standard deviation of the beam due to scatering { and a gas-filled RF cavity with a quality factor in the range 400 - 800.« less

Off-axis spectral beam combining of Bragg reflection waveguide photonic crystal diode lasers

NASA Astrophysics Data System (ADS)

Sun, Fangyuan; Wang, Lijie; Zhao, Yufei; Hou, Guanyu; Shu, Shili; Zhang, Jun; Peng, Hangyu; Tian, Sicong; Tong, Cunzhu; Wang, Lijun

2018-06-01

The spectral beam combining (SBC) of Bragg reflection waveguide photonic crystal (BRW-PC) diode lasers was studied for the first time. An off-axis feedback system was constructed using a stripe mirror and a spatial filter to control beam quality in the external cavity. It was found that the BRW-PC diode lasers with a low divergence and a circular beam provided a simplified and cost-effective SBC. The off-axis feedback broke the beam quality limit of a single element, and an M 2 factor of 3.8 times lower than that of a single emitter in the slow axis was demonstrated.

FusionArc optimization: a hybrid volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) planning strategy.

PubMed

Matuszak, Martha M; Steers, Jennifer M; Long, Troy; McShan, Daniel L; Fraass, Benedick A; Romeijn, H Edwin; Ten Haken, Randall K

2013-07-01

To introduce a hybrid volumetric modulated arc therapy/intensity modulated radiation therapy (VMAT/IMRT) optimization strategy called FusionArc that combines the delivery efficiency of single-arc VMAT with the potentially desirable intensity modulation possible with IMRT. A beamlet-based inverse planning system was enhanced to combine the advantages of VMAT and IMRT into one comprehensive technique. In the hybrid strategy, baseline single-arc VMAT plans are optimized and then the current cost function gradients with respect to the beamlets are used to define a metric for predicting which beam angles would benefit from further intensity modulation. Beams with the highest metric values (called the gradient factor) are converted from VMAT apertures to IMRT fluence, and the optimization proceeds with the mixed variable set until convergence or until additional beams are selected for conversion. One phantom and two clinical cases were used to validate the gradient factor and characterize the FusionArc strategy. Comparisons were made between standard IMRT, single-arc VMAT, and FusionArc plans with one to five IMRT∕hybrid beams. The gradient factor was found to be highly predictive of the VMAT angles that would benefit plan quality the most from beam modulation. Over the three cases studied, a FusionArc plan with three converted beams achieved superior dosimetric quality with reductions in final cost ranging from 26.4% to 48.1% compared to single-arc VMAT. Additionally, the three beam FusionArc plans required 22.4%-43.7% fewer MU∕Gy than a seven beam IMRT plan. While the FusionArc plans with five converted beams offer larger reductions in final cost--32.9%-55.2% compared to single-arc VMAT--the decrease in MU∕Gy compared to IMRT was noticeably smaller at 12.2%-18.5%, when compared to IMRT. A hybrid VMAT∕IMRT strategy was implemented to find a high quality compromise between gantry-angle and intensity-based degrees of freedom. This optimization method will allow patients to be simultaneously planned for dosimetric quality and delivery efficiency without switching between delivery techniques. Example phantom and clinical cases suggest that the conversion of only three VMAT segments to modulated beams may result in a good combination of quality and efficiency.

The advantages of absorbed-dose calibration factors.

PubMed

Rogers, D W

1992-01-01

A formalism for clinical external beam dosimetry based on use of ion chamber absorbed-dose calibration factors is outlined in the context and notation of the AAPM TG-21 protocol. It is shown that basing clinical dosimetry on absorbed-dose calibration factors ND leads to considerable simplification and reduced uncertainty in dose measurement. In keeping with a protocol which is used in Germany, a quantity kQ is defined which relates an absorbed-dose calibration factor in a beam of quality Q0 to that in a beam of quality Q. For 38 cylindrical ion chambers, two sets of values are presented for ND/NX and Ngas/ND and for kQ for photon beams with beam quality specified by the TPR20(10) ratio. One set is based on TG-21's protocol to allow the new formalism to be used while maintaining equivalence to the TG-21 protocol. To demonstrate the magnitude of the overall error in the TG-21 protocol, the other set uses corrected versions of the TG-21 equations and the more consistent physical data of the IAEA Code of Practice. Comparisons are made to procedures based on air-kerma or exposure calibration factors and it is shown that accuracy and simplicity are gained by avoiding the determination of Ngas from NX. It is also shown that the kQ approach simplifies the use of plastic phantoms in photon beams since kQ values change by less than 0.6% compared to those in water although an overall correction factor of 0.973 is needed to go from absorbed dose in water calibration factors to those in PMMA or polystyrene. Values of kQ calculated using the IAEA Code of Practice are presented but are shown to be anomalous because of the way the effective point of measurement changes for 60Co beams. In photon beams the major difference between the IAEA Code of Practice and the corrected AAPM TG-21 protocol is shown to be the Prepl correction factor. Calculated kQ curves and three parameter equations for them are presented for each wall material and are shown to represent accurately the kQ curve for all ion chambers in this study with a wall of that specified material and a thickness less than 0.25 g/cm2. Values of kQ can be measured using the primary standards for absorbed dose in photon beams.

High power broadband all fiber super-fluorescent source with linear polarization and near diffraction-limited beam quality.

PubMed

Ma, Pengfei; Huang, Long; Wang, Xiaolin; Zhou, Pu; Liu, Zejin

2016-01-25

In this manuscript, a high power broadband superfluorescent source (SFS) with linear polarization and near-diffraction-limited beam quality is achieved based on an ytterbium-doped (Yb-doped), all fiberized and polarization-maintained master oscillator power amplifier (MOPA) configuration. The MOPA structure generates a linearly polarized output power of 1427 W with a slope efficiency of 80% and a full width at half maximum (FWHM) of 11 nm, which is power scaled by an order of magnitude compared with the previously reported SFSs with linear polarization. In the experiment, both the polarization extinction ratio (PER) and beam quality (M(2) factor) are degraded little during the power scaling process. At maximal output power, the PER and M(2) factor are measured to be 19.1dB and 1.14, respectively. The root-mean-square (RMS) and peak-vale (PV) values of the power fluctuation at maximal output power are just 0.48% and within 3%, respectively. Further power scaling of the whole system is limited by the available pump sources. To the best of our knowledge, this is the first demonstration of kilowatt level broadband SFS with linear polarization and near-diffraction-limited beam quality.

Methods for slow axis beam quality improvement of high power broad area diode lasers

NASA Astrophysics Data System (ADS)

An, Haiyan; Xiong, Yihan; Jiang, Ching-Long J.; Schmidt, Berthold; Treusch, Georg

2014-03-01

For high brightness direct diode laser systems, it is of fundamental importance to improve the slow axis beam quality of the incorporated laser diodes regardless what beam combining technology is applied. To further advance our products in terms of increased brightness at a high power level, we must optimize the slow axis beam quality despite the far field blooming at high current levels. The later is caused predominantly by the built-in index step in combination with the thermal lens effect. Most of the methods for beam quality improvements reported in publications sacrifice the device efficiency and reliable output power. In order to improve the beam quality as well as maintain the efficiency and reliable output power, we investigated methods of influencing local heat generation to reduce the thermal gradient across the slow axis direction, optimizing the built-in index step and discriminating high order modes. Based on our findings, we have combined different methods in our new device design. Subsequently, the beam parameter product (BPP) of a 10% fill factor bar has improved by approximately 30% at 7 W/emitter without efficiency penalty. This technology has enabled fiber coupled high brightness multi-kilowatt direct diode laser systems. In this paper, we will elaborate on the methods used as well as the results achieved.

Poster - 23: Dosimetric Characterization and Transferability of an Accessory Mounted Mini-Beam Collimator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davis, William; Crewson, Cody; Alexander, Andrew

Objective: The dosimetric characterization of an accessory-mounted mini-beam collimator across three beam matched linear accelerators. Materials and Methods: Percent depth dose and profiles were measured for the open and mini-beam collimated fields. The average beam quality and peak-to-valley dose ratio (PVDR), the ratio of average peak dose to average valley dose, were obtained from these measurements. The open field relative output and the mini-beam collimator factor, the ratio of the mini-beam dose to open field dose at the beam center, were measured for square fields of side 2, 3, 4, and 5 cm. Mini-beam output as a function of collimatormore » inclination angle relative to the central axis was also investigated. Results and Discussion: Beam quality for both the open and mini-beam collimated fields agreed across all linacs to within ±1.0%. The PVDR was found to vary by up to ±6.6% from the mean. For the 2, 3, and 4 cm fields the average open field relative output with respect to the 5 cm field was 0.874±0.4%, 0.921±0.3%, and 0.962±0.1%. The average collimator factors were 0.450±3.9%, 0.443±3.9%, 0.438±3.9%, and 0.434±3.9%. A decrease in collimator factor greater than 7% was found for an inclination angle change of 0.09°. Conclusion: The mini-beam collimator has revealed a difference between the three linacs not apparent in the open field data, yet transferability can still be attained through thorough dosimetric characterization.« less

Thin disk laser with unstable resonator and reduced output coupler

NASA Astrophysics Data System (ADS)

Gavili, Anwar; Shayganmanesh, Mahdi

2018-05-01

In this paper, feasibility of using unstable resonator with reduced output coupling in a thin disk laser is studied theoretically. Unstable resonator is modeled by wave-optics using Collins integral and iterative method. An Yb:YAG crystal with 250 micron thickness is considered as a quasi-three level active medium and modeled by solving rate equations of energy levels populations. The amplification of laser beam in the active medium is calculated based on the Beer-Lambert law and Rigrod method. Using generalized beam parameters method, laser beam parameters like, width, divergence, M2 factor, output power as well as near and far-field beam profiles are calculated for unstable resonator. It is demonstrated that for thin disk laser (with single disk) in spite of the low thickness of the disk which leads to low gain factor, it is possible to use unstable resonator (with reduced output coupling) and achieve good output power with appropriate beam quality. Also, the behavior of output power and beam quality versus equivalent Fresnel number is investigated and optimized value of output coupling for maximum output power is achieved.

An argon ion beam milling process for native AlOx layers enabling coherent superconducting contacts

NASA Astrophysics Data System (ADS)

Grünhaupt, Lukas; von Lüpke, Uwe; Gusenkova, Daria; Skacel, Sebastian T.; Maleeva, Nataliya; Schlör, Steffen; Bilmes, Alexander; Rotzinger, Hannes; Ustinov, Alexey V.; Weides, Martin; Pop, Ioan M.

2017-08-01

We present an argon ion beam milling process to remove the native oxide layer forming on aluminum thin films due to their exposure to atmosphere in between lithographic steps. Our cleaning process is readily integrable with conventional fabrication of Josephson junction quantum circuits. From measurements of the internal quality factors of superconducting microwave resonators with and without contacts, we place an upper bound on the residual resistance of an ion beam milled contact of 50 mΩ μm2 at a frequency of 4.5 GHz. Resonators for which only 6% of the total foot-print was exposed to the ion beam milling, in areas of low electric and high magnetic fields, showed quality factors above 106 in the single photon regime, and no degradation compared to single layer samples. We believe these results will enable the development of increasingly complex superconducting circuits for quantum information processing.

Influence of the Integral Quality Monitor transmission detector on high energy photon beams: A multi-centre study.

PubMed

Casar, Bozidar; Pasler, Marlies; Wegener, Sonja; Hoffman, David; Talamonti, Cinzia; Qian, Jianguo; Mendez, Ignasi; Brojan, Denis; Perrin, Bruce; Kusters, Martijn; Canters, Richard; Pallotta, Stefania; Peterlin, Primoz

2017-09-01

The influence of the Integral Quality Monitor (IQM) transmission detector on photon beam properties was evaluated in a preclinical phase, using data from nine participating centres: (i) the change of beam quality (beam hardening), (ii) the influence on surface dose, and (iii) the attenuation of the IQM detector. For 6 different nominal photon energies (4 standard, 2 FFF) and square field sizes from 1×1cm 2 to 20×20cm 2 , the effect of IQM on beam quality was assessed from the PDD 20,10 values obtained from the percentage dose depth (PDD) curves, measured with and without IQM in the beam path. The change in surface dose with/without IQM was assessed for all available energies and field sizes from 4×4cm 2 to 20×20cm 2 . The transmission factor was calculated by means of measured absorbed dose at 10cm depth for all available energies and field sizes. (i) A small (0.11-0.53%) yet statistically significant beam hardening effect was observed, depending on photon beam energy. (ii) The increase in surface dose correlated with field size (p<0.01) for all photon energies except for 18MV. The change in surface dose was smaller than 3.3% in all cases except for the 20×20cm 2 field and 10MV FFF beam, where it reached 8.1%. (iii) For standard beams, transmission of the IQM showed a weak dependence on the field size, and a pronounced dependence on the beam energy (0.9412 for 6MV to 0.9578 for 18MV and 0.9440 for 6MV FFF; 0.9533 for 10MV FFF). The effects of the IQM detector on photon beam properties were found to be small yet statistically significant. The magnitudes of changes which were found justify treating IQM either as tray factors within the treatment planning system (TPS) for a particular energy or alternatively as modified outputs for specific beam energy of linear accelerators, which eases the introduction of the IQM into clinical practice. Copyright © 2017. Published by Elsevier GmbH.

R & D of a Gas-Filled RF Beam Profile Monitor for Intense Neutrino Beam Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yonehara, K.; Backfish, M.; Moretti, A.

We report the R&D of a novel radiation-robust hadron beam profile monitor based on a gas-filled RF cavity for intense neutrino beam experiments. An equivalent RF circuit model was made and simulated to optimize the RF parameter in a wide beam intensity range. As a result, the maximum acceptable beam intensity in the monitor is significantly increased by using a low-quality factor RF cavity. The plan for the demonstration test is set up to prepare for future neutrino beam experiments.

Propagation factors of multi-sinc Schell-model beams in non-Kolmogorov turbulence.

PubMed

Song, Zhenzhen; Liu, Zhengjun; Zhou, Keya; Sun, Qiongge; Liu, Shutian

2016-01-25

We derive several analytical expressions for the root-mean-square (rms) angular width and the M(2)-factor of the multi-sinc Schell-model (MSSM) beams propagating in non-Kolmogorov turbulence with the extended Huygens-Fresnel principle and the second-order moments of the Wigner distribution function. Numerical results show that a MSSM beam with dark-hollow far fields in free space has advantage over the one with flat-topped or multi-rings far fields for reducing the turbulence-induced degradation, which will become more obvious with larger dark-hollow size. Beam quality of MSSM beams can be further improved with longer wavelength and larger beam width, or under the condition of weaker turbulence. We also demonstrate that the non-Kolmogorov turbulence has significantly less effect on the MSSM beams than the Gaussian Schell-model beam.

Molecular beam epitaxial growth and structural characterization of ZnS on (001) GaAs

NASA Technical Reports Server (NTRS)

Benz, R. G., II; Huang, P. C.; Stock, S. R.; Summers, C. J.

1988-01-01

The effect of surface nucleation processes on the quality of ZnS layers grown on (001) GaAs substrates by molecular beam epitaxy is reported. Reflection high energy electron diffraction indicated that nucleation at high temperatures produced more planar surfaces than nucleation at low temperatures, but the crystalline quality as assessed by X-ray double crystal diffractometry is relatively independent of nucleation temperature. A critical factor in layer quality was the initial roughness of the GaAs surfaces.

Energy correction factors of LiF powder TLDs irradiated in high-energy electron beams and applied to mailed dosimetry for quality assurance networks.

PubMed

Marre, D; Ferreira, I H; Bridier, A; Björeland, A; Svensson, H; Dutreix, A; Chavaudra, J

2000-12-01

Absorbed dose determination with thermoluminescent dosimeters (TLDs) generally relies on calibration in 60Co gamma-ray reference beams. The energy correction factor fCo(E) for electron beams takes into account the difference between the response of the TLD in the beam of energy E and in the 60Co gamma-ray beam. In this work, fCo(E) was evaluated for an LiF powder irradiated in electron beams of 6 to 20 MeV (Varian 2300C/D) and 10 to 50 MeV (Racetrack MM50), and its variation with electron energy, TLD size and nature of the surrounding medium was also studied for LiF powder. The results have been applied to the ESTRO-EQUAL mailed dosimetry quality assurance network. Monte Carlo calculations (EGS4, PENELOPE) and experiments have been performed for the LiF powder (rho = 1.4 g cm3) (DTL937, Philitech, France), read on a home made reader and a PCL3 automatic reader (Fimel, France). The TLDs were calibrated using Fricke dosimetry and compared with three ionization chambers (NE2571, NACP02, ROOS). The combined uncertainties in the experimental fCo(E) factors determined in this work are less than about 0.4% (1 SD), which is appreciably smaller than the uncertainties up to 1.4% (1 SD) reported for other calculated values in the literature. Concerning the Varian 2300C/D beams, the measured fCo(E) values decrease from 1.065 to 1.049 +/- 0.004 (1 SD) when the energy at depth in water increases from 2.6 to 14.1 MeV; the agreement with Monte Carlo calculations is better than 0.5%. For the Racetrack MM50 pulsed-scanned beams, the average experimental value of fCo(E) is 1.071 +/- 0.005 (1 SD) for a mean electron energy at depth Ez ranging from 4.3 to 36.3 MeV: fCo(E) is up to 2% higher for the MM50 beams than for the 2300C/D beams in the range of the tested energies. The energy correction factor for LiF powder (3 mm diameter and 15 mm length) varies with beam quality and type (pulsed or pulsed-scanning), cavity size and nature of the surrounding medium. The fCo(E) values obtained for the LiF powder (3 mm diameter and 15 mm length) irradiated in water, have been applied to the EQUAL external audit network, leading to a good agreement between stated and measured doses, with a mean value of 1.002 +/- 0.022 (1 SD), for 170 beam outputs checked (36 electron beam energies) in 13 'reference' radiotherapy centres in Europe. Such fCo(E) data improve the accuracy of the absorbed dose TLD determination in electron beams, justifying their use for quality control in radiotherapy.

SU-F-T-551: Beam Hardening and Attenuation of Photon Beams Using Integral Quality Monitor in Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casar, B; Carot, I Mendez; Peterlin, P

2016-06-15

Purpose: Aim of the multi-centre study was to analyse beam hardening effect of the Integral Quality Monitor (IQM) for high energy photon beams used in radiotherapy with linear accelerators. Generic values for attenuation coefficient k(IQM) of IQM system were additionally investigated. Methods: Beam hardening effect of the IQM system was studied for a set of standard nominal photon energies (6 MV–18 MV) and two flattening filter free (FFF) energies (6 MV FFF and 10 MV FFF). PDD curves were measured and analysed for various square radiation fields, with and without IQM in place. Differences between PDD curves were statistically analysedmore » through comparison of respective PDD-20,10 values. Attenuation coefficients k(IQM) were determined for the same range of photon energies. Results: Statistically significant differences in beam qualities for all evaluated high energy photon beams were found, comparing PDD-20,10 values derived from PDD curves with and without IQM in place. Significance of beam hardening effect was statistically proven with high confidence (p < 0,01) for all analysed photon beams except for 15 MV (p = 0,078), although relative differences in beam qualities were minimal, ranging from 0,1 % to 0,5 %. Attenuation of the IQM system showed negligible dependence on radiation field size. However, clinically important dependence of kIQM versus TPRs20,10 was found: 0,941 for 6 MV photon beams, to 0,959 for 18 MV photon beams, with highest uncertainty below 0,006. k(IQM) versus TPRs were tabulated and polynomial equation for the determination of k(IQM) is suggested for clinical use. Conclusion: There was no clinically relevant beam hardening, when IQM system was on linear accelerators. Consequently, no additional commissioning is needed for the IQM system regarding the determination of beam qualities. Generic values for k(IQM) are proposed and can be used as tray factors for complete range of examined photon beam energies.« less

A method to incorporate the effect of beam quality on image noise in a digitally reconstructed radiograph (DRR) based computer simulation for optimisation of digital radiography

NASA Astrophysics Data System (ADS)

Moore, Craig S.; Wood, Tim J.; Saunderson, John R.; Beavis, Andrew W.

2017-09-01

The use of computer simulated digital x-radiographs for optimisation purposes has become widespread in recent years. To make these optimisation investigations effective, it is vital simulated radiographs contain accurate anatomical and system noise. Computer algorithms that simulate radiographs based solely on the incident detector x-ray intensity (‘dose’) have been reported extensively in the literature. However, while it has been established for digital mammography that x-ray beam quality is an important factor when modelling noise in simulated images there are no such studies for diagnostic imaging of the chest, abdomen and pelvis. This study investigates the influence of beam quality on image noise in a digital radiography (DR) imaging system, and incorporates these effects into a digitally reconstructed radiograph (DRR) computer simulator. Image noise was measured on a real DR imaging system as a function of dose (absorbed energy) over a range of clinically relevant beam qualities. Simulated ‘absorbed energy’ and ‘beam quality’ DRRs were then created for each patient and tube voltage under investigation. Simulated noise images, corrected for dose and beam quality, were subsequently produced from the absorbed energy and beam quality DRRs, using the measured noise, absorbed energy and beam quality relationships. The noise images were superimposed onto the noiseless absorbed energy DRRs to create the final images. Signal-to-noise measurements in simulated chest, abdomen and spine images were within 10% of the corresponding measurements in real images. This compares favourably to our previous algorithm where images corrected for dose only were all within 20%.

Adaptive conversion of a high-order mode beam into a near-diffraction-limited beam.

PubMed

Zhao, Haichuan; Wang, Xiaolin; Ma, Haotong; Zhou, Pu; Ma, Yanxing; Xu, Xiaojun; Zhao, Yijun

2011-08-01

We present a new method for efficiently transforming a high-order mode beam into a nearly Gaussian beam with much higher beam quality. The method is based on modulation of phases of different lobes by stochastic parallel gradient descent algorithm and coherent addition after phase flattening. We demonstrate the method by transforming an LP11 mode into a nearly Gaussian beam. The experimental results reveal that the power in the diffraction-limited bucket in the far field is increased by more than a factor of 1.5.

Noncoplanar Beam Angle Class Solutions to Replace Time-Consuming Patient-Specific Beam Angle Optimization in Robotic Prostate Stereotactic Body Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rossi, Linda, E-mail: l.rossi@erasmusmc.nl; Breedveld, Sebastiaan; Aluwini, Shafak

Purpose: To investigate development of a recipe for the creation of a beam angle class solution (CS) for noncoplanar prostate stereotactic body radiation therapy to replace time-consuming individualized beam angle selection (iBAS) without significant loss in plan quality, using the in-house “Erasmus-iCycle” optimizer for fully automated beam profile optimization and iBAS. Methods and Materials: For 30 patients, Erasmus-iCycle was first used to generate 15-, 20-, and 25-beam iBAS plans for a CyberKnife equipped with a multileaf collimator. With these plans, 6 recipes for creation of beam angle CSs were investigated. Plans of 10 patients were used to create CSs based on themore » recipes, and the other 20 to independently test them. For these tests, Erasmus-iCycle was also used to generate intensity modulated radiation therapy plans for the fixed CS beam setups. Results: Of the tested recipes for CS creation, only 1 resulted in 15-, 20-, and 25-beam noncoplanar CSs without plan deterioration compared with iBAS. For the patient group, mean differences in rectum D{sub 1cc}, V{sub 60GyEq}, V{sub 40GyEq}, and D{sub mean} between 25-beam CS plans and 25-beam plans generated with iBAS were 0.2 ± 0.4 Gy, 0.1% ± 0.2%, 0.2% ± 0.3%, and 0.1 ± 0.2 Gy, respectively. Differences between 15- and 20-beam CS and iBAS plans were also negligible. Plan quality for CS plans relative to iBAS plans was also preserved when narrower planning target volume margins were arranged and when planning target volume dose inhomogeneity was decreased. Using a CS instead of iBAS reduced the computation time by a factor of 14 to 25, mainly depending on beam number, without loss in plan quality. Conclusions: A recipe for creation of robust beam angle CSs for robotic prostate stereotactic body radiation therapy has been developed. Compared with iBAS, computation times decreased by a factor 14 to 25. The use of a CS may avoid long planning times without losses in plan quality.« less

Self-focusing and group-velocity dispersion of pulsed laser beams in the inhomogeneous atmosphere.

PubMed

Zhang, Yuqiu; Ji, Xiaoling; Zhang, Hao; Li, Xiaoqing; Wang, Tao; Wang, Huan; Deng, Yu

2018-05-28

We study self-focusing and group-velocity dispersion (GVD) effects in the inhomogeneous atmosphere on pulsed-laser space debris removal facilitated by a ground-based laser. It is found that changes of the pulse duration and the beam spot size with the propagation distance are noticeable due to the interplay of the GVD effect and the self-focusing effect, which is quite different from the behavior in the linear case. It is shown that the temporal pulse splitting may appear on the space debris, and the spatial side lobe usually appears together with the temporal pulse splitting. As compared with the linear case, the beam width and the pulse width on the debris target increase. On the other hand, crucial formulae of the modified focal length and the M 2 -factor for laser debris removal are also derived. It is found that the beam quality on the debris target becomes better if our modified focal length is adopted, and the beam quality on the debris target will be good if the value of M 2 -factor is less than 1.6.

Assessment of ionization chamber correction factors in photon beams using a time saving strategy with PENELOPE code.

PubMed

Reis, C Q M; Nicolucci, P

2016-02-01

The purpose of this study was to investigate Monte Carlo-based perturbation and beam quality correction factors for ionization chambers in photon beams using a saving time strategy with PENELOPE code. Simulations for calculating absorbed doses to water using full spectra of photon beams impinging the whole water phantom and those using a phase-space file previously stored around the point of interest were performed and compared. The widely used NE2571 ionization chamber was modeled with PENELOPE using data from the literature in order to calculate absorbed doses to the air cavity of the chamber. Absorbed doses to water at reference depth were also calculated for providing the perturbation and beam quality correction factors for that chamber in high energy photon beams. Results obtained in this study show that simulations with phase-space files appropriately stored can be up to ten times shorter than using a full spectrum of photon beams in the input-file. Values of kQ and its components for the NE2571 ionization chamber showed good agreement with published values in the literature and are provided with typical statistical uncertainties of 0.2%. Comparisons to kQ values published in current dosimetry protocols such as the AAPM TG-51 and IAEA TRS-398 showed maximum percentage differences of 0.1% and 0.6% respectively. The proposed strategy presented a significant efficiency gain and can be applied for a variety of ionization chambers and clinical photon beams. Copyright © 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Signal acquisition and scale calibration for beam power density distribution of electron beam welding

NASA Astrophysics Data System (ADS)

Peng, Yong; Li, Hongqiang; Shen, Chunlong; Guo, Shun; Zhou, Qi; Wang, Kehong

2017-06-01

The power density distribution of electron beam welding (EBW) is a key factor to reflect the beam quality. The beam quality test system was designed for the actual beam power density distribution of high-voltage EBW. After the analysis of characteristics and phase relationship between the deflection control signal and the acquisition signal, the Post-Trigger mode was proposed for the signal acquisition meanwhile the same external clock source was shared by the control signal and the sampling clock. The power density distribution of beam cross-section was reconstructed using one-dimensional signal that was processed by median filtering, twice signal segmentation and spatial scale calibration. The diameter of beam cross-section was defined by amplitude method and integral method respectively. The measured diameter of integral definition is bigger than that of amplitude definition, but for the ideal distribution the former is smaller than the latter. The measured distribution without symmetrical shape is not concentrated compared to Gaussian distribution.

Low dose megavoltage cone beam computed tomography with an unflattened 4 MV beam from a carbon target

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faddegon, Bruce A.; Wu, Vincent; Pouliot, Jean

2008-12-15

Megavoltage cone beam computed tomography (MVCBCT) is routinely used for visualizing anatomical structures and implanted fiducials for patient positioning in radiotherapy. MVCBCT using a 6 MV treatment beam with high atomic number (Z) target and flattening filter in the beamline, as done conventionally, has lower image quality than can be achieved with a MV beam due to heavy filtration of the low-energy bremsstrahlung. The unflattened beam of a low Z target has an abundance of diagnostic energy photons, detected with modern flat panel detectors with much higher efficiency given the same dose to the patient. This principle guided the developmentmore » of a new megavoltage imaging beamline (IBL) for a commercial radiotherapy linear accelerator. A carbon target was placed in one of the electron primary scattering foil slots on the target-foil slide. A PROM on a function controller board was programed to put the carbon target in place for MVCBCT. A low accelerating potential of 4.2 MV was used for the IBL to restrict leakage of primary electrons through the target such that dose from x rays dominated the signal in the monitor chamber and the patient surface dose. Results from phantom and cadaver images demonstrated that the IBL had much improved image quality over the treatment beam. For similar imaging dose, the IBL improved the contrast-to-noise ratio by as much as a factor of 3 in soft tissue over that of the treatment beam. The IBL increased the spatial resolution by about a factor of 2, allowing the visualization of finer anatomical details. Images of the cadaver contained useful information with doses as low as 1 cGy. The IBL may be installed on certain models of linear accelerators without mechanical modification and results in significant improvement in the image quality with the same dose, or images of the same quality with less than one-third of the dose.« less

Comparison of IPSM 1990 photon dosimetry code of practice with IAEA TRS‐398 and AAPM TG‐51.

PubMed Central

Henríquez, Francisco Cutanda

2009-01-01

Several codes of practice for photon dosimetry are currently used around the world, supported by different organizations. A comparison of IPSM 1990 with both IAEA TRS‐398 and AAPM TG‐51 has been performed. All three protocols are based on the calibration of ionization chambers in terms of standards of absorbed dose to water, as it is the case with other modern codes of practice. This comparison has been carried out for photon beams of nominal energies: 4 MV, 6 MV, 8 MV, 10 MV and 18 MV. An NE 2571 graphite ionization chamber was used in this study, cross‐calibrated against an NE 2611A Secondary Standard, calibrated in the National Physical Laboratory (NPL). Absolute dose in reference conditions was obtained using each of these three protocols including: beam quality indices, beam quality conversion factors both theoretical and NPL experimental ones, correction factors for influence quantities and absolute dose measurements. Each protocol recommendations have been strictly followed. Uncertainties have been obtained according to the ISO Guide to the Expression of Uncertainty in Measurement. Absorbed dose obtained according to all three protocols agree within experimental uncertainty. The largest difference between absolute dose results for two protocols is obtained for the highest energy: 0.7% between IPSM 1990 and IAEA TRS‐398 using theoretical beam quality conversion factors. PACS number: 87.55.tm

Monte Carlo calculations of k{sub Q}, the beam quality conversion factor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muir, B. R.; Rogers, D. W. O.

2010-11-15

Purpose: To use EGSnrc Monte Carlo simulations to directly calculate beam quality conversion factors, k{sub Q}, for 32 cylindrical ionization chambers over a range of beam qualities and to quantify the effect of systematic uncertainties on Monte Carlo calculations of k{sub Q}. These factors are required to use the TG-51 or TRS-398 clinical dosimetry protocols for calibrating external radiotherapy beams. Methods: Ionization chambers are modeled either from blueprints or manufacturers' user's manuals. The dose-to-air in the chamber is calculated using the EGSnrc user-code egs{sub c}hamber using 11 different tabulated clinical photon spectra for the incident beams. The dose to amore » small volume of water is also calculated in the absence of the chamber at the midpoint of the chamber on its central axis. Using a simple equation, k{sub Q} is calculated from these quantities under the assumption that W/e is constant with energy and compared to TG-51 protocol and measured values. Results: Polynomial fits to the Monte Carlo calculated k{sub Q} factors as a function of beam quality expressed as %dd(10){sub x} and TPR{sub 10}{sup 20} are given for each ionization chamber. Differences are explained between Monte Carlo calculated values and values from the TG-51 protocol or calculated using the computer program used for TG-51 calculations. Systematic uncertainties in calculated k{sub Q} values are analyzed and amount to a maximum of one standard deviation uncertainty of 0.99% if one assumes that photon cross-section uncertainties are uncorrelated and 0.63% if they are assumed correlated. The largest components of the uncertainty are the constancy of W/e and the uncertainty in the cross-section for photons in water. Conclusions: It is now possible to calculate k{sub Q} directly using Monte Carlo simulations. Monte Carlo calculations for most ionization chambers give results which are comparable to TG-51 values. Discrepancies can be explained using individual Monte Carlo calculations of various correction factors which are more accurate than previously used values. For small ionization chambers with central electrodes composed of high-Z materials, the effect of the central electrode is much larger than that for the aluminum electrodes in Farmer chambers.« less

The influence of body mass index, age, implants, and dental restorations on image quality of cone beam computed tomography.

PubMed

Ritter, Lutz; Mischkowski, Robert A; Neugebauer, Jörg; Dreiseidler, Timo; Scheer, Martin; Keeve, Erwin; Zöller, Joachim E

2009-09-01

The aim was to determine the influence of patient age, gender, body mass index (BMI), amount of dental restorations, and implants on image quality of cone-beam computerized tomography (CBCT). Fifty CBCT scans of a preretail version of Galileos (Sirona, Germany) were investigated retrospectively by 4 observers regarding image quality of 6 anatomic structures, pathologic findings detection, subjective exposure quality, and artifacts. Patient age, BMI, gender, amount of dental restorations, and implants were recorded and statistically tested for correlations to image quality. A negative effect on image quality was found statistically significantly correlated with age and the amount of dental restorations. None of the investigated image features were garbled by any of the investigated influence factors. Age and the amount of dental restorations appear to have a negative impact on CBCT image quality, whereas gender and BMI do not. Image quality of mental foramen, mandibular canal, and nasal floor are affected negatively by age but not by the amount of dental restorations. Further studies are required to elucidate influence factors on CBCT image quality.

Reference dosimetry of proton pencil beams based on dose-area product: a proof of concept.

PubMed

Gomà, Carles; Safai, Sairos; Vörös, Sándor

2017-06-21

This paper describes a novel approach to the reference dosimetry of proton pencil beams based on dose-area product ([Formula: see text]). It depicts the calibration of a large-diameter plane-parallel ionization chamber in terms of dose-area product in a 60 Co beam, the Monte Carlo calculation of beam quality correction factors-in terms of dose-area product-in proton beams, the Monte Carlo calculation of nuclear halo correction factors, and the experimental determination of [Formula: see text] of a single proton pencil beam. This new approach to reference dosimetry proves to be feasible, as it yields [Formula: see text] values in agreement with the standard and well-established approach of determining the absorbed dose to water at the centre of a broad homogeneous field generated by the superposition of regularly-spaced proton pencil beams.

Enhancement of beam pulse controllability for a single-pulse formation system of a cyclotron.

PubMed

Kurashima, Satoshi; Miyawaki, Nobumasa; Kashiwagi, Hirotsugu; Okumura, Susumu; Taguchi, Mitsumasa; Fukuda, Mitsuhiro

2015-07-01

The single-pulse formation technique using a beam chopping system consisting of two types of high-voltage beam kickers was improved to enhance the quality and intensity of the single-pulse beam with a pulse interval over 1 μs at the Japan Atomic Energy Agency cyclotron facility. A contamination rate of neighboring beam bunches in the single-pulse beam was reduced to less than 0.1%. Long-term purification of the single pulse beam was guaranteed by the well-controlled magnetic field stabilization system for the cyclotron magnet. Reduction of the multi-turn extraction number for suppressing the neighboring beam bunch contamination was achieved by restriction of a beam phase width and precise optimization of a particle acceleration phase. In addition, the single-pulse beam intensity was increased by a factor of two or more by a combination of two types of beam bunchers using sinusoidal and saw-tooth voltage waveforms. Provision of the high quality intense single-pulse beam contributed to improve the accuracy of experiments for investigation of scintillation light time-profile and for neutron energy measurement by a time-of-flight method.

Enhancement of beam pulse controllability for a single-pulse formation system of a cyclotron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kurashima, Satoshi, E-mail: kurashima.satoshi@jaea.go.jp; Miyawaki, Nobumasa; Kashiwagi, Hirotsugu

The single-pulse formation technique using a beam chopping system consisting of two types of high-voltage beam kickers was improved to enhance the quality and intensity of the single-pulse beam with a pulse interval over 1 μs at the Japan Atomic Energy Agency cyclotron facility. A contamination rate of neighboring beam bunches in the single-pulse beam was reduced to less than 0.1%. Long-term purification of the single pulse beam was guaranteed by the well-controlled magnetic field stabilization system for the cyclotron magnet. Reduction of the multi-turn extraction number for suppressing the neighboring beam bunch contamination was achieved by restriction of amore » beam phase width and precise optimization of a particle acceleration phase. In addition, the single-pulse beam intensity was increased by a factor of two or more by a combination of two types of beam bunchers using sinusoidal and saw-tooth voltage waveforms. Provision of the high quality intense single-pulse beam contributed to improve the accuracy of experiments for investigation of scintillation light time-profile and for neutron energy measurement by a time-of-flight method.« less

Coherent and incoherent off-axis Hermite-Gaussian beam combinations.

PubMed

Lü, B; Ma, H

2000-03-10

A detailed study of the coherent and the incoherent combinations of two-dimensional off-axis Hermite-Gaussian beams with rectangular symmetry is made. The closed-form propagation formulas of the resulting beam are derived, and the resulting beam quality in terms of the M(2) factor and power in the bucket is discussed and compared for the coherent and the incoherent combinations. In addition, it is shown that the resulting astigmatic beam can be symmetrized in the sense of the second-moment definition of beam width. However, the symmetrizing transformation of the resulting astigmatic beams is incomplete, because there exist different irradiance profiles.

Feasibility of using a dose-area product ratio as beam quality specifier for photon beams with small field sizes.

PubMed

Pimpinella, Maria; Caporali, Claudio; Guerra, Antonio Stefano; Silvi, Luca; De Coste, Vanessa; Petrucci, Assunta; Delaunay, Frank; Dufreneix, Stéphane; Gouriou, Jean; Ostrowsky, Aimé; Rapp, Benjamin; Bordy, Jean-Marc; Daures, Josiane; Le Roy, Maïwenn; Sommier, Line; Vermesse, Didier

2018-01-01

To investigate the feasibility of using the ratio of dose-area product at 20 cm and 10 cm water depths (DAPR 20,10 ) as a beam quality specifier for radiotherapy photon beams with field diameter below 2 cm. Dose-area product was determined as the integral of absorbed dose to water (D w ) over a surface larger than the beam size. 6 MV and 10 MV photon beams with field diameters from 0.75 cm to 2 cm were considered. Monte Carlo (MC) simulations were performed to calculate energy-dependent dosimetric parameters and to study the DAPR 20,10 properties. Aspects relevant to DAPR 20,10 measurement were explored using large-area plane-parallel ionization chambers with different diameters. DAPR 20,10 was nearly independent of field size in line with the small differences among the corresponding mean beam energies. Both MC and experimental results showed a dependence of DAPR 20,10 on the measurement setup and the surface over which D w is integrated. For a given setup, DAPR 20,10 values obtained using ionization chambers with different air-cavity diameters agreed with one another within 0.4%, after the application of MC correction factors accounting for effects due to the chamber size. DAPR 20,10 differences among the small field sizes were within 1% and sensitivity to the beam energy resulted similar to that of established beam quality specifiers based on the point measurement of D w . For a specific measurement setup and integration area, DAPR 20,10 proved suitable to specify the beam quality of small photon beams for the selection of energy-dependent dosimetric parameters. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

1030 nm high power polarization maintained fiber laser with narrow linewidth and near-diffraction-limited beam quality

NASA Astrophysics Data System (ADS)

Chu, Qiuhui; Zhao, Pengfei; Li, Chengyu; Wang, Bopeng; Lin, Honghuan; Guo, Chao; Liu, Yu; Jing, Feng; Tang, Chuanxiang

2018-03-01

A high power 1030 nm ytterbium-doped polarization maintained fiber laser with optimized parameters is presented in this paper. The master oscillator power amplifier system with counter-pumped amplifier is established. The output power is 900 W, along with a light-to-light efficiency of 64.2%. The amplified spontaneous emission suppression ratio of spectrum reaches to 40 dB with 3 dB linewidth of 0.14 nm. The polarization extinction ratio is 12 dB, and the beam quality factor is M2x=1.07, M2y=1.12. To the best of our knowledge, this is the first demonstration of 1030 nm high power fiber laser with narrow linewidth, near linear polarization, and neardiffraction-limited beam quality

Comparison of the IAEA TRS-398 and AAPM TG-51 absorbed dose to water protocols in the dosimetry of high-energy photon and electron beams

NASA Astrophysics Data System (ADS)

Saiful Huq, M.; Andreo, Pedro; Song, Haijun

2001-11-01

The International Atomic Energy Agency (IAEA TRS-398) and the American Association of Physicists in Medicine (AAPM TG-51) have published new protocols for the calibration of radiotherapy beams. These protocols are based on the use of an ionization chamber calibrated in terms of absorbed dose to water in a standards laboratory's reference quality beam. This paper compares the recommendations of the two protocols in two ways: (i) by analysing in detail the differences in the basic data included in the two protocols for photon and electron beam dosimetry and (ii) by performing measurements in clinical photon and electron beams and determining the absorbed dose to water following the recommendations of the two protocols. Measurements were made with two Farmer-type ionization chambers and three plane-parallel ionization chamber types in 6, 18 and 25 MV photon beams and 6, 8, 10, 12, 15 and 18 MeV electron beams. The Farmer-type chambers used were NE 2571 and PTW 30001, and the plane-parallel chambers were a Scanditronix-Wellhöfer NACP and Roos, and a PTW Markus chamber. For photon beams, the measured ratios TG-51/TRS-398 of absorbed dose to water Dw ranged between 0.997 and 1.001, with a mean value of 0.999. The ratios for the beam quality correction factors kQ were found to agree to within about +/-0.2% despite significant differences in the method of beam quality specification for photon beams and in the basic data entering into kQ. For electron beams, dose measurements were made using direct ND,w calibrations of cylindrical and plane-parallel chambers in a 60Co gamma-ray beam, as well as cross-calibrations of plane-parallel chambers in a high-energy electron beam. For the direct ND,w calibrations the ratios TG-51/TRS-398 of absorbed dose to water Dw were found to lie between 0.994 and 1.018 depending upon the chamber and electron beam energy used, with mean values of 0.996, 1.006, and 1.017, respectively, for the cylindrical, well-guarded and not well-guarded plane-parallel chambers. The Dw ratios measured for the cross-calibration procedures varied between 0.993 and 0.997. The largest discrepancies for electron beams between the two protocols arise from the use of different data for the perturbation correction factors pwall and pdis of cylindrical and plane-parallel chambers, all in 60Co. A detailed analysis of the reasons for the discrepancies is made which includes comparing the formalisms, correction factors and the quantities in the two protocols.

SU-E-T-525: Ionization Chamber Perturbation in Flattening Filter Free Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Czarnecki, D; Voigts-Rhetz, P von; Zink, K

2015-06-15

Purpose: Changing the characteristic of a photon beam by mechanically removing the flattening filter may impact the dose response of ionization chambers. Thus, perturbation factors of cylindrical ionization chambers in conventional and flattening filter free photon beams were calculated by Monte Carlo simulations. Methods: The EGSnrc/BEAMnrc code system was used for all Monte Carlo calculations. BEAMnrc models of nine different linear accelerators with and without flattening filter were used to create realistic photon sources. Monte Carlo based calculations to determine the fluence perturbations due to the presens of the chambers components, the different material of the sensitive volume (air insteadmore » of water) as well as the volume effect were performed by the user code egs-chamber. Results: Stem, central electrode, wall, density and volume perturbation factors for linear accelerators with and without flattening filter were calculated as a function of the beam quality specifier TPR{sub 20/10}. A bias between the perturbation factors as a function of TPR{sub 20/10} for flattening filter free beams and conventional linear accelerators could not be observed for the perturbations caused by the components of the ionization chamber and the sensitive volume. Conclusion: The results indicate that the well-known small bias between the beam quality correction factor as a function of TPR20/10 for the flattening filter free and conventional linear accelerators is not caused by the geometry of the detector but rather by the material of the sensitive volume. This suggest that the bias for flattening filter free photon fields is only caused by the different material of the sensitive volume (air instead of water)« less

On charged particle equilibrium violation in external photon fields.

PubMed

Bouchard, Hugo; Seuntjens, Jan; Palmans, Hugo

2012-03-01

In a recent paper by Bouchard et al. [Med. Phys. 36(10), 4654-4663 (2009)], a theoretical model of quality correction factors for idealistic so-called plan-class specific reference (PCSR) fields was proposed. The reasoning was founded on the definition of PCSR fields made earlier by Alfonso et al. [Med. Phys. 35(11), 5179-5186 (2008)], requiring the beam to achieve charged particle equilibrium (CPE), in a time-averaged sense, in the reference medium. The relation obtained by Bouchard et al. was derived using Fano's theorem (1954) which states that if CPE is established in a given medium, the dose is independent of point-to-point density variations. A potential misconception on the achievability of the condition required by Fano (1954) might be responsible for false practical conclusions, both in the definition of PCSR fields as well as the theoretical model of quality correction factor. In this paper, the practical achievability of CPE in external beams is treated in detail. The fact that this condition is not achievable in single or composite deliveries is illustrated by an intuitive method and is also formally demonstrated. Fano's theorem is not applicable in external beam radiation dosimetry without (virtually) removing attenuation effects, and therefore, the relation conditionally defined by Bouchard et al. (2009) cannot be valid in practice. A definition of PCSR fields in the recent formalism for nonstandard beams proposed by Alfonso et al. (2008) should be modified, revising the criterion of CPE condition. The authors propose reconsidering the terminology used to describe standard and nonstandard beams. The authors argue that quality correction factors of intensity modulated radiation therapy PCSR fields (i.e., k(Q(pcsr),Q) (f(pcsr),f(ref) )) could be unity under ideal conditions, but it is concluded that further investigation is necessary to confirm that hypothesis.

Experience of using MOSFET detectors for dose verification measurements in an end-to-end 192Ir brachytherapy quality assurance system.

PubMed

Persson, Maria; Nilsson, Josef; Carlsson Tedgren, Åsa

Establishment of an end-to-end system for the brachytherapy (BT) dosimetric chain could be valuable in clinical quality assurance. Here, the development of such a system using MOSFET (metal oxide semiconductor field effect transistor) detectors and experience gained during 2 years of use are reported with focus on the performance of the MOSFET detectors. A bolus phantom was constructed with two implants, mimicking prostate and head & neck treatments, using steel needles and plastic catheters to guide the 192 Ir source and house the MOSFET detectors. The phantom was taken through the BT treatment chain from image acquisition to dose evaluation. During the 2-year evaluation-period, delivered doses were verified a total of 56 times using MOSFET detectors which had been calibrated in an external 60 Co beam. An initial experimental investigation on beam quality differences between 192 Ir and 60 Co is reported. The standard deviation in repeated MOSFET measurements was below 3% in the six measurement points with dose levels above 2 Gy. MOSFET measurements overestimated treatment planning system doses by 2-7%. Distance-dependent experimental beam quality correction factors derived in a phantom of similar size as that used for end-to-end tests applied on a time-resolved measurement improved the agreement. MOSFET detectors provide values stable over time and function well for use as detectors for end-to-end quality assurance purposes in 192 Ir BT. Beam quality correction factors should address not only distance from source but also phantom dimensions. Copyright © 2017 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.

SU-G-TeP2-03: Comparison of Standard Dosimetry Protocol in Japan and AAPM TG-51 Addendum in Order to Establish Optimal Dosimetry for FFF Beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsunaga, T; Adachi, Y; Hayashi, N

Purpose: Japan Standard Dosimetry of Absorbed dose to water in external beam radiotherapy (JSDP12) is widely used to measure radiation dose in radiotherapy. However, JSDP12 does not take flattening-filter-free (FFF) beam into consideration. In addition, JSDP12 applied TPR20,10 for dose quality index for photon beam. The purpose of this study is to compare JSDP12 with AAPM TG-51 addendum in order to establish optimal dosimetry procedure for FFF beam. Method: We evaluated the ion-recombination factor (ks) and the correction factor of radial beam profile (Prp) in FFF beam dosimetry. The ks was introduced by 2 voltages method and verified by Jaffe’smore » plot. The Prp was given by both film measurement and calculation of treatment planning system, and compared them. Next, we compared the dose quality indexes (kQ) between TPR20,10 method and PDD(10)x method. Finally we considered optimal dosimetry protocol for FFF photon beam using JSDP12 with referring TG-51 addendum protocols. The FFF photon beams of 6 MV (6X-FFF) and 10 MV (10X-FFF) from TrueBeam were investigated in this study. Results: The ks for 6X-FFF and 10X-FFF beams were 1.005 and 1.010, respectively. The Prp of 0.6 cc ionization chamber for 6X-FFF and 10X-FFF beams (Film, TPS) were (1.004, 1.008) and (1.005, 1.008), respectively. The kQ for 6X-FFF and 10X-FFF beams (JSDP12, TG-51 addendum) were (0.9950, 0.9947) and (0.9851, 0.9845), respectively. The most effective factor for uncertainty in FFF photon beam measurement was Prp for JSDP12 formalism. Total dosimetric differences between JSDP12 and TG-51 addendum for 6X-FFF and 10X-FFF were -0.47% and -0.73%, respectively. Conclusion: The total dosimetric difference between JSDP12 and TG-51 addendum was within 1%. The introduction of kQ given by JSDP is feasible for FFF photon beam dosimetry. However, we think Prp should be considered for optimal dosimetry procedure even if JSDP12 is used for FFF photon beam dosimetry.« less

Characterization of the nanoDot OSLD dosimeter in CT.

PubMed

Scarboro, Sarah B; Cody, Dianna; Alvarez, Paola; Followill, David; Court, Laurence; Stingo, Francesco C; Zhang, Di; McNitt-Gray, Michael; Kry, Stephen F

2015-04-01

The extensive use of computed tomography (CT) in diagnostic procedures is accompanied by a growing need for more accurate and patient-specific dosimetry techniques. Optically stimulated luminescent dosimeters (OSLDs) offer a potential solution for patient-specific CT point-based surface dosimetry by measuring air kerma. The purpose of this work was to characterize the OSLD nanoDot for CT dosimetry, quantifying necessary correction factors, and evaluating the uncertainty of these factors. A characterization of the Landauer OSL nanoDot (Landauer, Inc., Greenwood, IL) was conducted using both measurements and theoretical approaches in a CT environment. The effects of signal depletion, signal fading, dose linearity, and angular dependence were characterized through direct measurement for CT energies (80-140 kV) and delivered doses ranging from ∼5 to >1000 mGy. Energy dependence as a function of scan parameters was evaluated using two independent approaches: direct measurement and a theoretical approach based on Burlin cavity theory and Monte Carlo simulated spectra. This beam-quality dependence was evaluated for a range of CT scanning parameters. Correction factors for the dosimeter response in terms of signal fading, dose linearity, and angular dependence were found to be small for most measurement conditions (<3%). The relative uncertainty was determined for each factor and reported at the two-sigma level. Differences in irradiation geometry (rotational versus static) resulted in a difference in dosimeter signal of 3% on average. Beam quality varied with scan parameters and necessitated the largest correction factor, ranging from 0.80 to 1.15 relative to a calibration performed in air using a 120 kV beam. Good agreement was found between the theoretical and measurement approaches. Correction factors for the measurement of air kerma were generally small for CT dosimetry, although angular effects, and particularly effects due to changes in beam quality, could be more substantial. In particular, it would likely be necessary to account for variations in CT scan parameters and measurement location when performing CT dosimetry using OSLD.

Response of TLD-100 in mixed fields of photons and electrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lawless, Michael J.; Junell, Stephanie; Hammer, Cliff

Purpose: Thermoluminescent dosimeters (TLDs) are routinely used for dosimetric measurements of high energy photon and electron fields. However, TLD response in combined fields of photon and electron beam qualities has not been characterized. This work investigates the response of TLD-100 (LiF:Mg,Ti) to sequential irradiation by high-energy photon and electron beam qualities. Methods: TLDs were irradiated to a known dose by a linear accelerator with a 6 MV photon beam, a 6 MeV electron beam, and a NIST-traceable {sup 60}Co beam. TLDs were also irradiated in a mixed field of the 6 MeV electron beam and the 6 MV photon beam.more » The average TLD response per unit dose of the TLDs for each linac beam quality was normalized to the average response per unit dose of the TLDs irradiated by the {sup 60}Co beam. Irradiations were performed in water and in a Virtual Water Trade-Mark-Sign phantom. The 6 MV photon beam and 6 MeV electron beam were used to create dose calibration curves relating TLD response to absorbed dose to water, which were applied to the TLDs irradiated in the mixed field. Results: TLD relative response per unit dose in the mixed field was less sensitive than the relative response in the photon field and more sensitive than the relative response in the electron field. Application of the photon dose calibration curve to the TLDs irradiated in a mixed field resulted in an underestimation of the delivered dose, while application of the electron dose calibration curve resulted in an overestimation of the dose. Conclusions: The relative response of TLD-100 in mixed fields fell between the relative response in the photon-only and electron-only fields. TLD-100 dosimetry of mixed fields must account for this intermediate response to minimize the estimation errors associated with calibration factors obtained from a single beam quality.« less

Response of TLD-100 in mixed fields of photons and electrons.

PubMed

Lawless, Michael J; Junell, Stephanie; Hammer, Cliff; DeWerd, Larry A

2013-01-01

Thermoluminescent dosimeters (TLDs) are routinely used for dosimetric measurements of high energy photon and electron fields. However, TLD response in combined fields of photon and electron beam qualities has not been characterized. This work investigates the response of TLD-100 (LiF:Mg,Ti) to sequential irradiation by high-energy photon and electron beam qualities. TLDs were irradiated to a known dose by a linear accelerator with a 6 MV photon beam, a 6 MeV electron beam, and a NIST-traceable (60)Co beam. TLDs were also irradiated in a mixed field of the 6 MeV electron beam and the 6 MV photon beam. The average TLD response per unit dose of the TLDs for each linac beam quality was normalized to the average response per unit dose of the TLDs irradiated by the (60)Co beam. Irradiations were performed in water and in a Virtual Water™ phantom. The 6 MV photon beam and 6 MeV electron beam were used to create dose calibration curves relating TLD response to absorbed dose to water, which were applied to the TLDs irradiated in the mixed field. TLD relative response per unit dose in the mixed field was less sensitive than the relative response in the photon field and more sensitive than the relative response in the electron field. Application of the photon dose calibration curve to the TLDs irradiated in a mixed field resulted in an underestimation of the delivered dose, while application of the electron dose calibration curve resulted in an overestimation of the dose. The relative response of TLD-100 in mixed fields fell between the relative response in the photon-only and electron-only fields. TLD-100 dosimetry of mixed fields must account for this intermediate response to minimize the estimation errors associated with calibration factors obtained from a single beam quality.

Sci-Fri PM: Planning-10: The replacement correction factors for cylindrical chambers in megavoltage beams.

PubMed

Wang, L; Rogers, Dwo

2008-07-01

The replacement correction factor (P repl ) in ion chamber dosimetry accounts for the effects of the medium being replaced by the air cavity of the chamber. In TG-21, P repl was conceptually separated into two components: fluence correction, P fl , and gradient correction, P gr . In TG-51, for electron beams, the calibration is at d ref where P gr is required for cylindrical chambers and P fl is unknown and assumed to be the same as that for a beam having the same mean electron energy at d max . For cylindrical chambers in high-energy photon beams, P repl also represents a major uncertainty in current dosimetry protocols. In this study, P repl is calculated with high precision (<0.1%) by the Monte Carlo method as the ratio of the dose in a phantom to the dose scored in water-walled cylindrical cavities of various radii (with the center of the cavity being the point of measurement) in both high energy photon and electron beams. It is found that, for electron beams, the mean electron energy at depth is a good beam quality specifier for P fl ; and TG-51's adoption of P fl at d max with the same mean electron energy for use at d ref is proven to be accurate. For Farmer chambers in photon beams, there is essentially no beam quality dependence for P repl values. In a Co photon beam, the calculated P repl is about 0.4-0.6% higher than the TG-21 value, indicating TG-21 (and TG-51) used incorrect values of P repl for cylindrical chambers. © 2008 American Association of Physicists in Medicine.

VideoBeam portable laser communicator

NASA Astrophysics Data System (ADS)

Mecherle, G. Stephen; Holcomb, Terry L.

1999-01-01

A VideoBeamTM portable laser communicator has been developed which provides full duplex communication links consisting of high quality analog video and stereo audio. The 3.2-pound unit resembles a binocular-type form factor and has an operational range of over two miles (clear air) with excellent jam-resistance and low probability of interception characteristics. The VideoBeamTM unit is ideally suited for numerous military scenarios, surveillance/espionage, industrial precious mineral exploration, and campus video teleconferencing applications.

Improved power and efficiency for tapered lasers with optimized photonic crystal structures

NASA Astrophysics Data System (ADS)

Ma, Xiaolong; Qu, Hongwei; Zhao, Shaoyu; Zhou, Xuyan; Lin, Yuzhe; Zheng, Wanhua

2017-10-01

High power and high beam quality laser sources are required in numerous applications such as nonlinear frequency conversion, optical pumping of solid-state and fiber lasers, material processing and others. Tapered lasers can provide a high output power while keeping a high beam quality. However, the conventional tapered lasers suffer from a large vertical beam divergence. We have demonstrated 2-mm long tapered lasers with photonic crystal structures. A high beam quality and a narrow vertical divergence are achieved. In this paper, we optimized the photonic crystal structure and fabricated a 4-mm long tapered laser to further increase the output power and the wall-plug efficiency. Compared with our precious wafer, the optimized structure has a lower doping level to reduce the internal loss. The period of the photonic crystal structure and the thickness of the upper cladding are also reduced. The device has a 1-mm long ridge-waveguide section and a 3-mm long tapered section. The taper angle is 4°. An output power of 7.3 W is achieved with a peak wall-plug efficiency of 46% in continuous-wave mode. The threshold current is around 500 mA and the slope efficiency is 0.93 W/A. In pulsed mode, the output power is 15.6 W and the maximum wall-plug efficiency is 48.1%. The far-field divergence with full width at half maximum is 6.3° for the lateral direction at 3 A. The vertical far-field beam divergence is around 11° at different injection levels. High beam qualities are demonstrated by beam quality factor M2 of 1.52 for the lateral direction and 1.54 for the vertical direction.

Monte Carlo modeling of HD120 multileaf collimator on Varian TrueBeam linear accelerator for verification of 6X and 6X FFF VMAT SABR treatment plans

PubMed Central

Gete, Ermias; Duzenli, Cheryl; Teke, Tony

2014-01-01

A Monte Carlo (MC) validation of the vendor‐supplied Varian TrueBeam 6 MV flattened (6X) phase‐space file and the first implementation of the Siebers‐Keall MC MLC model as applied to the HD120 MLC (for 6X flat and 6X flattening filterfree (6X FFF) beams) are described. The MC model is validated in the context of VMAT patient‐specific quality assurance. The Monte Carlo commissioning process involves: 1) validating the calculated open‐field percentage depth doses (PDDs), profiles, and output factors (OF), 2) adapting the Siebers‐Keall MLC model to match the new HD120‐MLC geometry and material composition, 3) determining the absolute dose conversion factor for the MC calculation, and 4) validating this entire linac/MLC in the context of dose calculation verification for clinical VMAT plans. MC PDDs for the 6X beams agree with the measured data to within 2.0% for field sizes ranging from 2 × 2 to 40 × 40 cm2. Measured and MC profiles show agreement in the 50% field width and the 80%‐20% penumbra region to within 1.3 mm for all square field sizes. MC OFs for the 2 to 40 cm2 square fields agree with measurement to within 1.6%. Verification of VMAT SABR lung, liver, and vertebra plans demonstrate that measured and MC ion chamber doses agree within 0.6% for the 6X beam and within 2.0% for the 6X FFF beam. A 3D gamma factor analysis demonstrates that for the 6X beam, > 99% of voxels meet the pass criteria (3%/3 mm). For the 6X FFF beam, > 94% of voxels meet this criteria. The TrueBeam accelerator delivering 6X and 6X FFF beams with the HD120 MLC can be modeled in Monte Carlo to provide an independent 3D dose calculation for clinical VMAT plans. This quality assurance tool has been used clinically to verify over 140 6X and 16 6X FFF TrueBeam treatment plans. PACS number: 87.55.K‐ PMID:24892341

Ion Figuring of Replicated X-Ray Optics

NASA Technical Reports Server (NTRS)

Cantey, Thomas M.; Gregory, Don A.

1997-01-01

This investigation included experiments to demonstrate ion beam figuring effects on electroless nickel with the expressed desire to figure X-ray optic mandrels. It was important to establish that ion beam figuring did not induce any adverse effects to the nickel surface. The ion beam has consistently been shown to be an excellent indicator of the quality of the subsurface. Polishing is not the only cause for failure in the ion beam final figuring process, the material composition is equally important. Only by careful consideration of both these factors can the ion beam final figuring process achieve its greatest potential. The secondary goal was to construct a model for representing the ion beam material removal rate. Representing the ion beam removal rate is only an approximation and has a number of limiting factors. The resolution of the metrology apparatus limits the modeling of the beam function as well. As the surface error corrections demand more precision in the final figuring, the model representing beam function must be equally precise. The precision to which the beam function can be represented is not only determined by the model but also by the measurements producing that model. The method developed for determining the beam function has broad application to any material destined to be ion beam figured.

SU-F-T-326: Diode Array Transmission Detector Systems Evaluation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoffman, D; Dyer, B; Kumaran Nair, C

2016-06-15

Purpose: A new transmission detector, Delta4 Discover, developed by Scandidos (Uppsala, Sweden) was evaluated for external photon beam verification and quality assurance. The device is an array of 4040 diodes designed to be mounted on the linac accessory tray to measure photon field shape, position and fluence during patient treatment. Interfractional measurements are compared to a baseline measurement made during delivery quality assurance. The aim of this work is to evaluate the stability of the device and its effect on the shape and magnitude of the treatment beam. Methods: Beam profiles, percent depth dose, and beam attenuation was measured formore » 6, 10, and 15 MV photon beams with and without the device in place for 1×1 and 30×30 cm2 fields. Changes in profile and percent depth dose was quantified to evaluate the need to recommission the treatment beam, or account for the device with a tray factor. The stability of the radiation measurements was evaluated by measuring the deviation of each diode measurement during repeated prostate VMAT treatment delivery. Results: Photon beam profiles changed by < 1.25% in the nonpenumbra regions of the 30×30 cm2 beam. Percent depth dose curves show a 5–7% increased dose at depths < 2.5cm, but agreed within 1% at depths > 2.5cm. This indicates increased skin dose, similar to the use of a physical beam wedge. The device attenuated 6, 10, and 15 MV photon beams by 1.71±0.02%, 1.36±0.03%, and 1.17±0.03%, respectively. The diode array reproduced dosimetric measurements within 0.5% standard deviation for repeated prostate VMAT measurement. Conclusion: The device demonstrated stabile radiation measurements, while not changing the treatment beam shape in a clinically significantly manner. Use of this device can be accounted for with a tray factor, as opposed to recommissioning the treatment beam.« less

Diode-pumped dual-wavelength Nd:LSO laser at 1059 and 1067  nm with nearly diffraction-limited beam quality.

PubMed

Huang, Xiaoxu; Lan, Jinglong; Lin, Zhi; Wang, Yi; Xu, Bin; Xu, Huiying; Cai, Zhiping; Xu, Xiaodong; Zhang, Jian; Xu, Jun

2016-04-10

We report a diode-pumped continuous-wave simultaneous dual-wavelength Nd:LSO laser at 1059 and 1067 nm. By employing a specially coated output coupler with relatively high transmissions at high-gain emission lines of 1075 and 1079 nm, the two low-gain emission lines, 1059 and 1067 nm, can be achieved, for the first time to our knowledge, with maximum output power of 1.27 W and slope efficiency of about 29.2%. The output power is only limited by the available pump power. Output beam quality is also measured to be about 1.19 and 1.21 of the beam propagation factors in the x and y directions, respectively.

Dynamical stability of slip-stacking particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eldred, Jeffrey; Zwaska, Robert

2014-09-01

We study the stability of particles in slip-stacking configuration, used to nearly double proton beam intensity at Fermilab. We introduce universal area factors to calculate the available phase space area for any set of beam parameters without individual simulation. We find perturbative solutions for stable particle trajectories. We establish Booster beam quality requirements to achieve 97% slip-stacking efficiency. We show that slip-stacking dynamics directly correspond to the driven pendulum and to the system of two standing-wave traps moving with respect to each other.

Nonlinear analysis of a relativistic beam-plasma cyclotron instability

NASA Technical Reports Server (NTRS)

Sprangle, P.; Vlahos, L.

1986-01-01

A self-consistent set of nonlinear and relativistic wave-particle equations are derived for a magnetized beam-plasma system interacting with electromagnetic cyclotron waves. In particular, the high-frequency cyclotron mode interacting with a streaming and gyrating electron beam within a background plasma is considered in some detail. This interaction mode may possibly find application as a high-power source of coherent short-wavelength radiation for laboratory devices. The background plasma, although passive, plays a central role in this mechanism by modifying the dielectric properties in which the magnetized electron beam propagates. For a particular choice of the transverse beam velocity (i.e., the speed of light divided by the relativistic mass factor), the interaction frequency equals the nonrelativistic electron cyclotron frequency times the relativistic mass factor. For this choice of transverse beam velocity the detrimental effects of a longitudinal beam velocity spread is virtually removed. Power conversion efficiencies in excess of 18 percent are both analytically calculated and obtained through numerical simulations of the wave-particle equations. The quality of the electron beam, degree of energy and pitch angle spread, and its effect on the beam-plasma cyclotron instability is studied.

Incorporating BEAMing technology as a liquid biopsy into clinical practice for the management of colorectal cancer patients: an expert taskforce review.

PubMed

García-Foncillas, J; Alba, E; Aranda, E; Díaz-Rubio, E; López-López, R; Tabernero, J; Vivancos, A

2017-12-01

The importance of mutation identification for advanced colorectal cancer treatment with anti-epidermal growth factor receptor agents is well established. However, due to delays in turnaround time, low-quality tissue samples, and/or lack of standardization of testing methods a significant proportion of patients are being treated without the information that Kirsten rat sarcoma and neuroblastoma rat sarcoma (RAS) testing can provide. The detection of mutated circulating tumor DNA by BEAMing technology addresses this gap in care and allows these patients to receive international guideline-recommended expanded RAS testing with rapid turnaround times. Furthermore, the overall concordance between OncoBEAM RAS colorectal cancer testing and standard of care tissue testing is very high (93.3%). This article presents an overview of the clinical utility and potential applications of this minimally invasive method, such as early detection of emergent resistance to anti-epidermal growth factor receptor therapy. If appropriately implemented, BEAMing technology holds considerable promise to enhance the quality of patient care and improve clinical outcomes. © The Author 2017. Published by Oxford University Press on behalf of the European Society for Medical Oncology.

SU-E-T-408: Determination of KQ,Q0-Factors From Water and Graphite Calorimetry in a 60 MeV Proton Beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rossomme, S; Renaud, J; Sarfehnia, A

2014-06-01

Purpose: To reduce the uncertainty of the beam quality correction factor k Q,Q0, for scattered proton beams (SPB). This factor is used in dosimetry protocols, to determine absorbed dose-to-water with ionization chambers. For the Roos plane parallel chambers (RPPICs), the IAEA TRS-398 protocol estimates k Q,Q0-factor to be 1.004(for a beam quality Rres=2 g.cm{sup 2}), with an uncertainty of 2.1%. Methods: A graphite calorimeter (GCal), a water calorimeter (WCal) and RPPICs were exposed, in a single experiment, to a 60 MeV non-modulated SPB. RPPICs were calibrated in terms of absorbed dose-to-water in a 20 MeV electron beam. The calibration coefficientmore » is traceable to NPL's absorbed dose standards. Chamber measurements were corrected for environmental conditions, recombination and polarity. The WCal corrections include heat loss, heat defect and vessel perturbation. The GCal corrections include heat loss and absorbed dose conversion. Except for heat loss correction and its uncertainty in the WCal system, all major corrections were included in the analysis. Other minor corrections, such as beam profile non-uniformity, are still to be evaluated. Experimental k Q,Q0-factors were derived by comparing the results obtained with both calorimeters and ionometry. Results: The absorbed dose-to-water from both calorimeters was found to be within 1.3% with an uncertainty of 1.2%. k Q,Q0-factor for a RPPIC was found to be 0.998 and 1.011, with a standard uncertainty of 1.4% and 0.9% when the dose is based on the GCal and the WCal, respectively. Conclusion: Results suggest the possibility to determine k Q,Q0-values for PPICs in SPB with a lower uncertainty than specified in the TRS-398 thereby helping to reduce uncertainty on absorbed dose-to-water. The agreement between calorimeters confirms the possibility to use GCal or WCal as primary standard in SPB. Because of the dose conversion, the use of GCal may lead to slightly higher uncertainty, but is, at present, considerably easier to operate.« less

Novel, compact, and simple ND:YVO4 laser with 12 W of CW optical output power and good beam quality

NASA Astrophysics Data System (ADS)

Zimer, H.; Langer, B.; Wittrock, U.; Heine, F.; Hildebrandt, U.; Seel, S.; Lange, R.

2017-11-01

We present first, promising experiments with a novel, compact and simple Nd:YVO4 slab laser with 12 W of 1.06 μm optical output power and a beam quality factor M2 2.5. The laser is made of a diffusion-bonded YVO4/Nd:YVO4 composite crystal that exhibits two unique features. First, it ensures a one-dimensional heat removal from the laser crystal, which leads to a temperature profile without detrimental influence on the laser beam. Thus, the induced thermo-optical aberrations to the laser field are low, allowing power scaling with good beam quality. Second, the composite crystal itself acts as a waveguide for the 809 nm pump-light that is supplied from a diode laser bar. Pump-light shaping optics, e.g. fast- or slow-axis collimators can be omitted, reducing the complexity of the system. Pump-light redundancy can be easily achieved. Eventually, the investigated slab laser might be suitable for distortion-free high gain amplification of weak optical signals.

Measurement of the M² beam propagation factor using a focus-tunable liquid lens.

PubMed

Niederriter, Robert D; Gopinath, Juliet T; Siemens, Mark E

2013-03-10

We demonstrate motion-free beam quality M² measurements of stigmatic, simple astigmatic, and general astigmatic (twisted) beams using only a focus-tunable liquid lens and a CCD camera. We extend the variable-focus technique to the characterization of general astigmatic beams by measuring the 10 second-order moments of the power density distribution for the twisted beam produced by passage through multimode optical fiber. Our method measures the same M² values as the traditional variable-distance method for a wide range of laser beam sources, including nearly TEM(00) (M²≈1) and general astigmatic multimode beams (M²≈8). The method is simple and compact, with no moving parts or complex apparatus and measurement precision comparable to the standard variable-distance method.

An analysis of stepped trapezoidal-shaped microcantilever beams for MEMS-based devices

NASA Astrophysics Data System (ADS)

Ashok, Akarapu; Gangele, Aparna; Pal, Prem; Pandey, Ashok Kumar

2018-07-01

Microcantilever beams are the most widely used mechanical elements in the design and fabrication of MEMS/NEMS-based sensors and actuators. In this work, we have proposed a new microcantilever beam design based on a stepped trapezoidal-shaped microcantilever. Single-, double-, triple- and quadruple-stepped trapezoidal-shaped microcantilever beams along with conventional rectangular-shaped microcantilever beams were analysed experimentally, numerically and analytically. The microcantilever beams were fabricated from silicon dioxide material using wet bulk micromachining in 25 wt% TMAH. The length, width and thickness of the microcantilever beams were fixed at 200, 40 and 0.96 µm, respectively. A laser vibrometer was utilized to measure the resonance frequency and Q-factor of the microcantilever beams in vacuum as well as in ambient conditions. Furthermore, finite element analysis software, ANSYS, was employed to numerically analyse the resonance frequency, maximum deflection and torsional end rotation of all the microcantilever beam designs. The analytical and numerical resonance frequencies are found to be in good agreement with the experimental resonance frequencies. In the stepped trapezoidal-shaped microcantilever beams with an increasing number of steps, the Q-factor, maximum deflection and torsional end rotation were improved, whereas the resonance frequency was slightly reduced. Nevertheless, the resonance frequency is higher than the basic rectangular-shaped microcantilever beam. The observed quality factor, maximum deflection and torsional end rotation for a quadruple-stepped trapezoidal-shaped microcantilever are 38%, 41% and 52%, respectively, which are higher than those of conventional rectangular-shaped microcantilever beams. Furthermore, for an applied concentrated mass of 1 picogram on the cantilever surface, a greater shift in frequency is obtained for all the stepped trapezoidal-shaped microcantilever beam designs compared to the conventional rectangular microcantilever beam.

Characteristics of a KA-band third-harmonic peniotron driven by a high-quality linear axis-encircling electron beam

NASA Astrophysics Data System (ADS)

Zhao, Xiaoyun; Tuo, Xianguo; Ge, Qing; Peng, Ying

2017-12-01

We employ a high-quality linear axis-encircling electron beam generated by a Cuccia coupler to drive a Ka-band third-harmonic peniotron and develop a self-consistent nonlinear calculation code to numerically analyze the characteristics of the designed peniotron. It is demonstrated that through a Cuccia coupler, a 6 kV, 0.5 A pencil beam and an input microwave power of 16 kW at 10 GHz can generate a 37 kV, 0.5 A linear axis-encircling beam, and it is characterized by a very low velocity spread. Moreover, the electron beam guiding center deviation can be adjusted easily. Driven by such a beam, a 30 GHz, Ka-band third-harmonic peniotron is predicted to achieve a conversion efficiency of 51.0% and a microwave output power of 9.44 kW; the results are in good agreement with the Magic3D simulation. Using this code, we studied the factors influencing the peniotron performance, and it can provide some guidelines for the design of a Ka-band third-harmonic peniotron driven by a linear electron beam and can promote the application of high-harmonic peniotrons in practice.

Design and characteristic analysis of shaping optics for optical trepanning

NASA Astrophysics Data System (ADS)

Zeng, D.; Latham, W. P.; Kar, A.

2005-08-01

Optical trepanning is a new laser drilling method using an annular beam. The annular beams allow numerous irradiance profiles to supply laser energy to the workpiece and thus provide more flexibility in affecting the hole quality than a traditional circular laser beam. The refractive axicon system has been designed to generating a collimated annular beam. In this article, calculations of intensity distributions produced by this refractive system are made by evaluating the Kirchhoff-Fresnel diffraction. It is shown that the refractive system is able to transform a Gaussian beam into a full Gaussian annular beam. The base angle of the axicon lens, input laser beam diameter and intensity profiles are found to be important factors for the axcion refractive system. Their effects on the annular beam profiles are analyzed based on the numerical solutions of the diffraction patterns.

Laser-phased-array beam steering based on crystal fiber

NASA Astrophysics Data System (ADS)

Yang, Deng-cai; Zhao, Si-si; Wang, Da-yong; Wang, Zhi-yong; Zhang, Xiao-fei

2011-06-01

Laser-phased-array system provides an elegant means for achieving the inertial-free, high-resolution, rapid and random beam steering. In laser-phased-array system, phase controlling is the most important factor that impacts the system performance. A novel scheme is provided in this paper, the beam steering is accomplished by using crystal fiber array, the difference length between adjacent fiber is fixed. The phase difference between adjacent fiber decides the direction of the output beam. When the wavelength of the input fiber laser is tuned, the phase difference between the adjacent elements has changed. Therefore, the laser beam direction has changed and the beam steering has been accomplished. In this article, based on the proposed scheme, the steering angle of the laser beam is calculated and analyzed theoretically. Moreover, the far-field steering beam quality is discussed.

Characterization of the nanoDot OSLD dosimeter in CT

PubMed Central

Scarboro, Sarah B.; Cody, Dianna; Alvarez, Paola; Followill, David; Court, Laurence; Stingo, Francesco C.; Zhang, Di; Kry, Stephen F.

2015-01-01

Purpose: The extensive use of computed tomography (CT) in diagnostic procedures is accompanied by a growing need for more accurate and patient-specific dosimetry techniques. Optically stimulated luminescent dosimeters (OSLDs) offer a potential solution for patient-specific CT point-based surface dosimetry by measuring air kerma. The purpose of this work was to characterize the OSLD nanoDot for CT dosimetry, quantifying necessary correction factors, and evaluating the uncertainty of these factors. Methods: A characterization of the Landauer OSL nanoDot (Landauer, Inc., Greenwood, IL) was conducted using both measurements and theoretical approaches in a CT environment. The effects of signal depletion, signal fading, dose linearity, and angular dependence were characterized through direct measurement for CT energies (80–140 kV) and delivered doses ranging from ∼5 to >1000 mGy. Energy dependence as a function of scan parameters was evaluated using two independent approaches: direct measurement and a theoretical approach based on Burlin cavity theory and Monte Carlo simulated spectra. This beam-quality dependence was evaluated for a range of CT scanning parameters. Results: Correction factors for the dosimeter response in terms of signal fading, dose linearity, and angular dependence were found to be small for most measurement conditions (<3%). The relative uncertainty was determined for each factor and reported at the two-sigma level. Differences in irradiation geometry (rotational versus static) resulted in a difference in dosimeter signal of 3% on average. Beam quality varied with scan parameters and necessitated the largest correction factor, ranging from 0.80 to 1.15 relative to a calibration performed in air using a 120 kV beam. Good agreement was found between the theoretical and measurement approaches. Conclusions: Correction factors for the measurement of air kerma were generally small for CT dosimetry, although angular effects, and particularly effects due to changes in beam quality, could be more substantial. In particular, it would likely be necessary to account for variations in CT scan parameters and measurement location when performing CT dosimetry using OSLD. PMID:25832070

Characterization of the nanoDot OSLD dosimeter in CT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scarboro, Sarah B.; Graduate School of Biomedical Sciences, The University of Texas Health Science Center Houston, Houston, Texas 77030; The Methodist Hospital, Houston, Texas 77030

Purpose: The extensive use of computed tomography (CT) in diagnostic procedures is accompanied by a growing need for more accurate and patient-specific dosimetry techniques. Optically stimulated luminescent dosimeters (OSLDs) offer a potential solution for patient-specific CT point-based surface dosimetry by measuring air kerma. The purpose of this work was to characterize the OSLD nanoDot for CT dosimetry, quantifying necessary correction factors, and evaluating the uncertainty of these factors. Methods: A characterization of the Landauer OSL nanoDot (Landauer, Inc., Greenwood, IL) was conducted using both measurements and theoretical approaches in a CT environment. The effects of signal depletion, signal fading, dosemore » linearity, and angular dependence were characterized through direct measurement for CT energies (80–140 kV) and delivered doses ranging from ∼5 to >1000 mGy. Energy dependence as a function of scan parameters was evaluated using two independent approaches: direct measurement and a theoretical approach based on Burlin cavity theory and Monte Carlo simulated spectra. This beam-quality dependence was evaluated for a range of CT scanning parameters. Results: Correction factors for the dosimeter response in terms of signal fading, dose linearity, and angular dependence were found to be small for most measurement conditions (<3%). The relative uncertainty was determined for each factor and reported at the two-sigma level. Differences in irradiation geometry (rotational versus static) resulted in a difference in dosimeter signal of 3% on average. Beam quality varied with scan parameters and necessitated the largest correction factor, ranging from 0.80 to 1.15 relative to a calibration performed in air using a 120 kV beam. Good agreement was found between the theoretical and measurement approaches. Conclusions: Correction factors for the measurement of air kerma were generally small for CT dosimetry, although angular effects, and particularly effects due to changes in beam quality, could be more substantial. In particular, it would likely be necessary to account for variations in CT scan parameters and measurement location when performing CT dosimetry using OSLD.« less

Effect of laser incidence angle on cut quality of 4 mm thick stainless steel sheet using fiber laser

NASA Astrophysics Data System (ADS)

Mullick, Suvradip; Agrawal, Arpit Kumar; Nath, Ashish Kumar

2016-07-01

Fiber laser has potential to outperform the more traditionally used CO2 lasers in sheet metal cutting applications due to its higher efficiency, better beam quality, reliability and ease of beam delivery through optical fiber. It has been however, reported that the higher focusability and shorter wavelength are advantageous for cutting thin metal sheets up to about 2 mm only. Better focasability results in narrower kerf-width, which leads to an earlier flow separation in the flow of assist gas within the kerf, resulting in uncontrolled material removal and poor cut quality. However, the advarse effect of tight focusability can be taken care by shifting the focal point position towards the bottom surface of work-piece, which results in a wider kerf size. This results in a more stable flow within the kerf for a longer depth, which improves the cut quality. It has also been reported that fiber laser has an unfavourable angle of incidence during cutting of thick sections, resulting in poor absorption at the metal surface. Therefore, the effect of laser incidence angle, along with other process parameters, viz. cutting speed and assist gas pressure on the cut quality of 4 mm thick steel sheet has been investigated. The change in laser incidence angle has been incorporated by inclining the beam towards and away from the cut front, and the quality factors are taken as the ratio of kerf width and the striation depth. Besides the absorption of laser radiation, beam inclination is also expected to influence the gas flow characteristics inside the kerf, shear force phenomena on the molten pool, laser beam coupling and laser power distribution at the inclined cut surface. Design of experiment has been used by implementing response surface methodology (RSM) to study the parametric dependence of cut quality, as well as to find out the optimum cut quality. An improvement in quality has been observed for both the inclination due to the combined effect of multiple phenomena.

Nonadiabatic Electron-Optical System of a Technological Gyrotron

NASA Astrophysics Data System (ADS)

Goldenberg, A. L.; Glyavin, M. Yu.; Leshcheva, K. A.; Manuilov, V. N.

2017-10-01

We consider a new version of the nonadiabatic system for the formation of a helical electron beam in a gyrotron, in which electrons acquire initial oscillatory velocities when a rectilinear beam is injected at an angle to the magnetic field. In such an electron gun, the influence of thermal electron velocities and roughness of the emitting surface can be decreased, as compared with the conventional electron-optical systems of gyrotrons. This makes it possible to increase significantly the system efficiency. The main factors affecting the quality of the formed beam are considered.

Morphometric analysis - Cone beam computed tomography to predict bone quality and quantity.

PubMed

Hohlweg-Majert, B; Metzger, M C; Kummer, T; Schulze, D

2011-07-01

Modified quantitative computed tomography is a method used to predict bone quality and quantify the bone mass of the jaw. The aim of this study was to determine whether bone quantity or quality was detected by cone beam computed tomography (CBCT) combined with image analysis. MATERIALS AND PROCEDURES: Different measurements recorded on two phantoms (Siemens phantom, Comac phantom) were evaluated on images taken with the Somatom VolumeZoom (Siemens Medical Solutions, Erlangen, Germany) and the NewTom 9000 (NIM s.r.l., Verona, Italy) in order to calculate a calibration curve. The spatial relationships of six sample cylinders and the repositioning from four pig skull halves relative to adjacent defined anatomical structures were assessed by means of three-dimensional visualization software. The calibration curves for computer tomography (CT) and cone beam computer tomography (CBCT) using the Siemens phantom showed linear correlation in both modalities between the Hounsfield Units (HU) and bone morphology. A correction factor for CBCT was calculated. Exact information about the micromorphology of the bone cylinders was only available using of micro computer tomography. Cone-beam computer tomography is a suitable choice for analysing bone mass, but, it does not give any information about bone quality. 2010 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.

Update on POCIT portable optical communicators: VideoBeam and EtherBeam

NASA Astrophysics Data System (ADS)

Mecherle, G. Stephen; Holcomb, Terry L.

2000-05-01

LDSC is developing the POCITTM (Portable Optical Communication Integrated Transceiver) family of products which includes VideoBeamTM and the latest addition, EtherBeamTM. Each is a full duplex portable laser communicator: VideoBeamTM providing near-broadcast- quality analog video and stereo audio, and EtherBeamTM providing standard Ethernet connectivity. Each POCITTM transceiver consists of a 3.5-pound unit with a binocular- type form factor, which can be manually pointed, tripod- mounted or gyro-stabilized. Both units have an operational range of over two miles (clear air) with excellent jam- resistance and low probability of interception characteristics. The transmission wavelength of 1550 nm enables Class 1 eyesafe operation (ANSI, IEC). The POCITTM units are ideally suited for numerous military scenarios, surveillance/espionage, industrial precious mineral exploration, and campus video teleconferencing applications. VideoBeam will be available second quarter 2000, followed by EtherBeam in third quarter 2000.

Monte Carlo study of si diode response in electron beams.

PubMed

Wang, Lilie L W; Rogers, David W O

2007-05-01

Silicon semiconductor diodes measure almost the same depth-dose distributions in both photon and electron beams as those measured by ion chambers. A recent study in ion chamber dosimetry has suggested that the wall correction factor for a parallel-plate ion chamber in electron beams changes with depth by as much as 6%. To investigate diode detector response with respect to depth, a silicon diode model is constructed and the water/silicon dose ratio at various depths in electron beams is calculated using EGSnrc. The results indicate that, for this particular diode model, the diode response per unit water dose (or water/diode dose ratio) in both 6 and 18 MeV electron beams is flat within 2% versus depth, from near the phantom surface to the depth of R50 (with calculation uncertainty <0.3%). This suggests that there must be some other correction factors for ion chambers that counter-balance the large wall correction factor at depth in electron beams. In addition, the beam quality and field-size dependence of the diode model are also calculated. The results show that the water/diode dose ratio remains constant within 2% over the electron energy range from 6 to 18 MeV. The water/diode dose ratio does not depend on field size as long as the incident electron beam is broad and the electron energy is high. However, for a very small beam size (1 X 1 cm(2)) and low electron energy (6 MeV), the water/diode dose ratio may decrease by more than 2% compared to that of a broad beam.

Monte Carlo-based investigations on the impact of removing the flattening filter on beam quality specifiers for photon beam dosimetry.

PubMed

Czarnecki, Damian; Poppe, Björn; Zink, Klemens

2017-06-01

The impact of removing the flattening filter in clinical electron accelerators on the relationship between dosimetric quantities such as beam quality specifiers and the mean photon and electron energies of the photon radiation field was investigated by Monte Carlo simulations. The purpose of this work was to determine the uncertainties when using the well-known beam quality specifiers or energy-based beam specifiers as predictors of dosimetric photon field properties when removing the flattening filter. Monte Carlo simulations applying eight different linear accelerator head models with and without flattening filter were performed in order to generate realistic radiation sources and calculate field properties such as restricted mass collision stopping power ratios (L¯/ρ)airwater, mean photon and secondary electron energies. To study the impact of removing the flattening filter on the beam quality correction factors k Q , this factor for detailed ionization chamber models was calculated by Monte Carlo simulations. Stopping power ratios (L¯/ρ)airwater and k Q values for different ionization chambers as a function of TPR1020 and %dd(10) x were calculated. Moreover, mean photon energies in air and at the point of measurement in water as well as mean secondary electron energies at the point of measurement were calculated. The results revealed that removing the flattening filter led to a change within 0.3% in the relationship between %dd(10) x and (L¯/ρ)airwater, whereby the relationship between TPR1020 and (L¯/ρ)airwater changed up to 0.8% for high energy photon beams. However, TPR1020 was a good predictor of (L¯/ρ)airwater for both types of linear accelerator with energies < 10 MeV with a maximal deviation between both types of accelerators of 0.23%. According to the results, the mean photon energy below the linear accelerators head as well as at the point of measurement may not be suitable as a predictor of (L¯/ρ)airwater and k Q to merge the dosimetry of both linear accelerator types. It was possible to derive (L¯/ρ)airwater using the mean secondary electron energy at the point of measurement as a predictor with an accuracy of 0.17%. A bias between k Q for linear accelerators with and without flattening filter within 1.1% and 1.6% was observed for TPR1020 and %dd(10) x respectively. The results of this study have shown that removing the flattening filter led to a change in the relationship between the well-known beam quality specifiers and dosimetric quantities at the point of measurement, namely (L¯/ρ)airwater, mean photon and electron energy. Furthermore, the results show that a beam profile correction is important for dose measurements with large ionization chambers in flattening filter free beams. © 2017 American Association of Physicists in Medicine.

Characterizing a pulse-resolved dosimetry system for complex radiotherapy beams using organic scintillators.

PubMed

Beierholm, Anders R; Ottosson, Rickard O; Lindvold, Lars R; Behrens, Claus F; Andersen, Claus E

2011-05-21

A fast-readout dosimetry system based on fibre-coupled organic scintillators has been developed for the purpose of conducting point measurements of absorbed dose in radiotherapy beams involving high spatial and temporal dose gradients. The system measures the dose for each linac radiation pulse with millimetre spatial resolution. To demonstrate the applicability of the system in complex radiotherapy fields, output factors and per cent depth dose measurements were performed in solid water for a 6 MV photon beam and compared with Monte Carlo simulated doses for square fields down to 0.6 cm × 0.6 cm size. No significant differences between measurements and simulations were observed. The temporal resolution of the system was demonstrated by measuring dose per pulse, beam start-up transients and the quality factor for 6 MV. The precision of dose per pulse measurements was within 2.7% (1 SD) for a 10 cm × 10 cm field at 10 cm depth. The dose per pulse behaviour compared well with linac target current measurements and accumulated dose measurements, and the system was able to resolve transient dose delivery differences between two Varian linac builds. The system therefore shows promise for reference dosimetry and quality assurance of complex radiotherapy treatments.

Automation of a Linear Accelerator Dosimetric Quality Assurance Program

NASA Astrophysics Data System (ADS)

Lebron Gonzalez, Sharon H.

According to the American Society of Radiation Oncology, two-thirds of all cancer patients will receive radiation therapy during their illness with the majority of the treatments been delivered by a linear accelerator (linac). Therefore, quality assurance (QA) procedures must be enforced in order to deliver treatments with a machine in proper conditions. The overall goal of this project is to automate the linac's dosimetric QA procedures by analyzing and accomplishing various tasks. First, the photon beam dosimetry (i.e. total scatter correction factor, infinite percentage depth dose (PDD) and profiles) were parameterized. Parameterization consists of defining the parameters necessary for the specification of a dosimetric quantity model creating a data set that is portable and easy to implement for different applications including: beam modeling data input into a treatment planning system (TPS), comparing measured and TPS modelled data, the QA of a linac's beam characteristics, and the establishment of a standard data set for comparison with other data, etcetera. Second, this parameterization model was used to develop a universal method to determine the radiation field size of flattened (FF), flattening-filter-free (FFF) and wedge beams which we termed the parameterized gradient method (PGM). Third, the parameterized model was also used to develop a profile-based method for assessing the beam quality of photon FF and FFF beams using an ionization chamber array. The PDD and PDD change was also predicted from the measured profile. Lastly, methods were created to automate the multileaf collimator (MLC) calibration and QA procedures as well as the acquisition of the parameters included in monthly and annual photon dosimetric QA. A two field technique was used for the calculation of the MLC leaf relative offsets using an electronic portal imaging device (EPID). A step-and-shoot technique was used to accurately acquire the radiation field size, flatness, symmetry, output and beam quality specifiers in a single delivery to an ionization chamber array for FF and FFF beams.

Influence of scatter reduction method and monochromatic beams on image quality and dose in mammography.

PubMed

Moeckli, Raphaël; Verdun, Francis R; Fiedler, Stefan; Pachoud, Marc; Bulling, Shelley; Schnyder, Pierre; Valley, Jean-François

2003-12-01

In mammography, the image contrast and dose delivered to the patient are determined by the x-ray spectrum and the scatter to primary ratio S/P. Thus the quality of the mammographic procedure is highly dependent on the choice of anode and filter material and on the method used to reduce the amount of scattered radiation reaching the detector. Synchrotron radiation is a useful tool to study the effect of beam energy on the optimization of the mammographic process because it delivers a high flux of monochromatic photons. Moreover, because the beam is naturally flat collimated in one direction, a slot can be used instead of a grid for scatter reduction. We have measured the ratio S/P and the transmission factors for grids and slots for monoenergetic synchrotron radiation. In this way the effect of beam energy and scatter rejection method were separated, and their respective importance for image quality and dose analyzed. Our results show that conventional mammographic spectra are not far from optimum and that the use of a slot instead of a grid has an important effect on the optimization of the mammographic process. We propose a simple numerical model to quantify this effect.

Cryo-tomography Tilt-series Alignment with Consideration of the Beam-induced Sample Motion

PubMed Central

Fernandez, Jose-Jesus; Li, Sam; Bharat, Tanmay A. M.; Agard, David A.

2018-01-01

Recent evidence suggests that the beam-induced motion of the sample during tilt-series acquisition is a major resolution-limiting factor in electron cryo-tomography (cryoET). It causes suboptimal tilt-series alignment and thus deterioration of the reconstruction quality. Here we present a novel approach to tilt-series alignment and tomographic reconstruction that considers the beam-induced sample motion through the tilt-series. It extends the standard fiducial-based alignment approach in cryoET by introducing quadratic polynomials to model the sample motion. The model can be used during reconstruction to yield a motion-compensated tomogram. We evaluated our method on various datasets with different sample sizes. The results demonstrate that our method could be a useful tool to improve the quality of tomograms and the resolution in cryoET. PMID:29410148

Laser transmission welding of Acrylonitrile-Butadiene-Styrene (ABS) using a tailored high power diode-laser optical fiber coupled system

NASA Astrophysics Data System (ADS)

Rodríguez-Vidal, E.; Quintana, I.; Etxarri, J.; Otaduy, D.; González, F.; Moreno, F.

2012-06-01

Laser transmission welding (LTW) of polymers is a direct bonding technique which is already used in different industrial applications sectors such as automobile, microfluidic, electronic and biomedicine. This technique offers several advantages over conventional methods, especially when a local deposition of energy and minimum thermal distortions are required. In LTW one of the polymeric materials needs to be transparent to the laser wavelength and the second part needs to be designed to be absorbed in IR spectrum. This report presents a study of laser weldability of ABS (acrylonitrile/butadiene/styrene) filled with two different concentrations of carbon nanotubes (0.01% and 0.05% CNTs). These additives are used as infrared absorbing components in the laser welding process, affecting the thermal and optical properties of the material and, hence, the final quality of the weld seam. A tailored laser system has been designed to obtain high quality weld seams with widths between 0.4 and 1.0mm. It consists of two diode laser bars (50W per bar) coupled into an optical fiber using a non-imaging solution: equalization of the beam quality factor (M2) in the slow and fast axes by a pair of micro step-mirrors. The beam quality factor has been analyzed at different laser powers with the aim to guarantee a coupling efficiency to the multimode optical fiber. The power scaling is carried out by means of multiplexing polarization technique. The analysis of energy balance and beam quality is performed in two linked steps: first by means ray tracing simulations (ZEMAX®) and second, by validation. Quality of the weld seams is analyzed in terms of the process parameters (welding speed, laser power and clamping pressure) by visual and optical microscope inspections. The optimum laser power range for three different welding speeds is determinate meanwhile the clamping pressure is held constant. Additionally, the corresponding mechanical shear tests were carried out to analyze the mechanical properties of the weld seams. This work provides a detailed study concerning the effect of the material microstructure and laser beam quality on the final weld formation and surface integrity.

POCIT portable optical communicators: VideoBeam and EtherBeam

NASA Astrophysics Data System (ADS)

Mecherle, G. Stephen; Holcomb, Terry L.

1999-12-01

LDSC is developing the POCITTM (Portable Optical Communication Integrated Transceiver) family of products which now includes VideoBeamTM and the latest addition, EtherBeamTM. Each is a full duplex portable laser communicator: VideoBeamTM providing near-broadcast- quality analog video and stereo audio, and EtherBeamTM providing standard Ethernet connectivity. Each POCITTM transceiver consists of a 3.5-pound unit with a binocular- type form factor, which can be manually pointed, tripod- mounted or gyro-stabilized. Both units have an operational range of over two miles (clear air) with excellent jam- resistance and low probability of interception characteristics. The transmission wavelength of 1550 nm enables Class I eyesafe operation (ANSI, IEC). The POCITTM units are ideally suited for numerous miliary scenarios, surveillance/espionage, industrial precious mineral exploration, and campus video teleconferencing applications.

Hidden symmetry and nonlinear paraxial atom optics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Impens, Francois

2009-12-15

A hidden symmetry of the nonlinear wave equation is exploited to analyze the propagation of paraxial and uniform atom-laser beams in time-independent and quadratic transverse potentials with cylindrical symmetry. The quality factor and the paraxial ABCD formalism are generalized to account exactly for mean-field interaction effects in such beams. Using an approach based on moments, these theoretical tools provide a simple yet exact picture of the interacting beam profile evolution. Guided atom laser experiments are discussed. This treatment addresses simultaneously optical and atomic beams in a unified manner, exploiting the formal analogy between nonlinear optics, nonlinear paraxial atom optics, andmore » the physics of two-dimensional Bose-Einstein condensates.« less

An investigation of the operating characteristics of two PTW diamond detectors in photon and electron beams.

PubMed

De Angelis, C; Onori, S; Pacilio, M; Cirrone, G A P; Cuttone, G; Raffaele, L; Bucciolini, M; Mazzocchi, S

2002-02-01

The dosimetric properties of two PTW Riga diamond detectors type 60003 were studied in high-energy photon and electron therapy beam. Properties under study were current-voltage characteristic, polarization effect, time stability of response, dose response, dose-rate dependence, temperature stability, and beam quality dependence of the sensitivity factor. Differences were shown between the two detectors for most of the previous properties. Also, the observed behavior was, to some extent, different from what was reported in the PTW technical specifications. The necessity to characterize each diamond detector individually was addressed.

Low-Loss Superconducting Nanowire Circuits Using a Neon Focused Ion Beam

NASA Astrophysics Data System (ADS)

Burnett, J.; Sagar, J.; Kennedy, O. W.; Warburton, P. A.; Fenton, J. C.

2017-07-01

We present low-temperature measurements of low-loss superconducting nanowire-embedded resonators in the low-power limit relevant for quantum circuits. The superconducting resonators are embedded with superconducting nanowires with widths down to 20 nm using a neon focused ion beam. In the low-power limit, we demonstrate an internal quality factor up to 3.9 ×105 at 300 mK [implying a two-level-system-limited quality factor up to 2 ×105 at 10 mK], not only significantly higher than in similar devices but also matching the state of the art of conventional Josephson-junction-embedded resonators. We also show a high sensitivity of the nanowire to stray infrared photons, which is controllable by suitable precautions to minimize stray photons in the sample environment. Our results suggest that there are excellent prospects for superconducting-nanowire-based quantum circuits.

A laser beam quality definition based on induced temperature rise.

PubMed

Miller, Harold C

2012-12-17

Laser beam quality metrics like M(2) can be used to describe the spot sizes and propagation behavior of a wide variety of non-ideal laser beams. However, for beams that have been diffracted by limiting apertures in the near-field, or those with unusual near-field profiles, the conventional metrics can lead to an inconsistent or incomplete description of far-field performance. This paper motivates an alternative laser beam quality definition that can be used with any beam. The approach uses a consideration of the intrinsic ability of a laser beam profile to heat a material. Comparisons are made with conventional beam quality metrics. An analysis on an asymmetric Gaussian beam is used to establish a connection with the invariant beam propagation ratio.

Navy Shipboard Lasers for Surface, Air, and Missile Defense: Background and Issues for Congress

DTIC Science & Technology

2012-10-19

quality (BQ) is a measure of how well focused the beam is.17 Additional factors affecting a laser’s ability to disable a target include: • atmospheric ...and turbulence , suitable for use to evaluate notional maritime beam director subsystems, and shall include studies in adaptive optics for improved...terms of atmospheric transmission to permit the laser to disable targets of interest at tactically useful ranges, and that development work is

Optimization of Selective Laser Melting by Evaluation Method of Multiple Quality Characteristics

NASA Astrophysics Data System (ADS)

Khaimovich, A. I.; Stepanenko, I. S.; Smelov, V. G.

2018-01-01

Article describes the adoption of the Taguchi method in selective laser melting process of sector of combustion chamber by numerical and natural experiments for achieving minimum temperature deformation. The aim was to produce a quality part with minimum amount of numeric experiments. For the study, the following optimization parameters (independent factors) were chosen: the laser beam power and velocity; two factors for compensating the effect of the residual thermal stresses: the scale factor of the preliminary correction of the part geometry and the number of additional reinforcing elements. We used an orthogonal plan of 9 experiments with a factor variation at three levels (L9). As quality criterias, the values of distortions for 9 zones of the combustion chamber and the maximum strength of the material of the chamber were chosen. Since the quality parameters are multidirectional, a grey relational analysis was used to solve the optimization problem for multiple quality parameters. As a result, according to the parameters obtained, the combustion chamber segments of the gas turbine engine were manufactured.

On a silicon-based photonic-crystal cavity for the near-IR region: Numerical simulation and formation technology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Serafimovich, P. G.; Stepikhova, M. V., E-mail: mst@ipm.sci-nnov.ru; Kazanskiy, N. L.

2016-08-15

The production technology of a photonic-crystal cavity formed as a group of holes in a silicon strip waveguide by ion-beam etching is described. The parasitic effect associated with hole conicity which develops upon hole formation by the given technology is studied. Numerical simulation shows that the hole-conicity induced decrease in the cavity quality factor can be compensated with consideration for the hole volume. The influence of the waveguide thickness on the resonance wavelength and quality factor of the photonic-crystal cavity is analyzed.

Influence of detector collimation and beam pitch for identification and image quality of ground-glass attenuation and nodules on 16- and 64-detector row CT systems: experimental study using chest phantom.

PubMed

Ohno, Yoshiharu; Koyama, Hisanobu; Kono, Astushi; Terada, Mari; Inokawa, Hiroyasu; Matsumoto, Sumiaki; Sugimura, Kazuro

2007-12-01

The purpose of the present study was to determine the influence of detector collimation and beam pitch for identification and image quality of ground-glass attenuation (GGA) and nodules on 16- and 64-detector row CTs, by using a commercially available chest phantom. A chest CT phantom including simulated GGAs and nodules was scanned with different detector collimations, beam pitches and tube currents. The probability and image quality of each simulated abnormality was visually assessed with a five-point scoring system. ROC-analysis and ANOVA were then performed to compare the identification and image quality of either protocol with standard values. Detection rates of low-dose CTs were significantly reduced when tube currents were set at 40mA or less by using detector collimation 16 and 64x0.5mm and 16 and 32mmx1.0mm for low pitch, and at 100mA or less by using detector collimation 16 and 64x0.5mm and 16 and 32mmx1.0mm for high pitch (p<0.05). Image qualities of low-dose CTs deteriorated significantly when tube current was set at 100mA or less by using detector collimation 16 and 64x0.5mm and 16 and 32x1.0mm for low pitch, and at 150mA or less by using detector collimation 16 and 64x0.5mm and 16 and 32x1.0mm for high pitch (p<0.05). Detector collimation and beam pitch were important factors for the image quality and identification of GGA and nodules by 16- and 64-detector row CT.

Design of experiments in medical physics: Application to the AAA beam model validation.

PubMed

Dufreneix, S; Legrand, C; Di Bartolo, C; Bremaud, M; Mesgouez, J; Tiplica, T; Autret, D

2017-09-01

The purpose of this study is to evaluate the usefulness of the design of experiments in the analysis of multiparametric problems related to the quality assurance in radiotherapy. The main motivation is to use this statistical method to optimize the quality assurance processes in the validation of beam models. Considering the Varian Eclipse system, eight parameters with several levels were selected: energy, MLC, depth, X, Y 1 and Y 2 jaw dimensions, wedge and wedge jaw. A Taguchi table was used to define 72 validation tests. Measurements were conducted in water using a CC04 on a TrueBeam STx, a TrueBeam Tx, a Trilogy and a 2300IX accelerator matched by the vendor. Dose was computed using the AAA algorithm. The same raw data was used for all accelerators during the beam modelling. The mean difference between computed and measured doses was 0.1±0.5% for all beams and all accelerators with a maximum difference of 2.4% (under the 3% tolerance level). For all beams, the measured doses were within 0.6% for all accelerators. The energy was found to be an influencing parameter but the deviations observed were smaller than 1% and not considered clinically significant. Designs of experiment can help define the optimal measurement set to validate a beam model. The proposed method can be used to identify the prognostic factors of dose accuracy. The beam models were validated for the 4 accelerators which were found dosimetrically equivalent even though the accelerator characteristics differ. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

A high-quality factor of 267 000 micromechanical silicon resonator utilizing TED-free torsional vibration mode

NASA Astrophysics Data System (ADS)

Nakamura, K.; Naito, Y.; Onishi, K.; Kawakatsu, H.

2012-12-01

In industrial applications of a micromechanical silicon resonator as a physical sensor, a high-quality factor Q and a low-temperature coefficient of Q (TCQ) are required for high sensitivity in a wide temperature range. Although the newly developed thin film encapsulation technique enables a beam to operate with low viscous damping in a vacuum cavity, the Q of a flexural vibration mode is limited by thermo-elastic damping (TED). We proposed a torsional beam resonator which features both a high Q and a low TCQ because theoretically the torsional vibration mode does not suffer from TED. From experiments, Q of 267 000 and TCQ of 1.4 for the 20 MHz torsional vibration mode were observed which were superior to those of the flexural mode. The pressure of the residual gas in the cavity of only 20 pl volume, which is one of the energy loss factors limiting the Q, was successfully estimated to be 1-14 Pa. Finally, the possibilities of improving the Q and the difference of the measured TCQ from a theoretical value were discussed.

Joint Services Electronics Program: Electronics Research at the University of Texas at Austin

DTIC Science & Technology

1990-12-31

large area 2-dimensional phased arrays , and improved beam qualities . This device structure is expected to impact laser technology over a wide range...energy. In the following pages we report on two significant accomplishments. The first involves the influence oi mirror-quantum well optical coupling on... intensity enhancements in the normal direction to the mirror of a 24 (Research Unit SSE89-1, "Growth of Ill-V Compounds by Molecular Beam Epitaxy") factor of

Concept and properties of an infrared hybrid single-beam spectrum and its application to eliminate solvent bands and other background interferences.

PubMed

Chen, Yujing; Wang, Hai-Shui; Morisawa, Yusuke; Ozaki, Yukihiro

2014-02-01

For infrared (IR) spectral measurements, if a quality single-beam background spectrum with desired intensity could be obtained, the contributions from solvent and other background components could be completely suppressed and their bands would not appear in a final transmittance/absorbance spectrum. In order to achieve this ideal but difficult goal, the concept of hybrid single-beam spectrum is introduced in this paper. The hybrid single-beam spectrum (φ h) is defined as a mixture of two single-beam spectra (φ b1 and φ b2) of the same sample but with different pathlengths (b1 and b2), namely, φ h = αφ b1+(1-α)φ b2, where α (0 ≤ α ≤ 1) is the component factor. The properties of the hybrid spectrum have been investigated. Under conditions of b2 > b1 ≥ 0.7 b2 and A max ≤ 0.60 (Amax is the maximum absorbance of b2 sample in the spectral range of interest), all the synthesized hybrid spectra are free from significant distortion regardless of the component factor. Therefore, the hybrid single-beam spectrum with desired intensity can be easily obtained simply by choosing an appropriate component factor. The proposed methodology has been demonstrated experimentally by the complete removal of the interference from the atmospheric water vapor and solvent. © 2013 Elsevier B.V. All rights reserved.

10 kHz ps 1342 nm laser generation by an electro-optically cavity-dumped mode-locked Nd:YVO4 laser

NASA Astrophysics Data System (ADS)

Chen, Ying; Liu, Ke; He, Li-jiao; Yang, Jing; Zong, Nan; Yang, Feng; Gao, Hong-wei; Liu, Zhao; Yuan, Lei; Lan, Ying-jie; Bo, Yong; Peng, Qin-jun; Cui, Da-fu; Xu, Zu-yan

2017-01-01

We have demonstrated an electro-optically cavity-dumped mode-locked (CDML) picosecond Nd:YVO4 laser at 1342 nm with 880 nm diode-laser direct pumping. At a repetition rate of 10 kHz, an average output power of 0.119 W was achieved, corresponding to a pulse energy of 11.9 μJ. Compared with the continuous wave mode-locking pulse energy of 17.5 nJ, the CDML pulse energy was 680 times higher. The pulse width was measured to be 33.4 ps, resulting in the peak power of 356 kW. Meanwhile, the beam quality was nearly diffraction limited with an average beam quality factor M2 of 1.29.

High pumping-power fiber combiner for double-cladding fiber lasers and amplifiers

NASA Astrophysics Data System (ADS)

Zheng, Jinkun; Zhao, Wei; Zhao, Baoyin; Li, Zhe; Chang, Chang; Li, Gang; Gao, Qi; Ju, Pei; Gao, Wei; She, Shengfei; Wu, Peng; Hou, Chaoqi; Li, Weinan

2018-03-01

A high pumping-power fiber combiner for backward pumping configurations is fabricated and demonstrated by manufacturing process refinement. The pump power handling capability of every pump fiber can extend to 600 W, corresponding to the average pump coupling efficiency of 94.83%. Totally, 2.67-kW output power with the beam quality factor M2 of 1.41 was obtained, using this combiner in the fiber amplifier experimental setup. In addition, the temperature of the splicing region was less than 50.0°C in the designed combiner under the action of circulating cooling water. The experimental results prove that the designed combiner is a promising integrated all-fiber device for multikilowatt continuous-wave fiber laser with excellent beam quality.

PTW-diamond detector: dose rate and particle type dependence.

PubMed

Fidanzio, A; Azario, L; Miceli, R; Russo, A; Piermattei, A

2000-11-01

In this paper the suitability of a PTW natural diamond detector (DD) for relative and reference dosimetry of photon and electron beams, with dose per pulse between 0.068 mGy and 0.472 mGy, was studied and the results were compared with those obtained by a stereotactic silicon detector (SFD). The results show that, in the range of the examined dose per pulse the DD sensitivity changes up to 1.8% while the SFD sensitivity changes up to 4.5%. The fitting parameter, delta, used to correct the dose per pulse dependence of solid state detectors, was delta = 0.993 +/- 0.002 and delta = 1.025 +/- 0.002 for the diamond detector and for the silicon diode, respectively. The delta values were found to be independent of particle type of two conventional beams (a 10 MV x-ray beam and a 21 MeV electron beam). So if delta is determined for a radiotherapy beam, it can be used to correct relative dosimetry for other conventional radiotherapy beams. Moreover the diamond detector shows a calibration factor which is independent of beam quality and particle type, so an empirical dosimetric formalism is proposed here to obtain the reference dosimetry. This formalism is based on a dose-to-water calibration factor and on an empirical coefficient, that takes into account the reading dependence on the dose per pulse.

The perturbation correction factors for cylindrical ionization chambers in high-energy photon beams.

PubMed

Yoshiyama, Fumiaki; Araki, Fujio; Ono, Takeshi

2010-07-01

In this study, we calculated perturbation correction factors for cylindrical ionization chambers in high-energy photon beams by using Monte Carlo simulations. We modeled four Farmer-type cylindrical chambers with the EGSnrc/Cavity code and calculated the cavity or electron fluence correction factor, P (cav), the displacement correction factor, P (dis), the wall correction factor, P (wall), the stem correction factor, P (stem), the central electrode correction factor, P (cel), and the overall perturbation correction factor, P (Q). The calculated P (dis) values for PTW30010/30013 chambers were 0.9967 +/- 0.0017, 0.9983 +/- 0.0019, and 0.9980 +/- 0.0019, respectively, for (60)Co, 4 MV, and 10 MV photon beams. The value for a (60)Co beam was about 1.0% higher than the 0.988 value recommended by the IAEA TRS-398 protocol. The P (dis) values had a substantial discrepancy compared to those of IAEA TRS-398 and AAPM TG-51 at all photon energies. The P (wall) values were from 0.9994 +/- 0.0020 to 1.0031 +/- 0.0020 for PTW30010 and from 0.9961 +/- 0.0018 to 0.9991 +/- 0.0017 for PTW30011/30012, in the range of (60)Co-10 MV. The P (wall) values for PTW30011/30012 were around 0.3% lower than those of the IAEA TRS-398. Also, the chamber response with and without a 1 mm PMMA water-proofing sleeve agreed within their combined uncertainty. The calculated P (stem) values ranged from 0.9945 +/- 0.0014 to 0.9965 +/- 0.0014, but they are not considered in current dosimetry protocols. The values were no significant difference on beam qualities. P (cel) for a 1 mm aluminum electrode agreed within 0.3% with that of IAEA TRS-398. The overall perturbation factors agreed within 0.4% with those for IAEA TRS-398.

Modeling of the laser beam shape for high-power applications

NASA Astrophysics Data System (ADS)

Jabczyński, Jan K.; Kaskow, Mateusz; Gorajek, Lukasz; Kopczyński, Krzysztof; Zendzian, Waldemar

2018-04-01

Aperture losses and thermo-optic effects (TOE) inside optics as well as the effective beam width in far field should be taken into account in the analysis of the most appropriate laser beam profile for high-power applications. We have theoretically analyzed such a problem for a group of super-Gaussian beams taking first only diffraction limitations. Furthermore, we have investigated TOE on far-field parameters of such beams to determine the influence of absorption in optical elements on beam quality degradation. The best compromise gives the super-Gaussian profile of index p = 5, for which beam quality does not decrease noticeably and the thermo-optic higher order aberrations are compensated. The simplified formulas were derived for beam quality metrics (parameter M2 and Strehl ratio), which enable estimation of the influence of heat deposited in optics on degradation of beam quality. The method of dynamic compensation of such effect was proposed.

Investigating output and energy variations and their relationship to delivery QA results using Statistical Process Control for helical tomotherapy.

PubMed

Binny, Diana; Mezzenga, Emilio; Lancaster, Craig M; Trapp, Jamie V; Kairn, Tanya; Crowe, Scott B

2017-06-01

The aims of this study were to investigate machine beam parameters using the TomoTherapy quality assurance (TQA) tool, establish a correlation to patient delivery quality assurance results and to evaluate the relationship between energy variations detected using different TQA modules. TQA daily measurement results from two treatment machines for periods of up to 4years were acquired. Analyses of beam quality, helical and static output variations were made. Variations from planned dose were also analysed using Statistical Process Control (SPC) technique and their relationship to output trends were studied. Energy variations appeared to be one of the contributing factors to delivery output dose seen in the analysis. Ion chamber measurements were reliable indicators of energy and output variations and were linear with patient dose verifications. Crown Copyright © 2017. Published by Elsevier Ltd. All rights reserved.

Accelerating an Ordered-Subset Low-Dose X-Ray Cone Beam Computed Tomography Image Reconstruction with a Power Factor and Total Variation Minimization.

PubMed

Huang, Hsuan-Ming; Hsiao, Ing-Tsung

2016-01-01

In recent years, there has been increased interest in low-dose X-ray cone beam computed tomography (CBCT) in many fields, including dentistry, guided radiotherapy and small animal imaging. Despite reducing the radiation dose, low-dose CBCT has not gained widespread acceptance in routine clinical practice. In addition to performing more evaluation studies, developing a fast and high-quality reconstruction algorithm is required. In this work, we propose an iterative reconstruction method that accelerates ordered-subsets (OS) reconstruction using a power factor. Furthermore, we combine it with the total-variation (TV) minimization method. Both simulation and phantom studies were conducted to evaluate the performance of the proposed method. Results show that the proposed method can accelerate conventional OS methods, greatly increase the convergence speed in early iterations. Moreover, applying the TV minimization to the power acceleration scheme can further improve the image quality while preserving the fast convergence rate.

Accelerating an Ordered-Subset Low-Dose X-Ray Cone Beam Computed Tomography Image Reconstruction with a Power Factor and Total Variation Minimization

PubMed Central

Huang, Hsuan-Ming; Hsiao, Ing-Tsung

2016-01-01

In recent years, there has been increased interest in low-dose X-ray cone beam computed tomography (CBCT) in many fields, including dentistry, guided radiotherapy and small animal imaging. Despite reducing the radiation dose, low-dose CBCT has not gained widespread acceptance in routine clinical practice. In addition to performing more evaluation studies, developing a fast and high-quality reconstruction algorithm is required. In this work, we propose an iterative reconstruction method that accelerates ordered-subsets (OS) reconstruction using a power factor. Furthermore, we combine it with the total-variation (TV) minimization method. Both simulation and phantom studies were conducted to evaluate the performance of the proposed method. Results show that the proposed method can accelerate conventional OS methods, greatly increase the convergence speed in early iterations. Moreover, applying the TV minimization to the power acceleration scheme can further improve the image quality while preserving the fast convergence rate. PMID:27073853

Beam quality management by periodic reproduction of wavefront aberrations in end-pumped Nd:YVO₄ laser amplifiers.

PubMed

Liu, Bin; Liu, Chong; Shen, Lifeng; Wang, Chunhua; Ye, Zhibin; Liu, Dong; Xiang, Zhen

2016-04-18

A method for beam quality management is presented in a master oscillator power amplifier (MOPA) using Nd:YVO₄ as the gain medium by extra-cavity periodic reproduction of wavefront aberrations. The wavefront aberration evolution of the intra-cavity beams is investigated for both symmetrical and asymmetrical resonators. The wavefront aberration reproduction process is successfully realized outside the cavity in four-stage amplifiers. In the MOPA with a symmetrical oscillator, the laser power increases linearly and the beam quality hardly changes. In the MOPA with an asymmetrical oscillator, the beam quality is deteriorated after the odd-stage amplifier and is improved after the even-stage amplifier. The wavefront aberration reproduction during the extra-cavity beam propagation in the amplifiers is equivalent to that during the intra-cavity propagation. This solution helps to achieve the effective beam quality management in laser amplifier chains.

Laser Beam and Resonator Calculations on Desktop Computers.

NASA Astrophysics Data System (ADS)

Doumont, Jean-Luc

There is a continuing interest in the design and calculation of laser resonators and optical beam propagation. In particular, recently, interest has increased in developing concepts such as one-sided unstable resonators, supergaussian reflectivity profiles, diode laser modes, beam quality concepts, mode competition, excess noise factors, and nonlinear Kerr lenses. To meet these calculation needs, I developed a general-purpose software package named PARAXIA ^{rm TM}, aimed at providing optical scientists and engineers with a set of powerful design and analysis tools that provide rapid and accurate results and are extremely easy to use. PARAXIA can handle separable paraxial optical systems in cartesian or cylindrical coordinates, including complex-valued and misaligned ray matrices, with full diffraction effects between apertures. It includes the following programs:. ABCD provides complex-valued ray-matrix and gaussian -mode analyses for arbitrary paraxial resonators and optical systems, including astigmatism and misalignment in each element. This program required that I generalize the theory of gaussian beam propagation to the case of an off-axis gaussian beam propagating through a misaligned, complex -valued ray matrix. FRESNEL uses FFT and FHT methods to propagate an arbitrary wavefront through an arbitrary paraxial optical system using Huygens' integral in rectangular or radial coordinates. The wavefront can be multiplied by an arbitrary mirror profile and/or saturable gain sheet on each successive propagation through the system. I used FRESNEL to design a one-sided negative-branch unstable resonator for a free -electron laser, and to show how a variable internal aperture influences the mode competition and beam quality in a stable cavity. VSOURCE implements the virtual source analysis to calculate eigenvalues and eigenmodes for unstable resonators with both circular and rectangular hard-edged mirrors (including misaligned rectangular systems). I used VSOURCE to show the validity of the virtual source approach (by comparing its results to those of FRESNEL), to study the properties of hard-edged unstable resonators, and to obtain numerical values of the excess noise factors in such resonators. VRM carries out mode calculations for gaussian variable-reflectivity-mirror lasers. It implements complicated analytical results that I derived to point out the large numerical value of the excess noise factor in geometrically unstable resonators.

Coherent X-ray beam metrology using 2D high-resolution Fresnel-diffraction analysis.

PubMed

Ruiz-Lopez, M; Faenov, A; Pikuz, T; Ozaki, N; Mitrofanov, A; Albertazzi, B; Hartley, N; Matsuoka, T; Ochante, Y; Tange, Y; Yabuuchi, T; Habara, T; Tanaka, K A; Inubushi, Y; Yabashi, M; Nishikino, M; Kawachi, T; Pikuz, S; Ishikawa, T; Kodama, R; Bleiner, D

2017-01-01

Direct metrology of coherent short-wavelength beamlines is important for obtaining operational beam characteristics at the experimental site. However, since beam-time limitation imposes fast metrology procedures, a multi-parametric metrology from as low as a single shot is desirable. Here a two-dimensional (2D) procedure based on high-resolution Fresnel diffraction analysis is discussed and applied, which allowed an efficient and detailed beamline characterization at the SACLA XFEL. So far, the potential of Fresnel diffraction for beamline metrology has not been fully exploited because its high-frequency fringes could be only partly resolved with ordinary pixel-limited detectors. Using the high-spatial-frequency imaging capability of an irradiated LiF crystal, 2D information of the coherence degree, beam divergence and beam quality factor M 2 were retrieved from simple diffraction patterns. The developed beam metrology was validated with a laboratory reference laser, and then successfully applied at a beamline facility, in agreement with the source specifications.

Visualization of the influence of the air conditioning system to the high-power laser beam quality with the modulation coherent imaging method.

PubMed

Tao, Hua; Veetil, Suhas P; Pan, Xingchen; Liu, Cheng; Zhu, Jianqiang

2015-08-01

Air conditioning systems can lead to dynamic phase change in the laser beams of high-power laser facilities for the inertial confinement fusion, and this kind of phase change cannot be measured by most of the commonly employed Hartmann wavefront sensor or interferometry due to some uncontrollable factors, such as too large laser beam diameters and the limited space of the facility. It is demonstrated that this problem can be solved using a scheme based on modulation coherent imaging, and thus the influence of the air conditioning system on the performance of the high-power facility can be evaluated directly.

High-pulse energy Q-switched Tm3+:YAG laser for nonlinear frequency conversion to the mid-IR

NASA Astrophysics Data System (ADS)

Stöppler, Georg; Kieleck, Christelle; Eichhorn, Marc

2010-10-01

For some medical fields in laser surgery and as a pump source for nonlinear materials to generate mid-IR radiation, e.g. for countermeasure applications, it is very useful to have a solid-state laser with high pulse energy at 2 μm. The rare earth ion Thulium offers a cross relaxation and can thus be directly diode pumped with common laser diodes around 800 nm for an efficient pumping. However, it was not considered for high pulse energy operation due to the high saturation fluence of around 62 J/cm2 at 2 μm. A limiting factor has always been the damage threshold of the optical elements inside the cavity. One of the reasons is the strong thermal lens of YAG, which affects a change of the beam radius inside the resonator and additionally degrades the beam quality with increasing pump power. Using a new pump geometry of the Tm3+:YAG laser system, it is now possible to reach pulse energies > 13 mJ at a diffraction limited beam quality of M2 < 1.1. The Q-switched Tm3+:YAG laser system uses an AOM operating at 100 Hz and will be described in detail. Due to the high pulse energy and very good beam quality, this laser is very interesting for nonlinear parametric frequency conversion.

Image quality in thoracic 4D cone-beam CT: A sensitivity analysis of respiratory signal, binning method, reconstruction algorithm, and projection angular spacing

PubMed Central

Shieh, Chun-Chien; Kipritidis, John; O’Brien, Ricky T.; Kuncic, Zdenka; Keall, Paul J.

2014-01-01

Purpose: Respiratory signal, binning method, and reconstruction algorithm are three major controllable factors affecting image quality in thoracic 4D cone-beam CT (4D-CBCT), which is widely used in image guided radiotherapy (IGRT). Previous studies have investigated each of these factors individually, but no integrated sensitivity analysis has been performed. In addition, projection angular spacing is also a key factor in reconstruction, but how it affects image quality is not obvious. An investigation of the impacts of these four factors on image quality can help determine the most effective strategy in improving 4D-CBCT for IGRT. Methods: Fourteen 4D-CBCT patient projection datasets with various respiratory motion features were reconstructed with the following controllable factors: (i) respiratory signal (real-time position management, projection image intensity analysis, or fiducial marker tracking), (ii) binning method (phase, displacement, or equal-projection-density displacement binning), and (iii) reconstruction algorithm [Feldkamp–Davis–Kress (FDK), McKinnon–Bates (MKB), or adaptive-steepest-descent projection-onto-convex-sets (ASD-POCS)]. The image quality was quantified using signal-to-noise ratio (SNR), contrast-to-noise ratio, and edge-response width in order to assess noise/streaking and blur. The SNR values were also analyzed with respect to the maximum, mean, and root-mean-squared-error (RMSE) projection angular spacing to investigate how projection angular spacing affects image quality. Results: The choice of respiratory signals was found to have no significant impact on image quality. Displacement-based binning was found to be less prone to motion artifacts compared to phase binning in more than half of the cases, but was shown to suffer from large interbin image quality variation and large projection angular gaps. Both MKB and ASD-POCS resulted in noticeably improved image quality almost 100% of the time relative to FDK. In addition, SNR values were found to increase with decreasing RMSE values of projection angular gaps with strong correlations (r ≈ −0.7) regardless of the reconstruction algorithm used. Conclusions: Based on the authors’ results, displacement-based binning methods, better reconstruction algorithms, and the acquisition of even projection angular views are the most important factors to consider for improving thoracic 4D-CBCT image quality. In view of the practical issues with displacement-based binning and the fact that projection angular spacing is not currently directly controllable, development of better reconstruction algorithms represents the most effective strategy for improving image quality in thoracic 4D-CBCT for IGRT applications at the current stage. PMID:24694143

Highly Efficient Small Form Factor LED Retrofit Lamp

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steven Allen; Fred Palmer; Ming Li

2011-09-11

This report summarizes work to develop a high efficiency LED-based MR16 lamp downlight at OSRAM SYLVANIA under US Department of Energy contract DE-EE0000611. A new multichip LED package, electronic driver, and reflector optic were developed for these lamps. At steady-state, the lamp luminous flux was 409 lumens (lm), luminous efficacy of 87 lumens per watt (LPW), CRI (Ra) of 87, and R9 of 85 at a correlated color temperature (CCT) of 3285K. The LED alone achieved 120 lumens per watt efficacy and 600 lumen flux output at 25 C. The driver had 90% electrical conversion efficiency while maintaining excellent powermore » quality with power factor >0.90 at a power of only 5 watts. Compared to similar existing MR16 lamps using LED sources, these lamps had much higher efficacy and color quality. The objective of this work was to demonstrate a LED-based MR16 retrofit lamp for replacement of 35W halogen MR16 lamps having (1) luminous flux of 500 lumens, (2) luminous efficacy of 100 lumens per watt, (3) beam angle less than 40{sup o} and center beam candlepower of at least 1000 candelas, and (4) excellent color quality.« less

Average intensity and beam quality of optical coherence lattices in oceanic turbulence with anisotropy.

PubMed

Huang, Xianwei; Deng, Zhixiang; Shi, Xiaohui; Bai, Yanfeng; Fu, Xiquan

2018-02-19

Based on the extended Huygens-Fresnel principle, we have derived the analytical expression of the average intensity of optical coherence lattices (OCLs) in oceanic turbulence with anisotropy, and then the beam quality parameters including the Strehl ratio (SR) and the power-in-the-bucket (PIB) are obtained. One can find that the OCLs will eventually evolve into Gaussian shape with the periodicity reciprocity gradually breaking down when propagating through the anisotropic ocean water, and that the trend of evolving into Gaussian can be accelerated for increasing the ratio of temperature and salinity contributions to the refractive index spectrum ω, the lattice constant a and the rate of dissipation of mean square temperature χT or decreasing the anisotropic factor ξ and the rate of dissipation of turbulent kinetic energy per unit mass of fluid ε. Further, the SR and PIB in the target plane under the effects of oceanic parameters are discussed in detail, and the SR and PIB can be increased for the larger ξ and ε or the smaller χT and ω, namely, the beam quality becomes better. Our results can find potential application in the future optical communication system in an oceanic environment.

Lorenz curve of a light beam: evaluating beam quality from a majorization perspective.

PubMed

Porras, Miguel A; Gonzalo, Isabel; Ahmir Malik, M

2017-08-01

We introduce a novel approach for the characterization of the quality of a laser beam that is not based on particular criteria for beam width definition. The Lorenz curve of a light beam is a sophisticated version of the so-called power-in-the-bucket curve, formed by the partial sums of discretized joint intensity distribution in the near and far fields, sorted in decreasing order. According to majorization theory, a higher Lorenz curve implies that all measures of spreading in phase space, and, in particular, all Rényi (and Shannon) entropy-based measures of the beam width products in near and far fields, are unanimously smaller, providing a strong assessment of a better beam quality. Two beams whose Lorenz curves intersect can be considered of relatively better or lower quality only according to specific criteria, which can be inferred from the plot of the respective Lorenz curves.

Analysis of optical scheme for medium-range directed energy laser weapon system

NASA Astrophysics Data System (ADS)

Jabczyński, Jan K.; Kaśków, Mateusz; Gorajek, Łukasz; Kopczyński, Krzysztof

2017-10-01

The relations between range of operation and aperture of laser weapon system were investigated, taking into account diffraction and technical limitations as beam quality, accuracy of point tracking, technical quality of optical train, etc. As a result for the medium ranges of 1 - 2 km we restricted the analysis to apertures not wider than 150 mm and the optical system without adaptive optics. To choose the best laser beam shape, the minimization of aperture losses and thermooptical effects inside optics as well as the effective width of laser beam in far field should be taken into account. We have analyzed theoretically such a problem for the group of a few most interesting from that point of view profiles including for reference two limiting cases of Gaussian beam and `top hat' profile. We have found that the most promising is the SuperGaussian profile of index p = 2 for which the surfaces of beam shaper elements can be manufactured in the acceptable cost-effective way and beam quality does not decrease noticeably. Further, we have investigated the thermo-optic effects on the far field parameters of Gaussian and `top hat' beams to determine the influence of absorption in optical elements on beam quality degradation. The simplified formulae were derived for beam quality measures (parameter M2 and Strehl ratio) which enables to estimate the influence of absorption losses on degradation of beam quality.

Dose distribution for dental cone beam CT and its implication for defining a dose index

PubMed Central

Pauwels, R; Theodorakou, C; Walker, A; Bosmans, H; Jacobs, R; Horner, K; Bogaerts, R

2012-01-01

Objectives To characterize the dose distribution for a range of cone beam CT (CBCT) units, investigating different field of view sizes, central and off-axis geometries, full or partial rotations of the X-ray tube and different clinically applied beam qualities. The implications of the dose distributions on the definition and practicality of a CBCT dose index were assessed. Methods Dose measurements on CBCT devices were performed by scanning cylindrical head-size water and polymethyl methacrylate phantoms, using thermoluminescent dosemeters, a small-volume ion chamber and radiochromic films. Results It was found that the dose distribution can be asymmetrical for dental CBCT exposures throughout a homogeneous phantom, owing to an asymmetrical positioning of the isocentre and/or partial rotation of the X-ray source. Furthermore, the scatter tail along the z-axis was found to have a distinct shape, generally resulting in a strong drop (90%) in absorbed dose outside the primary beam. Conclusions There is no optimal dose index available owing to the complicated exposure geometry of CBCT and the practical aspects of quality control measurements. Practical validation of different possible dose indices is needed, as well as the definition of conversion factors to patient dose. PMID:22752320

Note: High-efficiency broadband acoustic energy harvesting using Helmholtz resonator and dual piezoelectric cantilever beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Aichao; Li, Ping, E-mail: liping@cqu.edu.cn; Wen, Yumei

2014-06-15

A high-efficiency broadband acoustic energy harvester consisting of a compliant-top-plate Helmholtz resonator (HR) and dual piezoelectric cantilever beams is proposed. Due to the high mechanical quality factor of beams and the strong multimode coupling of HR cavity, top plate and beams, the high efficiency in a broad bandwidth is obtained. Experiment exhibits that the proposed harvester at 170–206 Hz has 28–188 times higher efficiency than the conventional harvester using a HR with a piezoelectric composite diaphragm. For input acoustic pressure of 2.0 Pa, the proposed harvester exhibits 0.137–1.43 mW output power corresponding to 0.035–0.36 μW cm{sup −3} volume power density atmore » 170–206 Hz.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Richter, Christian; Pawelke, Joerg; Karsch, Leonhard

Purpose: The aim of this article is to investigate the energy dependence of the radiochromic film type, Gafchromic EBT-1, when scanned with a flatbed scanner for film readout. Methods: Dose response curves were determined for 12 different beam qualities ranging from a 10 kVp x-ray beam to a 15 MVp x-ray beam and include also two high energy electron beam qualities (6 and 18 MeV). The dose responses measured as net optical density (netOD) for the different beam qualities were normalized to the response of a reference beam quality (6 MVp). Results: A strong systematic energy dependence of the filmmore » response was found. The lower the effective beam energy, the less sensitive the EBT-1 films get. The maximum decrease in dose for the same film response between the 25 kVp and 6 MVp beam qualities was 44%. Additionally, a difference in energy dependence for different doses was discovered, meaning that higher doses show a smaller dependency on energy than lower doses. The maximum decrease in the normalized netOD was found to be 25% for a dose of 0.5 Gy relative to the normalized netOD for 10 Gy. Moreover, a scaling procedure is introduced, allowing the correction of the energy dependence for the investigated beam qualities and also for comparable x-ray beam qualities within the energy range studied. Conclusions: A strong energy dependence for EBT-1 radiochromic films was found. The films were readout with a flatbed scanner. If the effective beam energy is known, the energy dependence can be corrected with the introduced scaling procedure. Further investigation of the influence of the spectral band of the readout device on energy dependence is needed to understand the reason for the different energy dependences found in this and previous works.« less

SU-F-T-428: An Optimization-Based Commissioning Tool for Finite Size Pencil Beam Dose Calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Y; Tian, Z; Song, T

Purpose: Finite size pencil beam (FSPB) algorithms are commonly used to pre-calculate the beamlet dose distribution for IMRT treatment planning. FSPB commissioning, which usually requires fine tuning of the FSPB kernel parameters, is crucial to the dose calculation accuracy and hence the plan quality. Yet due to the large number of beamlets, FSPB commissioning could be very tedious. This abstract reports an optimization-based FSPB commissioning tool we have developed in MatLab to facilitate the commissioning. Methods: A FSPB dose kernel generally contains two types of parameters: the profile parameters determining the dose kernel shape, and a 2D scaling factors accountingmore » for the longitudinal and off-axis corrections. The former were fitted using the penumbra of a reference broad beam’s dose profile with Levenberg-Marquardt algorithm. Since the dose distribution of a broad beam is simply a linear superposition of the dose kernel of each beamlet calculated with the fitted profile parameters and scaled using the scaling factors, these factors could be determined by solving an optimization problem which minimizes the discrepancies between the calculated dose of broad beams and the reference dose. Results: We have commissioned a FSPB algorithm for three linac photon beams (6MV, 15MV and 6MVFFF). Dose of four field sizes (6*6cm2, 10*10cm2, 15*15cm2 and 20*20cm2) were calculated and compared with the reference dose exported from Eclipse TPS system. For depth dose curves, the differences are less than 1% of maximum dose after maximum dose depth for most cases. For lateral dose profiles, the differences are less than 2% of central dose at inner-beam regions. The differences of the output factors are within 1% for all the three beams. Conclusion: We have developed an optimization-based commissioning tool for FSPB algorithms to facilitate the commissioning, providing sufficient accuracy of beamlet dose calculation for IMRT optimization.« less

Study on the quality assurance of diagnostic X-ray machines and assessment of the absorbed dose to patients

NASA Astrophysics Data System (ADS)

Hassan, G. M.; Rabie, N.; Mustafa, K. A.; Abdel-Khalik, S. S.

2012-09-01

Radiation exposure and image quality in X-ray diagnostic radiology provide a clear understanding of the relationship between the radiation dose delivered to a patient and image quality in optimizing medical diagnostic radiology. Because a certain amount of radiation is unavoidably delivered to patients, this should be as low as reasonably achievable. Several X-ray diagnostic machines were used at different medical diagnostic centers in Egypt for studying the beam quality and the dose delivered to the patient. This article studies the factors affecting the beam quality, such as the kilo-volt peak (kVp), exposure time (mSc), tube current (mAs) and the absorbed dose in (μGy) for different examinations. The maximum absorbed dose measured per mAs was 594±239 and 12.5±3.7 μGy for the abdomen and the chest, respectively, while the absorbed dose at the elbow was 18±6 μGy, which was the minimum dose recorded. The compound and expanded uncertainties accompanying these measurements were 4±0.35% and 8±0.7%, respectively. The measurements were done through quality control tests as acceptance procedures.

SU-C-304-07: Are Small Field Detector Correction Factors Strongly Dependent On Machine-Specific Characteristics?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mathew, D; Tanny, S; Parsai, E

2015-06-15

Purpose: The current small field dosimetry formalism utilizes quality correction factors to compensate for the difference in detector response relative to dose deposited in water. The correction factors are defined on a machine-specific basis for each beam quality and detector combination. Some research has suggested that the correction factors may only be weakly dependent on machine-to-machine variations, allowing for determinations of class-specific correction factors for various accelerator models. This research examines the differences in small field correction factors for three detectors across two Varian Truebeam accelerators to determine the correction factor dependence on machine-specific characteristics. Methods: Output factors were measuredmore » on two Varian Truebeam accelerators for equivalently tuned 6 MV and 6 FFF beams. Measurements were obtained using a commercial plastic scintillation detector (PSD), two ion chambers, and a diode detector. Measurements were made at a depth of 10 cm with an SSD of 100 cm for jaw-defined field sizes ranging from 3×3 cm{sup 2} to 0.6×0.6 cm{sup 2}, normalized to values at 5×5cm{sup 2}. Correction factors for each field on each machine were calculated as the ratio of the detector response to the PSD response. Percent change of correction factors for the chambers are presented relative to the primary machine. Results: The Exradin A26 demonstrates a difference of 9% for 6×6mm{sup 2} fields in both the 6FFF and 6MV beams. The A16 chamber demonstrates a 5%, and 3% difference in 6FFF and 6MV fields at the same field size respectively. The Edge diode exhibits less than 1.5% difference across both evaluated energies. Field sizes larger than 1.4×1.4cm2 demonstrated less than 1% difference for all detectors. Conclusion: Preliminary results suggest that class-specific correction may not be appropriate for micro-ionization chamber. For diode systems, the correction factor was substantially similar and may be useful for class-specific reference conditions.« less

NOTE: Monte Carlo simulation of correction factors for IAEA TLD holders

NASA Astrophysics Data System (ADS)

Hultqvist, Martha; Fernández-Varea, José M.; Izewska, Joanna

2010-03-01

The IAEA standard thermoluminescent dosimeter (TLD) holder has been developed for the IAEA/WHO TLD postal dose program for audits of high-energy photon beams, and it is also employed by the ESTRO-QUALity assurance network (EQUAL) and several national TLD audit networks. Factors correcting for the influence of the holder on the TL signal under reference conditions have been calculated in the present work from Monte Carlo simulations with the PENELOPE code for 60Co γ-rays and 4, 6, 10, 15, 18 and 25 MV photon beams. The simulation results are around 0.2% smaller than measured factors reported in the literature, but well within the combined standard uncertainties. The present study supports the use of the experimentally obtained holder correction factors in the determination of the absorbed dose to water from the TL readings; the factors calculated by means of Monte Carlo simulations may be adopted for the cases where there are no measured data.

Beam related response of in vivo diode detectors for external radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baci, Syrja, E-mail: sbarci2013@gmail.com; Telhaj, Ervis; Malkaj, Partizan

2016-03-25

In Vivo Dosimetry (IVD) is a set of methods used in cancer treatment clinics to determine the real dose of radiation absorbed by target volume in a patient’s body. IVD has been widely implemented in radiotherapy treatment centers and is now recommended part of Quality Assurance program by many International health and radiation organizations. Because of cost and lack of specialized personnel, IVD has not been practiced as yet, in Albanian radiotherapy clinics. At Hygeia Hospital Tirana, patients are irradiated with high energy photons generated by Elekta Synergy Accelerators. We have recently started experimenting with the purpose of establishing anmore » IVD practice at this hospital. The first set of experiments was aimed at calibration of diodes that are going to be used for IVD. PMMA, phantoms by PTW were used to calibrate p – type Si, semiconductor diode dosimeters, made by PTW Freiburg for entrance dose. Response of the detectors is affected by energy of the beam, accumulated radiation dose, dose rate, temperature, angle against the beam axis, etc. Here we present the work done for calculating calibration factor and correction factors of source to surface distance, field size, and beam incidence for the entrance dose for both 6 MV photon beam and 18 MV photon beam. Dependence of dosimeter response was found to be more pronounced with source to surface distance as compared to other variables investigated.« less

Propagation of rotational Risley-prism-array-based Gaussian beams in turbulent atmosphere

NASA Astrophysics Data System (ADS)

Chen, Feng; Ma, Haotong; Dong, Li; Ren, Ge; Qi, Bo; Tan, Yufeng

2018-03-01

Limited by the size and weight of prism and optical assembling, Rotational Risley-prism-array system is a simple but effective way to realize high power and superior beam quality of deflecting laser output. In this paper, the propagation of the rotational Risley-prism-array-based Gaussian beam array in atmospheric turbulence is studied in detail. An analytical expression for the average intensity distribution at the receiving plane is derived based on nonparaxial ray tracing method and extended Huygens-Fresnel principle. Power in the diffraction-limited bucket is chosen to evaluate beam quality. The effect of deviation angle, propagation distance and intensity of turbulence on beam quality is studied in detail by quantitative simulation. It reveals that with the propagation distance increasing, the intensity distribution gradually evolves from multiple-petal-like shape into the pattern that contains one main-lobe in the center with multiple side-lobes in weak turbulence. The beam quality of rotational Risley-prism-array-based Gaussian beam array with lower deviation angle is better than its counterpart with higher deviation angle when propagating in weak and medium turbulent (i.e. Cn2 < 10-13m-2/3), the beam quality of higher deviation angle arrays degrades faster as the intensity of turbulence gets stronger. In the case of propagating in strong turbulence, the long propagation distance (i.e. z > 10km ) and deviation angle have no influence on beam quality.

Cone Beam CT vs. Fan Beam CT: A Comparison of Image Quality and Dose Delivered Between Two Differing CT Imaging Modalities.

PubMed

Lechuga, Lawrence; Weidlich, Georg A

2016-09-12

A comparison of image quality and dose delivered between two differing computed tomography (CT) imaging modalities-fan beam and cone beam-was performed. A literature review of quantitative analyses for various image quality aspects such as uniformity, signal-to-noise ratio, artifact presence, spatial resolution, modulation transfer function (MTF), and low contrast resolution was generated. With these aspects quantified, cone beam computed tomography (CBCT) shows a superior spatial resolution to that of fan beam, while fan beam shows a greater ability to produce clear and anatomically correct images with better soft tissue differentiation. The results indicate that fan beam CT produces superior images to that of on-board imaging (OBI) cone beam CT systems, while providing a considerably less dose to the patient.

SU-E-T-146: Reference Dosimetry for Protons and Light-Ion Beams Based on Graphite Calorimetry.

PubMed

Rossomme, S; Palmans, H; Thomas, R; Lee, N; Bailey, M; Shipley, D; Al-Sulaiti, L; Cirrone, P; Romano, F; Kacperek, A; Bertrand, D; Vynckier, S

2012-06-01

The IAEA TRS-398 code of practice can be applied for the measurement of absorbed dose to water under reference conditions with an ionization chamber. For protons, the combined relative standard uncertainty on those measurements is less than 2% while for light-ion beams, it is considerably larger, i.e. 3.2%, mainly due to the higher uncertainty contributions for the water to air stopping power ration and the W air-value on the beam quality correction factors kQ,Q 0 . To decrease this uncertainty, a quantification of kQ,Q 0 is proposed using a primary standard level graphite calorimeter. This work includes numerical and experimental determinations of dose conversion factors to derive dose to water from graphite calorimetry. It also reports on the first experimental data obtained with the graphite calorimeter in proton, alpha and carbon ion beams. Firstly, the dose conversion has been calculated with by Geant4 Monte-Carlo simulations through the determination of the water to graphite stopping power ratio and the fluence correction factor. The latter factor was also derived by comparison of measured ionization curves in graphite and water. Secondly, kQ,Q 0 was obtained by comparison of the dose response of ionization chambers with that of the calorimeter. Stopping power ratios are found to vary by no more than 0.35% up to the Bragg peak, while fluence correction factors are shown to increase slightly above unity close to the Bragg peak. The comparison of the calorimeter with ionization chambers is currently under analysis. For the modulated proton beam, preliminary results on W air confirm the value recommended in TRS-398. Data in both the non-modulated proton and light-ion beams indicate higher values but further investigation of heat loss corrections is needed. The application of graphite calorimetry to proton, alpha and carbon ion beams has been demonstrated successfully. Other experimental campaigns will be held in 2012. This work is supported by the BioWin program of the Wallon Government. © 2012 American Association of Physicists in Medicine.

Laser ion source for heavy ion inertial fusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okamura, Masahiro

The proposed heavy ion inertial fusion (HIF) scenarios require ampere class low charge state ion beams of heavy species. A laser ion source (LIS) is recognized as one of the promising candidates of ion beam providers, since it can deliver high brightness heavy ion beams to accelerators. A design of LIS for the HIF depends on the accelerator structure and accelerator complex following the source. In this article, we discuss the specifications and design of an appropriate LIS assuming two major types of the accelerators: radio frequency (RF) high quality factor cavity type and non-resonant induction core type. We believemore » that a properly designed LIS satisfies the requirements of both types, however some issues need to be verified experimentally.« less

Laser ion source for heavy ion inertial fusion

DOE PAGES

Okamura, Masahiro

2018-01-10

The proposed heavy ion inertial fusion (HIF) scenarios require ampere class low charge state ion beams of heavy species. A laser ion source (LIS) is recognized as one of the promising candidates of ion beam providers, since it can deliver high brightness heavy ion beams to accelerators. A design of LIS for the HIF depends on the accelerator structure and accelerator complex following the source. In this article, we discuss the specifications and design of an appropriate LIS assuming two major types of the accelerators: radio frequency (RF) high quality factor cavity type and non-resonant induction core type. We believemore » that a properly designed LIS satisfies the requirements of both types, however some issues need to be verified experimentally.« less

A SiPM based real time dosimeter for radiotherapic beams

NASA Astrophysics Data System (ADS)

Berra, A.; Conti, V.; Lietti, D.; Milan, L.; Novati, C.; Ostinelli, A.; Prest, M.; Romanó, C.; Vallazza, E.

2015-02-01

This paper describes the development of a scintillator dosimeter prototype for radiotherapic applications based on plastic scintillating fibers readout by Silicon PhotoMultipliers. The dosimeter, whose probes are water equivalent, could be used for quality control measurements, beam characterization and in vivo dosimetry, allowing a real time measurement of the dose spatial distribution. This paper describes the preliminary percentual depth dose scan performed with clinical 6 and 18 MV photon beams, comparing the results with a reference curve. The measurements were performed using a Varian Clinac iX linear accelerator at the Radiotherapy Department of the St. Anna Hospital in Como (IT). The prototype has given promising results, allowing real time measurements of relative dose without applying any correction factors.

Accounting for patient size in the optimization of dose and image quality of pelvis cone beam CT protocols on the Varian OBI system.

PubMed

Wood, Tim J; Moore, Craig S; Horsfield, Carl J; Saunderson, John R; Beavis, Andrew W

2015-01-01

The purpose of this study was to develop size-based radiotherapy kilovoltage cone beam CT (CBCT) protocols for the pelvis. Image noise was measured in an elliptical phantom of varying size for a range of exposure factors. Based on a previously defined "small pelvis" reference patient and CBCT protocol, appropriate exposure factors for small, medium, large and extra-large patients were derived which approximate the image noise behaviour observed on a Philips CT scanner (Philips Medical Systems, Best, Netherlands) with automatic exposure control (AEC). Selection criteria, based on maximum tube current-time product per rotation selected during the radiotherapy treatment planning scan, were derived based on an audit of patient size. It has been demonstrated that 110 kVp yields acceptable image noise for reduced patient dose in pelvic CBCT scans of small, medium and large patients, when compared with manufacturer's default settings (125 kVp). Conversely, extra-large patients require increased exposure factors to give acceptable images. 57% of patients in the local population now receive much lower radiation doses, whereas 13% require higher doses (but now yield acceptable images). The implementation of size-based exposure protocols has significantly reduced radiation dose to the majority of patients with no negative impact on image quality. Increased doses are required on the largest patients to give adequate image quality. The development of size-based CBCT protocols that use the planning CT scan (with AEC) to determine which protocol is appropriate ensures adequate image quality whilst minimizing patient radiation dose.

Evanescent Microwave Probes on High-Resistivity Silicon and its Application in Characterization of Semiconductors

NASA Technical Reports Server (NTRS)

Tabib-Azar, M.; Akinwande, D.; Ponchak, George E.; LeClair, S. R.

1999-01-01

In this article we report the design, fabrication, and characterization of very high quality factor 10 GHz microstrip resonators on high-resistivity (high-rho) silicon substrates. Our experiments show that an external quality factor of over 13 000 can be achieved on microstripline resonators on high-rho silicon substrates. Such a high Q factor enables integration of arrays of previously reported evanescent microwave probe (EMP) on silicon cantilever beams. We also demonstrate that electron-hole pair recombination and generation lifetimes of silicon can be conveniently measured by illuminating the resonator using a pulsed light. Alternatively, the EMP was also used to nondestructively monitor excess carrier generation and recombination process in a semiconductor placed near the two-dimensional resonator.

SU-F-J-205: Effect of Cone Beam Factor On Cone Beam CT Number Accuracy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yao, W; Hua, C; Farr, J

Purpose: To examine the suitability of a Catphan™ 700 phantom for image quality QA of a cone beam computed tomography (CBCT) system deployed for proton therapy. Methods: Catphan phantoms, particularly Catphan™ 504, are commonly used in image quality QA for CBCT. As a newer product, Catphan™ 700 offers more tissue equivalent inserts which may be useful for generating the electron density – CT number curve for CBCT based treatment planning. The sensitometry-and-geometry module used in Catphan™ 700 is located at the end of the phantom and after the resolution line pair module. In Catphan™ 504 the line pair module ismore » located at the end of the phantom and after the sensitometry-and-geometry module. To investigate the effect of difference in location on CT number accuracy due to the cone beam factor, we scanned the Catphan™ 700 with the central plane of CBCT at the center of the phantom, line pair and sensitometry-andgeometry modules of the phantom, respectively. The protocol head and thorax scan modes were used. For each position, scans were repeated 4 times. Results: For the head scan mode, the standard deviation (SD) of the CT numbers of each insert under 4 repeated scans was up to 20 HU, 11 HU, and 11 HU, respectively, for the central plane of CBCT located at the center of the phantom, line pair, and sensitometry-and-geometry modules of the phantom. The mean of the SD was 9.9 HU, 5.7 HU, and 5.9 HU, respectively. For the thorax mode, the mean of the SD was 4.5 HU, 4.4 HU, and 4.4 HU, respectively. The assessment of image quality based on resolution and spatial linearity was not affected by imaging location changes. Conclusion: When the Catphan™ 700 was aligned to the center of imaging region, the CT number accuracy test may not meet expectations. We recommend reconfiguration of the modules.« less

BPM Button Optimization to Minimize Distortion Due to Trapped Mode Heating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cameron,P.; Blednyk, A.; Kosciuk, B.

2009-05-04

The outer circumference of a BPM button and the inner circumference of the button housing comprise a transmission line. This transmission line typically presents an impedance of a few tens of ohms to the beam, and couples very weakly to the 50 ohm coaxial transmission line that comprises the signal path out of the button. The modes which are consequently excited and trapped often have quality factors of several hundred, permitting resonant excitation by the beam. The thermal distortion resulting from trapped mode heating is potentially problematic for achieving the high precision beam position measurements needed to provide the sub-micronmore » beam position stability required by light source users. We present a button design that has been optimized via material selection and component geometry to minimize both the trapped mode heating and the resulting thermal distortion.« less

Clinical implementation of photon beam flatness measurements to verify beam quality.

PubMed

Goodall, Simon; Harding, Nicholas; Simpson, Jake; Alexander, Louise; Morgan, Steve

2015-11-08

This work describes the replacement of Tissue Phantom Ratio (TPR) measurements with beam profile flatness measurements to determine photon beam quality during routine quality assurance (QA) measurements. To achieve this, a relationship was derived between the existing TPR15/5 energy metric and beam flatness, to provide baseline values and clinically relevant tolerances. The beam quality was varied around two nominal beam energy values for four matched Elekta linear accelerators (linacs) by varying the bending magnet currents and reoptimizing the beam. For each adjusted beam quality the TPR15/5 was measured using an ionization chamber and Solid Water phantom. Two metrics of beam flatness were evaluated using two identical commercial ionization chamber arrays. A linear relationship was found between TPR15/5 and both metrics of flatness, for both nominal energies and on all linacs. Baseline diagonal flatness (FDN) values were measured to be 103.0% (ranging from 102.5% to 103.8%) for 6 MV and 102.7% (ranging from 102.6% to 102.8%) for 10 MV across all four linacs. Clinically acceptable tolerances of ± 2% for 6 MV, and ± 3% for 10 MV, were derived to equate to the current TPR15/5 clinical tolerance of ± 0.5%. Small variations in the baseline diagonal flatness values were observed between ionization chamber arrays; however, the rate of change of TPR15/5 with diagonal flatness was found to remain within experimental uncertainty. Measurements of beam flatness were shown to display an increased sensitivity to variations in the beam quality when compared to TPR measurements. This effect is amplified for higher nominal energy photons. The derivation of clinical baselines and associated tolerances has allowed this method to be incorporated into routine QA, streamlining the process whilst also increasing versatility. In addition, the effect of beam adjustment can be observed in real time, allowing increased practicality during corrective and preventive maintenance interventions.

Characterization of a 2.5 MV inline portal imaging beam

PubMed Central

Owen, Jennifer; Eduardo Villarreal‐Barajas, J.; Khan, Rao F.H.

2016-01-01

A new megavoltage (MV) energy was recently introduced on Varian TrueBeam linear accelerators for imaging applications. This work describes the experimental characterization of a 2.5 MV inline portal imaging beam for commissioning, routine clinical use, and quality assurance purposes. The beam quality of the 2.5 MV beam was determined by measuring a percent depth dose, PDD, in water phantom for 10×10 cm2 field at source‐to‐surface distance 100 cm with a CC13 ion chamber, plane parallel Markus chamber, and GafChromic EBT3 film. Absolute dosimetric output calibration of the beam was performed using a traceable calibrated ionization chamber, following the AAPM Task Group 51 procedure. EBT3 film measurements were also performed to measure entrance dose. The output stability of the imaging beam was monitored for five months. Coincidence of 2.5 MV imaging beam with 6 MV therapy beam was verified with hidden‐target cubic phantom. Image quality was studied using the Leeds and QC3 phantom. The depth of maximum dose, dmax, and percent dose at 10 cm depth were, respectively, 5.7 mm and 51.7% for CC13, 6.1 mm and 51.9% for Markus chamber, and 5.1 mm and 51.9% for EBT3 film. The 2.5 MV beam quality is slightly inferior to that of a  60Co teletherapy beam; however, an estimated kQ of 1.00 was used for output calibration purposes. The beam output was found to be stable to within 1% over a five‐month period. The relative entrance dose as measured with EBT3 films was 63%, compared to 23% for a clinical 6 MV beam for a 10×10 cm2 field. Overall coincidence of the 2.5 MV imaging beam with the 6 MV clinical therapy beam was within 0.2 mm. Image quality results for two commonly used imaging phantoms were superior for the 2.5 MV beam when compared to the conventional 6 MV beam. The results from measurements on two TrueBeam accelerators show that 2.5 MV imaging beam is slightly softer than a therapeutic  60Co beam, it provides superior image quality than a 6 MV therapy beam, and has excellent output stability. These 2.5 MV beam characterization results can serve as reference for clinics planning to commission and use this novel energy‐image modality. PACS number(s): 87.57.‐s, 87.59.‐e, 06.20.fb, 87.53.Bn PMID:27685135

Program Predicts Performance of Optical Parametric Oscillators

NASA Technical Reports Server (NTRS)

Cross, Patricia L.; Bowers, Mark

2006-01-01

A computer program predicts the performances of solid-state lasers that operate at wavelengths from ultraviolet through mid-infrared and that comprise various combinations of stable and unstable resonators, optical parametric oscillators (OPOs), and sum-frequency generators (SFGs), including second-harmonic generators (SHGs). The input to the program describes the signal, idler, and pump beams; the SFG and OPO crystals; and the laser geometry. The program calculates the electric fields of the idler, pump, and output beams at three locations (inside the laser resonator, just outside the input mirror, and just outside the output mirror) as functions of time for the duration of the pump beam. For each beam, the electric field is used to calculate the fluence at the output mirror, plus summary parameters that include the centroid location, the radius of curvature of the wavefront leaving through the output mirror, the location and size of the beam waist, and a quantity known, variously, as a propagation constant or beam-quality factor. The program provides a typical Windows interface for entering data and selecting files. The program can include as many as six plot windows, each containing four graphs.

Causes of cine image quality deterioration in cardiac catheterization laboratories.

PubMed

Levin, D C; Dunham, L R; Stueve, R

1983-10-01

Deterioration of cineangiographic image quality can result from malfunctions or technical errors at a number of points along the cine imaging chain: generator and automatic brightness control, x-ray tube, x-ray beam geometry, image intensifier, optics, cine camera, cine film, film processing, and cine projector. Such malfunctions or errors can result in loss of image contrast, loss of spatial resolution, improper control of film optical density (brightness), or some combination thereof. While the electronic and photographic technology involved is complex, physicians who perform cardiac catheterization should be conversant with the problems and what can be done to solve them. Catheterization laboratory personnel have control over a number of factors that directly affect image quality, including radiation dose rate per cine frame, kilovoltage or pulse width (depending on type of automatic brightness control), cine run time, selection of small or large focal spot, proper object-intensifier distance and beam collimation, aperture of the cine camera lens, selection of cine film, processing temperature, processing immersion time, and selection of developer.

Cone Beam CT vs. Fan Beam CT: A Comparison of Image Quality and Dose Delivered Between Two Differing CT Imaging Modalities

PubMed Central

Weidlich, Georg A.

2016-01-01

A comparison of image quality and dose delivered between two differing computed tomography (CT) imaging modalities—fan beam and cone beam—was performed. A literature review of quantitative analyses for various image quality aspects such as uniformity, signal-to-noise ratio, artifact presence, spatial resolution, modulation transfer function (MTF), and low contrast resolution was generated. With these aspects quantified, cone beam computed tomography (CBCT) shows a superior spatial resolution to that of fan beam, while fan beam shows a greater ability to produce clear and anatomically correct images with better soft tissue differentiation. The results indicate that fan beam CT produces superior images to that of on-board imaging (OBI) cone beam CT systems, while providing a considerably less dose to the patient. PMID:27752404

Effect of turbulence on the beam quality of apertured partially coherent beams.

PubMed

Ji, Xiaoling; Ji, Guangming

2008-06-01

The effects of turbulence on the beam quality of apertured partially coherent beams have been studied both analytically and numerically. Taking the Gaussian Schell-model (GSM) beam as a typical example of partially coherent beams, closed-form expressions for the average intensity, mean-squared beam width, power in the bucket, beta parameter, and Strehl ratio of apertured partially coherent beams propagating through atmospheric turbulence are derived. It is shown that the smaller the beam truncation parameter is, the less affected by turbulence the apertured partially coherent beams are. Furthermore, the apertured partially coherent beams are less sensitive to the effects of turbulence than unapertured ones. The main results are interpreted physically.

Image quality in thoracic 4D cone-beam CT: A sensitivity analysis of respiratory signal, binning method, reconstruction algorithm, and projection angular spacing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shieh, Chun-Chien; Kipritidis, John; O’Brien, Ricky T.

Purpose: Respiratory signal, binning method, and reconstruction algorithm are three major controllable factors affecting image quality in thoracic 4D cone-beam CT (4D-CBCT), which is widely used in image guided radiotherapy (IGRT). Previous studies have investigated each of these factors individually, but no integrated sensitivity analysis has been performed. In addition, projection angular spacing is also a key factor in reconstruction, but how it affects image quality is not obvious. An investigation of the impacts of these four factors on image quality can help determine the most effective strategy in improving 4D-CBCT for IGRT. Methods: Fourteen 4D-CBCT patient projection datasets withmore » various respiratory motion features were reconstructed with the following controllable factors: (i) respiratory signal (real-time position management, projection image intensity analysis, or fiducial marker tracking), (ii) binning method (phase, displacement, or equal-projection-density displacement binning), and (iii) reconstruction algorithm [Feldkamp–Davis–Kress (FDK), McKinnon–Bates (MKB), or adaptive-steepest-descent projection-onto-convex-sets (ASD-POCS)]. The image quality was quantified using signal-to-noise ratio (SNR), contrast-to-noise ratio, and edge-response width in order to assess noise/streaking and blur. The SNR values were also analyzed with respect to the maximum, mean, and root-mean-squared-error (RMSE) projection angular spacing to investigate how projection angular spacing affects image quality. Results: The choice of respiratory signals was found to have no significant impact on image quality. Displacement-based binning was found to be less prone to motion artifacts compared to phase binning in more than half of the cases, but was shown to suffer from large interbin image quality variation and large projection angular gaps. Both MKB and ASD-POCS resulted in noticeably improved image quality almost 100% of the time relative to FDK. In addition, SNR values were found to increase with decreasing RMSE values of projection angular gaps with strong correlations (r ≈ −0.7) regardless of the reconstruction algorithm used. Conclusions: Based on the authors’ results, displacement-based binning methods, better reconstruction algorithms, and the acquisition of even projection angular views are the most important factors to consider for improving thoracic 4D-CBCT image quality. In view of the practical issues with displacement-based binning and the fact that projection angular spacing is not currently directly controllable, development of better reconstruction algorithms represents the most effective strategy for improving image quality in thoracic 4D-CBCT for IGRT applications at the current stage.« less

High-power narrow-linewidth quasi-CW diode-pumped TEM00 1064 nm Nd:YAG ring laser.

PubMed

Liu, Yuan; Wang, Bao-shan; Xie, Shi-yong; Bo, Yong; Wang, Peng-yuan; Zuo, Jun-wei; Xu, Yi-ting; Xu, Jia-lin; Peng, Qin-jun; Cui, Da-fu; Xu, Zu-yan

2012-04-01

We demonstrated a high average power, narrow-linewidth, quasi-CW diode-pumped Nd:YAG 1064 nm laser with near-diffraction-limited beam quality. A symmetrical three-mirror ring cavity with unidirectional operation elements and an etalon was employed to realize the narrow-linewidth laser output. Two highly efficient laser modules and a 90° quartz rotator for birefringence compensation were used for the high output power. The maximum average output power of 62.5 W with the beam quality factor M(2) of 1.15 was achieved under a pump power of 216 W at a repetition rate of 500 Hz, corresponding to the optical-to-optical conversion efficiency of 28.9%. The linewidth of the laser at the maximum output power was measured to be less than 0.2 GHz.

High beam quality of a Q-switched 2-µm Tm,Ho:LuVO4 laser

NASA Astrophysics Data System (ADS)

Wang, Wei; Yang, Xining; Shen, Yingjie; Li, Linjun; Zhou, Long; Yang, Yuqiang; Bai, Yunfeng; Xie, Wenqiang; Ye, Guangchao; Yu, Xiaoyang

2018-05-01

A diode-end-pumped 2.05-µm Q-switched Tm,Ho:LuVO4 laser is reported in this paper. The cryogenic Tm3+ (5.0 at.%),Ho3+ (0.5 at.%):LuVO4 crystal was pumped by an 800-nm laser diode. At a pulse repetition frequency of 10 kHz, the maximum average output power of 3.77 W was achieved at 77 K when an incident pump power of 14.7 W was used. The slope efficiency and optical-optical conversion efficiency were 28.3 and 25.6%, respectively. The maximum per pulse energy was 2.54 mJ for a pulse duration of 69.9 ns. The beam quality factor Mx 2 was approximately 1.17 and My 2 was approximately 1.01 for the Tm,Ho:LuVO4 laser.

Ionization chamber-based reference dosimetry of intensity modulated radiation beams.

PubMed

Bouchard, Hugo; Seuntjens, Jan

2004-09-01

The present paper addresses reference dose measurements using thimble ionization chambers for quality assurance in IMRT fields. In these radiation fields, detector fluence perturbation effects invalidate the application of open-field dosimetry protocol data for the derivation of absorbed dose to water from ionization chamber measurements. We define a correction factor C(Q)IMRT to correct the absorbed dose to water calibration coefficient N(D, w)Q for fluence perturbation effects in individual segments of an IMRT delivery and developed a calculation method to evaluate the factor. The method consists of precalculating, using accurate Monte Carlo techniques, ionization chamber, type-dependent cavity air dose, and in-phantom dose to water at the reference point for zero-width pencil beams as a function of position of the pencil beams impinging on the phantom surface. These precalculated kernels are convolved with the IMRT fluence distribution to arrive at the dose-to-water-dose-to-cavity air ratio [D(a)w (IMRT)] for IMRT fields and with a 10x10 cm2 open-field fluence to arrive at the same ratio D(a)w (Q) for the 10x10 cm2 reference field. The correction factor C(Q)IMRT is then calculated as the ratio of D(a)w (IMRT) and D(a)w (Q). The calculation method was experimentally validated and the magnitude of chamber correction factors in reference dose measurements in single static and dynamic IMRT fields was studied. The results show that, for thimble-type ionization chambers the correction factor in a single, realistic dynamic IMRT field can be of the order of 10% or more. We therefore propose that for accurate reference dosimetry of complete n-beam IMRT deliveries, ionization chamber fluence perturbation correction factors must explicitly be taken into account.

New micro-beam beamline at SPring-8, targeting at protein micro-crystallography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirata, Kunio; Ueno, Go; Nisawa, Atsushi

2010-06-23

A new protein micro-crystallography beamline BL32XU at SPring-8 is under construction and scheduled to start operation in 2010. The beamline is designed to provide the stabilized and brilliant micro-beam to collect high-quality data from micro-crystals. The beamline consists of a hybrid in-vacuum undulator, a liquid-nitrogen cooled double crystal monochromator, and K-B focusing mirrors with large magnification factor. Development of data acquisition system and end station consists of high-precision diffractometer, high-efficiency area detector, sample auto-changer etc. are also in progress.

Microspherical photonics: Sorting resonant photonic atoms by using light

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maslov, Alexey V., E-mail: avmaslov@yandex.ru; Astratov, Vasily N., E-mail: astratov@uncc.edu

2014-09-22

A method of sorting microspheres by resonant light forces in vacuum, air, or liquid is proposed. Based on a two-dimensional model, it is shown that the sorting can be realized by allowing spherical particles to traverse a focused beam. Under resonance with the whispering gallery modes, the particles acquire significant velocity along the beam direction. This opens a unique way of large-volume sorting of nearly identical photonic atoms with 1/Q accuracy, where Q is the resonance quality factor. This is an enabling technology for developing super-low-loss coupled-cavity structures and devices.

Highly stable, efficient Tm-doped fiber laser—a potential scalpel for low invasive surgery

NASA Astrophysics Data System (ADS)

Michalska, M.; Brojek, W.; Rybak, Z.; Sznelewski, P.; Mamajek, M.; Swiderski, J.

2016-11-01

We report an all-fiber, diode-pumped, continuous-wave Tm3+-doped fiber laser emitting 37.4 W of output power with a slope efficiency as high as 57% with respect to absorbed pump power at 790 nm. The laser operated at ~1.94 µm and the output beam quality factor M 2 was measured to be ~1.2. The output beam was very stable with power fluctuations  <1% measured over 1 h. The laser system is to be implemented as a scalpel for low-invasive soft-tissue surgery.

Thulium fiber laser for the use in low-invasive endoscopic and robotic surgery of soft biological tissues

NASA Astrophysics Data System (ADS)

Michalska, M.; Brojek, W.; Rybak, Z.; Sznelewski, P.; Mamajek, M.; Gogler, S.; Swiderski, J.

2016-12-01

An all-fiber, diode-pumped, continuous-wave Tm3+-doped fiber laser operated at a wavelength of 1.94 μm was developed. 37.4 W of output power with a slope efficiency as high as 57% with respect to absorbed pump power at 790 nm was demonstrated. The laser output beam quality factor M2 was measured to be 1.2. The output beam was very stable with power fluctuations <1% measured over 1 hour. The laser system is to be implemented as a scalpel for surgery of soft biological tissues.

Neodymium glass laser with a phase conjugate mirror producing 220 J pulses at 0.02 Hz repetition rate.

PubMed

Kuzmin, A A; Khazanov, E A; Kulagin, O V; Shaykin, A A

2014-08-25

For pumping multipetawatt Ti:sapphire laser facilities we developed a compact repetitively pulsed laser based on neodymium phosphate glass with pulse energy of 220 J, pulse repetition rate of 0.02 Hz, beam diameter of 43 mm, aperture fill factor of 0.8, and FWHM pulse duration of 30 ns. The phase distortions of laser radiation were compensated by optical phase conjugation via stimulated Brillouin scattering. The depolarization was reduced to 0.4% using linear compensation methods. The beam quality was 2.5 x diffraction limit (150 µrad).

Effects of magnetic field and pressure in magnetoelastic stress reconfigurable thin film resonators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Staruch, M.; Bussmann, K.; Finkel, P.

2015-07-20

Free-standing CoFe thin-film doubly clamped stress reconfigurable resonators were investigated as a function of magnetic field and pressure. A large uniaxial anisotropy resulting from residual uniaxial tensile stress, as revealed from magnetic hysteresis loops, leads to an easy magnetization axis aligned along the length of the beams. The quality factor of the driven resonator beams under vacuum is increased by 30 times, leading to an enhanced signal-to-noise ratio and a predicted reduction in the intrinsic magnetic noise by a factor of 6, potentially reaching as low as ∼25 pT/√Hz at 1 Torr. Stress reconfigurable sensors operating under vacuum could thus furthermore » improve the limit of detection and advance development of magnetic field sensing technology.« less

A singular value decomposition linear programming (SVDLP) optimization technique for circular cone based robotic radiotherapy.

PubMed

Liang, Bin; Li, Yongbao; Wei, Ran; Guo, Bin; Xu, Xuang; Liu, Bo; Li, Jiafeng; Wu, Qiuwen; Zhou, Fugen

2018-01-05

With robot-controlled linac positioning, robotic radiotherapy systems such as CyberKnife significantly increase freedom of radiation beam placement, but also impose more challenges on treatment plan optimization. The resampling mechanism in the vendor-supplied treatment planning system (MultiPlan) cannot fully explore the increased beam direction search space. Besides, a sparse treatment plan (using fewer beams) is desired to improve treatment efficiency. This study proposes a singular value decomposition linear programming (SVDLP) optimization technique for circular collimator based robotic radiotherapy. The SVDLP approach initializes the input beams by simulating the process of covering the entire target volume with equivalent beam tapers. The requirements on dosimetry distribution are modeled as hard and soft constraints, and the sparsity of the treatment plan is achieved by compressive sensing. The proposed linear programming (LP) model optimizes beam weights by minimizing the deviation of soft constraints subject to hard constraints, with a constraint on the l 1 norm of the beam weight. A singular value decomposition (SVD) based acceleration technique was developed for the LP model. Based on the degeneracy of the influence matrix, the model is first compressed into lower dimension for optimization, and then back-projected to reconstruct the beam weight. After beam weight optimization, the number of beams is reduced by removing the beams with low weight, and optimizing the weights of the remaining beams using the same model. This beam reduction technique is further validated by a mixed integer programming (MIP) model. The SVDLP approach was tested on a lung case. The results demonstrate that the SVD acceleration technique speeds up the optimization by a factor of 4.8. Furthermore, the beam reduction achieves a similar plan quality to the globally optimal plan obtained by the MIP model, but is one to two orders of magnitude faster. Furthermore, the SVDLP approach is tested and compared with MultiPlan on three clinical cases of varying complexities. In general, the plans generated by the SVDLP achieve steeper dose gradient, better conformity and less damage to normal tissues. In conclusion, the SVDLP approach effectively improves the quality of treatment plan due to the use of the complete beam search space. This challenging optimization problem with the complete beam search space is effectively handled by the proposed SVD acceleration.

A singular value decomposition linear programming (SVDLP) optimization technique for circular cone based robotic radiotherapy

NASA Astrophysics Data System (ADS)

Liang, Bin; Li, Yongbao; Wei, Ran; Guo, Bin; Xu, Xuang; Liu, Bo; Li, Jiafeng; Wu, Qiuwen; Zhou, Fugen

2018-01-01

With robot-controlled linac positioning, robotic radiotherapy systems such as CyberKnife significantly increase freedom of radiation beam placement, but also impose more challenges on treatment plan optimization. The resampling mechanism in the vendor-supplied treatment planning system (MultiPlan) cannot fully explore the increased beam direction search space. Besides, a sparse treatment plan (using fewer beams) is desired to improve treatment efficiency. This study proposes a singular value decomposition linear programming (SVDLP) optimization technique for circular collimator based robotic radiotherapy. The SVDLP approach initializes the input beams by simulating the process of covering the entire target volume with equivalent beam tapers. The requirements on dosimetry distribution are modeled as hard and soft constraints, and the sparsity of the treatment plan is achieved by compressive sensing. The proposed linear programming (LP) model optimizes beam weights by minimizing the deviation of soft constraints subject to hard constraints, with a constraint on the l 1 norm of the beam weight. A singular value decomposition (SVD) based acceleration technique was developed for the LP model. Based on the degeneracy of the influence matrix, the model is first compressed into lower dimension for optimization, and then back-projected to reconstruct the beam weight. After beam weight optimization, the number of beams is reduced by removing the beams with low weight, and optimizing the weights of the remaining beams using the same model. This beam reduction technique is further validated by a mixed integer programming (MIP) model. The SVDLP approach was tested on a lung case. The results demonstrate that the SVD acceleration technique speeds up the optimization by a factor of 4.8. Furthermore, the beam reduction achieves a similar plan quality to the globally optimal plan obtained by the MIP model, but is one to two orders of magnitude faster. Furthermore, the SVDLP approach is tested and compared with MultiPlan on three clinical cases of varying complexities. In general, the plans generated by the SVDLP achieve steeper dose gradient, better conformity and less damage to normal tissues. In conclusion, the SVDLP approach effectively improves the quality of treatment plan due to the use of the complete beam search space. This challenging optimization problem with the complete beam search space is effectively handled by the proposed SVD acceleration.

[Radiation load on the skin using a silicone-coated polyamide wound dressing during photon and electron radiotherapy].

PubMed

Thilmann, C; Adamietz, I A; Ramm, U; Mose, S; Saran, F; Böttcher, H D

1996-05-01

Silicone-coated polyamide wound dressing is frequently used for the supportive treatment in patients with radiation induced skin lesions. The use of this kind of dressing during radiotherapy with high energy beams shifts the dose built-up effect towards the skin surface. Thus the dose delivered to the skin increases. The present work quantifies changes of the skin dose by a commercial silicon-coated polyamide wound dressing. The dependence on the beam quality and on different treatment techniques is investigated. Measurements were performed with photon (60Co, 6 MV, 42 MV) and electron (7 MeV, 20 MeV, 40 MeV) beams using thin LiF thermoluminescence dosimeters (TLD) in a perspex phantom. The beams were directed perpendicularly to the phantom surface. For 60Co and 6 MV photon beams the skin dose was evaluated in vivo at different beam arrangements and at a given reference dose. For 60Co, 6 MV and 42 MV photon beams wound dressing caused a dose increase on the surface of the perspex phantom by a factor of 1.65, 1.39 and 1.33 respectively. Using oblique or rotational techniques for 60Co and 6 MV photon irradiation the wound dressing increased the skin dose but less compared to perpendicular beam direction. For electron beams the skin dose is relatively high (from 84% to 92%) and an increase by a dressing has no clinical relevance (factor 1.03 to 1.05). The silicone-coated polyamide wound dressing causes no relevant skin dose increase during radiation treatment with electron beams and can be left on the skin during irradiation. During radiation treatment with photon beams like 60Co and 6 MV the protective procedure should be adapted to skin changes, in case of strong skin reactions a removal during the time of irradiation should be considered.

Examination of the dental cone-beam CT equipped with flat-panel-detector (FPD)

NASA Astrophysics Data System (ADS)

Ito, Rieko; Fujita, Naotoshi; Kodera, Yoshie

2011-03-01

In dentistry, computed tomography (CT) is essential for diagnosis. Recently, cone-beam CT has come into use. We used an "Alphard 3030" cone-beam CT equipped with an FPD system. This system can obtain fluoroscopic and CT images. Moreover, the Alphard has 4 exposure modes for CT, and each mode has a different field of view (FOV) and voxel size. We examined the image quality of kinetic and CT images obtained using the cone-beam CT system. To evaluate kinetic image quality, we calculated the Wiener spectrum (WS) and modulation transfer function (MTF). We then analyzed the lag images and exposed a phantom. To evaluate CT image quality, we calculated WS and MTF at various places in the FOV and examined the influence of extension of the cone beam X-ray on voxel size. Furthermore, we compared the WS and MTF values of cone-beam CT to those of another CT system. Evaluation of the kinetic images showed that cone-beam CT is sufficient for clinical diagnosis and provides better image quality than the other system tested. However, during exposure of a CT image, the distance from the center influences image quality (especially MTF). Further, differences in voxel size affect image quality. It is therefore necessary to carefully position the region of interest and select an appropriate mode.

Adjuvant radiotherapy for stage I endometrial cancer.

PubMed

Kong, A; Johnson, N; Cornes, P; Simera, I; Collingwood, M; Williams, C; Kitchener, H

2007-04-18

The role of adjuvant radiotherapy (both pelvic external beam radiotherapy and vaginal intracavity brachytherapy) in stage I endometrial cancer following total abdominal hysterectomy and bilateral salpingo-oophorectomy (TAH and BSO) remains unclear. To assess the efficacy of adjuvant radiotherapy following surgery for stage I endometrial cancer. The Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, CancerLit, Physician Data Query (PDQ) of National Cancer Institute. Handsearching was also carried out where appropriate. Randomised controlled trials (RCTs) which compared adjuvant radiotherapy versus no radiotherapy following surgery for patients with stage I endometrial cancer were included. Quality of the studies was assessed and data collected using a predefined data collection form. The primary endpoint was overall survival. Secondary endpoints were locoregional recurrence, distant recurrence and endometrial cancer death. Data on quality of life (QOL) and morbidity were also collected. A meta-analysis on included trials was performed using the Cochrane Collaboration Review Manager Software 4.2. The meta-analysis was performed on four trials (1770 patients). The addition of pelvic external beam radiotherapy to surgery reduced locoregional recurrence, a relative risk (RR) of 0.28 (95% confidence interval (CI) 0.17 to 0.44, p < 0.00001), which is a 72% reduction in the risk of pelvic relapse (95% CI 56% to 83%) and an absolute risk reduction of 6% (95% CI of 4 to 8%). The number needed to treat (NNT) to prevent one locoregional recurrence is 16.7 patients (95% CI 12.5 to 25). The reduction in the risk of locoregional recurrence did not translate into either a reduction in the risk of distant recurrence or death from all causes or endometrial cancer death. A subgroup analysis of women with multiple high risk factors (including stage 1c and grade 3) showed a trend toward the reduction in the risk of death from all causes and endometrial cancer death in patients who underwent adjuvant external beam radiotherapy. Patients with stage I endometrial carcinoma have different risks of local and distant recurrence depending on the presence of risk factors including stage 1c, grade 3, lymphovascular space invasion and age. Though external beam pelvic radiotherapy reduced locoregional recurrence by 72%, there is no evidence to suggest that it reduced the risk of death. In patients with multiple high risk factors, including stage 1c and grade 3, there was a trend towards a survival benefit and adjuvant external beam radiotherapy may be justified. For patients with only one risk factor, grade 3 or stage 1c, no definite conclusion can be made and data from ongoing studies ( ASTEC; Lukka) are awaited. External beam radiotherapy carries a risk of toxicity and should be avoided in stage 1 endometrial cancer patients with no high risk factors.

Analytical study of beam handling and emittance control

NASA Astrophysics Data System (ADS)

Thompson, James R.; Sloan, M. L.

1993-12-01

The thrust of our research on beam handling and emittance control was to explore how one might design high current electron accelerators, with the preservation of high beam quality designed as the primary design consideration. We considered high current, induction linacs in the parameter class of the ETA/ATA accelerators at LLNL, but with improvements to the accelerator gap design and other features to permit a significant increase in the deliverable beam brightness. Our approach for beam quality control centered on the use of solenoidal magnetic focusing through such induction accelerators, together with gently-shaped (adiabatic) acceleration gaps. This approach offers several tools for the control of beam quality. The strength and axial variation in the solenoidal magnetic field may be designed, as may the length and shape of the acceleration gaps, the loading of the gaps, and the axial spacing from gap to gap. This research showed that each of these design features may individually be optimized to contribute to improved beam quality control, and by exploiting these features, it appears feasible to produce high current, high energy electron beams possessing breakthrough beam quality and brightness. Applications which have been technologically unachievable may for the first time become possible. One such application is the production of high performance free electron lasers at very short wavelengths, extending down to the optical (less than 1 micron) regime.

Analytic image reconstruction from partial data for a single-scan cone-beam CT with scatter correction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Min, Jonghwan; Pua, Rizza; Cho, Seungryong, E-mail: scho@kaist.ac.kr

Purpose: A beam-blocker composed of multiple strips is a useful gadget for scatter correction and/or for dose reduction in cone-beam CT (CBCT). However, the use of such a beam-blocker would yield cone-beam data that can be challenging for accurate image reconstruction from a single scan in the filtered-backprojection framework. The focus of the work was to develop an analytic image reconstruction method for CBCT that can be directly applied to partially blocked cone-beam data in conjunction with the scatter correction. Methods: The authors developed a rebinned backprojection-filteration (BPF) algorithm for reconstructing images from the partially blocked cone-beam data in amore » circular scan. The authors also proposed a beam-blocking geometry considering data redundancy such that an efficient scatter estimate can be acquired and sufficient data for BPF image reconstruction can be secured at the same time from a single scan without using any blocker motion. Additionally, scatter correction method and noise reduction scheme have been developed. The authors have performed both simulation and experimental studies to validate the rebinned BPF algorithm for image reconstruction from partially blocked cone-beam data. Quantitative evaluations of the reconstructed image quality were performed in the experimental studies. Results: The simulation study revealed that the developed reconstruction algorithm successfully reconstructs the images from the partial cone-beam data. In the experimental study, the proposed method effectively corrected for the scatter in each projection and reconstructed scatter-corrected images from a single scan. Reduction of cupping artifacts and an enhancement of the image contrast have been demonstrated. The image contrast has increased by a factor of about 2, and the image accuracy in terms of root-mean-square-error with respect to the fan-beam CT image has increased by more than 30%. Conclusions: The authors have successfully demonstrated that the proposed scanning method and image reconstruction algorithm can effectively estimate the scatter in cone-beam projections and produce tomographic images of nearly scatter-free quality. The authors believe that the proposed method would provide a fast and efficient CBCT scanning option to various applications particularly including head-and-neck scan.« less

Design study of a re-bunching RFQ for the SPES project

NASA Astrophysics Data System (ADS)

Shin, Seung Wook; Palmieri, A.; Comunian, M.; Grespan, F.; Chai, Jong Seo

2014-05-01

An upgrade to the 2nd generation of the selective production of exotic species (SPES) to produce a radioactive ion beam (RIB) has been studied at the istituto nazionale di fisica nucleare — laboratory nazionali di Legnaro (INFN-LNL). Due to the long distance between the isotope separator online (ISOL) facility and the superconducting quarter wave resonator (QWR) cavity acceleratore lineare per ioni (ALPI), a new re-buncher cavity must be introduced to maintain the high beam quality during the beam transport. A particular radio frequency quadrupole (RFQ) structure has been suggested to meet the requirements of this project. A window-type RFQ, which has a high mode separation, less power dissipation and compact size compared to the conventional normal 4-vane RFQ, has been introduced. The RF design has been studied considering the requirements of the re-bunching machine for high figures of merit such as a proper operation frequency, a high shunt impedance, a high quality factor, a low power dissipation, etc. A sensitivity analysis of the fabrication and the misalignment error has been conducted. A micro-movement slug tuner has been introduced to compensate for the frequency variations that may occur due to the beam loading, the thermal instability, the microphonic effect, etc.

LD-pumped erbium and neodymium lasers with high energy and output beam quality

NASA Astrophysics Data System (ADS)

Kabanov, Vladimir V.; Bezyazychnaya, Tatiana V.; Bogdanovich, Maxim V.; Grigor'ev, Alexandr V.; Lebiadok, Yahor V.; Lepchenkov, Kirill V.; Ryabtsev, Andrew G.; Ryabtsev, Gennadii I.; Shchemelev, Maxim A.

2013-05-01

Physical and fabrication peculiarities which provide the high output energy and beam quality for the diode pumped erbium glass and Nd:YAG lasers are considered. Developed design approach allow to make passively Q-switched erbium glass eye-safe portable laser sources with output energy 8 - 12 mJ (output pulse duration is less than 25 ns, pulse repetition rate up to 5 Hz) and beam quality M2 less than 1.3. To reach these values the erbium laser pump unit parameters were optimized also. Namely, for the powerful laser diode arrays the optimal near-field fill-factor, output mirror reflectivity and heterostructure properties were determined. Construction of advanced diode and solid-state lasers as well as the optical properties of the active element and the pump unit make possible the lasing within a rather wide temperature interval (e.g. from minus forty till plus sixty Celsius degree) without application of water-based chillers. The transversally pumped Nd:YAG laser output beam uniformity was investigated depending on the active element (AE) pump conditions. In particular, to enhance the pump uniformity within AE volume, a special layer which practically doesn't absorb the pump radiation but effectively scatters the pump and lasing beams, was used. Application of such layer results in amplified spontaneous emission suppression and improvement of the laser output beam uniformity. The carried out investigations allow us to fabricate the solid-state Nd:YAG lasers (1064 nm) with the output energy up to 420 mJ at the pulse repetition rate up to 30 Hz and the output energy up to 100 mJ at the pulse repetition rate of of 100 Hz. Also the laser sources with following characteristics: 35 mJ, 30 Hz (266 nm); 60 mJ, 30 Hz (355 nm); 100 mJ, 30 Hz (532 nm) were manufactured on the base of the developed Nd:YAG quantrons.

SU-E-T-223: Computed Radiography Dose Measurements of External Radiotherapy Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aberle, C; Kapsch, R

2015-06-15

Purpose: To obtain quantitative, two-dimensional dose measurements of external radiotherapy beams with a computed radiography (CR) system and to derive volume correction factors for ionization chambers in small fields. Methods: A commercial Kodak ACR2000i CR system with Kodak Flexible Phosphor Screen HR storage foils was used. Suitable measurement conditions and procedures were established. Several corrections were derived, including image fading, length-scale corrections and long-term stability corrections. Dose calibration curves were obtained for cobalt, 4 MV, 8 MV and 25 MV photons, and for 10 MeV, 15 MeV and 18 MeV electrons in a water phantom. Inherent measurement inhomogeneities were studiedmore » as well as directional dependence of the response. Finally, 2D scans with ionization chambers were directly compared to CR measurements, and volume correction factors were derived. Results: Dose calibration curves (0.01 Gy to 7 Gy) were obtained for multiple photon and electron beam qualities. For each beam quality, the calibration curves can be described by a single fit equation over the whole dose range. The energy dependence of the dose response was determined. The length scale on the images was adjusted scan-by-scan, typically by 2 percent horizontally and by 3 percent vertically. The remaining inhomogeneities after the system’s standard calibration procedure were corrected for. After correction, the homogeneity is on the order of a few percent. The storage foils can be rotated by up to 30 degrees without a significant effect on the measured signal. First results on the determination of volume correction factors were obtained. Conclusion: With CR, quantitative, two-dimensional dose measurements with a high spatial resolution (sub-mm) can be obtained over a large dose range. In order to make use of these advantages, several calibrations, corrections and supporting measurements are needed. This work was funded by the European Metrology Research Programme (EMRP) project HLT09 MetrExtRT Metrology for Radiotherapy using Complex Radiation Fields.« less

An X-band high-impedance relativistic klystron amplifier with an annular explosive cathode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Danni; Zhang, Jun, E-mail: zhangjun@nudt.edu.cn; Zhong, Huihuang

2015-11-15

The feasibility of employing an annular beam instead of a solid one in the X-band high-impedance relativistic klystron amplifier (RKA) is investigated in theory and simulation. Small-signal theory analysis indicates that the optimum bunching distance, fundamental current modulation depth, beam-coupling coefficient, and beam-loaded quality factor of annular beams are all larger than the corresponding parameters of solid beams at the same beam voltage and current. An annular beam RKA and a solid beam RKA with almost the same geometric parameters are compared in particle-in-cell simulation. Output microwave power of 100 MW, gain of 50 dB, and power conversion efficiency of 42% aremore » obtained in an annular beam RKA. The annular beam needs a 15% lower uniform guiding magnetic field than the solid beam. Our investigations demonstrate that we are able to use a simple annular explosive cathode immersed in a lower uniform magnetic field instead of a solid thermionic cathode in a complicated partially shielding magnetic field for designing high-impedance RKA, which avoids high temperature requirement, complicated electron-optical system, large area convergence, high current density, and emission uniformity for the solid beam. An equivalent method for the annular beam and the solid beam on bunching features is proposed and agrees with the simulation. The annular beam has the primary advantages over the solid beam that it can employ the immersing uniform magnetic field avoiding the complicated shielding magnetic field system and needs a lower optimum guiding field due to the smaller space charge effect.« less

On-site audits to investigate the quality of radiation physics of radiation therapy institutions in the Republic of Korea.

PubMed

Park, Jong Min; Park, So-Yeon; Chun, Minsoo; Kim, Sang-Tae

2017-08-01

To investigate and improve the domestic standard of radiation therapy in the Republic of Korea. On-site audits were performed for 13 institutions in the Republic of Korea. Six items were investigated by on-site visits of each radiation therapy institution, including collimator, gantry, and couch rotation isocenter check; coincidence between light and radiation fields; photon beam flatness and symmetry; electron beam flatness and symmetry; physical wedge transmission factors; and photon beam and electron beam outputs. The average deviations of mechanical collimator, gantry, and couch rotation isocenter were less than 1mm. Those of radiation isocenter were also less than 1mm. The average difference between light and radiation fields was 0.9±0.6mm for the field size of 20cm×20cm. The average values of flatness and symmetry of the photon beams were 2.9%±0.6% and 1.1%±0.7%, respectively. Those of electron beams were 2.5%±0.7% and 0.6%±1.0%, respectively. Every institutions showed wedge transmission factor deviations less than 2% except one institution. The output deviations of both photon and electron beams were less than ±3% for every institution. Through the on-site audit program, we could effectively detect an inappropriately operating linacs and provide some recommendations. The standard of radiation therapy in Korea is expected to improve through such on-site audits. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Angular dependence of the nanoDot OSL dosimeter.

PubMed

Kerns, James R; Kry, Stephen F; Sahoo, Narayan; Followill, David S; Ibbott, Geoffrey S

2011-07-01

Optically stimulated luminescent detectors (OSLDs) are quickly gaining popularity as passive dosimeters, with applications in medicine for linac output calibration verification, brachytherapy source verification, treatment plan quality assurance, and clinical dose measurements. With such wide applications, these dosimeters must be characterized for numerous factors affecting their response. The most abundant commercial OSLD is the InLight/OSL system from Landauer, Inc. The purpose of this study was to examine the angular dependence of the nanoDot dosimeter, which is part of the InLight system. Relative dosimeter response data were taken at several angles in 6 and 18 MV photon beams, as well as a clinical proton beam. These measurements were done within a phantom at a depth beyond the build-up region. To verify the observed angular dependence, additional measurements were conducted as well as Monte Carlo simulations in MCNPX. When irradiated with the incident photon beams parallel to the plane of the dosimeter, the nanoDot response was 4% lower at 6 MV and 3% lower at 18 MV than the response when irradiated with the incident beam normal to the plane of the dosimeter. Monte Carlo simulations at 6 MV showed similar results to the experimental values. Examination of the results in Monte Carlo suggests the cause as partial volume irradiation. In a clinical proton beam, no angular dependence was found. A nontrivial angular response of this OSLD was observed in photon beams. This factor may need to be accounted for when evaluating doses from photon beams incident from a variety of directions.

Angular dependence of the nanoDot OSL dosimeter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kerns, James R.; Kry, Stephen F.; Sahoo, Narayan

Purpose: Optically stimulated luminescent detectors (OSLDs) are quickly gaining popularity as passive dosimeters, with applications in medicine for linac output calibration verification, brachytherapy source verification, treatment plan quality assurance, and clinical dose measurements. With such wide applications, these dosimeters must be characterized for numerous factors affecting their response. The most abundant commercial OSLD is the InLight/OSL system from Landauer, Inc. The purpose of this study was to examine the angular dependence of the nanoDot dosimeter, which is part of the InLight system. Methods: Relative dosimeter response data were taken at several angles in 6 and 18 MV photon beams, asmore » well as a clinical proton beam. These measurements were done within a phantom at a depth beyond the build-up region. To verify the observed angular dependence, additional measurements were conducted as well as Monte Carlo simulations in MCNPX. Results: When irradiated with the incident photon beams parallel to the plane of the dosimeter, the nanoDot response was 4% lower at 6 MV and 3% lower at 18 MV than the response when irradiated with the incident beam normal to the plane of the dosimeter. Monte Carlo simulations at 6 MV showed similar results to the experimental values. Examination of the results in Monte Carlo suggests the cause as partial volume irradiation. In a clinical proton beam, no angular dependence was found. Conclusions: A nontrivial angular response of this OSLD was observed in photon beams. This factor may need to be accounted for when evaluating doses from photon beams incident from a variety of directions.« less

Angular dependence of the nanoDot OSL dosimeter

PubMed Central

Kerns, James R.; Kry, Stephen F.; Sahoo, Narayan; Followill, David S.; Ibbott, Geoffrey S.

2011-01-01

Purpose: Optically stimulated luminescent detectors (OSLDs) are quickly gaining popularity as passive dosimeters, with applications in medicine for linac output calibration verification, brachytherapy source verification, treatment plan quality assurance, and clinical dose measurements. With such wide applications, these dosimeters must be characterized for numerous factors affecting their response. The most abundant commercial OSLD is the InLight∕OSL system from Landauer, Inc. The purpose of this study was to examine the angular dependence of the nanoDot dosimeter, which is part of the InLight system.Methods: Relative dosimeter response data were taken at several angles in 6 and 18 MV photon beams, as well as a clinical proton beam. These measurements were done within a phantom at a depth beyond the build-up region. To verify the observed angular dependence, additional measurements were conducted as well as Monte Carlo simulations in MCNPX.Results: When irradiated with the incident photon beams parallel to the plane of the dosimeter, the nanoDot response was 4% lower at 6 MV and 3% lower at 18 MV than the response when irradiated with the incident beam normal to the plane of the dosimeter. Monte Carlo simulations at 6 MV showed similar results to the experimental values. Examination of the results in Monte Carlo suggests the cause as partial volume irradiation. In a clinical proton beam, no angular dependence was found.Conclusions: A nontrivial angular response of this OSLD was observed in photon beams. This factor may need to be accounted for when evaluating doses from photon beams incident from a variety of directions. PMID:21858992

An analysis of the ArcCHECK-MR diode array's performance for ViewRay quality assurance.

PubMed

Ellefson, Steven T; Culberson, Wesley S; Bednarz, Bryan P; DeWerd, Larry A; Bayouth, John E

2017-07-01

The ArcCHECK-MR diode array utilizes a correction system with a virtual inclinometer to correct the angular response dependencies of the diodes. However, this correction system cannot be applied to measurements on the ViewRay MR-IGRT system due to the virtual inclinometer's incompatibility with the ViewRay's multiple simultaneous beams. Additionally, the ArcCHECK's current correction factors were determined without magnetic field effects taken into account. In the course of performing ViewRay IMRT quality assurance with the ArcCHECK, measurements were observed to be consistently higher than the ViewRay TPS predictions. The goals of this study were to quantify the observed discrepancies and test whether applying the current factors improves the ArcCHECK's accuracy for measurements on the ViewRay. Gamma and frequency analysis were performed on 19 ViewRay patient plans. Ion chamber measurements were performed at a subset of diode locations using a PMMA phantom with the same dimensions as the ArcCHECK. A new method for applying directionally dependent factors utilizing beam information from the ViewRay TPS was developed in order to analyze the current ArcCHECK correction factors. To test the current factors, nine ViewRay plans were altered to be delivered with only a single simultaneous beam and were measured with the ArcCHECK. The current correction factors were applied using both the new and current methods. The new method was also used to apply corrections to the original 19 ViewRay plans. It was found the ArcCHECK systematically reports doses higher than those actually delivered by the ViewRay. Application of the current correction factors by either method did not consistently improve measurement accuracy. As dose deposition and diode response have both been shown to change under the influence of a magnetic field, it can be concluded the current ArcCHECK correction factors are invalid and/or inadequate to correct measurements on the ViewRay system. © 2017 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.

Influence of laser beam incidence angle on laser lap welding quality of galvanized steels

NASA Astrophysics Data System (ADS)

Mei, Lifang; Yan, Dongbing; Chen, Genyu; Wang, Zhenhui; Chen, Shuixuan

2017-11-01

Based on the characteristics of laser welded structural parts of auto bodies, the influence of variation in laser beam incidence angle on the lap welding performance of galvanized auto-body sheets was studied. Lap welding tests were carried out on the galvanized sheets for auto-body application at different laser beam incidence angles by using the optimal welding parameters obtained through orthogonal experiment. The effects of incidence angle variation on seam appearance, cross-sectional shape, joint mechanical properties and microstructure of weldments were analyzed. In addition, the main factors influencing the value of incidence angle were investigated. According to the results, the weld seams had a good appearance as well as a fine, and uniform microstructure when the laser beam incidence angle was smaller than the critical incidence angle, and thus they could withstand great tensile and shear loads. Moreover, all tensile-shear specimens were fractured in the base material zone. When the laser beam incidence angle was larger than the critical incidence angle, defects like shrinkage and collapse tended to emerge, thereby resulting in the deteriorated weldability of specimens. Meanwhile, factors like the type and thickness of sheet, weld width as well as inter-sheet gap all had a certain effect on the value of laser beam incidence angle. When the sheet thickness was small and the weld width was narrow, the laser beam incidence angle could be increased appropriately. At the same time, small changes in the inter-sheet gap could greatly impact the value of incidence angle. When the inter-sheet gap was small, the laser beam incidence angle should not be too large.

SU-F-T-175: Absorbed Dose Measurement Using Radiophotoluminescent Glass Dosimeter in Therapeutic Proton Beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, W; National Institute of Radiological Sciences, Chiba, Chiba; Koba, Y

Purpose: To measure the absorbed dose to water Dw in therapeutic proton beam with radiophotoluminescent glass dosimeter (RGD), a methodology was proposed. In this methodology, the correction factor for the LET dependence of radiophotoluminescent (RPL) efficiency and the variation of mass stopping power ratio of water to RGD (SPRw, RGD) were adopted. The feasibility of proposed method was evaluated in this report. Methods: The calibration coefficient in terms of Dw for RGDs (GD-302M, Asahi Techno Glass) was obtained using 60Co beam. The SPRw, RGD was calculated by Monte Carlo simulation toolkit Geant4. The LET dependence of RPL efficiency was investigatedmore » experimentally by using a 70 MeV proton beam at National Institute of Radiological Sciences. For clinical usage, the residual range Rres was used as a quality index to determine the correction factor for RPL efficiency. The proposed method was evaluated by measuring Dw at difference depth in the 200 MeV proton beam. Results: For both modulated and non-modulated proton beam, the SPRw, RGD increases more than 3 % where Rres are less than 1 cm. RPL efficiency decreases with increasing LET and it reaches 0.6 at LET of 10 keV µm{sup −1}. Dw measured by RGD (Dw, RGD) shows good agreement with that measured by ionization chamber (Dw, IC) and the relative difference between Dw, RGD and Dw, IC are within 3 % where Rres is larger than 1 cm. Conclusion: In this work, a methodology for using RGD in proton dosimetry was proposed and the SPRw, RGD and the LET dependence of RPL efficiency in therapeutic proton beam was investigated. The results revealed that the proposed method is useful for RGD in the dosimetry of proton beams.« less

Novel high-brightness fiber coupled diode laser device

NASA Astrophysics Data System (ADS)

Haag, Matthias; Köhler, Bernd; Biesenbach, Jens; Brand, Thomas

2007-02-01

High brightness becomes more and more important in diode laser applications for fiber laser pumping and materials processing. For OEM customers fiber coupled devices have great advantages over direct beam modules: the fiber exit is a standardized interface, beam guiding is easy with nearly unlimited flexibility. In addition to the transport function the fiber serves as homogenizer: the beam profile of the laser radiation emitted from a fiber is symmetrical with highly repeatable beam quality and pointing stability. However, efficient fiber coupling requires an adaption of the slow-axis beam quality to the fiber requirements. Diode laser systems based on standard 10mm bars usually employ beam transformation systems to rearrange the highly asymmetrical beam of the laser bar or laser stack. These beam transformation systems (prism arrays, lens arrays, fiber bundles etc.) are expensive and become inefficient with increasing complexity. This is especially true for high power devices with small fiber diameters. On the other hand, systems based on single emitters are claimed to have good potential in cost reduction. Brightness of the inevitable fiber bundles, though, is limited due to inherent fill-factor losses. At DILAS a novel diode laser device has been developed combining the advantages of diode bars and single emitters: high brightness at high reliability with single emitter cost structure. Heart of the device is a specially tailored laser bar (T-Bar), which epitaxial and lateral structure was designed such that only standard fast- and slow-axis collimator lenses are required to couple the beam into a 200μm fiber. Up to 30 of these T-Bars of one wavelength can be combined to reach a total of > 500W ex fiber in the first step. Going to a power level of today's single emitter diodes even 1kW ex 200μm fiber can be expected.

Self-excitation of microwave oscillations in plasma-assisted slow-wave oscillators by an electron beam with a movable focus

NASA Astrophysics Data System (ADS)

Bliokh, Yu. P.; Nusinovich, G. S.; Shkvarunets, A. G.; Carmel, Y.

2004-10-01

Plasma-assisted slow-wave oscillators (pasotrons) operate without external magnetic fields, which makes these devices quite compact and lightweight. Beam focusing in pasotrons is provided by ions, which appear in the device due to the impact ionization of a neutral gas by beam electrons. Typically, the ionization time is on the order of the rise time of the beam current. This means that, during the rise of the current, beam focusing by ions becomes stronger. Correspondingly, a beam of electrons, which was initially diverging radially due to the self-electric field, starts to be focused by ions, and this focus moves towards the gun as the ion density increases. This feature makes the self-excitation of electromagnetic (em) oscillations in pasotrons quite different from practically all other microwave sources where em oscillations are excited by a stationary electron beam. The process of self-excitation of em oscillations has been studied both theoretically and experimentally. It is shown that in pasotrons, during the beam current rise the amount of current entering the interaction space and the beam coupling to the em field vary. As a result, the self-excitation can proceed faster than in conventional microwave sources with similar operating parameters such as the operating frequency, cavity quality-factor and the beam current and voltage.

Modified M20 Beam Position Monitor Testing

NASA Astrophysics Data System (ADS)

Koros, Jessica; Musson, John

2017-09-01

Beam position monitors (BPMs) are used to measure lateral beam position. Two pairs of modified wire BPMs are being evaluated for installation into the injector at Jefferson Lab (JLab). The BPMs were coated with a Non-Evaporable Getter (NEG) to aid in pumping at the electron gun, as an ultra-high vacuum is required to protect the gun and to avoid scattering the beam. Beam in the injector has a large diameter, allowing extraction of second moments to give information about beam profile and emittance. The purpose of this project is to determine the effects of NEG coating on the BPMs and to calculate second moments from beam models on the Goubau Line (G-Line). Using the G-Line, scans of the BPMs were taken before and after NEG coating. Each scan produced an electrical field map, which characterizes properties of the BPM, including scale factors and coupling. Second moments were calculated using superposition of previous scan data, and verification of this method was attempted using several beam models. Results show the BPMs responded well to NEG and that measurement of second moments is possible. Once the BPMs are installed, they will enhance gun vacuum and enable monitoring of shape and trajectory of the beam as it exits the electron gun to ensure quality beam for experiments. This work is made possible through support from NSF award 1659177 to Old Dominion University.

Experimental verification of beam quality in high-contrast imaging with orthogonal bremsstrahlung photon beams.

PubMed

Sarfehnia, Arman; Jabbari, Keyvan; Seuntjens, Jan; Podgorsak, Ervin B

2007-07-01

Since taken with megavoltage, forward-directed bremsstrahlung beams, the image quality of current portal images is inferior to that of diagnostic quality images produced by kilovoltage beams. In this paper, the beam quality of orthogonal bremsstrahlung beams defined as the 90 degrees component of the bremsstrahlung distribution produced from megavoltage electron pencil beams striking various targets is presented, and the suitability of their use for improved radiotherapy imaging is evaluated. A 10 MeV electron beam emerging through the research port of a Varian Clinac-18 linac was made to strike targets of carbon, aluminum, and copper. PDD and attenuation measurements of both the forward and orthogonal beams were carried out, and the results were also used to estimate the effective and mean energy of the beams. The mean energy of a spectrum produced by a carbon target dropped by 83% from 1296 keV in the forward direction to 217 keV in the orthogonal direction, while for an aluminum target it dropped by 77% to 412 keV, and for a copper target by 65% to 793 keV. An in-depth Monte Carlo study of photon yield and electron contamination was also performed. Photon yield and effective energy are lower for orthogonal beams than for forward beams, and the differences are more pronounced for targets of lower atomic number. Using their relatively low effective energy, orthogonal bremsstrahlung beams produced by megavoltage electrons striking low atomic number targets yield images with a higher contrast in comparison with forward bremsstrahlung beams.

Development and implementation of EPID-based quality assurance tests for the small animal radiation research platform (SARRP).

PubMed

Anvari, Akbar; Poirier, Yannick; Sawant, Amit

2018-04-28

Although small animal image-guided radiotherapy (SA-IGRT) systems are used increasingly in preclinical research, tools for performing routine quality assurance (QA) have not been optimized and are not readily available. Robust, efficient, and reliable QA tools are needed to ensure the accuracy and reproducibility of SA-IGRT systems. Several investigators have reported custom-made phantoms and protocols for SA-IGRT systems QA. These are typically time and resource intensive and are therefore not well suited to the preclinical radiotherapy environment, in which physics support is limited and routine QA is performed by technical staff. We investigated the use of the inbuilt electronic portal imaging device (EPID) to develop and validate routine QA tests and procedures. In this work, we focus on the Xstrahl Small Animal Radiation Research Platform (SARRP) EPID. However, the methodology and tests developed here are applicable to any SA-IGRT system that incorporates an EPID. We performed a comprehensive characterization of the dosimetric properties of the camera-based EPID at kilovoltage energies over a 11-month period, including detector warm-up time, radiation dose history effect, stability and short- and long-term reproducibility, gantry angle dependency, output factor, and linearity of the EPID response. We developed a test to measure the constancy of beam quality in terms of half-value layer and tube peak potential using the EPID. We verified the SARRP daily output and beam profile constancy using the imager. We investigated the use of the imager to monitor beam-targeting accuracy at various gantry and couch angles. The EPID response was stable and reproducible, exhibiting maximum variations of ≤0.3% and ≤1.9% for short and long terms, respectively. The detector showed no dependence on response at different gantry angles, with a maximum variation ≤0.5%. We found close agreement in output factor measurement between the portal imager and reference dosimeters, with maximum differences ≤3% for ionization chamber and ≤1.7% for Gafchromic EBT3 dosimetry film, respectively. We have shown that the EPID response is linear with tube current (mA) for the entire range of tube kilovoltage peak. Notably, a close relationship was seen between the detector response vs mA slope, and the kilovoltage peak, allowing an independent verification of kilovoltage peak stability based solely on EPID response. In addition to dosimetry tests, according to the beam-targeting measurement using portal images, maximum displacement of the central axis of the x-ray beam (due to sag) was 0.76 ± 0.09 mm at gantry 135°/couch 0° and 0.89 ± 0.06 mm at gantry 0°/couch -135°. We performed the first comprehensive analysis on the dosimetric properties of an EPID operating at kilovoltage x-ray energies. We characterized the detector performance over a 11-month period. Our results indicate that the imager is a stable and convenient tool for SARRP routine QA tests. We then developed EPID-based tests to perform routine SA-IGRT systems QA tasks, such as verifying constancy of beam quality, energy, output, and profile measurements, relative output factors, and beam targeting. © 2018 American Association of Physicists in Medicine.

Effect of injection-gas concentration on the electron beam quality from a laser-plasma accelerator

NASA Astrophysics Data System (ADS)

Mirzaie, Mohammad; Zhang, Guobo; Li, Song; Gao, Kai; Li, Guangyu; Ain, Quratul; Hafz, Nasr A. M.

2018-04-01

By using 25-45 TW ultra-short (30 fs) laser pulses, we report on the effect of the injection gas concentration on the quality of electron beams generated by a laser-driven plasma wakefield acceleration employing the ionization-injection. For a plasma formed from helium-nitrogen gas mixture and depending on the concentration of the nitrogen gas, we could distinguish a clear trend for the quality of the generated electron beams in terms of their peak energy, energy-spread, divergence angle, and beam charge. The results clearly showed that the lower the nitrogen concentration, the better the quality (higher peak energy, smaller energy spread, and smaller emittance) of the generated electron beams. The results are in reasonable agreement with two-dimensional particle-in-cell simulations.

Intercomparison of methods for image quality characterization. II. Noise power spectrum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dobbins, James T. III; Samei, Ehsan; Ranger, Nicole T.

Second in a two-part series comparing measurement techniques for the assessment of basic image quality metrics in digital radiography, in this paper we focus on the measurement of the image noise power spectrum (NPS). Three methods were considered: (1) a method published by Dobbins et al. [Med. Phys. 22, 1581-1593 (1995)] (2) a method published by Samei et al. [Med. Phys. 30, 608-622 (2003)], and (3) a new method sanctioned by the International Electrotechnical Commission (IEC 62220-1, 2003), developed as part of an international standard for the measurement of detective quantum efficiency. In addition to an overall comparison of themore » estimated NPS between the three techniques, the following factors were also evaluated for their effect on the measured NPS: horizontal versus vertical directional dependence, the use of beam-limiting apertures, beam spectrum, and computational methods of NPS analysis, including the region-of-interest (ROI) size and the method of ROI normalization. Of these factors, none was found to demonstrate a substantial impact on the amplitude of the NPS estimates ({<=}3.1% relative difference in NPS averaged over frequency, for each factor considered separately). Overall, the three methods agreed to within 1.6%{+-}0.8% when averaged over frequencies >0.15 mm{sup -1}.« less

Out-of-Field Dose Equivalents Delivered by Passively Scattered Therapeutic Proton Beams for Clinically Relevant Field Configurations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wroe, Andrew; Centre for Medical Radiation Physics, University of Wollongong, Wollongong; Clasie, Ben

2009-01-01

Purpose: Microdosimetric measurements were performed at Massachusetts General Hospital, Boston, MA, to assess the dose equivalent external to passively delivered proton fields for various clinical treatment scenarios. Methods and Materials: Treatment fields evaluated included a prostate cancer field, cranial and spinal medulloblastoma fields, ocular melanoma field, and a field for an intracranial stereotactic treatment. Measurements were completed with patient-specific configurations of clinically relevant treatment settings using a silicon-on-insulator microdosimeter placed on the surface of and at various depths within a homogeneous Lucite phantom. The dose equivalent and average quality factor were assessed as a function of both lateral displacement frommore » the treatment field edge and distance downstream of the beam's distal edge. Results: Dose-equivalent value range was 8.3-0.3 mSv/Gy (2.5-60-cm lateral displacement) for a typical prostate cancer field, 10.8-0.58 mSv/Gy (2.5-40-cm lateral displacement) for the cranial medulloblastoma field, 2.5-0.58 mSv/Gy (5-20-cm lateral displacement) for the spinal medulloblastoma field, and 0.5-0.08 mSv/Gy (2.5-10-cm lateral displacement) for the ocular melanoma field. Measurements of external field dose equivalent for the stereotactic field case showed differences as high as 50% depending on the modality of beam collimation. Average quality factors derived from this work ranged from 2-7, with the value dependent on the position within the phantom in relation to the primary beam. Conclusions: This work provides a valuable and clinically relevant comparison of the external field dose equivalents for various passively scattered proton treatment fields.« less

Accounting for patient size in the optimization of dose and image quality of pelvis cone beam CT protocols on the Varian OBI system

PubMed Central

Moore, Craig S; Horsfield, Carl J; Saunderson, John R; Beavis, Andrew W

2015-01-01

Objective: The purpose of this study was to develop size-based radiotherapy kilovoltage cone beam CT (CBCT) protocols for the pelvis. Methods: Image noise was measured in an elliptical phantom of varying size for a range of exposure factors. Based on a previously defined “small pelvis” reference patient and CBCT protocol, appropriate exposure factors for small, medium, large and extra-large patients were derived which approximate the image noise behaviour observed on a Philips CT scanner (Philips Medical Systems, Best, Netherlands) with automatic exposure control (AEC). Selection criteria, based on maximum tube current–time product per rotation selected during the radiotherapy treatment planning scan, were derived based on an audit of patient size. Results: It has been demonstrated that 110 kVp yields acceptable image noise for reduced patient dose in pelvic CBCT scans of small, medium and large patients, when compared with manufacturer's default settings (125 kVp). Conversely, extra-large patients require increased exposure factors to give acceptable images. 57% of patients in the local population now receive much lower radiation doses, whereas 13% require higher doses (but now yield acceptable images). Conclusion: The implementation of size-based exposure protocols has significantly reduced radiation dose to the majority of patients with no negative impact on image quality. Increased doses are required on the largest patients to give adequate image quality. Advances in knowledge: The development of size-based CBCT protocols that use the planning CT scan (with AEC) to determine which protocol is appropriate ensures adequate image quality whilst minimizing patient radiation dose. PMID:26419892

SU-E-T-216: TPS QC Supporting Program by a Third-Party Evaluation Agency in Japan.

PubMed

Fukata, K; Minemura, T; Kurokawa, C; Miyagishi, T; Itami, J

2012-06-01

To equalize the quality of radiation therapy in Japan by supporting quality control of radiation treatment planning system. Center for Cancer Control and Information Service in National Cancer Center supports the QA-QC of the cancer core hospitals in Japan as a third-party evaluation agency. Recently, a program for assessing the quality of treatment planning system (TPS) began as a part of our QA-QC supporting activities. In this program, a questionnaire about TPS was sent to 45 prefectural cancer core hospitals in Japan. The object of this questionnaire is to assess the proper commissioning, implement and applications of TPSs. The contents of the questionnaire are as follows; 1) calculate MUs which deliver 1000 cGy to the point of SSD = 100 cm, 10 cm depth with field sizes ranging from 5×5 to 30 × 30 cm 2 , and obtain doses at several depths for the calculated MUs, 2) calculate MUs which deliver 1000 cGy to the point of SSD = 100 cm, 10 cm depth for wedge fields whose angles are from 15 to 60 degrees, and obtain doses at several depths with the MUs, 3) calculate MU which deliver 1000 cGy to the point of STD = 100 cm, 10 cm depth with 10×10 cm 2 field size and obtain doses at several depths with the MU. In this program, 179 beam data from 44 facilities were collected. Data were compared in terms of dose per MU, output factor, wedge factor and TMR. It was found that 90% of the data agreed within 2%. The quality of the treatment planning system was investigated through the questionnaire including the information of essential beam data. We compared 179 beam data in TPSs sent from 44 facilities and 90% of the data showed good agreement. © 2012 American Association of Physicists in Medicine.

980 nm tapered lasers with photonic crystal structure for low vertical divergence

NASA Astrophysics Data System (ADS)

Ma, Xiaolong; Qu, Hongwei; Zhao, Pengchao; Liu, Yun; Zheng, Wanhua

2016-10-01

High power tapered lasers with nearly diffraction-limited beam quality have attracted much attention in numerous applications such as nonlinear frequency conversion, optical pumping of solid-state and fiber lasers, medical treatment and others. However, the large vertical divergence of conventional tapered lasers is a disadvantage, which makes beam shaping difficult and expensive in applications. Diode lasers with photonic crystal structure can achieve a large mode size and a narrow vertical divergence. In this paper, we present tapered lasers with photonic crystal structure emitting at 980 nm. The epitaxial layer is grown using metal organic chemical vapor deposition. The device has a total cavity length of 2 mm, which consists of a 400-um long ridge-waveguide section and a 1600-um long tapered section. The taper angle is 4°. An output power of 3.3 W is achieved with a peak conversion efficiency of 35% in pulsed mode. The threshold current is 240 mA and the slope efficiency is 0.78 W/A. In continuous wave mode, the output power is 2.87 W, which is limited by a suddenly failure resulting from catastrophic optical mirror damage. The far field divergences with full width at half maximum are 12.3° in the vertical direction and 2.9° in the lateral direction at 0.5 A. At high injection level the vertical divergence doesn't exceed 16°. Beam quality factor M2 is measured based on second moment definition in CW mode. High beam quality is demonstrated by M2 value of less than 2 in both vertical and lateral directions.

The effects of ion gun beam voltage on the electrical characteristics of NbCN/PbBi edge junctions

NASA Technical Reports Server (NTRS)

Lichtenberger, A. W.; Feldman, M. J.; Mattauch, R. J.; Cukauskas, E. J.

1989-01-01

The authors have succeeded in fabricating high-quality submicron NbCN edge junctions using a technique which is commonly used to make Nb edge junctions. A modified commercial ion gun was used to cut an edge in SiO2/NbCN films partially covered with photoresist. An insulating barrier was then formed on the exposed edge by reactive ion beam oxidation, and a counterelectrode of PbBi was deposited. The electrical quality of the resulting junctions was found to be strongly influenced by the ion beam acceleration voltages used to cut the edge and to oxidize it. For low ion beam voltages, the junction quality parameter was as high as Vm = 55 mV (measured at 3 mV), but higher ion beam voltages yielded strikingly poorer quality junctions. In light of the small coherence length of NbN, the dependence of the electrical characteristics on ion beam voltage is presumably due to mechanical damage of the NbCN surface. In contrast, for similar ion beam voltages, no such dependence was found for Nb edge junctions.

CyberArc: a non-coplanar-arc optimization algorithm for CyberKnife

NASA Astrophysics Data System (ADS)

Kearney, Vasant; Cheung, Joey P.; McGuinness, Christopher; Solberg, Timothy D.

2017-07-01

The goal of this study is to demonstrate the feasibility of a novel non-coplanar-arc optimization algorithm (CyberArc). This method aims to reduce the delivery time of conventional CyberKnife treatments by allowing for continuous beam delivery. CyberArc uses a 4 step optimization strategy, in which nodes, beams, and collimator sizes are determined, source trajectories are calculated, intermediate radiation models are generated, and final monitor units are calculated, for the continuous radiation source model. The dosimetric results as well as the time reduction factors for CyberArc are presented for 7 prostate and 2 brain cases. The dosimetric quality of the CyberArc plans are evaluated using conformity index, heterogeneity index, local confined normalized-mutual-information, and various clinically relevant dosimetric parameters. The results indicate that the CyberArc algorithm dramatically reduces the treatment time of CyberKnife plans while simultaneously preserving the dosimetric quality of the original plans.

CyberArc: a non-coplanar-arc optimization algorithm for CyberKnife.

PubMed

Kearney, Vasant; Cheung, Joey P; McGuinness, Christopher; Solberg, Timothy D

2017-06-26

The goal of this study is to demonstrate the feasibility of a novel non-coplanar-arc optimization algorithm (CyberArc). This method aims to reduce the delivery time of conventional CyberKnife treatments by allowing for continuous beam delivery. CyberArc uses a 4 step optimization strategy, in which nodes, beams, and collimator sizes are determined, source trajectories are calculated, intermediate radiation models are generated, and final monitor units are calculated, for the continuous radiation source model. The dosimetric results as well as the time reduction factors for CyberArc are presented for 7 prostate and 2 brain cases. The dosimetric quality of the CyberArc plans are evaluated using conformity index, heterogeneity index, local confined normalized-mutual-information, and various clinically relevant dosimetric parameters. The results indicate that the CyberArc algorithm dramatically reduces the treatment time of CyberKnife plans while simultaneously preserving the dosimetric quality of the original plans.

Nd-glass laser for deep-penetration welding and hardening

NASA Astrophysics Data System (ADS)

Kayukov, Serguei V.; Yaresko, Sergey I.; Mikheyev, Pavel A.

2000-04-01

Pulsed Nd-glass lasers usually have low beam quality (200 - 300 mm-mrad), and are used only for surface hardening of metals. However, high pulse energy make them feasible for deep penetration welding if their beam quality could be improved. We investigated beam properties of Nd-glass laser with unstable resonator with semitransparent output coupler (URSOC). We had found that beam divergence of the laser with URSOC was an order of magnitude smaller than that of the laser with stable resonator. The achieved beam quality (40 - 50 mm-mrad) permitted to perform deep penetration welding with the aspect ratio of approximately 8. For beam divergence of 3 mrad melt depth of 6.3 mm was achieved with the ratio of depth to pulse energy of 0.27 mm/J.

Two-beam combined 3.36  J, 100  Hz diode-pumped high beam quality Nd:YAG laser system.

PubMed

Qiu, J S; Tang, X X; Fan, Z W; Wang, H C; Liu, H

2016-07-20

In this paper, we develop a diode-pumped all-solid-state high-energy and high beam quality Nd:YAG laser system. A master oscillator power amplifier structure is used to provide a high pulse energy laser output with a high repetition rate. In order to decrease the amplifier working current so as to reduce the impact of the thermal effect on the beam quality, a beam splitting-amplifying-combining scheme is adopted. The energy extraction efficiency of the laser system is 50.68%. We achieve 3.36 J pulse energy at a 100 Hz repetition rate with a pulse duration of 7.1 ns, a far-field beam spot 1.71 times the diffraction limit, and 1.07% energy stability (RMS).

Effects of detuning of electron beam quality for annular beam Cyclotron Autoresonance Accelerator (CARA)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, C.; Hirshfield, J.L.; Ganguly, K.

1995-04-01

For high frequency gyrotrons or high gyroharmonic conversion, an axis encircling beam of high voltage is required to allow coupling to whispering gallery fields near the walls. Lower voltage is required for an annular beam of similar velocity ratio {alpha}. Here the authors present simulation results using a modified CARA for preparation of a 320 kV, 20 A, {alpha} = 1.5 annular beam driven at 11.424 GHz with an rf power of 5 MW and an injection voltage of 75 kV. It is shown that the beam quality can be considerably improved by so-called {open_quotes}detuning{close_quotes}, where the tapered axial magneticmore » field profiles in the CARA are caused to deviate a small amount from exact resonance. Under typical operating conditions, beams with axial velocity spreads of the order of 1% are predicted. This approach could be used to provide a high quality annular gyrating beam for multi-megawatt millimeter wave sources in the 100-200 GHz range.« less

Effect of fluoroscopic X-ray beam spectrum on air-kerma measurement accuracy: implications for establishing correction coefficients on interventional fluoroscopes with KAP meters.

PubMed

Wunderle, Kevin A; Rakowski, Joseph T; Dong, Frank F

2016-05-08

The first goal of this study was to investigate the accuracy of the displayed reference plane air kerma (Ka,r) or air kerma-area product (Pk,a) over a broad spectrum of X-ray beam qualities on clinically used interventional fluoroscopes incorporating air kerma-area product meters (KAP meters) to measure X-ray output. The second goal was to investigate the accuracy of a correction coefficient (CC) determined at a single beam quality and applied to the measured Ka,r over a broad spectrum of beam qualities. Eleven state-of-the-art interventional fluoroscopes were evaluated, consisting of eight Siemens Artis zee and Artis Q systems and three Philips Allura FD systems. A separate calibrated 60 cc ionization chamber (external chamber) was used to determine the accuracy of the KAP meter over a broad range of clinically used beam qualities. For typical adult beam qualities, applying a single CC deter-mined at 100 kVp with copper (Cu) in the beam resulted in a deviation of < 5% due to beam quality variation. This result indicates that applying a CC determined using The American Association of Physicists in Medicine Task Group 190 protocol or a similar protocol provides very good accuracy as compared to the allowed ± 35% deviation of the KAP meter in this limited beam quality range. For interventional fluoroscopes dedicated to or routinely used to perform pediatric interventions, using a CC established with a low kVp (~ 55-60 kVp) and large amount of Cu filtration (~ 0.6-0.9 mm) may result in greater accuracy as compared to using the 100 kVp values. KAP meter responses indicate that fluoroscope vendors are likely normalizing or otherwise influencing the KAP meter output data. Although this may provide improved accuracy in some instances, there is the potential for large discrete errors to occur, and these errors may be difficult to identify.

Structured Laguerre-Gaussian beams for mitigation of spherical aberration in tightly focused regimes

NASA Astrophysics Data System (ADS)

Haddadi, S.; Bouzid, O.; Fromager, M.; Hasnaoui, A.; Harfouche, A.; Cagniot, E.; Forbes, A.; Aït-Ameur, K.

2018-04-01

Many laser applications utilise a focused laser beam having a single-lobed intensity profile in the focal plane, ideally with the highest possible on-axis intensity. Conventionally, this is achieved with the lowest-order Laguerre-Gaussian mode (LG00), the Gaussian beam, in a tight focusing configuration. However, tight focusing often involves significant spherical aberration due to the high numerical aperture of the systems involved, thus degrading the focal quality. Here, we demonstrate that a high-order radial LG p0 mode can be tailored to meet and in some instances exceed the performance of the Gaussian. We achieve this by phase rectification of the mode using a simple binary diffractive optic. By way of example, we show that the focusing of a rectified LG50 beam is almost insensitive to a spherical aberration coefficient of over three wavelengths, in contrast with the usual Gaussian beam for which the intensity of the focal spot is reduced by a factor of two. This work paves the way towards enhanced focal spots using structured light.

Dual Q-switched laser outputs from a single lasing medium using an intracavity MEMS micromirror array.

PubMed

Bauer, Ralf; Lubeigt, Walter; Uttamchandani, Deepak

2012-09-01

An intracavity array of individually controlled microelectromechanical system scanning micromirrors was used to actively Q-switch a single side-pumped Nd:YAG gain medium. Two equal power independent laser outputs were simultaneously obtained by separate actuation of two adjacent micromirrors with a combined average output power of 125 mW. Pulse durations of 28 ns FWHM at 8.7 kHz repetition frequency and 34 ns FWHM at 7.9 kHz repetition frequency were observed for the two output beams with beam quality factors M2 of 1.2 and 1.1 and peak powers of 253 W and 232 W, respectively.

Method for obtaining a collimated near-unity aspect ratio output beam from a DFB-GSE laser with good beam quality.

PubMed

Liew, S K; Carlson, N W

1992-05-20

A simple method for obtaining a collimated near-unity aspect ratio output beam from laser sources with extremely large (> 100:1) aspect ratios is demonstrated by using a distributed-feedback grating-surfaceemitting laser. Far-field power-in-the-bucket measurements of the laser indicate good beam quality with a high Strehl ratio.

The quality assessment of radial and tangential neutron radiography beamlines of TRR

NASA Astrophysics Data System (ADS)

Choopan Dastjerdi, M. H.; Movafeghi, A.; Khalafi, H.; Kasesaz, Y.

2017-07-01

To achieve a quality neutron radiographic image in a relatively short exposure time, the neutron radiography beam must be of good quality and relatively high neutron flux. Characterization of a neutron radiography beam, such as determination of the image quality and the neutron flux, is vital for producing quality radiographic images and also provides a means to compare the quality of different neutron radiography facilities. This paper provides a characterization of the radial and tangential neutron radiography beamlines at the Tehran research reactor. This work includes determination of the facilities category according to the American Society for Testing and Materials (ASTM) standards, and also uses the gold foils to determine the neutron beam flux. The radial neutron beam is a Category I neutron radiography facility, the highest possible quality level according to the ASTM. The tangential beam is a Category IV neutron radiography facility. Gold foil activation experiments show that the measured neutron flux for radial beamline with length-to-diameter ratio (L/D) =150 is 6.1× 106 n cm-2 s-1 and for tangential beamline with (L/D)=115 is 2.4× 104 n cm-2 s-1.

Betatron radiation based diagnostics for plasma wakefield accelerated electron beams at the SPARC_LAB test facility

NASA Astrophysics Data System (ADS)

Shpakov, V.; Anania, M. P.; Biagioni, A.; Chiadroni, E.; Cianchi, A.; Curcio, A.; Dabagov, S.; Ferrario, M.; Filippi, F.; Marocchino, A.; Paroli, B.; Pompili, R.; Rossi, A. R.; Zigler, A.

2016-09-01

Recent progress with wake-field acceleration has shown a great potential in providing high gradient acceleration fields, while the quality of the beams remains relatively poor. Precise knowledge of the beam size at the exit from the plasma and matching conditions for the externally injected beams are the key for improvement of beam quality. Betatron radiation emitted by the beam during acceleration in the plasma is a powerful tool for the transverse beam size measurement, being also non-intercepting. In this work we report on the technical solutions chosen at SPARC_LAB for such diagnostics tool, along with expected parameters of betatron radiation.

A large capacity time division multiplexed (TDM) laser beam combining technique enabled by nanosecond speed KTN deflector

NASA Astrophysics Data System (ADS)

Yin, Stuart (Shizhuo); Chao, Ju-Hung; Zhu, Wenbin; Chen, Chang-Jiang; Campbell, Adrian; Henry, Michael; Dubinskiy, Mark; Hoffman, Robert C.

2017-08-01

In this paper, we present a novel large capacity (a 1000+ channel) time division multiplexing (TDM) laser beam combining technique by harnessing a state-of-the-art nanosecond speed potassium tantalate niobate (KTN) electro-optic (EO) beam deflector as the time division multiplexer. The major advantages of TDM approach are: (1) large multiplexing capability (over 1000 channels), (2) high spatial beam quality (the combined beam has the same spatial profile as the individual beam), (3) high spectral beam quality (the combined beam has the same spectral width as the individual beam, and (4) insensitive to the phase fluctuation of individual laser because of the nature of the incoherent beam combining. The quantitative analyses show that it is possible to achieve over one hundred kW average power, single aperture, single transverse mode solid state and/or fiber laser by pursuing this innovative beam combining method, which represents a major technical advance in the field of high energy lasers. Such kind of 100+ kW average power diffraction limited beam quality lasers can play an important role in a variety of applications such as laser directed energy weapons (DEW) and large-capacity high-speed laser manufacturing, including cutting, welding, and printing.

Spiking suppression of high power QCW pulse 1319 nm Nd:YAG laser with different intracavity doublers

NASA Astrophysics Data System (ADS)

Bian, Qi; Zuo, Jun-Wei; Guo, Chuan; Xu, Chang; Shen, Yu; Zong, Nan; Bo, Yong; Peng, Qin-Jun; Chen, Hong-Bin; Cui, Da-Fu; Xu, Zu-Yan

2016-09-01

We describe the results of our efforts in suppressing spiking of a high power, high beam quality 1319 nm Nd:YAG microsecond-pulse laser with three different intracavity frequency doublers. The 1319 nm laser is generated by a quasi-continuous-wave diode-pumped Nd:YAG ring laser system. One potassium titanyl phosphate (KTP), two KTPs and one lithium triborate (LBO) as frequency doublers are installed in the ring resonator and tested, respectively. At 800 Hz repetition rate, with a pulse width of 100 µs, performances of spiking suppression for each case are observed. The average output power are 23.6 W, 22.7 W and 23.4 W with beam quality factors of M 2  =  2.21, 1.28 and 1.25 for one KTP, two KTPs and one LBO, respectively. The corresponding brightness are 270 MW/(cm2·sr), 780 MW/(cm2·sr) and 860 MW/(cm2·sr). With better beam quality, higher brightness, and easier maintainability, the LBO is the best option of the three. A laser rate equation model including the insertion loss of the doubler is applied for theoretical analysis of the output temporal pulse shape and power, and the simulated results agree well with the experimental data.

A systematic characterization of the low-energy photon response of plastic scintillation detectors.

PubMed

Boivin, Jonathan; Beddar, Sam; Bonde, Chris; Schmidt, Daniel; Culberson, Wesley; Guillemette, Maxime; Beaulieu, Luc

2016-08-07

To characterize the low energy behavior of scintillating materials used in plastic scintillation detectors (PSDs), 3 PSDs were developed using polystyrene-based scintillating materials emitting in different wavelengths. These detectors were exposed to National Institute of Standards and Technology (NIST)-matched low-energy beams ranging from 20 kVp to 250 kVp, and to (137)Cs and (60)Co beams. The dose in polystyrene was compared to the dose in air measured by NIST-calibrated ionization chambers at the same location. Analysis of every beam quality spectrum was used to extract the beam parameters and the effective mass energy-absorption coefficient. Monte Carlo simulations were also performed to calculate the energy absorbed in the scintillators' volume. The scintillators' expected response was then compared to the experimental measurements and an energy-dependent correction factor was identified to account for low-energy quenching in the scintillators. The empirical Birks model was then compared to these values to verify its validity for low-energy electrons. The clear optical fiber response was below 0.2% of the scintillator's light for x-ray beams, indicating that a negligible amount of fluorescence contamination was produced. However, for higher-energy beams ((137)Cs and (60)Co), the scintillators' response was corrected for the Cerenkov stem effect. The scintillators' response increased by a factor of approximately 4 from a 20 kVp to a (60)Co beam. The decrease in sensitivity from ionization quenching reached a local minimum of about [Formula: see text] between 40 keV and 60 keV x-ray beam mean energy, but dropped by 20% for very low-energy (13 keV) beams. The Birks model may be used to fit the experimental data, but it must take into account the energy dependence of the kB quenching parameter. A detailed comprehension of intrinsic scintillator response is essential for proper calibration of PSD dosimeters for radiology.

A systematic characterization of the low-energy photon response of plastic scintillation detectors

NASA Astrophysics Data System (ADS)

Boivin, Jonathan; Beddar, Sam; Bonde, Chris; Schmidt, Daniel; Culberson, Wesley; Guillemette, Maxime; Beaulieu, Luc

2016-08-01

To characterize the low energy behavior of scintillating materials used in plastic scintillation detectors (PSDs), 3 PSDs were developed using polystyrene-based scintillating materials emitting in different wavelengths. These detectors were exposed to National Institute of Standards and Technology (NIST)-matched low-energy beams ranging from 20 kVp to 250 kVp, and to 137Cs and 60Co beams. The dose in polystyrene was compared to the dose in air measured by NIST-calibrated ionization chambers at the same location. Analysis of every beam quality spectrum was used to extract the beam parameters and the effective mass energy-absorption coefficient. Monte Carlo simulations were also performed to calculate the energy absorbed in the scintillators’ volume. The scintillators’ expected response was then compared to the experimental measurements and an energy-dependent correction factor was identified to account for low-energy quenching in the scintillators. The empirical Birks model was then compared to these values to verify its validity for low-energy electrons. The clear optical fiber response was below 0.2% of the scintillator’s light for x-ray beams, indicating that a negligible amount of fluorescence contamination was produced. However, for higher-energy beams (137Cs and 60Co), the scintillators’ response was corrected for the Cerenkov stem effect. The scintillators’ response increased by a factor of approximately 4 from a 20 kVp to a 60Co beam. The decrease in sensitivity from ionization quenching reached a local minimum of about 11%+/- 1% between 40 keV and 60 keV x-ray beam mean energy, but dropped by 20% for very low-energy (13 keV) beams. The Birks model may be used to fit the experimental data, but it must take into account the energy dependence of the kB quenching parameter. A detailed comprehension of intrinsic scintillator response is essential for proper calibration of PSD dosimeters for radiology.

Adaptive slab laser beam quality improvement using a weighted least-squares reconstruction algorithm.

PubMed

Chen, Shanqiu; Dong, LiZhi; Chen, XiaoJun; Tan, Yi; Liu, Wenjin; Wang, Shuai; Yang, Ping; Xu, Bing; Ye, YuTang

2016-04-10

Adaptive optics is an important technology for improving beam quality in solid-state slab lasers. However, there are uncorrectable aberrations in partial areas of the beam. In the criterion of the conventional least-squares reconstruction method, it makes the zones with small aberrations nonsensitive and hinders this zone from being further corrected. In this paper, a weighted least-squares reconstruction method is proposed to improve the relative sensitivity of zones with small aberrations and to further improve beam quality. Relatively small weights are applied to the zones with large residual aberrations. Comparisons of results show that peak intensity in the far field improved from 1242 analog digital units (ADU) to 2248 ADU, and beam quality β improved from 2.5 to 2.0. This indicates the weighted least-squares method has better performance than the least-squares reconstruction method when there are large zonal uncorrectable aberrations in the slab laser system.

Beam uniformity analysis of infrared laser illuminators

NASA Astrophysics Data System (ADS)

Allik, Toomas H.; Dixon, Roberta E.; Proffitt, R. Patrick; Fung, Susan; Ramboyong, Len; Soyka, Thomas J.

2015-02-01

Uniform near-infrared (NIR) and short-wave infrared (SWIR) illuminators are desired in low ambient light detection, recognition, and identification of military applications. Factors that contribute to laser illumination image degradation are high frequency, coherent laser speckle and low frequency nonuniformities created by the laser or external laser cavity optics. Laser speckle analysis and beam uniformity improvements have been independently studied by numerous authors, but analysis to separate these two effects from a single measurement technique has not been published. In this study, profiles of compact, diode laser NIR and SWIR illuminators were measured and evaluated. Digital 12-bit images were recorded with a flat-field calibrated InGaAs camera with measurements at F/1.4 and F/16. Separating beam uniformity components from laser speckle was approximated by filtering the original image. The goal of this paper is to identify and quantify the beam quality variation of illumination prototypes, draw awareness to its impact on range performance modeling, and develop measurement techniques and methodologies for military, industry, and vendors of active sources.

Efficient dielectric metasurface collimating lenses for mid-infrared quantum cascade lasers.

PubMed

Arbabi, Amir; Briggs, Ryan M; Horie, Yu; Bagheri, Mahmood; Faraon, Andrei

2015-12-28

Light emitted from single-mode semiconductor lasers generally has large divergence angles, and high numerical aperture lenses are required for beam collimation. Visible and near infrared lasers are collimated using aspheric glass or plastic lenses, yet collimation of mid-infrared quantum cascade lasers typically requires more costly aspheric lenses made of germanium, chalcogenide compounds, or other infrared-transparent materials. Here we report mid-infrared dielectric metasurface flat lenses that efficiently collimate the output beam of single-mode quantum cascade lasers. The metasurface lenses are composed of amorphous silicon posts on a flat sapphire substrate and can be fabricated at low cost using a single step conventional UV binary lithography. Mid-infrared radiation from a 4.8 μm distributed-feedback quantum cascade laser is collimated using a polarization insensitive metasurface lens with 0.86 numerical aperture and 79% transmission efficiency. The collimated beam has a half divergence angle of 0.36° and beam quality factor of M2=1.02.

The Design and Performance Evaluation of Hydroformed Tubular Torsion Beam Axle

NASA Astrophysics Data System (ADS)

Kim, Jaehyun; Oh, Jinho; Choi, Hanho

2010-06-01

Suspensions for vehicles are structural devices used for suspending a vehicle body and absorbing shocks from the road. Thus, the suspensions must be designed such that they can attenuate shocks from a road and make passengers feel comfortable despite the shocks, and improve steering stability, determined by the ground contact force of tires during running of vehicles. Another important factor to be considered while designing suspensions is that the suspensions must maintain desired stiffness and desired durability despite the repeated application of shocks from roads thereto. The present relates, in general, to a tubular torsion beam for rear suspensions of vehicles and a manufacturing method thereof and, more particularly, to the provision of tubular torsion beams having excellent roll stiffness and excellent roll strength, produced through hydroforming. The hydroforming technology has a lot of benefit which is shape accuracy, good durability caused by compressive pressure, and good forming quality. In this study, the performance evaluation of the hydroformed tubular torsion beam axle is evaluated.

Efficient dielectric metasurface collimating lenses for mid-infrared quantum cascade lasers

DOE PAGES

Arbabi, Amir; Briggs, Ryan M.; Horie, Yu; ...

2015-01-01

Light emitted from single-mode semiconductor lasers generally has large divergence angles, and high numerical aperture lenses are required for beam collimation. Visible and near infrared lasers are collimated using aspheric glass or plastic lenses, yet collimation of mid-infrared quantum cascade lasers typically requires more costly aspheric lenses made of germanium, chalcogenide compounds, or other infrared-transparent materials. We report mid-infrared dielectric metasurface flat lenses that efficiently collimate the output beam of single-mode quantum cascade lasers. The metasurface lenses are composed of amorphous silicon posts on a flat sapphire substrate and can be fabricated at low cost using a single step conventionalmore » UV binary lithography. Mid-infrared radiation from a 4.8 μm distributed-feedback quantum cascade laser is collimated using a polarization insensitive metasurface lens with 0.86 numerical aperture and 79% transmission efficiency. The collimated beam has a half divergence angle of 0.36° and beam quality factor of M² =1.02.« less

Beam Characterization at the Neutron Radiography Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sarah Morgan; Jeffrey King

The quality of a neutron imaging beam directly impacts the quality of radiographic images produced using that beam. Fully characterizing a neutron beam, including determination of the beam’s effective length-to-diameter ratio, neutron flux profile, energy spectrum, image quality, and beam divergence, is vital for producing quality radiographic images. This project characterized the east neutron imaging beamline at the Idaho National Laboratory Neutron Radiography Reactor (NRAD). The experiments which measured the beam’s effective length-to-diameter ratio and image quality are based on American Society for Testing and Materials (ASTM) standards. An analysis of the image produced by a calibrated phantom measured themore » beam divergence. The energy spectrum measurements consist of a series of foil irradiations using a selection of activation foils, compared to the results produced by a Monte Carlo n-Particle (MCNP) model of the beamline. Improvement of the existing NRAD MCNP beamline model includes validation of the model’s energy spectrum and the development of enhanced image simulation methods. The image simulation methods predict the radiographic image of an object based on the foil reaction rate data obtained by placing a model of the object in front of the image plane in an MCNP beamline model.« less

Development and reproducibility evaluation of a Monte Carlo-based standard LINAC model for quality assurance of multi-institutional clinical trials.

PubMed

Usmani, Muhammad Nauman; Takegawa, Hideki; Takashina, Masaaki; Numasaki, Hodaka; Suga, Masaki; Anetai, Yusuke; Kurosu, Keita; Koizumi, Masahiko; Teshima, Teruki

2014-11-01

Technical developments in radiotherapy (RT) have created a need for systematic quality assurance (QA) to ensure that clinical institutions deliver prescribed radiation doses consistent with the requirements of clinical protocols. For QA, an ideal dose verification system should be independent of the treatment-planning system (TPS). This paper describes the development and reproducibility evaluation of a Monte Carlo (MC)-based standard LINAC model as a preliminary requirement for independent verification of dose distributions. The BEAMnrc MC code is used for characterization of the 6-, 10- and 15-MV photon beams for a wide range of field sizes. The modeling of the LINAC head components is based on the specifications provided by the manufacturer. MC dose distributions are tuned to match Varian Golden Beam Data (GBD). For reproducibility evaluation, calculated beam data is compared with beam data measured at individual institutions. For all energies and field sizes, the MC and GBD agreed to within 1.0% for percentage depth doses (PDDs), 1.5% for beam profiles and 1.2% for total scatter factors (Scps.). Reproducibility evaluation showed that the maximum average local differences were 1.3% and 2.5% for PDDs and beam profiles, respectively. MC and institutions' mean Scps agreed to within 2.0%. An MC-based standard LINAC model developed to independently verify dose distributions for QA of multi-institutional clinical trials and routine clinical practice has proven to be highly accurate and reproducible and can thus help ensure that prescribed doses delivered are consistent with the requirements of clinical protocols. © The Author 2014. Published by Oxford University Press on behalf of The Japan Radiation Research Society and Japanese Society for Radiation Oncology.

Design and analysis of a radio frequency extractor in an S-band relativistic klystron amplifier.

PubMed

Zhang, Zehai; Zhang, Jun; Shu, Ting; Qi, Zumin

2012-09-01

A radio frequency (RF) extractor converts the energy of a strongly modulated intense relativistic electron beam (IREB) into the energy of high power microwave in relativistic klystron amplifier (RKA). In the aim of efficiently extracting the energy of the modulated IREB, a RF extractor with all round coupling structure is proposed. Due to the all round structure, the operating transverse magnetic mode can be established easily and its resonant property can be investigated with an approach of group delay time. Furthermore, the external quality factor can be low enough. The design and analysis of the extractor applied in an S-band RKA are carried out, and the performance of the extractor is validated with three-dimensional (3D) particle-in-cell simulations. The extraction efficiency reaches 27% in the simulation with a totally 3D model of the whole RKA. The primary experiments are also carried out and the results show that the RF extractor with the external quality factor of 7.9 extracted 22% of the beam power and transformed it into the high power microwave. Better results are expected after the parasitic mode between the input and middle cavities is suppressed.

Design and analysis of a radio frequency extractor in an S-band relativistic klystron amplifier

NASA Astrophysics Data System (ADS)

Zhang, Zehai; Zhang, Jun; Shu, Ting; Qi, Zumin

2012-09-01

A radio frequency (RF) extractor converts the energy of a strongly modulated intense relativistic electron beam (IREB) into the energy of high power microwave in relativistic klystron amplifier (RKA). In the aim of efficiently extracting the energy of the modulated IREB, a RF extractor with all round coupling structure is proposed. Due to the all round structure, the operating transverse magnetic mode can be established easily and its resonant property can be investigated with an approach of group delay time. Furthermore, the external quality factor can be low enough. The design and analysis of the extractor applied in an S-band RKA are carried out, and the performance of the extractor is validated with three-dimensional (3D) particle-in-cell simulations. The extraction efficiency reaches 27% in the simulation with a totally 3D model of the whole RKA. The primary experiments are also carried out and the results show that the RF extractor with the external quality factor of 7.9 extracted 22% of the beam power and transformed it into the high power microwave. Better results are expected after the parasitic mode between the input and middle cavities is suppressed.

A fast and sensitive TLD method for measurement of energy and homogeneity of electron beams using transmitted radiation through lead.

PubMed

Pradhan, A S; Quast, U; Sharma, P K

1994-09-01

A simple and fast, but sensitive TLD method for the measurement of energy and homogeneity of therapeutically used electron beams has been developed and tested. This method is based on the fact that when small thicknesses of high-Z absorbers such as lead are interposed in the high-energy electron beams, the transmitted radiation increases with the energy of the electron beams. Consequently, the ratio of readouts of TLDS held on the two sides of a lead plate varied sharply (by factor of 70) with a change in energy of the electron beam from 5 MeV to 18 MeV, offering a very sensitive method for the measurement of the energy of electron beams. By using the ratio of TL readouts of two types of TLD ribbon with widely different sensitivities, LiF TLD-700 ribbons on the upstream side and highly sensitive CaF2:Dy TLD-200 ribbons on the downstream side, an electron energy discrimination of better than +/- 0.1 MeV could be achieved. The homogeneity of the electron beam energy and the absorbed dose was measured by using a jig in which the TLDS were held in the desired array on both sides of a 4 mm thick lead plate. The method takes minimal beam time and makes it possible to carry out measurements for the audit of the quality of electron beams as well as for intercomparison of beams by mail.

Accounting for partiality in serial crystallography using ray-tracing principles.

PubMed

Kroon-Batenburg, Loes M J; Schreurs, Antoine M M; Ravelli, Raimond B G; Gros, Piet

2015-09-01

Serial crystallography generates `still' diffraction data sets that are composed of single diffraction images obtained from a large number of crystals arbitrarily oriented in the X-ray beam. Estimation of the reflection partialities, which accounts for the expected observed fractions of diffraction intensities, has so far been problematic. In this paper, a method is derived for modelling the partialities by making use of the ray-tracing diffraction-integration method EVAL. The method estimates partialities based on crystal mosaicity, beam divergence, wavelength dispersion, crystal size and the interference function, accounting for crystallite size. It is shown that modelling of each reflection by a distribution of interference-function weighted rays yields a `still' Lorentz factor. Still data are compared with a conventional rotation data set collected from a single lysozyme crystal. Overall, the presented still integration method improves the data quality markedly. The R factor of the still data compared with the rotation data decreases from 26% using a Monte Carlo approach to 12% after applying the Lorentz correction, to 5.3% when estimating partialities by EVAL and finally to 4.7% after post-refinement. The merging R(int) factor of the still data improves from 105 to 56% but remains high. This suggests that the accuracy of the model parameters could be further improved. However, with a multiplicity of around 40 and an R(int) of ∼50% the merged still data approximate the quality of the rotation data. The presented integration method suitably accounts for the partiality of the observed intensities in still diffraction data, which is a critical step to improve data quality in serial crystallography.

Fabrication of precision high quality facets on molecular beam epitaxy material

DOEpatents

Petersen, Holly E.; Goward, William D.; Dijaili, Sol P.

2001-01-01

Fabricating mirrored vertical surfaces on semiconductor layered material grown by molecular beam epitaxy (MBE). Low energy chemically assisted ion beam etching (CAIBE) is employed to prepare mirrored vertical surfaces on MBE-grown III-V materials under unusually low concentrations of oxygen in evacuated etching atmospheres of chlorine and xenon ion beams. UV-stabilized smooth-surfaced photoresist materials contribute to highly vertical, high quality mirrored surfaces during the etching.

A surrogate-based metaheuristic global search method for beam angle selection in radiation treatment planning.

PubMed

Zhang, H H; Gao, S; Chen, W; Shi, L; D'Souza, W D; Meyer, R R

2013-03-21

An important element of radiation treatment planning for cancer therapy is the selection of beam angles (out of all possible coplanar and non-coplanar angles in relation to the patient) in order to maximize the delivery of radiation to the tumor site and minimize radiation damage to nearby organs-at-risk. This category of combinatorial optimization problem is particularly difficult because direct evaluation of the quality of treatment corresponding to any proposed selection of beams requires the solution of a large-scale dose optimization problem involving many thousands of variables that represent doses delivered to volume elements (voxels) in the patient. However, if the quality of angle sets can be accurately estimated without expensive computation, a large number of angle sets can be considered, increasing the likelihood of identifying a very high quality set. Using a computationally efficient surrogate beam set evaluation procedure based on single-beam data extracted from plans employing equallyspaced beams (eplans), we have developed a global search metaheuristic process based on the nested partitions framework for this combinatorial optimization problem. The surrogate scoring mechanism allows us to assess thousands of beam set samples within a clinically acceptable time frame. Tests on difficult clinical cases demonstrate that the beam sets obtained via our method are of superior quality.

A surrogate-based metaheuristic global search method for beam angle selection in radiation treatment planning

PubMed Central

Zhang, H H; Gao, S; Chen, W; Shi, L; D’Souza, W D; Meyer, R R

2013-01-01

An important element of radiation treatment planning for cancer therapy is the selection of beam angles (out of all possible coplanar and non-coplanar angles in relation to the patient) in order to maximize the delivery of radiation to the tumor site and minimize radiation damage to nearby organs-at-risk. This category of combinatorial optimization problem is particularly difficult because direct evaluation of the quality of treatment corresponding to any proposed selection of beams requires the solution of a large-scale dose optimization problem involving many thousands of variables that represent doses delivered to volume elements (voxels) in the patient. However, if the quality of angle sets can be accurately estimated without expensive computation, a large number of angle sets can be considered, increasing the likelihood of identifying a very high quality set. Using a computationally efficient surrogate beam set evaluation procedure based on single-beam data extracted from plans employing equally-spaced beams (eplans), we have developed a global search metaheuristic process based on the Nested Partitions framework for this combinatorial optimization problem. The surrogate scoring mechanism allows us to assess thousands of beam set samples within a clinically acceptable time frame. Tests on difficult clinical cases demonstrate that the beam sets obtained via our method are superior quality. PMID:23459411

Five-cell superconducting RF module with a PBG coupler cell: design and cold testing of the copper prototype

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arsenyev, Sergey Andreyevich; Simakov, Evgenya Ivanovna; Shchegolkov, Dmitry

2015-04-29

We report the design and experimental data for a copper prototype of a superconducting radio-frequency (SRF) accelerator module. The five-cell module has an incorporated photonic band gap (PBG) cell with couplers. The purpose of the PBG cell is to achieve better higher order mode (HOM) damping, which is vital for preserving the quality of high-current electron beams. Better HOM damping raises the current threshold for beam instabilities in novel SRF accelerators. The PBG design also increases the real-estate gradient of the linac because both HOM damping and the fundamental power coupling can be done through the PBG cell instead ofmore » on the beam pipe via complicated end assemblies. First, we will discuss the design and accelerating properties of the structure. The five-cell module was optimized to provide good HOM damping while maintaining the same accelerating properties as conventional elliptical-cell modules. We will then discuss the process of tuning the structure to obtain the desired accelerating gradient profile. Finally, we will list measured quality factors for the accelerating mode and the most dangerous HOMs.« less

A MEMS disk resonator-based band pass filter electrical equivalent circuit simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sundaram, G. M.; Angira, Mahesh; Gupta, Navneet

In this paper, coupled beam bandpass Disk filter is designed for 1 MHz bandwidth. Filter electrical equivalent circuit simulation is performed using circuit simulators. Important filter parameters such as insertion loss, shape factor and Q factor aresetimated using coventorware simulation. Disk resonator based radial contour mode filter provides 1.5 MHz bandwidth and unloaded quality factor of resonator and filter as 233480, 21797 respectively. From the simulation result it’s found that insertion loss minimum is 151.49 dB, insertion loss maximum is 213.94 dB, and 40 dB shape factor is 4.17.

Long bunch trains measured using a prototype cavity beam position monitor for the Compact Linear Collider

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cullinan, F. J.; Boogert, S. T.; Farabolini, W.

2015-11-19

The Compact Linear Collider (CLIC) requires beam position monitors (BPMs) with 50 nm spatial resolution for alignment of the beam line elements in the main linac and beam delivery system. Furthermore, the BPMs must be able to make multiple independent measurements within a single 156 ns long bunch train. A prototype cavity BPM for CLIC has been manufactured and tested on the probe beam line at the 3rd CLIC Test Facility (CTF3) at CERN. The transverse beam position is determined from the electromagnetic resonant modes excited by the beam in the two cavities of the pickup, the position cavity and the referencemore » cavity. The mode that is measured in each cavity resonates at 15 GHz and has a loaded quality factor that is below 200. Analytical expressions for the amplitude, phase and total energy of signals from long trains of bunches have been derived and the main conclusions are discussed. The results of the beam tests are presented. The variable gain of the receiver electronics has been characterized using beam excited signals and the form of the signals for different beam pulse lengths with the 2/3 ns bunch spacing has been observed. The sensitivity of the reference cavity signal to charge and the horizontal position signal to beam offset have been measured and are compared with theoretical predictions based on laboratory measurements of the BPM pickup and the form of the resonant cavity modes as determined by numerical simulation. Lastly, the BPM was calibrated so that the beam position jitter at the BPM location could be measured. It is expected that the beam jitter scales linearly with the beam size and so the results are compared to predicted values for the latter.« less

Long bunch trains measured using a prototype cavity beam position monitor for the Compact Linear Collider

NASA Astrophysics Data System (ADS)

Cullinan, F. J.; Boogert, S. T.; Farabolini, W.; Lefevre, T.; Lunin, A.; Lyapin, A.; Søby, L.; Towler, J.; Wendt, M.

2015-11-01

The Compact Linear Collider (CLIC) requires beam position monitors (BPMs) with 50 nm spatial resolution for alignment of the beam line elements in the main linac and beam delivery system. Furthermore, the BPMs must be able to make multiple independent measurements within a single 156 ns long bunch train. A prototype cavity BPM for CLIC has been manufactured and tested on the probe beam line at the 3rd CLIC Test Facility (CTF3) at CERN. The transverse beam position is determined from the electromagnetic resonant modes excited by the beam in the two cavities of the pickup, the position cavity and the reference cavity. The mode that is measured in each cavity resonates at 15 GHz and has a loaded quality factor that is below 200. Analytical expressions for the amplitude, phase and total energy of signals from long trains of bunches have been derived and the main conclusions are discussed. The results of the beam tests are presented. The variable gain of the receiver electronics has been characterized using beam excited signals and the form of the signals for different beam pulse lengths with the 2 /3 ns bunch spacing has been observed. The sensitivity of the reference cavity signal to charge and the horizontal position signal to beam offset have been measured and are compared with theoretical predictions based on laboratory measurements of the BPM pickup and the form of the resonant cavity modes as determined by numerical simulation. Finally, the BPM was calibrated so that the beam position jitter at the BPM location could be measured. It is expected that the beam jitter scales linearly with the beam size and so the results are compared to predicted values for the latter.

Resonant frequency method for bearing ball inspection

DOEpatents

Khuri-Yakub, B. T.; Hsieh, Chung-Kao

1993-01-01

The present invention provides for an inspection system and method for detecting defects in test objects which includes means for generating expansion inducing energy focused upon the test object at a first location, such expansion being allowed to contract, thereby causing pressure wave within and on the surface of the test object. Such expansion inducing energy may be provided by, for example, a laser beam or ultrasonic energy. At a second location, the amplitudes and phases of the acoustic waves are detected and the resonant frequencies' quality factors are calculated and compared to predetermined quality factor data, such comparison providing information of whether the test object contains a defect. The inspection system and method also includes means for mounting the bearing ball for inspection.

Resonant frequency method for bearing ball inspection

DOEpatents

Khuri-Yakub, B.T.; Chungkao Hsieh.

1993-11-02

The present invention provides for an inspection system and method for detecting defects in test objects which includes means for generating expansion inducing energy focused upon the test object at a first location, such expansion being allowed to contract, thereby causing pressure wave within and on the surface of the test object. Such expansion inducing energy may be provided by, for example, a laser beam or ultrasonic energy. At a second location, the amplitudes and phases of the acoustic waves are detected and the resonant frequencies' quality factors are calculated and compared to predetermined quality factor data, such comparison providing information of whether the test object contains a defect. The inspection system and method also includes means for mounting the bearing ball for inspection. 5 figures.

MO-F-CAMPUS-I-04: Characterization of Fan Beam Coded Aperture Coherent Scatter Spectral Imaging Methods for Differentiation of Normal and Neoplastic Breast Structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morris, R; Albanese, K; Lakshmanan, M

Purpose: This study intends to characterize the spectral and spatial resolution limits of various fan beam geometries for differentiation of normal and neoplastic breast structures via coded aperture coherent scatter spectral imaging techniques. In previous studies, pencil beam raster scanning methods using coherent scatter computed tomography and selected volume tomography have yielded excellent results for tumor discrimination. However, these methods don’t readily conform to clinical constraints; primarily prolonged scan times and excessive dose to the patient. Here, we refine a fan beam coded aperture coherent scatter imaging system to characterize the tradeoffs between dose, scan time and image quality formore » breast tumor discrimination. Methods: An X-ray tube (125kVp, 400mAs) illuminated the sample with collimated fan beams of varying widths (3mm to 25mm). Scatter data was collected via two linear-array energy-sensitive detectors oriented parallel and perpendicular to the beam plane. An iterative reconstruction algorithm yields images of the sample’s spatial distribution and respective spectral data for each location. To model in-vivo tumor analysis, surgically resected breast tumor samples were used in conjunction with lard, which has a form factor comparable to adipose (fat). Results: Quantitative analysis with current setup geometry indicated optimal performance for beams up to 10mm wide, with wider beams producing poorer spatial resolution. Scan time for a fixed volume was reduced by a factor of 6 when scanned with a 10mm fan beam compared to a 1.5mm pencil beam. Conclusion: The study demonstrates the utility of fan beam coherent scatter spectral imaging for differentiation of normal and neoplastic breast tissues has successfully reduced dose and scan times whilst sufficiently preserving spectral and spatial resolution. Future work to alter the coded aperture and detector geometries could potentially allow the use of even wider fans, thereby making coded aperture coherent scatter imaging a clinically viable method for breast cancer detection. United States Department of Homeland Security; Duke University Medical Center - Department of Radiology; Carl E Ravin Advanced Imaging Laboratories; Duke University Medical Physics Graduate Program.« less

Method to improve optical parametric oscillator beam quality

DOEpatents

Smith, Arlee V.; Alford, William J.; Bowers, Mark S.

2003-11-11

A method to improving optical parametric oscillator (OPO) beam quality having an optical pump, which generates a pump beam at a pump frequency greater than a desired signal frequency, a nonlinear optical medium oriented so that a signal wave at the desired signal frequency and a corresponding idler wave are produced when the pump beam (wave) propagates through the nonlinear optical medium, resulting in beam walk off of the signal and idler waves, and an optical cavity which directs the signal wave to repeatedly pass through the nonlinear optical medium, said optical cavity comprising an equivalently even number of non-planar mirrors that produce image rotation on each pass through the nonlinear optical medium. Utilizing beam walk off where the signal wave and said idler wave have nonparallel Poynting vectors in the nonlinear medium and image rotation, a correlation zone of distance equal to approximately .rho.L.sub.crystal is created which, through multiple passes through the nonlinear medium, improves the beam quality of the OPO output.

Response of LiF:Mg,Ti thermoluminescent dosimeters at photon energies relevant to the dosimetry of brachytherapy (<1 MeV).

PubMed

Tedgren, Asa Carlsson; Hedman, Angelica; Grindborg, Jan-Erik; Carlsson, Gudrun Alm

2011-10-01

High energy photon beams are used in calibrating dosimeters for use in brachytherapy since absorbed dose to water can be determined accurately and with traceability to primary standards in such beams, using calibrated ion chambers and standard dosimetry protocols. For use in brachytherapy, beam quality correction factors are needed, which include corrections for differences in mass energy absorption properties between water and detector as well as variations in detector response (intrinsic efficiency) with radiation quality, caused by variations in the density of ionization (linear energy transfer (LET) -distributions) along the secondary electron tracks. The aim of this work was to investigate experimentally the detector response of LiF:Mg,Ti thermoluminescent dosimeters (TLD) for photon energies below 1 MeV relative to (60)Co and to address discrepancies between the results found in recent publications of detector response. LiF:Mg,Ti dosimeters of formulation MTS-N Poland were irradiated to known values of air kerma free-in-air in x-ray beams at tube voltages 25-250 kV, in (137)Cs- and (60)Co-beams at the Swedish Secondary Standards Dosimetry Laboratory. Conversions from air kerma free-in-air into values of mean absorbed dose in the dosimeters in the actual irradiation geometries were made using EGSnrc Monte Carlo simulations. X-ray energy spectra were measured or calculated for the actual beams. Detector response relative to that for (60)Co was determined at each beam quality. An increase in relative response was seen for all beam qualities ranging from 8% at tube voltage 25 kV (effective energy 13 keV) to 3%-4% at 250 kV (122 keV effective energy) and (137)Cs with a minimum at 80 keV effective energy (tube voltage 180 kV). The variation with effective energy was similar to that reported by Davis et al. [Radiat. Prot. Dosim. 106, 33-43 (2003)] with our values being systematically lower by 2%-4%. Compared to the results by Nunn et al. [Med. Phys. 35, 1861-1869 (2008)], the relative detector response as a function of effective energy differed in both shape and magnitude. This could be explained by the higher maximum read-out temperature (350 °C) used by Nunn et al. [Med. Phys. 35, 1861-1869 (2008)], allowing light emitted from high-temperature peaks with a strong LET dependence to be registered. Use of TLD-100 by Davis et al. [Radiat. Prot. Dosim. 106, 33-43 (2003)] with a stronger super-linear dose response compared to MTS-N was identified as causing the lower relative detector response in this work. Both careful dosimetry and strict protocols for handling the TLDs are required to reach solid experimental data on relative detector response. This work confirms older findings that an over-response relative to (60)Co exists for photon energies below 200-300 keV. Comparison with the results from the literature indicates that using similar protocols for annealing and read-out, dosimeters of different makes (TLD-100, MTS-N) differ in relative detector response. Though universality of the results has not been proven and further investigation is needed, it is anticipated that with the use of strict protocols for annealing and read-out, it will be possible to determine correction factors that can be used to reduce uncertainties in dose measurements around brachytherapy sources at photon energies where primary standards for absorbed dose to water are not available.

Strength and stiffness of small glued-laminated beams with different qualities of tension laminations

Treesearch

Catherine M. Marx; Russell C. Moody

1981-01-01

A total of 180 small Douglas Fir–Larch (DF-L) or Southern Pine (SP) glued-laminated beams were evaluated to determine the tension lamination quality necessary to obtain desired design stresses. The test beams had either the regular laminating grades of L1 DF-L/No. 1D SP or the special 302-24 laminating grade as tension laminations. Because an initial set of SP beams...

Nitrogen Plasma Optimization for High-Quality Dilute Nitrides

DTIC Science & Technology

2005-02-01

Available online 1 February 2005Abstract Growth of GaInNAs by molecular beam epitaxy (MBE) generally requires a nitrogen plasma, which complicates growth...InGaAs and InGaAsP lasers. This paper addresses several of the challenges of plasma-assisted molecular beam epitaxy (MBE) of high-quality dilute nitrides...A.L. Holmes, Using beam flux monitor as Langmuir probe for plasma-assisted molecular beam epitaxy , J. Vac. Sci. Technol. B, in press.

Diffractive beam shaping for enhanced laser polymer welding

NASA Astrophysics Data System (ADS)

Rauschenberger, J.; Vogler, D.; Raab, C.; Gubler, U.

2015-03-01

Laser welding of polymers increasingly finds application in a large number of industries such as medical technology, automotive, consumer electronics, textiles or packaging. More and more, it replaces other welding technologies for polymers, e. g. hot-plate, vibration or ultrasonic welding. At the same rate, demands on the quality of the weld, the flexibility of the production system and on processing speed have increased. Traditionally, diode lasers were employed for plastic welding with flat-top beam profiles. With the advent of fiber lasers with excellent beam quality, the possibility to modify and optimize the beam profile by beam-shaping elements has opened. Diffractive optical elements (DOE) can play a crucial role in optimizing the laser intensity profile towards the optimal M-shape beam for enhanced weld seam quality. We present results on significantly improved weld seam width constancy and enlarged process windows compared to Gaussian or flat-top beam profiles. Configurations in which the laser beam diameter and shape can be adapted and optimized without changing or aligning the laser, fiber-optic cable or optical head are shown.

Health-Related Quality of Life After Single-Fraction High-Dose-Rate Brachytherapy and Hypofractionated External Beam Radiotherapy for Prostate Cancer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morton, Gerard C., E-mail: gerard.morton@sunnybrook.ca; Loblaw, D. Andrew; Chung, Hans

Purpose: To investigate the change in health-related quality of life for men after high-dose-rate brachytherapy and external beam radiotherapy for prostate cancer and the factors associated with this change. Methods and Materials: Eligible patients had clinically localized intermediate-risk prostate cancer. The patients received high-dose-rate brachytherapy as a single 15-Gy implant, followed by external beam radiotherapy to 37.5 Gy in 15 fractions. The patients were monitored prospectively for toxicity (Common Terminology Criteria for Adverse Events, version 3.0) and health-related quality of life (Expanded Prostate Cancer Index Composite [EPIC]). The proportion of patients developing a clinically significant difference in the EPIC domainmore » score (minimally important difference of >0.5 standard deviation) was determined and correlated with the baseline clinical and dosimetric factors. The study accrued 125 patients, with a median follow-up of 24 months. Results: By 24 months, 23% had Grade 2 urinary toxicity and only 5% had Grade 2 bowel toxicity, with no Grade 3 toxicity. The proportion of patients reporting a significant decrease in EPIC urinary, bowel, sexual, and hormonal domain scores was 53%, 51%, 45%, and 40% at 12 months and 57%, 65%, 51%, and 30% at 24 months, respectively. The proportion with a >1 standard deviation decrease in the EPIC urinary, bowel, sexual, and hormonal domain scores was 38%, 36%, 24%, and 20% at 12 months and 46%, 48%, 19%, and 8% at 24 months, respectively. On multivariate analysis, the dose to 10% of the urethra was associated with a decreasing EPIC urinary domain score (p = .0089) and, less strongly (p = .0312) with a decreasing hormonal domain score. No association was found between the prostate volume, bladder dose, or high-dose volume and urinary health-related quality of life. A high baseline International Index of Erectile Function score was associated (p = .0019) with a decreasing sexual domain score. The optimal maximal dose to 10% of the urethra cutpoint for urinary health-related quality of life was 120% of the prescription dose. Conclusion: EPIC was a more sensitive tool for detecting the effects on function and bother than were the generic toxicity scales. The urethral dose had the strongest association with a deteriorating urinary quality of life.« less

Evaluation of factors to convert absorbed dose calibrations from graphite to water for the NPL high-energy photon calibration service.

PubMed

Nutbrown, R F; Duane, S; Shipley, D R; Thomas, R A S

2002-02-07

The National Physical Laboratory (NPL) provides a high-energy photon calibration service using 4-19 MV x-rays and 60Co gamma-radiation for secondary standard dosemeters in terms of absorbed dose to water. The primary standard used for this service is a graphite calorimeter and so absorbed dose calibrations must be converted from graphite to water. The conversion factors currently in use were determined prior to the launch of this service in 1988. Since then, it has been found that the differences in inherent filtration between the NPL LINAC and typical clinical machines are large enough to affect absorbed dose calibrations and, since 1992, calibrations have been performed in heavily filtered qualities. The conversion factors for heavily filtered qualities were determined by interpolation and extrapolation of lightly filtered results as a function of tissue phantom ratio 20,10 (TPR20,10). This paper aims to evaluate these factors for all mega-voltage photon energies provided by the NPL LINAC for both lightly and heavily filtered qualities and for 60Co y-radiation in two ways. The first method involves the use of the photon fluence-scaling theorem. This states that if two blocks of different material are irradiated by the same photon beam, and if all dimensions are scaled in the inverse ratio of the electron densities of the two media, then, assuming that all photon interactions occur by Compton scatter the photon attenuation and scatter factors at corresponding scaled points of measurement in the phantom will be identical. The second method involves making in-phantom measurements of chamber response at a constant target-chamber distance. Monte Carlo techniques are then used to determine the corresponding dose to the medium in order to determine the chamber calibration factor directly. Values of the ratio of absorbed dose calibration factors in water and in graphite determined in these two ways agree with each other to within 0.2% (1sigma uncertainty). The best fit to both sets of results agrees with values determined in previous work to within 0.3% (1sigma uncertainty). It is found that the conversion factor is not sensitive to beam filtration.

Beam orientation optimization for intensity-modulated radiation therapy using mixed integer programming

NASA Astrophysics Data System (ADS)

Yang, Ruijie; Dai, Jianrong; Yang, Yong; Hu, Yimin

2006-08-01

The purpose of this study is to extend an algorithm proposed for beam orientation optimization in classical conformal radiotherapy to intensity-modulated radiation therapy (IMRT) and to evaluate the algorithm's performance in IMRT scenarios. In addition, the effect of the candidate pool of beam orientations, in terms of beam orientation resolution and starting orientation, on the optimized beam configuration, plan quality and optimization time is also explored. The algorithm is based on the technique of mixed integer linear programming in which binary and positive float variables are employed to represent candidates for beam orientation and beamlet weights in beam intensity maps. Both beam orientations and beam intensity maps are simultaneously optimized in the algorithm with a deterministic method. Several different clinical cases were used to test the algorithm and the results show that both target coverage and critical structures sparing were significantly improved for the plans with optimized beam orientations compared to those with equi-spaced beam orientations. The calculation time was less than an hour for the cases with 36 binary variables on a PC with a Pentium IV 2.66 GHz processor. It is also found that decreasing beam orientation resolution to 10° greatly reduced the size of the candidate pool of beam orientations without significant influence on the optimized beam configuration and plan quality, while selecting different starting orientations had large influence. Our study demonstrates that the algorithm can be applied to IMRT scenarios, and better beam orientation configurations can be obtained using this algorithm. Furthermore, the optimization efficiency can be greatly increased through proper selection of beam orientation resolution and starting beam orientation while guaranteeing the optimized beam configurations and plan quality.

SU-G-BRB-05: Automation of the Photon Dosimetric Quality Assurance Program of a Linear Accelerator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lebron, S; Lu, B; Yan, G

Purpose: To develop an automated method to calculate a linear accelerator (LINAC) photon radiation field size, flatness, symmetry, output and beam quality in a single delivery for flattened (FF) and flattening-filter-free (FFF) beams using an ionization chamber array. Methods: The proposed method consists of three control points that deliver 30×30, 10×10 and 5×5cm{sup 2} fields (FF or FFF) in a step-and-shoot sequence where the number of monitor units is weighted for each field size. The IC Profiler (Sun Nuclear Inc.) with 5mm detector spacing was used for this study. The corrected counts (CCs) were calculated and the locations of themore » maxima and minima values of the first-order gradient determined data of each sub field. Then, all CCs for each field size are summed in order to obtain the final profiles. For each profile, the radiation field size, symmetry, flatness, output factor and beam quality were calculated. For field size calculation, a parameterized gradient method was used. For method validation, profiles were collected in the detector array both, individually and as part of the step-and-shoot plan, with 9.9cm buildup for FF and FFF beams at 90cm source-to-surface distance. The same data were collected with the device (plus buildup) placed on a movable platform to achieve a 1mm resolution. Results: The differences between the dosimetric quantities calculated from both deliveries, individually and step-and-shoot, were within 0.31±0.20% and 0.04±0.02mm. The differences between the calculated field sizes with 5mm and 1mm resolution were ±0.1mm. Conclusion: The proposed single delivery method proved to be simple and efficient in automating the photon dosimetric monthly and annual quality assurance.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, S; Fan, Q; Lei, Y

Purpose: In-Water-Output-Ratio (IWOR) plays a significant role in linac-based radiotherapy treatment planning, linking MUs to delivered radiation dose. For an open rectangular field, IWOR depends on both its width and length, and changes rapidly when one of them becomes small. In this study, a universal functional form is proposed to fit the open field IWOR tables in Varian TrueBeam representative datasets for all photon energies. Methods: A novel Generalized Mean formula is first used to estimate the Equivalent Square (ES) for a rectangular field. The formula’s weighting factor and power index are determined by collapsing all data points as muchmore » as possible onto a single curve in IWOR vs. ES plot. The result is then fitted with a novel universal function IWOR=1+b*Log(ES/10cm)/(ES/10cm)^c via a least-square procedure to determine the optimal values for parameters b and c. The maximum relative residual error in IWOR over the entire two-dimensional measurement table with field sizes between 3cm and 40cm is used to evaluate the quality of fit for the function. Results: The two-step fitting strategy works very well in determining the optimal parameter values for open field IWOR of each photon energies in the Varian data-set. Relative residual error ≤0.71% is achieved for all photon energies (including Flattening-Filter-Free modes) with field sizes between 3cm and 40cm. The optimal parameter values change smoothly with regular photon beam quality. Conclusion: The universal functional form fits the Varian TrueBeam open field IWOR measurement tables accurately with small relative residual errors for all photon energies. Therefore, it can be an excellent choice to represent IWOR in absolute dose and MU calculations. The functional form can also be used as a QA/commissioning tool to verify the measured data quality and consistency by checking the IWOR data behavior against the function for new photon energies with arbitrary beam quality.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuess, Peter, E-mail: Peter.kuess@meduniwien.ac.at

Purpose: For commercially available linear accelerators (Linacs), the electron energies of flattening filter free (FFF) and flattened (FF) beams are either identical or the electron energy of the FFF beam is increased to match the percentage depth dose curve (PDD) of the FF beam (in reference geometry). This study focuses on the primary dose components of FFF beams for both kinds of settings, studied on the same Linac. Methods: The measurements were conducted on a VersaHD Linac (Elekta, Crawley, UK) for both FF and FFF beams with nominal energies of 6 and 10 MV. In the clinical setting of themore » VersaHD, the energy of FFF{sub M} (Matched) beams is set to match the PDDs of the FF beams. In contrast the incident electron beam of the FFF{sub U} beam was set to the same energy as for the FF beam. Half value layers (HVLs) and a dual parameter beam quality specifier (DPBQS) were determined. Results: For the 6 MV FFF{sub M} beam, HVL and DPBQS values were very similar compared to those of the 6 MV FF beam, while for the 10 MV FFF{sub M} and FF beams, only %dd(10){sub x} and HVL values were comparable (differences below 1.5%). This shows that matching the PDD at one depth does not guarantee other beam quality dependent parameters to be matched. For FFF{sub U} beams, all investigated beam quality specifiers were significantly different compared to those for FF beams of the same nominal accelerator potential. The DPBQS of the 6 MV FF and FFF{sub M} beams was equal within the measurement uncertainty and was comparable to published data of a machine with similar TPR{sub 20,10} and %dd(10){sub x}. In contrast to that, the DPBQS’s two parameters of the 10 MV FFF{sub M} beam were substantially higher compared to those for the 10 MV FF beam. Conclusions: PDD-matched FF and FFF beams of both nominal accelerator potentials were observed to have similar HVL values, indicating similarity of their primary dose components. Using the DPBQS revealed that the mean attenuation coefficient was found to be the same within the uncertainty of 0.8% for 6 MV FF and 6 MV FFF{sub M} beams, while for 10 MV beams, they differed by 6.4%. This shows that the DPBQS can provide a differentiation of photon beam characteristics that would remain hidden by the use of a single beam quality specifier, such as %dd(10){sub x} or HVL.« less

A line scanned light-sheet microscope with phase shaped self-reconstructing beams.

PubMed

Fahrbach, Florian O; Rohrbach, Alexander

2010-11-08

We recently demonstrated that Microscopy with Self-Reconstructing Beams (MISERB) increases both image quality and penetration depth of illumination beams in strongly scattering media. Based on the concept of line scanned light-sheet microscopy, we present an add-on module to a standard inverted microscope using a scanned beam that is shaped in phase and amplitude by a spatial light modulator. We explain technical details of the setup as well as of the holograms for the creation, positioning and scaling of static light-sheets, Gaussian beams and Bessel beams. The comparison of images from identical sample areas illuminated by different beams allows a precise assessment of the interconnection between beam shape and image quality. The superior propagation ability of Bessel beams through inhomogeneous media is demonstrated by measurements on various scattering media.

Correction of stopping power and LET quenching for radiophotoluminescent glass dosimetry in a therapeutic proton beam

NASA Astrophysics Data System (ADS)

Chang, Weishan; Koba, Yusuke; Katayose, Tetsurou; Yasui, Keisuke; Omachi, Chihiro; Hariu, Masatsugu; Saitoh, Hidetoshi

2017-12-01

To measure the absorbed dose to water D w in proton beams using a radiophotoluminescent glass dosimeter (RGD), a method with the correction for the change of the mass stopping power ratio (SPR) and the linear energy transfer (LET) dependence of radiophotoluminescent efficiency \\varepsilon LETRGD is proposed. The calibration coefficient in terms of D w for RGDs (GD-302M, Asahi Techno Glass) was obtained using a 60Co γ-ray. The SPR of water to the RGD was calculated by Monte Carlo simulation, and \\varepsilon LETRGD was investigated experimentally using a 70 MeV proton beam. For clinical usage, the residual range R res was used as a quality index to determine the correction factor for the beam quality kQ,{{Q0}}RGD and the LET quenching effect of the RGD kLETRGD . The proposed method was evaluated by measuring D w at different depths in a 200 MeV proton beam. For both non-modulated and modulated proton beams, kQ,{{Q0}}RGD decreases rapidly where R res is less than 4 cm. The difference in kQ,{{Q0}}RGD between a non-modulated and a modulated proton beam is less than 0.5% for the R res range from 0 cm to 22 cm. \\varepsilon LETRGD decreases rapidly at a LET range from 1 to 2 keV µm-1. In the evaluation experiments, D w using RGDs, Dw,QRGD showed good agreement with that obtained using an ionization chamber and the relative difference was within 3% where R res was larger than 1 cm. The uncertainty budget for Dw,QRGD in a proton beam was estimated to investigate the potential of RGD postal dosimetry in proton therapy. These results demonstrate the feasibility of RGD dosimetry in a therapeutic proton beam and the general versatility of the proposed method. In conclusion, the proposed methodology for RGDs in proton dosimetry is applicable where R res  >  1 cm and the RGD is feasible as a postal audit dosimeter for proton therapy.

Beam wander and M2-factor of partially coherent electromagnetic hollow Gaussian beam propagating through non-Kolmogorov turbulence

NASA Astrophysics Data System (ADS)

Xu, Yonggen; Tian, Huanhuan; Dan, Youquan; Feng, Hao; Wang, Shijian

2017-04-01

Propagation formulae for M2-factor and beam wander of partially coherent electromagnetic hollow Gaussian (PCEHG) beam in non-Kolmogorov turbulence are derived based on the extended Huygens-Fresnel principle and the second-order moments of the Wigner distribution function. Our results indicate that the normalized M2-factors of PCEHG beam with larger beam order, waist width, inner scale of turbulence, the generalized exponent parameter, and smaller transverse coherent widths, outer scale of turbulence, the generalized structure parameter are less affected by the turbulence. The root mean square beam wander and relative beam wander are more obvious for PCEHG beam with smaller beam order, larger inner and outer scales of turbulence, exponent parameter, transverse coherent widths, and the generalized structure parameter. What is more, the beam wander properties of PCEHG beam in non-Kolmogorov turbulence are very different from M2-factor and spreading properties of beam in turbulence.

Coherent Beam Combining of Fiber Amplifiers via LOCSET (Postprint)

DTIC Science & Technology

2012-07-10

load on final optics , and atmospheric turbulence compensation [20]. More importantly, tiled array systems are being investigated for extension to...compactness, near diffraction limited beam quality, superior thermal- optical properties, and high optical to optical conversion efficiencies. Despite...including: compactness, near diffraction limited beam quality, superior thermal- optical properties, and high optical to optical conversion efficiencies

Can small field diode correction factors be applied universally?

PubMed

Liu, Paul Z Y; Suchowerska, Natalka; McKenzie, David R

2014-09-01

Diode detectors are commonly used in dosimetry, but have been reported to over-respond in small fields. Diode correction factors have been reported in the literature. The purpose of this study is to determine whether correction factors for a given diode type can be universally applied over a range of irradiation conditions including beams of different qualities. A mathematical relation of diode over-response as a function of the field size was developed using previously published experimental data in which diodes were compared to an air core scintillation dosimeter. Correction factors calculated from the mathematical relation were then compared those available in the literature. The mathematical relation established between diode over-response and the field size was found to predict the measured diode correction factors for fields between 5 and 30 mm in width. The average deviation between measured and predicted over-response was 0.32% for IBA SFD and PTW Type E diodes. Diode over-response was found to be not strongly dependent on the type of linac, the method of collimation or the measurement depth. The mathematical relation was found to agree with published diode correction factors derived from Monte Carlo simulations and measurements, indicating that correction factors are robust in their transportability between different radiation beams. Copyright © 2014. Published by Elsevier Ireland Ltd.

Studies on design of 351  nm focal plane diagnostic system prototype and focusing characteristic of SGII-upgraded facility at half achievable energy performance.

PubMed

Liu, Chong; Ji, Lailin; Yang, Lin; Zhao, Dongfeng; Zhang, Yanfeng; Liu, Dong; Zhu, Baoqiang; Lin, Zunqi

2016-04-01

In order to obtain the intensity distribution of a 351 nm focal spot and smoothing by spectral dispersion (SSD) focal plane profile of a SGII-upgraded facility, a type of off-axis imaging system with three spherical mirrors, suitable for a finite distance source point to be imaged near the diffraction limit has been designed. The quality factor of the image system is 1.6 times of the diffraction limit tested by a 1053 nm point source. Because of the absence of a 351 nm point source, we can use a Collins diffraction imaging integral with respect to λ=351  nm, corresponding to a quality factor that is 3.8 times the diffraction limit at 351 nm. The calibration results show that at least the range of ±10  mrad of view field angle and ±50  mm along the axial direction around the optimum object distance can be satisfied with near diffraction limited image that is consistent with the design value. Using this image system, the No. 2 beam of the SGII-upgraded facility has been tested. The test result of the focal spot of final optics assembly (FOA) at 351 nm indicates that about 80% of energy is encompassed in 14.1 times the diffraction limit, while the output energy of the No. 2 beam is 908 J at 1053 nm. According to convolution theorem, the true value of a 351 nm focal spot of FOA is about 12 times the diffraction limit because of the influence of the quality factor. Further experimental studies indicate that the RMS value along the smoothing direction is less than 15.98% in the SSD spot test experiment. Computer simulations show that the quality factor of the image system used in the experiment has almost no effect on the SSD focal spot test. The image system can remarkably distort the SSD focal spot distribution under the circumstance of the quality factor 15 times worse than the diffraction limit. The distorted image shows a steep slope in the contour of the SSD focal spot along the smoothing direction that otherwise has a relatively flat top region around the focal spot center.

SU-F-T-352: Development of a Knowledge Based Automatic Lung IMRT Planning Algorithm with Non-Coplanar Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, W; Wu, Q; Yuan, L

Purpose: To improve the robustness of a knowledge based automatic lung IMRT planning method and to further validate the reliability of this algorithm by utilizing for the planning of clinical cases with non-coplanar beams. Methods: A lung IMRT planning method which automatically determines both plan optimization objectives and beam configurations with non-coplanar beams has been reported previously. A beam efficiency index map is constructed to guide beam angle selection in this algorithm. This index takes into account both the dose contributions from individual beams and the combined effect of multiple beams which is represented by a beam separation score. Wemore » studied the effect of this beam separation score on plan quality and determined the optimal weight for this score.14 clinical plans were re-planned with the knowledge-based algorithm. Significant dosimetric metrics for the PTV and OARs in the automatic plans are compared with those in the clinical plans by the two-sample t-test. In addition, a composite dosimetric quality index was defined to obtain the relationship between the plan quality and the beam separation score. Results: On average, we observed more than 15% reduction on conformity index and homogeneity index for PTV and V{sub 40}, V{sub 60} for heart while an 8% and 3% increase on V{sub 5}, V{sub 20} for lungs, respectively. The variation curve of the composite index as a function of angle spread score shows that 0.6 is the best value for the weight of the beam separation score. Conclusion: Optimal value for beam angle spread score in automatic lung IMRT planning is obtained. With this value, model can result in statistically the “best” achievable plans. This method can potentially improve the quality and planning efficiency for IMRT plans with no-coplanar angles.« less

Interface circuit for a multiple-beam tuning-fork gyroscope with high quality factors

NASA Astrophysics Data System (ADS)

Wang, Ren

This research work presents the design, theoretical analysis, fabrication, interface electronics, and experimental results of a Silicon-On-Insulator (SOI) based Multiple-Beam Tuning-Fork Gyroscope (MB-TFG). Based on a numerical model of Thermo-Elastic Damping (TED), a Multiple-Beam Tuning-Fork Structure (MB-TFS) is designed with high Quality factors (Qs) in its two operation modes. A comprehensive theoretical analysis of the MB-TFG design is conducted to relate the design parameters to its operation parameters and further performance parameters. In conjunction with a mask that defines the device through trenches to alleviate severe fabrication effect on anchor loss, a simple one-mask fabrication process is employed to implement this MB-TFG design on SOI wafers. The fabricated MB-TFGs are tested with PCB-level interface electronics and a thorough comparison between the experimental results and a theoretical analysis is conducted to verify the MB-TFG design and accurately interpret the measured performance. The highest measured Qs of the fabricated MB-TFGs in vacuum are 255,000 in the drive-mode and 103,000 in the sense-mode, at a frequency of 15.7kHz. Under a frequency difference of 4Hz between the two modes (operation frequency is 16.8kHz) and a drive-mode vibration amplitude of 3.0um, the measured rate sensitivity is 80mVpp/°/s with an equivalent impedance of 6MQ. The calculated overall rate resolution of this device is 0.37/hrhiElz, while the measured Angle Random Walk (ARW) and bias instability are 6.67°/'vhr and 95°/hr, respectively.

Performance of the LANSCE H^- Source and Low Energy Transport at Higher Peak Current

NASA Astrophysics Data System (ADS)

Pillai, Chandra; Stevens, Ralph; Fitzgerald, Daniel; Garnett, Robert; Ingllas, William; Merrill, Frank; Rybarcyk, Larry; Sander, Oscar

1997-05-01

The Los Alamos Neutron Science Center (LANSCE) 800 MeV linac facility uses a multicusp field, surface ion source to produce H^- beam for delivery to the Proton Storage Ring (PSR) and to the Weapon Neutron Research (WNR) areas. The source typically operates at a duty factor of 9.4% delivering a peak current of about 14 mA into the 750 keV LEBT. Each beam macropulse is chopped to create a sequence of 360 ns pulse, each with a 100 ns ``extraction notch'' for injection into PSR. The average current delivered to the short-pulse spallation target is nominally 70μA. One goal of the present PSR upgrade projects is an increase in the average beam current to 200μA. This will be accomplished by a combination of increased repetition rate (to 30 Hz), upgraded PSR bunchers, and a brighter H^- ion source that will produce higher peak current with lower beam emittance. The present ion source and injector system was studied to investigate the beam qualities of the source and the performance of the low energy transpot. The performance of the ion source at higher currents and the change in beam parameters in the low energy transport compared to those in the standard source conditions will be presented.

Enhanced dynamical stability with harmonic slip stacking

DOE PAGES

Eldred, Jeffrey; Zwaska, Robert

2016-10-26

We develop a configuration of radio-frequency (rf) cavities to dramatically improve the performance of slip-stacking. Slip-stacking is an accumulation technique used at Fermilab to nearly double proton intensity by maintaining two beams of different momenta in the same storage ring. The two particle beams are longitudinally focused in the Recycler by two 53 MHz 100 kV rf cavities with a small frequency difference between them. We propose an additional 106 MHz 20 kV rf cavity with a frequency at the double the average of the upper and lower main rf frequencies. We show the harmonic rf cavity cancels out themore » resonances generated between the two main rf cavities and we derive the relationship between the harmonic rf voltage and the main rf voltage. We find the area factors that can be used to calculate the available phase space area for any set of beam parameters without individual simulation. We establish Booster beam quality requirements to achieve 99\\% slip-stacking efficiency. We measure the longitudinal distribution of the Booster beam and use it to generate a realistic beam model for slip-stacking simulation. In conclusion, we demonstrate that the harmonic rf cavity can not only reduce particle loss during slip-stacking, but also reduce the final longitudinal emittance.« less

Enhanced dynamical stability with harmonic slip stacking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eldred, Jeffrey; Zwaska, Robert

We develop a configuration of radio-frequency (rf) cavities to dramatically improve the performance of slip-stacking. Slip-stacking is an accumulation technique used at Fermilab to nearly double proton intensity by maintaining two beams of different momenta in the same storage ring. The two particle beams are longitudinally focused in the Recycler by two 53 MHz 100 kV rf cavities with a small frequency difference between them. We propose an additional 106 MHz 20 kV rf cavity with a frequency at the double the average of the upper and lower main rf frequencies. We show the harmonic rf cavity cancels out themore » resonances generated between the two main rf cavities and we derive the relationship between the harmonic rf voltage and the main rf voltage. We find the area factors that can be used to calculate the available phase space area for any set of beam parameters without individual simulation. We establish Booster beam quality requirements to achieve 99\\% slip-stacking efficiency. We measure the longitudinal distribution of the Booster beam and use it to generate a realistic beam model for slip-stacking simulation. In conclusion, we demonstrate that the harmonic rf cavity can not only reduce particle loss during slip-stacking, but also reduce the final longitudinal emittance.« less

STUDIES OF A FREE ELECTRON LASER DRIVEN BY A LASER-PLASMA ACCELERATOR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Montgomery, A.; Schroeder, C.; Fawley, W.

A free electron laser (FEL) uses an undulator, a set of alternating magnets producing a periodic magnetic fi eld, to stimulate emission of coherent radiation from a relativistic electron beam. The Lasers, Optical Accelerator Systems Integrated Studies (LOASIS) group at Lawrence Berkeley National Laboratory (LBNL) will use an innovative laserplasma wakefi eld accelerator to produce an electron beam to drive a proposed FEL. In order to optimize the FEL performance, the dependence on electron beam and undulator parameters must be understood. Numerical modeling of the FEL using the simulation code GINGER predicts the experimental results for given input parameters. Amongmore » the parameters studied were electron beam energy spread, emittance, and mismatch with the undulator focusing. Vacuum-chamber wakefi elds were also simulated to study their effect on FEL performance. Energy spread was found to be the most infl uential factor, with output FEL radiation power sharply decreasing for relative energy spreads greater than 0.33%. Vacuum chamber wakefi elds and beam mismatch had little effect on the simulated LOASIS FEL at the currents considered. This study concludes that continued improvement of the laser-plasma wakefi eld accelerator electron beam will allow the LOASIS FEL to operate in an optimal regime, producing high-quality XUV and x-ray pulses.« less

Evaluation of a cone beam computed tomography geometry for image guided small animal irradiation.

PubMed

Yang, Yidong; Armour, Michael; Wang, Ken Kang-Hsin; Gandhi, Nishant; Iordachita, Iulian; Siewerdsen, Jeffrey; Wong, John

2015-07-07

The conventional imaging geometry for small animal cone beam computed tomography (CBCT) is that a detector panel rotates around the head-to-tail axis of an imaged animal ('tubular' geometry). Another unusual but possible imaging geometry is that the detector panel rotates around the anterior-to-posterior axis of the animal ('pancake' geometry). The small animal radiation research platform developed at Johns Hopkins University employs the pancake geometry where a prone-positioned animal is rotated horizontally between an x-ray source and detector panel. This study is to assess the CBCT image quality in the pancake geometry and investigate potential methods for improvement. We compared CBCT images acquired in the pancake geometry with those acquired in the tubular geometry when the phantom/animal was placed upright simulating the conventional CBCT geometry. Results showed signal-to-noise and contrast-to-noise ratios in the pancake geometry were reduced in comparison to the tubular geometry at the same dose level. But the overall spatial resolution within the transverse plane of the imaged cylinder/animal was better in the pancake geometry. A modest exposure increase to two folds in the pancake geometry can improve image quality to a level close to the tubular geometry. Image quality can also be improved by inclining the animal, which reduces streak artifacts caused by bony structures. The major factor resulting in the inferior image quality in the pancake geometry is the elevated beam attenuation along the long axis of the phantom/animal and consequently increased scatter-to-primary ratio in that orientation. Not withstanding, the image quality in the pancake-geometry CBCT is adequate to support image guided animal positioning, while providing unique advantages of non-coplanar and multiple mice irradiation. This study also provides useful knowledge about the image quality in the two very different imaging geometries, i.e. pancake and tubular geometry, respectively.

Evaluation of a Cone Beam Computed Tomography Geometry for Image Guided Small Animal Irradiation

PubMed Central

Yang, Yidong; Armour, Michael; Wang, Ken Kang-Hsin; Gandhi, Nishant; Iordachita, Iulian; Siewerdsen, Jeffrey; Wong, John

2015-01-01

The conventional imaging geometry for small animal cone beam computed tomography (CBCT) is that a detector panel rotates around the head-to-tail axis of an imaged animal (“tubular” geometry). Another unusual but possible imaging geometry is that the detector panel rotates around the anterior-to-posterior axis of the animal (“pancake” geometry). The small animal radiation research platform (SARRP) developed at Johns Hopkins University employs the pancake geometry where a prone-positioned animal is rotated horizontally between an x-ray source and detector panel. This study is to assess the CBCT image quality in the pancake geometry and investigate potential methods for improvement. We compared CBCT images acquired in the pancake geometry with those acquired in the tubular geometry when the phantom/animal was placed upright simulating the conventional CBCT geometry. Results showed signal-to-noise and contrast-to-noise ratios in the pancake geometry were reduced in comparison to the tubular geometry at the same dose level. But the overall spatial resolution within the transverse plane of the imaged cylinder/animal was better in the pancake geometry. A modest exposure increase to two folds in the pancake geometry can improve image quality to a level close to the tubular geometry. Image quality can also be improved by inclining the animal, which reduces streak artifacts caused by bony structures. The major factor resulting in the inferior image quality in the pancake geometry is the elevated beam attenuation along the long axis of the phantom/animal and consequently increased scatter-to-primary ratio in that orientation. Notwithstanding, the image quality in the pancake-geometry CBCT is adequate to support image guided animal positioning, while providing unique advantages of non-coplanar and multiple mice irradiation. This study also provides useful knowledge about the image quality in the two very different imaging geometries, i.e., pancake and tubular geometry, respectively. PMID:26083659

Beam propagation factor of partially coherent flat-topped beams in a turbulent atmosphere.

PubMed

Dan, Youquan; Zhang, Bin

2008-09-29

The Wigner distribution function (WDF) has been used to study the beam propagation factor (M(2)-factor) for partially coherent flat-topped (PCFT) beams with circular symmetry in a turbulent atmosphere. Based on the extended Huygens-Fresnel principle and the definition of the WDF, an expression for the WDF of PCFT beams in turbulence has been given. By use of the second-order moments of the WDF, the analytical formulas for the root-mean-square (rms) spatial width, the rms angular width, and the M(2)-factor of PCFT beams in turbulence have been derived, which can be applied to cases of different spatial power spectra of the refractive index fluctuations. The rms angular width and the M(2)-factor of PCFT beams in turbulence have been discussed with numerical examples. It can be shown that the M(2)-factor of PCFT beams in turbulence depends on the beam order, degree of global coherence of the source, waist width, wavelength, spatial power spectrum of the refractive index fluctuations, and propagation distance.

Parameter space for the collective laser coupling in the laser fusion driver based on the concept of fiber amplification network.

PubMed

Huang, Zhihua; Lin, Honghuan; Xu, Dangpeng; Li, Mingzhong; Wang, Jianjun; Deng, Ying; Zhang, Rui; Zhang, Yongliang; Tian, Xiaocheng; Wei, Xiaofeng

2013-07-15

Collective laser coupling of the fiber array in the inertial confinement fusion (ICF) laser driver based on the concept of fiber amplification network (FAN) is researched. The feasible parameter space is given for laser coupling of the fundamental, second and third harmonic waves by neglecting the influence of the frequency conversion on the beam quality under the assumption of beam quality factor conservation. Third harmonic laser coupling is preferred due to its lower output energy requirement from a single fiber amplifier. For coplanar fiber array, the energy requirement is around 0.4 J with an effective mode field diameter of around 500 μm while maintaining the fundamental mode operation which is more than one order of magnitude higher than what can be achieved with state-of-the-art technology. Novel waveguide structure needs to be developed to enlarge the fundamental mode size while mitigating the catastrophic self-focusing effect.

Accounting for partiality in serial crystallography using ray-tracing principles

PubMed Central

Kroon-Batenburg, Loes M. J.; Schreurs, Antoine M. M.; Ravelli, Raimond B. G.; Gros, Piet

2015-01-01

Serial crystallography generates ‘still’ diffraction data sets that are composed of single diffraction images obtained from a large number of crystals arbitrarily oriented in the X-ray beam. Estimation of the reflection partialities, which accounts for the expected observed fractions of diffraction intensities, has so far been problematic. In this paper, a method is derived for modelling the partialities by making use of the ray-tracing diffraction-integration method EVAL. The method estimates partialities based on crystal mosaicity, beam divergence, wavelength dispersion, crystal size and the interference function, accounting for crystallite size. It is shown that modelling of each reflection by a distribution of interference-function weighted rays yields a ‘still’ Lorentz factor. Still data are compared with a conventional rotation data set collected from a single lysozyme crystal. Overall, the presented still integration method improves the data quality markedly. The R factor of the still data compared with the rotation data decreases from 26% using a Monte Carlo approach to 12% after applying the Lorentz correction, to 5.3% when estimating partialities by EVAL and finally to 4.7% after post-refinement. The merging R int factor of the still data improves from 105 to 56% but remains high. This suggests that the accuracy of the model parameters could be further improved. However, with a multiplicity of around 40 and an R int of ∼50% the merged still data approximate the quality of the rotation data. The presented integration method suitably accounts for the partiality of the observed intensities in still diffraction data, which is a critical step to improve data quality in serial crystallography. PMID:26327370

Line spread instrumentation for propagation measurements

NASA Technical Reports Server (NTRS)

Bailey, W. H., Jr.

1980-01-01

A line spread device capable of yielding direct measure of a laser beam's line spread function (LSF) was developed and employed in propagation tests conducted in a wind tunnel to examine optimal acoustical suppression techniques for laser cavities exposed to simulated aircraft aerodynamic environments. Measurements were made on various aerodynamic fences and cavity air injection techniques that effect the LSF of a propagating laser. Using the quiescent tunnel as a control, the relative effect of each technique on laser beam quality was determined. The optical instrument employed enabled the comparison of relative beam intensity for each fence or mass injection. It was found that fence height had little effect on beam quality but fence porosity had a marked effect, i.e., 58% porosity alleviated cavity resonance and degraded the beam the least. Mass injection had little effect on the beam LSF. The use of a direct LSF measuring device proved to be a viable means of determining aerodynamic seeing qualities of flow fields.

Monte Carlo calculations for reporting patient organ doses from interventional radiology

NASA Astrophysics Data System (ADS)

Huo, Wanli; Feng, Mang; Pi, Yifei; Chen, Zhi; Gao, Yiming; Xu, X. George

2017-09-01

This paper describes a project to generate organ dose data for the purposes of extending VirtualDose software from CT imaging to interventional radiology (IR) applications. A library of 23 mesh-based anthropometric patient phantoms were involved in Monte Carlo simulations for database calculations. Organ doses and effective doses of IR procedures with specific beam projection, filed of view (FOV) and beam quality for all parts of body were obtained. Comparing organ doses for different beam qualities, beam projections, patients' ages and patient's body mass indexes (BMIs) which generated by VirtualDose-IR, significant discrepancies were observed. For relatively long time exposure, IR doses depend on beam quality, beam direction and patient size. Therefore, VirtualDose-IR, which is based on the latest anatomically realistic patient phantoms, can generate accurate doses for IR treatment. It is suitable to apply this software in clinical IR dose management as an effective tool to estimate patient doses and optimize IR treatment plans.

Backscattering enhancement factor dependence of a Laguerre-Gaussian laser beam propagating on the location path in the atmosphere on optical turbulence intensity

NASA Astrophysics Data System (ADS)

Rytchkov, D. S.

2017-11-01

The paper presents the results of a study of the backscattering enhancement factor (BSE) dependence of vortex LaguerreGaussian beams propagating on monostatic location paths in the atmosphere on optical turbulence intensity. The numeric simulation split-step method of laser beam propagation was used to obtain BSE factor values of a laser beam propagated on monostatic location path in the turbulent atmosphere and reflected from a diffuse target. It is shown that BSE factor of the averaged intensity of a backscattered vortex laser beam of any topological charge is less than BSE factor values of backscattered Gaussian beam in arbitrary turbulent conditions.

High power, high beam quality regenerative amplifier

DOEpatents

Hackel, L.A.; Dane, C.B.

1993-08-24

A regenerative laser amplifier system generates high peak power and high energy per pulse output beams enabling generation of X-rays used in X-ray lithography for manufacturing integrated circuits. The laser amplifier includes a ring shaped optical path with a limited number of components including a polarizer, a passive 90 degree phase rotator, a plurality of mirrors, a relay telescope, and a gain medium, the components being placed close to the image plane of the relay telescope to reduce diffraction or phase perturbations in order to limit high peak intensity spiking. In the ring, the beam makes two passes through the gain medium for each transit of the optical path to increase the amplifier gain to loss ratio. A beam input into the ring makes two passes around the ring, is diverted into an SBS phase conjugator and proceeds out of the SBS phase conjugator back through the ring in an equal but opposite direction for two passes, further reducing phase perturbations. A master oscillator inputs the beam through an isolation cell (Faraday or Pockels) which transmits the beam into the ring without polarization rotation. The isolation cell rotates polarization only in beams proceeding out of the ring to direct the beams out of the amplifier. The diffraction limited quality of the input beam is preserved in the amplifier so that a high power output beam having nearly the same diffraction limited quality is produced.

High power, high beam quality regenerative amplifier

DOEpatents

Hackel, Lloyd A.; Dane, Clifford B.

1993-01-01

A regenerative laser amplifier system generates high peak power and high energy per pulse output beams enabling generation of X-rays used in X-ray lithography for manufacturing integrated circuits. The laser amplifier includes a ring shaped optical path with a limited number of components including a polarizer, a passive 90 degree phase rotator, a plurality of mirrors, a relay telescope, and a gain medium, the components being placed close to the image plane of the relay telescope to reduce diffraction or phase perturbations in order to limit high peak intensity spiking. In the ring, the beam makes two passes through the gain medium for each transit of the optical path to increase the amplifier gain to loss ratio. A beam input into the ring makes two passes around the ring, is diverted into an SBS phase conjugator and proceeds out of the SBS phase conjugator back through the ring in an equal but opposite direction for two passes, further reducing phase perturbations. A master oscillator inputs the beam through an isolation cell (Faraday or Pockels) which transmits the beam into the ring without polarization rotation. The isolation cell rotates polarization only in beams proceeding out of the ring to direct the beams out of the amplifier. The diffraction limited quality of the input beam is preserved in the amplifier so that a high power output beam having nearly the same diffraction limited quality is produced.

Some aspects of precise laser machining - Part 2: Experimental

NASA Astrophysics Data System (ADS)

Grabowski, Marcin; Wyszynski, Dominik; Ostrowski, Robert

2018-05-01

The paper describes the role of laser beam polarization on quality of laser beam machined cutting tool edge. In micromachining the preparation of the cutting tools in play a key role on dimensional accuracy, sharpness and the quality of the cutting edges. In order to assure quality and dimensional accuracy of the cutting tool edge it is necessary to apply laser polarization control. In the research diode pumped Nd:YAG 532nm pulse laser was applied. Laser beam polarization used in the research was linear (horizontal, vertical). The goal of the carried out research was to describe impact of laser beam polarization on efficiency of the cutting process and quality of machined parts (edge, surface) made of polycrystalline diamond (PCD) and cubic boron nitride (cBN). Application of precise cutting tool in micromachining has significant impact on the minimum uncut chip thickness and quality of the parts. The research was carried within the INNOLOT program funded by the National Centre for Research and Development.

Accounting for partiality in serial crystallography using ray-tracing principles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kroon-Batenburg, Loes M. J., E-mail: l.m.j.kroon-batenburg@uu.nl; Schreurs, Antoine M. M.; Ravelli, Raimond B. G.

Serial crystallography generates partial reflections from still diffraction images. Partialities are estimated with EVAL ray-tracing simulations, thereby improving merged reflection data to a similar quality as conventional rotation data. Serial crystallography generates ‘still’ diffraction data sets that are composed of single diffraction images obtained from a large number of crystals arbitrarily oriented in the X-ray beam. Estimation of the reflection partialities, which accounts for the expected observed fractions of diffraction intensities, has so far been problematic. In this paper, a method is derived for modelling the partialities by making use of the ray-tracing diffraction-integration method EVAL. The method estimates partialitiesmore » based on crystal mosaicity, beam divergence, wavelength dispersion, crystal size and the interference function, accounting for crystallite size. It is shown that modelling of each reflection by a distribution of interference-function weighted rays yields a ‘still’ Lorentz factor. Still data are compared with a conventional rotation data set collected from a single lysozyme crystal. Overall, the presented still integration method improves the data quality markedly. The R factor of the still data compared with the rotation data decreases from 26% using a Monte Carlo approach to 12% after applying the Lorentz correction, to 5.3% when estimating partialities by EVAL and finally to 4.7% after post-refinement. The merging R{sub int} factor of the still data improves from 105 to 56% but remains high. This suggests that the accuracy of the model parameters could be further improved. However, with a multiplicity of around 40 and an R{sub int} of ∼50% the merged still data approximate the quality of the rotation data. The presented integration method suitably accounts for the partiality of the observed intensities in still diffraction data, which is a critical step to improve data quality in serial crystallography.« less

Preliminary experimental investigation of a Ku-band radial line oscillator based on transition radiation effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dang, Fangchao, E-mail: dangfangchao@sina.com; Zhang, Xiaoping; Zhong, Huihuang

2015-09-15

A Ku-band radial line oscillator (RLO) with low guiding magnetic field was proposed in our previous work. In order to weaken the impedance mismatch between the oscillator and an intense electron accelerator with higher impedance, a transverse electromagnetic reflector is added to improve the RLO, which is favorable to increase the Q-factor and accelerate the device saturation. A preliminary experiment is carried out to investigate the performance of the improved RLO. The radial-radiated electron beam is restrained well under the designed guiding magnetic field of 0.52 T. The preliminary experimental results indicates that high power microwaves with a power of 120 MWmore » and a frequency of 14.12 GHz are generated when the diode voltage is 420 kV and the beam current 14.2 kA. The experimental results suggest the feasibility of the presented RLO generating high power microwaves at a high frequency band. Additionally, more work is needed regarding promotion of the electron beam quality and the impedance match between the electron beam accelerator and the oscillator.« less

A comprehensive comparison of IMRT and VMAT plan quality for prostate cancer treatment

PubMed Central

QUAN, ENZHUO M.; LI, XIAOQIANG; LI, YUPENG; WANG, XIAOCHUN; KUDCHADKER, RAJAT J.; JOHNSON, JENNIFER L.; KUBAN, DEBORAH A.; LEE, ANDREW K.; ZHANG, XIAODONG

2013-01-01

Purpose We performed a comprehensive comparative study of the plan quality between volumetric modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) for the treatment of prostate cancer. Methods and Materials Eleven patients with prostate cancer treated at our institution were randomly selected for this study. For each patient, a VMAT plan and a series of IMRT plans using an increasing number of beams (8, 12, 16, 20, and 24 beams) were examined. All plans were generated using our in-house-developed automatic inverse planning (AIP) algorithm. An existing 8-beam clinical IMRT plan, which was used to treat the patient, was used as the reference plan. For each patient, all AIP-generated plans were optimized to achieve the same level of planning target volume (PTV) coverage as the reference plan. Plan quality was evaluated by measuring mean dose to and dose-volume statistics of the organs-at-risk, especially the rectum, from each type of plan. Results For the same PTV coverage, the AIP-generated VMAT plans had significantly better plan quality in terms of rectum sparing than the 8-beam clinical and AIP-generated IMRT plans (p < 0.0001). However, the differences between the IMRT and VMAT plans in all the dosimetric indices decreased as the number of beams used in IMRT increased. IMRT plan quality was similar or superior to that of VMAT when the number of beams in IMRT was increased to a certain number, which ranged from 12 to 24 for the set of patients studied. The superior VMAT plan quality resulted in approximately 30% more monitor units than the 8-beam IMRT plans, but the delivery time was still less than 3 minutes. Conclusions Considering the superior plan quality as well as the delivery efficiency of VMAT compared with that of IMRT, VMAT may be the preferred modality for treating prostate cancer. PMID:22704703

Investigation of cone-beam CT image quality trade-off for image-guided radiation therapy

NASA Astrophysics Data System (ADS)

Bian, Junguo; Sharp, Gregory C.; Park, Yang-Kyun; Ouyang, Jinsong; Bortfeld, Thomas; El Fakhri, Georges

2016-05-01

It is well-known that projections acquired over an angular range slightly over 180° (so-called short scan) are sufficient for fan-beam reconstruction. However, due to practical imaging conditions (projection data and reconstruction image discretization, physical factors, and data noise), the short-scan reconstructions may have different appearances and properties from the full-scan (scans over 360°) reconstructions. Nevertheless, short-scan configurations have been used in applications such as cone-beam CT (CBCT) for head-neck-cancer image-guided radiation therapy (IGRT) that only requires a small field of view due to the potential reduced imaging time and dose. In this work, we studied the image quality trade-off for full, short, and full/short scan configurations with both conventional filtered-backprojection (FBP) reconstruction and iterative reconstruction algorithms based on total-variation (TV) minimization for head-neck-cancer IGRT. Anthropomorphic and Catphan phantoms were scanned at different exposure levels with a clinical scanner used in IGRT. Both visualization- and numerical-metric-based evaluation studies were performed. The results indicate that the optimal exposure level and number of views are in the middle range for both FBP and TV-based iterative algorithms and the optimization is object-dependent and task-dependent. The optimal view numbers decrease with the total exposure levels for both FBP and TV-based algorithms. The results also indicate there are slight differences between FBP and TV-based iterative algorithms for the image quality trade-off: FBP seems to be more in favor of larger number of views while the TV-based algorithm is more robust to different data conditions (number of views and exposure levels) than the FBP algorithm. The studies can provide a general guideline for image-quality optimization for CBCT used in IGRT and other applications.

Investigation of cone-beam CT image quality trade-off for image-guided radiation therapy.

PubMed

Bian, Junguo; Sharp, Gregory C; Park, Yang-Kyun; Ouyang, Jinsong; Bortfeld, Thomas; El Fakhri, Georges

2016-05-07

It is well-known that projections acquired over an angular range slightly over 180° (so-called short scan) are sufficient for fan-beam reconstruction. However, due to practical imaging conditions (projection data and reconstruction image discretization, physical factors, and data noise), the short-scan reconstructions may have different appearances and properties from the full-scan (scans over 360°) reconstructions. Nevertheless, short-scan configurations have been used in applications such as cone-beam CT (CBCT) for head-neck-cancer image-guided radiation therapy (IGRT) that only requires a small field of view due to the potential reduced imaging time and dose. In this work, we studied the image quality trade-off for full, short, and full/short scan configurations with both conventional filtered-backprojection (FBP) reconstruction and iterative reconstruction algorithms based on total-variation (TV) minimization for head-neck-cancer IGRT. Anthropomorphic and Catphan phantoms were scanned at different exposure levels with a clinical scanner used in IGRT. Both visualization- and numerical-metric-based evaluation studies were performed. The results indicate that the optimal exposure level and number of views are in the middle range for both FBP and TV-based iterative algorithms and the optimization is object-dependent and task-dependent. The optimal view numbers decrease with the total exposure levels for both FBP and TV-based algorithms. The results also indicate there are slight differences between FBP and TV-based iterative algorithms for the image quality trade-off: FBP seems to be more in favor of larger number of views while the TV-based algorithm is more robust to different data conditions (number of views and exposure levels) than the FBP algorithm. The studies can provide a general guideline for image-quality optimization for CBCT used in IGRT and other applications.

Evaluation of support loss in micro-beam resonators: A revisit

NASA Astrophysics Data System (ADS)

Chen, S. Y.; Liu, J. Z.; Guo, F. L.

2017-12-01

This paper presents an analytical study on evaluation of support loss in micromechanical resonators undergoing in-plane flexural vibrations. Two-dimensional elastic wave theory is used to determine the energy transmission from the vibrating resonator to the support. Fourier transform and Green's function technique are adopted to solve the problem of wave motions on the surface of the support excited by the forces transmitted by the resonator onto the support. Analytical expressions of support loss in terms of quality factor, taking into account distributed normal stress and shear stress in the attachment region, and coupling between the normal stress and shear stress as well as material disparity between the support and the resonator, have been derived. Effects of geometry of micro-beam resonators, and material dissimilarity between support and resonator on support loss are examined. Numerical results show that 'harder resonator' and 'softer support' combination leads to larger support loss. In addition, the Perfectly Matched Layer (PML) numerical simulation technique is employed for validation of the proposed analytical model. Comparing with results of quality factor obtained by PML technique, we find that the present model agrees well with the results of PML technique and the pure-shear model overestimates support loss noticeably, especially for resonators with small aspect ratio and large material dissimilarity between the support and resonator.

Phase-locking of annular-combination CO2 laser

NASA Astrophysics Data System (ADS)

Qi, Tingxiang; Chen, Mei; Zhang, Rongzhu; Xiao, Qianyi

2015-07-01

A new annular-combination resonator structure adopting the external-injection phase-locking technology is presented theoretically for that the beam quality of stable annular resonator is not satisfying. The phase-locking principle and feasibility are characterized by energy density of injection beam and coupling coefficient. Based on the diffraction theory, output mode of the resonator with phase-locking is deduced and simulated. Results also confirm that injection beam have a good control effect on output mode. The intensity distributions of output beam are studied briefly and indicate that this new resonator which is adaptable to annular gain media can produce high-power laser beam with high quality.

Lick sodium laser guide star: performance during the 1998 LGS observing campaign

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bauman, B; Friedman, H; Gavel, D T

1999-07-19

The performance of a sodium laser guide star adaptive optics system depends crucially on the characteristics of the laser guide star in the sodium layer. System performance is quite sensitive to sodium layer spot radiance, that is, return per unit sterradian on the sky, hence we have been working to improve projected beam quality via improvements to the laser and changes to the launched beam format. The laser amplifier was reconfigured to a ''bounce-beam'' geometry, which considerably improves wavefront quality and allows a larger round instead of square launch beam aperture. The smaller beacon makes it easier to block themore » unwanted Rayleigh light and improves the accuracy of Hartmann sensor wavefront measurements in the A0 system. We present measurements of the beam quality and of the resulting sodium beacon and compare to similar measurements from last year.« less

Simulations of far-field optical beam quality influenced by the thermal distortion of the secondary mirror for high-power laser system

NASA Astrophysics Data System (ADS)

Guo, Ruhai; Chen, Ning; Zhuang, Xinyu; Wang, Bing

2015-02-01

In order to research the influence on the beam quality due to thermal deformation of the secondary mirror in the high power laser system, the theoretical simulation study is performed. Firstly, three typical laser power 10kW, 50kW and 100kW with the wavelength 1.064μm are selected to analyze thermal deformation of mirror through the finite element analyze of thermodynamics instantaneous method. Then the wavefront aberration can be calculated by ray-tracing theory. Finally, focus spot radius，beam quality (BQ) of far-filed beam can be calculated and comparably analyzed by Fresnel diffraction integration. The simulation results show that with the increasing laser power, the optical aberration of beam director gets worse, the far-field optical beam quality decrease, which makes the laser focus spot broadening and the peak optical intensity of center decreasing dramatically. Comparing the clamping ring and the three-point clamping, the former is better than the latter because the former only induces the rotation symmetric deformation and the latter introduces additional astigmatism. The far-field optical beam quality can be improved partly by simply adjusting the distance between the main mirror and the secondary mirror. But the far-field power density is still the one tenth as that without the heat distortion of secondary mirror. These results can also provide the reference to the thermal aberration analyze for high power laser system and can be applied to the field of laser communication system and laser weapon etc.

Development of Prior Image-based, High-Quality, Low-Dose Kilovoltage Cone Beam CT for Use in Adaptive Radiotherapy of Prostate Cancer

DTIC Science & Technology

2012-05-01

employs kilovoltage (KV) cone- beam CT (CBCT) for guiding treatment. High quality CBCT images are important in achieving improved treatment effect...necessary for achieving successful adaptive RT. Kilovoltage cone-beam CT (CBCT) has shown its capability of yielding such images to guide the prostate cancer...study of low-dose intra-operative cone-beam CT for image- guided surgery,” Proc. SPIE, 7961, 79615P, 2011 10. X. Han, E. Pearson, J. Bian, S. Cho, E. Y

Retrospective evaluation of pediatric cranio-spinal axis irradiation plans with the Hi-ART tomotherapy system.

PubMed

Penagaricano, José A; Yan, Yulong; Corry, Peter; Moros, Eduardo; Ratanatharathorn, Vaneerat

2007-08-01

Helical tomotherapy (HT) can be used for the delivery of cranio-spinal axis irradiation (CSAI) without the need for beam matching of conventional linac-based external beam irradiation. The aim of this study is to retrospectively evaluate HT plans used for treatment in nine patients treated with CSAI. Helical tomotherapy cranio-spinal axis irradiation (HT-CSAI) plans were created for each patient. Average length along the cranio-spinal axis of the PTV was 65.6 cm with a range between 53 and 74 cm. Treatment planning optimization and plan evaluation parameters were obtained from the HT planning station for each of the nine patients. PTV coverage by the 95% isodose surface ranged between 98.0 to 100.0% for all nine patients. The clinically acceptable dose variation within the PTV or tolerance range was between 0.7 and 2.5% for all nine patients. Doses to the organs at risk were clinically acceptable. An increasing length along the longitudinal axis of the PTV did not consistently increase the beam-on time indicating that using a larger jaw width had a greater impact on treatment time. With a larger jaw width it is possible to substantially reduce the normalized beam-on treatment time without compromising plan quality and sparing of organs at risk. By using a larger jaw width or lower modulation factor or both, normalized beam-on times were decreased by up to 61% as compared to the other evaluated treatment plans. From the nine cases reported in this study the minimum beam-on time was achieved with a jaw width of 5.0 cm, pitch of 0.287 and a modulation factor of 2.0. Large and long cylindrical volumes can be effectively treated with helical tomotherapy with both clinically acceptable dose distribution and beam-on time.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lessard, Francois; Archambault, Louis; Plamondon, Mathieu

Purpose: Photon dosimetry in the kilovolt (kV) energy range represents a major challenge for diagnostic and interventional radiology and superficial therapy. Plastic scintillation detectors (PSDs) are potentially good candidates for this task. This study proposes a simple way to obtain accurate correction factors to compensate for the response of PSDs to photon energies between 80 and 150 kVp. The performance of PSDs is also investigated to determine their potential usefulness in the diagnostic energy range. Methods: A 1-mm-diameter, 10-mm-long PSD was irradiated by a Therapax SXT 150 unit using five different beam qualities made of tube potentials ranging from 80more » to 150 kVp and filtration thickness ranging from 0.8 to 0.2 mmAl + 1.0 mmCu. The light emitted by the detector was collected using an 8-m-long optical fiber and a polychromatic photodiode, which converted the scintillation photons to an electrical current. The PSD response was compared with the reference free air dose rate measured with a calibrated Farmer NE2571 ionization chamber. PSD measurements were corrected using spectra-weighted corrections, accounting for mass energy-absorption coefficient differences between the sensitive volumes of the ionization chamber and the PSD, as suggested by large cavity theory (LCT). Beam spectra were obtained from x-ray simulation software and validated experimentally using a CdTe spectrometer. Correction factors were also obtained using Monte Carlo (MC) simulations. Percent depth dose (PDD) measurements were compensated for beam hardening using the LCT correction method. These PDD measurements were compared with uncorrected PSD data, PDD measurements obtained using Gafchromic films, Monte Carlo simulations, and previous data. Results: For each beam quality used, the authors observed an increase of the energy response with effective energy when no correction was applied to the PSD response. Using the LCT correction, the PSD response was almost energy independent, with a residual 2.1% coefficient of variation (COV) over the 80-150-kVp energy range. Monte Carlo corrections reduced the COV to 1.4% over this energy range. All PDD measurements were in good agreement with one another except for the uncorrected PSD data, in which an over-response was observed with depth (13% at 10 cm with a 100 kVp beam), showing that beam hardening had a non-negligible effect on the PSD response. A correction based on LCT compensated very well for this effect, reducing the over-response to 3%.Conclusion: In the diagnostic energy range, PSDs show high-energy dependence, which can be corrected using spectra-weighted mass energy-absorption coefficients, showing no considerable sign of quenching between these energies. Correction factors obtained by Monte Carlo simulations confirm that the approximations made by LCT corrections are valid. Thus, PSDs could be useful for real-time dosimetry in radiology applications.« less

Electric field-tunable Ba{sub x}Sr{sub 1-x}TiO{sub 3} films with high figures of merit grown by molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mikheev, Evgeny; Kajdos, Adam P.; Hauser, Adam J.

2012-12-17

We report on the dielectric properties of Ba{sub x}Sr{sub 1-x}TiO{sub 3} (BST) films grown by molecular beam epitaxy on epitaxial Pt bottom electrodes. Paraelectric films (x Less-Than-Or-Equivalent-To 0.5) exhibit dielectric losses that are similar to those of BST single crystals and ceramics. Films with device quality factors greater than 1000 and electric field tunabilities exceeding 1:5 are demonstrated. The results provide evidence for the importance of stoichiometry control and the use of a non-energetic deposition technique for achieving high figures of merit of tunable devices with BST thin films.

Wavelength-scale photonic-crystal laser formed by electron-beam-induced nano-block deposition.

PubMed

Seo, Min-Kyo; Kang, Ju-Hyung; Kim, Myung-Ki; Ahn, Byeong-Hyeon; Kim, Ju-Young; Jeong, Kwang-Yong; Park, Hong-Gyu; Lee, Yong-Hee

2009-04-13

A wavelength-scale cavity is generated by printing a carbonaceous nano-block on a photonic-crystal waveguide. The nanometer-size carbonaceous block is grown at a pre-determined region by the electron-beam-induced deposition method. The wavelength-scale photonic-crystal cavity operates as a single mode laser, near 1550 nm with threshold of approximately 100 microW at room temperature. Finite-difference time-domain computations show that a high-quality-factor cavity mode is defined around the nano-block with resonant wavelength slightly longer than the dispersion-edge of the photonic-crystal waveguide. Measured near-field images exhibit photon distribution well-localized in the proximity of the printed nano-block. Linearly-polarized emission along the vertical direction is also observed.

MO-D-BRB-02: The Radiological Physics Center's Quality Audit Program: Where Can We Improve?

PubMed

Followill, D; Lowenstein, J; Molineu, A; Alvarez, P; Aguirre, J; Kry, S; Summers, P; Ibbott, G

2012-06-01

To analyze the findings of the Radiological Physics Center's (RPC) QA audits of institutions participating in NCI sponsored clinical trials. The RPC has developed an extensive Quality Assurance (QA) program over the past 44 years. This program includes on-site dosimetry reviews where measurements on therapy machines are made, records are reviewed and personnel are interviewed. The program's remote audit tools include mailed dosimeters (OSLD/TLD) to verify output calibration, comparison of dosimetry data with RPC 'standard' data, evaluation of benchmark and patient calculations to verify the treatment planning algorithms, review of institution's QA procedures and records, and use of anthropomorphic phantoms to verify tumor dose delivery. The RPC endeavors to assist institutions in finding the origins of any detected discrepancies, and to resolve them. Ninety percent of institutions receiving dosimetry recommendations has remained level for the past 5 years. The most frequent recommendations were for not performing TG-40 QA tests, wedge factors, small field size output factors and off-axis factors. Since TG-51 was published, the number of beam calibrations audited during visits with ion chambers, that met the RPC's ±3% criterion, decreased initially but has risen to pre-TG-51 levels. The OSLD/TLD program shows that only ∼3% of the beams are outside our ±5% criteria, but these discrepancies are distributed over 12-20% of the institutions. The percent of institutions with ï, 3 l beam outside the RPC's criteria is approximately the same whether OSLD/TLD or ion chambers were used. The first time passing rate for the anthropomorphic phantoms is increasing with time. The prostate phantom has the highest pass rate while the spine phantom has the lowest. Numerous dosimetry errors continue to be discovered by the RPC's QA program and the RPC continues to play an important role in helping institutions resolve these errors. This work was supported by PHS grants CA10953 and CA081647 awarded by NCI. © 2012 American Association of Physicists in Medicine.

SU-E-T-186: Cloud-Based Quality Assurance Application for Linear Accelerator Commissioning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rogers, J

2015-06-15

Purpose: To identify anomalies and safety issues during data collection and modeling for treatment planning systems Methods: A cloud-based quality assurance system (AQUIRE - Automated QUalIty REassurance) has been developed to allow the uploading and analysis of beam data aquired during the treatment planning system commissioning process. In addition to comparing and aggregating measured data, tools have also been developed to extract dose from the treatment planning system for end-to-end testing. A gamma index is perfomed on the data to give a dose difference and distance-to-agreement for validation that a beam model is generating plans consistent with the beam datamore » collection. Results: Over 20 linear accelerators have been commissioning using this platform, and a variety of errors and potential saftey issues have been caught through the validation process. For example, the gamma index of 2% dose, 2mm DTA is quite sufficient to see curves not corrected for effective point of measurement. Also, data imported into the database is analyzed against an aggregate of similar linear accelerators to show data points that are outliers. The resulting curves in the database exhibit a very small standard deviation and imply that a preconfigured beam model based on aggregated linear accelerators will be sufficient in most cases. Conclusion: With the use of this new platform for beam data commissioning, errors in beam data collection and treatment planning system modeling are greatly reduced. With the reduction in errors during acquisition, the resulting beam models are quite similar, suggesting that a common beam model may be possible in the future. Development is ongoing to create routine quality assurance tools to compare back to the beam data acquired during commissioning. I am a medical physicist for Alzyen Medical Physics, and perform commissioning services.« less

Appropriate Measures and Consistent Standard for High Energy Laser Beam Quality (Postprint)

DTIC Science & Technology

2006-08-01

another. a We follow the 99% criteria [ Siegman , Lasers , chapter 17.1] which corresponds to a... Siegman , “ Lasers ” University Science Books, 1986. • A.E. Siegman , “New developments in laser resonators”, SPIE Vol. 1224, Optical Resonators, 1990...pp. 1-14. • Anthony E. Siegman & Steven W. Townsend, “Output Beam Propagation and Beam Quality from a Multimode Stable-Cavity Laser ”, IEEE Journal

High power diode laser Master Oscillator-Power Amplifier (MOPA)

NASA Technical Reports Server (NTRS)

Andrews, John R.; Mouroulis, P.; Wicks, G.

1994-01-01

High power multiple quantum well AlGaAs diode laser master oscillator - power amplifier (MOPA) systems were examined both experimentally and theoretically. For two pass operation, it was found that powers in excess of 0.3 W per 100 micrometers of facet length were achievable while maintaining diffraction-limited beam quality. Internal electrical-to-optical conversion efficiencies as high as 25 percent were observed at an internal amplifier gain of 9 dB. Theoretical modeling of multiple quantum well amplifiers was done using appropriate rate equations and a heuristic model of the carrier density dependent gain. The model gave a qualitative agreement with the experimental results. In addition, the model allowed exploration of a wider design space for the amplifiers. The model predicted that internal electrical-to-optical conversion efficiencies in excess of 50 percent should be achievable with careful system design. The model predicted that no global optimum design exists, but gain, efficiency, and optical confinement (coupling efficiency) can be mutually adjusted to meet a specific system requirement. A three quantum well, low optical confinement amplifier was fabricated using molecular beam epitaxial growth. Coherent beam combining of two high power amplifiers injected from a common master oscillator was also examined. Coherent beam combining with an efficiency of 93 percent resulted in a single beam having diffraction-limited characteristics. This beam combining efficiency is a world record result for such a system. Interferometric observations of the output of the amplifier indicated that spatial mode matching was a significant factor in the less than perfect beam combining. Finally, the system issues of arrays of amplifiers in a coherent beam combining system were investigated. Based upon experimentally observed parameters coherent beam combining could result in a megawatt-scale coherent beam with a 10 percent electrical-to-optical conversion efficiency.

Evaluation of Al2O3:C optically stimulated luminescence (OSL) dosimeters for passive dosimetry of high-energy photon and electron beams in radiotherapy.

PubMed

Yukihara, E G; Mardirossian, G; Mirzasadeghi, M; Guduru, S; Ahmad, S

2008-01-01

This article investigates the performance of Al2O3: C optically stimulated luminescence dosimeters (OSLDs) for application in radiotherapy. Central-axis depth dose curves and optically stimulated luminescence (OSL) responses were obtained in a water phantom for 6 and 18 MV photons, and for 6, 9, 12, 16, and 20 MeV electron beams from a Varian 21EX linear accelerator. Single OSL measurements could be repeated with a precision of 0.7% (one standard deviation) and the differences between absorbed doses measured with OSLDs and an ionization chamber were within +/- 1% for photon beams. Similar results were obtained for electron beams in the low-gradient region after correction for a 1.9% photon-to-electron bias. The distance-to-agreement values were of the order of 0.5-1.0 mm for electrons in high dose gradient regions. Additional investigations also demonstrated that the OSL response dependence on dose rate, field size, and irradiation temperature is less than 1% in the conditions of the present study. Regarding the beam energy/quality dependence, the relative response of the OSLD for 18 MV was (0.51 +/- 0.48)% of the response for the 6 MV photon beam. The OSLD response for the electron beams relative to the 6 MV photon beam. The OSLD response for the electron beams relative to the 6 MV photon beam was in average 1.9% higher, but this result requires further confirmation. The relative response did not seem to vary with electron energy at dmax within the experimental uncertainties (0.5% in average) and, therefore, a fixed correction factor of 1.9% eliminated the energy dependence in our experimental conditions.

Evaluation of Al{sub 2}O{sub 3}:C optically stimulated luminescence (OSL) dosimeters for passive dosimetry of high-energy photon and electron beams in radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yukihara, E. G.; Mardirossian, G.; Mirzasadeghi, M.

This article investigates the performance of Al{sub 2}O{sub 3}:C optically stimulated luminescence dosimeters (OSLDs) for application in radiotherapy. Central-axis depth dose curves and optically stimulated luminescence (OSL) responses were obtained in a water phantom for 6 and 18 MV photons, and for 6, 9, 12, 16, and 20 MeV electron beams from a Varian 21EX linear accelerator. Single OSL measurements could be repeated with a precision of 0.7% (one standard deviation) and the differences between absorbed doses measured with OSLDs and an ionization chamber were within {+-}1% for photon beams. Similar results were obtained for electron beams in the low-gradientmore » region after correction for a 1.9% photon-to-electron bias. The distance-to-agreement values were of the order of 0.5-1.0 mm for electrons in high dose gradient regions. Additional investigations also demonstrated that the OSL response dependence on dose rate, field size, and irradiation temperature is less than 1% in the conditions of the present study. Regarding the beam energy/quality dependence, the relative response of the OSLD for 18 MV was (0.51{+-}0.48)% of the response for the 6 MV photon beam. The OSLD response for the electron beams relative to the 6 MV photon beam. The OSLD response for the electron beams relative to the 6 MV photon beam was in average 1.9% higher, but this result requires further confirmation. The relative response did not seem to vary with electron energy at d{sub max} within the experimental uncertainties (0.5% in average) and, therefore, a fixed correction factor of 1.9% eliminated the energy dependence in our experimental conditions.« less

Energy optimization in gold nanoparticle enhanced radiation therapy.

PubMed

Sung, Wonmo; Schuemann, Jan

2018-06-25

Gold nanoparticles (GNPs) have been demonstrated as radiation dose enhancing agents. Kilovoltage external photon beams have been shown to yield the largest enhancement due to the high interaction probability with gold. While orthovoltage irradiations are feasible and promising, they suffer from a reduced tissue penetrating power. This study quantifies the effect of varying photon beam energies on various beam arrangements, body, tumor, and cellular GNP uptake geometries. Cell survival was modeled based on our previously developed GNP-local effect model with radial doses calculated using the TOPAS-nBio Monte Carlo code. Cell survival curves calculated for tumor sites with GNPs were used to calculate the relative biological effectiveness (RBE)-weighted dose. In order to evaluate the plan quality, the ratio of the mean dose between the tumor and normal tissue for 50-250 kVp beams with GNPs was compared to the standard of care using 6 MV photon beams without GNPs for breast and brain tumors. For breast using a single photon beam, kV  +  GNP was found to yield up to 2.73 times higher mean RBE-weighted dose to the tumor than two tangential megavoltage beams while delivering the same dose to healthy tissue. For irradiation of brain tumors using multiple photon beams, the GNP dose enhancement was found to be effective for energies above 50 keV. A small tumor at shallow depths was found to be the most effective treatment conditions for GNP enhanced radiation therapy. GNP uptake distributions in the cell (with or without nuclear uptake) and the beam arrangement were found to be important factors in determining the optimal photon beam energy.

The use of ion beam cleaning to obtain high quality cold welds with minimal deformation

NASA Technical Reports Server (NTRS)

Sater, B. L.; Moore, T. J.

1978-01-01

A variation of cold welding is described which utilizes an ion beam to clean mating surfaces prior to joining in a vacuum environment. High quality solid state welds were produced with minimal deformation.

A novel approach to TEM preparation with a (7-axis stage) triple-beam FIB-SEM system

NASA Astrophysics Data System (ADS)

Clarke, Jamil J.

2015-10-01

Preparation of lamellae from bulk to grid for Cs-corrected Transmission Electron Microscope (TEM) observation has mostly become routine work on the latest FIB-SEM systems, with standardized techniques that often are left to automation for the initial steps. The finalization of lamellae however, has mostly become, non-routine, non-repeatable and often driven by user experience level in most cases to produce high quality damage-less cross section. Materials processing of the latest technologies, with ever-shrinking Nano-sized structures pose challenges to modern FIB-SEM systems. This can often lead to specialized techniques and hyper-specific functions for producing ultra-thin high quality lamellae that often are lab specific, preventing practical use of such techniques across multiple materials and applications. Several factors that should be incorporated in processing fine structured materials successfully include how the use of electron and ion scan conditions can affect a thin section during ion milling, the type of ion species applied for material processing during the finalization of lamellae with gallium ions or of a smaller ion species type such as Ar/Xe, sample orientation of the lamella during the thinning process which is linked to ion beam incident angle as a direct relationship in the creation of waterfall effects or curtain effects, and how software can be employed to aid in the reduction of these artifacts with reproducible results regardless of FIB-SEM experience for site-specific lift outs. A traditional TEM preparation was performed of a fine structure specimen in pursuit of a process technique to produce a high quality TEM lamella which would address all of the factors mentioned. These new capabilities have been refined and improved upon during the FIB-SEM design and development stages with an end result of a new approach that yields an improvement in quality by the reduction of common ion milling artifacts such as curtain effects, amorphous material, and better pin pointing of the area of interest while reducing overall processing time for the TEM sample preparation process and enhancing repeatability through ease of use via software controls. The development of these new technologies, incorporating a third Ar/Xe ion beam column in conjunction with the electron and gallium ion beam column, a 7-axis stage for enhanced sample orientation with tilt functions in two axes and automated swing control along with a host of additional functions which address the factors aforementioned such as electron and ion scan techniques and curtain effect removal by the use of hardware and software components that are key to reduce typical FIB related artifacts, all of which are called "ACE [Anti Curtaining Effect] Technologies" are explained. The overall developments of these technologies are to address a significant point that productivity, throughput and repeatability are comprised by synergy between the user, application, software and hardware within a FIB-SEM system. The latest Hitachi FIB-SEM platform offers these innovations for reliability, repeatability and high quality lamella preparation for Cs-corrected (S)TEMs.

Combining tissue-phantom ratios to provide a beam-quality specifier for flattening filter free photon beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dalaryd, Mårten, E-mail: Marten.Dalaryd@med.lu.se; Knöös, Tommy; Ceberg, Crister

Purpose: There are currently several commercially available radiotherapy treatment units without a flattening filter in the beam line. Unflattened photon beams have an energy and lateral fluence distribution that is different from conventional beams and, thus, their attenuation properties differ. As a consequence, for flattening filter free (FFF) beams, the relationship between the beam-quality specifier TPR{sub 20,10} and the Spencer–Attix restricted water-to-air mass collision stopping-power ratios, (L{sup -}/ρ){sub air}{sup water}, may have to be refined in order to be used with equivalent accuracy as for beams with a flattening filter. The purpose of this work was twofold. First, to studymore » the relationship between TPR{sub 20,10} and (L{sup -}/ρ){sub air}{sup water} for FFF beams, where the flattening filter has been replaced by a metal plate as in most clinical FFF beams. Second, to investigate the potential of increasing the accuracy in determining (L{sup -}/ρ){sub air}{sup water} by adding another beam-quality metric, TPR{sub 10,5}. The relationship between (L{sup -}/ρ){sub air}{sup water} and %dd(10){sub x} for beams with and without a flattening filter was also included in this study. Methods: A total of 24 realistic photon beams (10 with and 14 without a flattening filter) from three different treatment units have been used to calculate (L{sup -}/ρ){sub air}{sup water}, TPR{sub 20,10}, and TPR{sub 10,5} using the EGSnrc Monte Carlo package. The relationship between (L{sup -}/ρ){sub air}{sup water} and the dual beam-quality specifier TPR{sub 20,10} and TPR{sub 10,5} was described by a simple bilinear equation. The relationship between the photon beam-quality specifier %dd(10){sub x} used in the AAPM’s TG-51 dosimetry protocol and (L{sup -}/ρ){sub air}{sup water} was also investigated for the beams used in this study, by calculating the photon component of the percentage depth dose at 10 cm depth with SSD 100 cm. Results: The calculated (L{sup -}/ρ){sub air}{sup water} for beams without a flattening filter was 0.3% lower, on average, than for beams with a flattening filter and comparable TPR{sub 20,10}. Using the relationship in IAEA, TRS-398 resulted in a root mean square deviation (RMSD) of 0.0028 with a maximum deviation of 0.0043 (0.39%) from Monte Carlo calculated values. For all beams in this study, the RMSD between the proposed model and the Monte Carlo calculated values was 0.0006 with a maximum deviation of 0.0013 (0.1%). Using an earlier proposed relationship [Xiong and Rogers, Med. Phys. 35, 2104–2109 (2008)] between %dd(10){sub x} and (L{sup -}/ρ){sub air}{sup water} gave a RMSD of 0.0018 with a maximum deviation of 0.0029 (0.26%) for all beams in this study (compared to RMSD 0.0015 and a maximum deviation of 0.0048 (0.47%) for the relationship used in AAPM TG-51 published by Almond et al. [Med. Phys. 26, 1847–1870 (1999)]). Conclusions: Using TPR{sub 20,10} as a beam-quality specifier, for the flattening filter free beams used in this study, gave a maximum difference of 0.39% between (L{sup -}/ρ){sub air}{sup water} predicted using IAEA TRS-398 and Monte Carlo calculations. An additional parameter for determining (L{sup -}/ρ){sub air}{sup water} has been presented. This parameter is easy to measure; it requires only an additional dose measurement at 5 cm depth with SSD 95 cm, and provides information for accurate determination of the (L{sup -}/ρ){sub air}{sup water} ratio for beams both with and without a flattening filter at the investigated energies.« less

Electron beam processing of fresh produce - A critical review

NASA Astrophysics Data System (ADS)

Pillai, Suresh D.; Shayanfar, Shima

2018-02-01

To meet the increasing global demand for fresh produce, robust processing methods that ensures both the safety and quality of fresh produce are needed. Since fresh produce cannot withstand thermal processing conditions, most of common safety interventions used in other foods are ineffective. Electron beam (eBeam) is a non-thermal technology that can be used to extend the shelf life and ensure the microbiological safety of fresh produce. There have been studies documenting the application of eBeam to ensure both safety and quality in fresh produce, however, there are still unexplored areas that still need further research. This is a critical review on the current literature on the application of eBeam technology for fresh produce.

Quality of life and satisfaction with information after radical prostatectomy, radical external beam radiotherapy and postoperative radiotherapy: a long-term follow-up study.

PubMed

Nicolaisen, Marianne; Müller, Stig; Patel, Hitendra R H; Hanssen, Tove Aminda

2014-12-01

To assess patients' symptoms, quality of life and satisfaction with information three to four years after radical prostatectomy, radical external beam radiotherapy and postoperative radiotherapy and to analyse differences between treatment groups and the relationship between disease-specific, health-related and overall quality of life and satisfaction with information. Radical prostate cancer treatments are associated with changes in quality of life. Differences between patients undergoing different treatments in symptoms and quality of life have been reported, but there are limited long-term data comparing radical prostatectomy with radical external beam radiotherapy and postoperative radiotherapy. A cross-sectional survey design was used. The study sample included 143 men treated with radical prostatectomy and/or radical external beam radiotherapy. Quality of life was measured using the 12-item Short Form Health Survey and the 50-item Expanded Prostate Cancer Index Composite Instrument. Questions assessing overall Quality of life and satisfaction with information were included. Descriptive statistics and interference statistical methods were applied to analyse the data. Radical external beam radiotherapy was associated with less urinary incontinence and better urinary function. There were no differences between the groups for disease-specific quality of life sum scores. Sexual quality of life was reported very low in all groups. Disease-specific quality of life and health-related quality of life were associated with overall quality of life. Patients having undergone surgery were more satisfied with information, and there was a positive correlation between quality of life and patient satisfaction. Pretreatment information and patient education lead to better quality of life and satisfaction. This study indicates a need for structured, pretreatment information and follow-up for all men going through radical prostate cancer treatment. Long-term quality of life effects should be considered when planning follow-up and information for men after radical prostate cancer treatment. Structured and organised information/education may increase preparedness for symptoms and bother after the treatment, improve symptom management strategies and result in improved quality of life. © 2014 John Wiley & Sons Ltd.

Measurement of absorbed dose with a bone-equivalent extrapolation chamber.

PubMed

DeBlois, François; Abdel-Rahman, Wamied; Seuntjens, Jan P; Podgorsak, Ervin B

2002-03-01

A hybrid phantom-embedded extrapolation chamber (PEEC) made of Solid Water and bone-equivalent material was used for determining absorbed dose in a bone-equivalent phantom irradiated with clinical radiation beams (cobalt-60 gamma rays; 6 and 18 MV x rays; and 9 and 15 MeV electrons). The dose was determined with the Spencer-Attix cavity theory, using ionization gradient measurements and an indirect determination of the chamber air-mass through measurements of chamber capacitance. The collected charge was corrected for ionic recombination and diffusion in the chamber air volume following the standard two-voltage technique. Due to the hybrid chamber design, correction factors accounting for scatter deficit and electrode composition were determined and applied in the dose equation to obtain absorbed dose in bone for the equivalent homogeneous bone phantom. Correction factors for graphite electrodes were calculated with Monte Carlo techniques and the calculated results were verified through relative air cavity dose measurements for three different polarizing electrode materials: graphite, steel, and brass in conjunction with a graphite collecting electrode. Scatter deficit, due mainly to loss of lateral scatter in the hybrid chamber, reduces the dose to the air cavity in the hybrid PEEC in comparison with full bone PEEC by 0.7% to approximately 2% depending on beam quality and energy. In megavoltage photon and electron beams, graphite electrodes do not affect the dose measurement in the Solid Water PEEC but decrease the cavity dose by up to 5% in the bone-equivalent PEEC even for very thin graphite electrodes (<0.0025 cm). In conjunction with appropriate correction factors determined with Monte Carlo techniques, the uncalibrated hybrid PEEC can be used for measuring absorbed dose in bone material to within 2% for high-energy photon and electron beams.

Fractography of interface after microtensile bond strength test using swept-source optical coherence tomography.

PubMed

Dao Luong, Minh Nguyet; Shimada, Yasushi; Turkistani, Alaa; Tagami, Junji; Sumi, Yasunori; Sadr, Alireza

2016-07-01

To determine the effect of crosshead speed and placement technique on interfacial crack formation in microtensile bond strength (MTBS) test using swept-source optical coherence tomography (SS-OCT). MTBS test beams (0.9×0.9mm(2)) were prepared from flat human dentin disks bonded with self-etch adhesive (Clearfil SE Bond, Kuraray) and universal composite (Clearfil AP-X, Kuraray) with or without flowable composite lining (Estelite Flow Quick, Tokuyama). Each beam was scanned under SS-OCT (Santec, Japan) at 1319nm center wavelength before MTBS test was performed at crosshead speed of either 1 or 10mm/min (n=10). The beams were scanned by SS-OCT again to detect and measure cracks at the debonded interface using digital image analysis software. Representative beams were observed under confocal laser scanning microscope to confirm the fractography findings. Two-way ANOVA showed that for MTBS the crosshead speed was not a significant factor (p>0.05), while there was a difference between placement techniques (p<0.001), with flowable lining yielding higher mean values. On the other hand, for crack formation, there was a significant difference between crosshead speeds (p<0.01), while the placement technique did not show up as a statistically significant factor (p>0.05). The interaction of factors were not significant (p>0.05). Testing MTBS samples at higher crosshead speeds induced more cracks in dentin. Lining with a flowable composite improved the bonding quality and increased the bond strength. SS-OCT can visualize interfacial cracks after restoration debonding. Copyright © 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yasmin-Karim, S; Makrigiorgos, GM; Moreau, M

Purpose: Oraya Therapy uses low-voltage, stereotactic, highly targeted X-rays for the treatment of wet age-related macular degeneration (AMD) — offering a new option for patients worldwide. Neovascular endothelial cells play a crucial role in the pathogenesis of this disease. This in-vitro study investigates the potential of gold nanoparticles (GNP) to enhance endothelial cell damage during low-voltage radiotherapy towards potential applications in the treatment of wet-AMD. Methods: Primary human umbilical cord vein endothelium cells (HUVEC) were treated with 1.4 nm sized GNPs for 24 hrs and then irradiated with variable X-ray doses using an Oraya therapy system (100 kVp) or amore » Small Animal Radiation and Research platform (SARRP) at other beam qualities (up to 220 kVp). Radio-sensitization was assessed by clonogenic assays. Variable concentrations of GNPs (0.05 mg/ml, 0.1 mg/ml, 0.25 mg/ml, 0.5 mg/ml, and 1 mg/ml) where employed. The dose enhancement factor (DEF) was calculated as the ratio of radiation doses required to give the same biological effect (survival factor, SF) with and without GNPs. Results: Preliminary results show DEFs of up to 2.62 for the different combinations of x-ray doses and GNP concentrations and beam qualities. In general the DEF increased with increase in GNP concentration. However, for high doses the effect of GNP becomes less apparent likely due to already high cell kill by the radiation alone. Conclusion: The findings suggest that targeted GNPs can play a significant synergistic role in enhancing stereotactic radiosurgery for wet AMD. The results also provide impetus for ongoing studies to find the optimal synergy between the doses or beam energies and GNPs concentration. This will benefit in-vivo studies towards development of nanoparticle-aided radiotherapy for treatment of wet-AMD and potentially ocular cancers.« less

MO-FG-CAMPUS-IeP1-05: New Ionization Chamber Dosimetry of Absorbed Dose to Water in Diagnostic KV X-Ray Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Araki, F; Ohno, T

Purpose: To develop new ionization chamber dosimetry of absorbed dose to water in diagnostic kV x-ray beams, by using a beam quality conversion factor, kQ, for Co-60 to kV x-ray and an ionization conversion factor for a water-substitute plastic phantom. Methods: kQ was calculated for aluminum half value-layers (Al-HVLs) of 1.5 mm to 8 mm which were generated by kV x-ray beams of 50 to 120 kVp. Twenty-two energy spectra for ten effective energies (Eeff) were calculated by a SpecCalc program. Depth doses in water were calculated at 5 × 5 to 30 × 30 cm{sup 2} fields. Output factorsmore » were also obtained from the dose ratio for a 10 × 10 cm{sup 2} field. kQ was obtained for a PTW30013 Former ion chamber. In addition, an ionization conversion factor of the PWDT phantom to water was calculated. All calculations were performed with EGSnrc/cavity code and egs-chamber codes. Results: The x-ray beam energies for 1.5 mm to 8 mm Al-HVLs ranged in Eeff of 25.7 to 54.3 keV. kQ for 1.5 mm to 8 mm Al-HVLs were 0.831 to 0.897, at 1 and 2 cm depths for a 10 × 10 cm2 field. Similarly, output factors for 5 × 5 to 30 × 30 cm{sup 2} fields were 0.937 to 1.033 for 25.7 keV and 0.857 to 1.168 for 54.3 keV. The depth dose in a PWDT phantom decreased up to 5% compared to that in water at depth of ten percent of maximum dose for 1.5 mm Al-HVL. The ionization ratios of water/PWDT phantoms for the PTW30013 chamber were 1.012 to 1.007 for 1.5 mm to 8 mm Al-HVLs at 1 cm depth. Conclusion: It became possible to directly measure the absorbed dose to water with the ionization chamber in diagnostic kV x-ray beams, by using kQ and the PWDT phantom.« less

Swept Line Electron Beam Annealing of Ion Implanted Semiconductors.

DTIC Science & Technology

1982-07-01

of my research to the mainstream of technology. The techniques used for beam processing are distinguished by their * ~.* beam source and method by...raster scanned CW lasers (CWL), pulsed ion beams (PI), area pulsed electron beams (PEE), raster scanned (RSEB) or multi - scanned electron beams (MSEB...where high quality or tailored profiles are required. Continuous wave lasers and multi -scanned or swept-line electron beams are the most likely candidates

Wavefront control of high-power laser beams in the National Ignition Facility (NIF)

NASA Astrophysics Data System (ADS)

Zacharias, Richard A.; Bliss, Erlan S.; Winters, Scott; Sacks, Richard A.; Feldman, Mark; Grey, Andrew; Koch, Jeffrey A.; Stolz, Christopher J.; Toeppen, John S.; Van Atta, Lewis; Woods, Bruce W.

2000-04-01

The use of lasers as the driver for inertial confinement fusion and weapons physics experiments is based on their ability to produce high-energy short pulses in a beam with low divergence. Indeed, the focusability of high quality laser beams far exceeds alternate technologies and is a major factor in the rationale for building high power lasers for such applications. The National Ignition Facility (NIF) is a large, 192-beam, high-power laser facility under construction at the Lawrence Livermore National Laboratory for fusion and weapons physics experiments. Its uncorrected minimum focal spot size is limited by laser system aberrations. The NIF includes a Wavefront Control System to correct these aberrations to yield a focal spot small enough for its applications. Sources of aberrations to be corrected include prompt pump-induced distortions in the laser amplifiers, previous-shot thermal distortions, beam off-axis effects, and gravity, mounting, and coating-induced optic distortions. Aberrations from gas density variations and optic-manufacturing figure errors are also partially corrected. This paper provides an overview of the NIF Wavefront Control System and describes the target spot size performance improvement it affords. It describes provisions made to accommodate the NIF's high fluence (laser beam and flashlamp), large wavefront correction range, wavefront temporal bandwidth, temperature and humidity variations, cleanliness requirements, and exception handling requirements (e.g. wavefront out-of-limits conditions).

Gene expression profiles in promoted-growth rice seedlings that germinated from the seeds implanted by low-energy N+ beam

PubMed Central

Ya, Huiyuan; Chen, Qiufang; Wang, Weidong; Chen, Wanguang; Qin, Guangyong; Jiao, Zhen

2012-01-01

The stimulation effect that some beneficial agronomic qualities have exhibited in present-generation plants have also been observed due to ion implantation on plants. However, there is relatively little knowledge regarding the molecular mechanism of the stimulation effects of ion-beam implantation. In order to extend our current knowledge about the functional genes related to this stimulation effect, we have reported a comprehensive microarray analysis of the transcriptome features of the promoted-growth rice seedlings germinating from seeds implanted by a low-energy N+ beam. The results showed that 351 up-regulated transcripts and 470 down-regulated transcripts, including signaling proteins, kinases, plant hormones, transposable elements, transcription factors, non-coding protein RNA (including miRNA), secondary metabolites, resistance proteins, peroxidase and chromatin modification, are all involved in the stimulating effects of ion-beam implantation. The divergences of the functional catalog between the vacuum and ion implantation suggest that ion implantation is the principle cause of the ion-beam implantation biological effects, and revealed the complex molecular networks required to adapt to ion-beam implantation stress in plants, including enhanced transposition of transposable elements, promoted ABA biosynthesis and changes in chromatin modification. Our data will extend the current understanding of the molecular mechanisms and gene regulation of stimulation effects. Further research on the candidates reported in this study should provide new insights into the molecular mechanisms of biological effects induced by ion-beam implantation. PMID:22843621

Novel high-energy physics studies using intense lasers and plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leemans, Wim P.; Bulanov, Stepan; Esarey, Eric

2015-06-29

In the framework of the project “Novel high-energy physics studies using intense lasers and plasmas” we conducted the study of ion acceleration and “flying mirrors” with high intensity lasers in order to develop sources of ion beams and high frequency radiation for different applications. Since some schemes of laser ion acceleration are also considered a good source of “flying mirrors”, we proposed to investigate the mechanisms of “mirror” formation. As a result we were able to study the laser ion acceleration from thin foils and near critical density targets. We identified several fundamental factors limiting the acceleration in the RPAmore » regime and proposed the target design to compensate these limitations. In the case of near critical density targets, we developed a concept for the laser driven ion source for the hadron therapy. Also we studied the mechanism of “flying mirror” generation during the intense laser interaction with thin solid density targets. As for the laser-based positron creation and capture we initially proposed to study different regimes of positron beam generation and positron beam cooling. Since the for some of these schemes a good quality electron beam is required, we studied the generation of ultra-low emittance electron beams. In order to understand the fundamental physics of high energy electron beam interaction with high intensity laser pulses, which may affect the efficient generation of positron beams, we studied the radiation reaction effects.« less

SU-F-T-260: Using Portal Image Device for Pre-Treatment QA in Volumetric Modulated Arc Plans with Flattening Filter Free (FFF) Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qu, H; Qi, P; Yu, N

Purpose: To implement and validate a method of using electronic portal image device (EPID) for pre-treatment quality assurance (QA) of volumetric modulated arc therapy (VMAT) plans using flattering filter free (FFF) beams for stereotactic body radiotherapy (SBRT). Methods: On Varian Edge with 6MV FFF beam, open field (from 2×2 cm to 20×20 cm) EPID images were acquired with 200 monitor unit (MU) at the image device to radiation source distance of 150cm. With 10×10 open field and calibration unit (CU) provided by vendor to EPID image pixel, a dose conversion factor was determined by dividing the center dose calculated frommore » the treatment planning system (TPS) to the corresponding CU readout on the image. Water phantom measured beam profile and the output factors for various field sizes were further correlated to those of EPID images. The dose conversion factor and correction factors were then used for converting the portal images to the planner dose distributions of clinical fields. A total of 28 VMAT fields of 14 SBRT plans (8 lung, 2 prostate, 2 liver and 2 spine) were measured. With 10% low threshold cutoff, the delivered dose distributions were compared to the reference doses calculated in water phantom from the TPS. A gamma index analysis was performed for the comparison in percentage dose difference/distance-to-agreement specifications. Results: The EPID device has a linear response to the open fields with increasing MU. For the clinical fields, the gamma indices between the converted EPID dose distributions and the TPS calculated 2D dose distributions were 98.7%±1.1%, 94.0%±3.4% and 70.3%±7.7% for the criteria of 3%/3mm, 2%/2mm and 1%/1mm, respectively. Conclusion: Using a portal image device, a high resolution and high accuracy portal dosimerty was achieved for pre-treatment QA verification for SBRT VMAT plans with FFF beams.« less

High-brightness 1.3 μm InAs/GaAs quantum dot tapered laser with high temperature stability.

PubMed

Cao, Yulian; Ji, Haiming; Xu, Pengfei; Gu, Yongxian; Ma, Wenquan; Yang, Tao

2012-10-01

We demonstrate high-brightness 1.3 μm tapered lasers with high temperature stability by using p-doped InAs/GaAs quantum dots (QDs) as the active region. It is found that the beam quality factor M(2) for the devices is almost unchanged as the light power and temperature increase. The almost constant M(2) results from the p-doped QD active region.

Homoepitaxial nonpolar (10-10) ZnO/ZnMgO monolithic microcavities: Towards reduced photonic disorder

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zuniga-Perez, J., E-mail: jzp@crhea.cnrs.fr; Kappei, L.; Deparis, C.

2016-06-20

Nonpolar ZnO/ZnMgO-based optical microcavities have been grown on (10-10) m-plane ZnO substrates by plasma-assisted molecular beam epitaxy. Reflectivity measurements indicate an exponential increase of the cavity quality factor with the number of layers in the distributed Bragg reflectors. Most importantly, microreflectivity spectra recorded with a spot size in the order of 2 μm show a negligible photonic disorder (well below 1 meV), leading to local quality factors equivalent to those obtained by macroreflectivity. The anisotropic character of the nonpolar heterostructures manifests itself both in the surface features, elongated parallel to the in-plane c direction, and in the optical spectra, with twomore » cavity modes being observed at different energies for orthogonal polarizations.« less

WE-G-BRA-06: Calibrating an Ionisation Chamber: Gaining Experience Using a Dosimetry 'flight Simulator'.

PubMed

Beavis, A; Saunderson, J; Ward, J

2012-06-01

Recently there has been great interest in the use of simulation training, with the view to enhance safety within radiotherapy practice. We have developed a Virtual Environment for Radiotherapy Training (VERT) which facilitates this, including the simulation of a number of 'Physics practices'. One such process is the calibration of an ionisation chamber for use in Linac photon beams. The VERT system was used to provide a life sized 3D virtual environment within which we were able to simulate the calibration of a departmental chamber for 6MV and 15 MV beams following the UK 1990 Code of Practice. The characteristics of the beams are fixed parameters in the simulation, whereas default (Absorbed dose to water) correction factors of the chambers are configurable thereby dictating their response in the virtual x-ray beam. When the simulation is started, a random, realistic temperature and pressure is assigned to the bunker. Measurement and chamber positional errors are assigned to the chambers. A virtual water phantom was placed on the Linac couch and irradiated through the side using a 10 × 10 field. With a chamber at the appropriate depths and irradiated iso-centrically, the Quality Indices (QI) of the beams were obtained. The two chambers were 'inter-compared', allowing the departmental chamber calibration factor to be calculated from that of the reference chamber. For the virtual 6/15 MV beams, the QI were found to be 0.668/ 0.761 and the inter-comparison ratios 0.4408/ 0.4402 respectively. The departmental chamber calibration factors were calculated; applying these and appropriate environmental corrections allowed the output of the Linac to be confirmed. We have shown how a virtual training environment can be used to demonstrate practical processes and reinforce learning. The UK CoP was used here, however any relevant protocol could be demonstrated. Two of the authors (Beavis and Ward) are Founders of Vertual Ltd, a spin-out company created to commercialise the research presented in this abstract. © 2012 American Association of Physicists in Medicine.

SU-F-J-211: Scatter Correction for Clinical Cone-Beam CT System Using An Optimized Stationary Beam Blocker with a Single Scan

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, X; Zhang, Z; Xie, Y

Purpose: X-ray scatter photons result in significant image quality degradation of cone-beam CT (CBCT). Measurement based algorithms using beam blocker directly acquire the scatter samples and achieve significant improvement on the quality of CBCT image. Within existing algorithms, single-scan and stationary beam blocker proposed previously is promising due to its simplicity and practicability. Although demonstrated effectively on tabletop system, the blocker fails to estimate the scatter distribution on clinical CBCT system mainly due to the gantry wobble. In addition, the uniform distributed blocker strips in our previous design results in primary data loss in the CBCT system and leads tomore » the image artifacts due to data insufficiency. Methods: We investigate the motion behavior of the beam blocker in each projection and design an optimized non-uniform blocker strip distribution which accounts for the data insufficiency issue. An accurate scatter estimation is then achieved from the wobble modeling. Blocker wobble curve is estimated using threshold-based segmentation algorithms in each projection. In the blocker design optimization, the quality of final image is quantified using the number of the primary data loss voxels and the mesh adaptive direct search algorithm is applied to minimize the objective function. Scatter-corrected CT images are obtained using the optimized blocker. Results: The proposed method is evaluated using Catphan@504 phantom and a head patient. On the Catphan©504, our approach reduces the average CT number error from 115 Hounsfield unit (HU) to 11 HU in the selected regions of interest, and improves the image contrast by a factor of 1.45 in the high-contrast regions. On the head patient, the CT number error is reduced from 97 HU to 6 HU in the soft tissue region and image spatial non-uniformity is decreased from 27% to 5% after correction. Conclusion: The proposed optimized blocker design is practical and attractive for CBCT guided radiation therapy. This work is supported by grants from Guangdong Innovative Research Team Program of China (Grant No. 2011S013), National 863 Programs of China (Grant Nos. 2012AA02A604 and 2015AA043203), the National High-tech R&D Program for Young Scientists by the Ministry of Science and Technology of China (Grant No. 2015AA020917)« less

Voice quality after treatment of early vocal cord cancer: a randomized trial comparing laser surgery with radiation therapy.

PubMed

Aaltonen, Leena-Maija; Rautiainen, Noora; Sellman, Jaana; Saarilahti, Kauko; Mäkitie, Antti; Rihkanen, Heikki; Laranne, Jussi; Kleemola, Leenamaija; Wigren, Tuija; Sala, Eeva; Lindholm, Paula; Grenman, Reidar; Joensuu, Heikki

2014-10-01

Early laryngeal cancer is usually treated with either transoral laser surgery or radiation therapy. The quality of voice achieved with these treatments has not been compared in a randomized trial. Male patients with carcinoma limited to 1 mobile vocal cord (T1aN0M0) were randomly assigned to receive either laser surgery (n=32) or external beam radiation therapy (n=28). Surgery consisted of tumor excision with a CO2 laser with the patient under general anaesthesia. External beam radiation therapy to the larynx was delivered to a cumulative dose of 66 Gy in 2-Gy daily fractions over 6.5 weeks. Voice quality was assessed at baseline and 6 and 24 months after treatment. The main outcome measures were expert-rated voice quality on a grade, roughness, breathiness, asthenia, and strain (GRBAS) scale, videolaryngostroboscopic findings, and the patients' self-rated voice quality and its impact on activities of daily living. Overall voice quality between the groups was rated similar, but voice was more breathy and the glottal gap was wider in patients treated with laser surgery than in those who received radiation therapy. Patients treated with radiation therapy reported less hoarseness-related inconvenience in daily living 2 years after treatment. Three patients in each group had local cancer recurrence within 2 years from randomization. Radiation therapy may be the treatment of choice for patients whose requirements for voice quality are demanding. Overall voice quality was similar in both treatment groups, however, indicating a need for careful consideration of patient-related factors in the choice of a treatment option. Copyright © 2014 Elsevier Inc. All rights reserved.

Voice Quality After Treatment of Early Vocal Cord Cancer: A Randomized Trial Comparing Laser Surgery With Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aaltonen, Leena-Maija, E-mail: leena-maija.aaltonen@hus.fi; Rautiainen, Noora; Sellman, Jaana

Objective: Early laryngeal cancer is usually treated with either transoral laser surgery or radiation therapy. The quality of voice achieved with these treatments has not been compared in a randomized trial. Methods and Materials: Male patients with carcinoma limited to 1 mobile vocal cord (T1aN0M0) were randomly assigned to receive either laser surgery (n=32) or external beam radiation therapy (n=28). Surgery consisted of tumor excision with a CO{sub 2} laser with the patient under general anaesthesia. External beam radiation therapy to the larynx was delivered to a cumulative dose of 66 Gy in 2-Gy daily fractions over 6.5 weeks. Voice quality wasmore » assessed at baseline and 6 and 24 months after treatment. The main outcome measures were expert-rated voice quality on a grade, roughness, breathiness, asthenia, and strain (GRBAS) scale, videolaryngostroboscopic findings, and the patients' self-rated voice quality and its impact on activities of daily living. Results: Overall voice quality between the groups was rated similar, but voice was more breathy and the glottal gap was wider in patients treated with laser surgery than in those who received radiation therapy. Patients treated with radiation therapy reported less hoarseness-related inconvenience in daily living 2 years after treatment. Three patients in each group had local cancer recurrence within 2 years from randomization. Conclusions: Radiation therapy may be the treatment of choice for patients whose requirements for voice quality are demanding. Overall voice quality was similar in both treatment groups, however, indicating a need for careful consideration of patient-related factors in the choice of a treatment option.« less

Gaussian content as a laser beam quality parameter.

PubMed

Ruschin, Shlomo; Yaakobi, Elad; Shekel, Eyal

2011-08-01

We propose the Gaussian content (GC) as an optional quality parameter for the characterization of laser beams. It is defined as the overlap integral of a given field with an optimally defined Gaussian. The definition is especially suited for applications where coherence properties are targeted. Mathematical definitions and basic calculation procedures are given along with results for basic beam profiles. The coherent combination of an array of laser beams and the optimal coupling between a diode laser and a single-mode fiber are elaborated as application examples. The measurement of the GC and its conservation upon propagation are experimentally confirmed.

DAΦNE operation with electron-cloud-clearing electrodes.

PubMed

Alesini, D; Drago, A; Gallo, A; Guiducci, S; Milardi, C; Stella, A; Zobov, M; De Santis, S; Demma, T; Raimondi, P

2013-03-22

The effects of an electron cloud (e-cloud) on beam dynamics are one of the major factors limiting performances of high intensity positron, proton, and ion storage rings. In the electron-positron collider DAΦNE, namely, a horizontal beam instability due to the electron-cloud effect has been identified as one of the main limitations on the maximum stored positron beam current and as a source of beam quality deterioration. During the last machine shutdown in order to mitigate such instability, special electrodes have been inserted in all dipole and wiggler magnets of the positron ring. It has been the first installation all over the world of this type since long metallic electrodes have been installed in all arcs of the collider positron ring and are currently used during the machine operation in collision. This has allowed a number of unprecedented measurements (e-cloud instabilities growth rate, transverse beam size variation, tune shifts along the bunch train) where the e-cloud contribution is clearly evidenced by turning the electrodes on and off. In this Letter we briefly describe a novel design of the electrodes, while the main focus is on experimental measurements. Here we report all results that clearly indicate the effectiveness of the electrodes for e-cloud suppression.

Quantitative approach for optimizing e-beam condition of photoresist inspection and measurement

NASA Astrophysics Data System (ADS)

Lin, Chia-Jen; Teng, Chia-Hao; Cheng, Po-Chung; Sato, Yoshishige; Huang, Shang-Chieh; Chen, Chu-En; Maruyama, Kotaro; Yamazaki, Yuichiro

2018-03-01

Severe process margin in advanced technology node of semiconductor device is controlled by e-beam metrology system and e-beam inspection system with scanning electron microscopy (SEM) image. By using SEM, larger area image with higher image quality is required to collect massive amount of data for metrology and to detect defect in a large area for inspection. Although photoresist is the one of the critical process in semiconductor device manufacturing, observing photoresist pattern by SEM image is crucial and troublesome especially in the case of large image. The charging effect by e-beam irradiation on photoresist pattern causes deterioration of image quality, and it affect CD variation on metrology system and causes difficulties to continue defect inspection in a long time for a large area. In this study, we established a quantitative approach for optimizing e-beam condition with "Die to Database" algorithm of NGR3500 on photoresist pattern to minimize charging effect. And we enhanced the performance of measurement and inspection on photoresist pattern by using optimized e-beam condition. NGR3500 is the geometry verification system based on "Die to Database" algorithm which compares SEM image with design data [1]. By comparing SEM image and design data, key performance indicator (KPI) of SEM image such as "Sharpness", "S/N", "Gray level variation in FOV", "Image shift" can be retrieved. These KPIs were analyzed with different e-beam conditions which consist of "Landing Energy", "Probe Current", "Scanning Speed" and "Scanning Method", and the best e-beam condition could be achieved with maximum image quality, maximum scanning speed and minimum image shift. On this quantitative approach of optimizing e-beam condition, we could observe dependency of SEM condition on photoresist charging. By using optimized e-beam condition, measurement could be continued on photoresist pattern over 24 hours stably. KPIs of SEM image proved image quality during measurement and inspection was stabled enough.

The Influence of the Form of a Wooden Beam on Its Stiffness and Strength II : Form Factors of Beams Subjected to Transverse Loading Only

NASA Technical Reports Server (NTRS)

Newlin, J A; Trayer, G W

1924-01-01

The general aim of the investigation described in this report is the achievement of efficient design in wing beams. The purpose of the tests was to determine factors to apply to the usual beam formula in order that the properties of wood based on tests of rectangular sections might be used as a basis of design for beams of any sections and if practical to develop formulas for determining such factors and to verify them by experiment. Such factors for various sections have been determined from test by comparing properties of the beam in question to similar properties of matched beams 2 by 2 inches in section. Furthermore, formulas were worked out, more or less empirical in character, which check all of these test values remarkably well.

Mask automation: need a revolution in mask makers and equipment industry

NASA Astrophysics Data System (ADS)

Moon, Seong-yong; Yu, Sang-yong; Noh, Young-hwa; Son, Ki-jung; Lee, Hyun-Joo; Cho, Han-Ku

2013-09-01

As improving device integration for the next generation, high performance and cost down are also required accordingly in semiconductor business. Recently, significant efforts have been given on putting EUV technology into fabrication in order to improve device integration. At the same time, 450mm wafer manufacturing environment has been considered seriously in many ways in order to boost up the productivity. Accordingly, 9-inch mask has been discussed in mask fabrication business recently to support 450mm wafer manufacturing environment successfully. Although introducing 9-inch mask can be crucial for mask industry, multi-beam technology is also expected as another influential turning point to overcome currently the most critical issue in mask industry, electron beam writing time. No matter whether 9-inch mask or multi-beam technology will be employed or not, mask quality and productivity will be the key factors to survive from the device competition. In this paper, the level of facility automation in mask industry is diagnosed and analyzed and the automation guideline is suggested for the next generation.

Integrated wide-angle scanner based on translating a curved mirror of acylindrical shape.

PubMed

Sabry, Yasser M; Khalil, Diaa; Saadany, Bassam; Bourouina, Tarik

2013-06-17

A wide angle microscanning architecture is presented in which the angular deflection is achieved by displacing the principle axis of a curved silicon micromirror of acylindrical shape, with respect to the incident beam optical axis. The micromirror curvature is designed to overcome the possible deformation of the scanned beam spot size during scanning. In the presented architecture, the optical axis of the beam lays in-plane with respect to the substrate opening the door for a completely integrated and self-aligned miniaturized scanner. A micro-optical bench scanning device, based on translating a 200 μm focal length micromirror by an electrostatic comb-drive actuator, is implemented on a silicon chip. The microelectromechanical system has a resonance frequency of 329 Hz and a quality factor of 22. A single-mode optical fiber is used as the optical source and inserted into a micromachined groove fabricated and lithographically aligned with the microbench. Optical deflection angles up to 110 degrees are demonstrated.

Fabrication of single crystalline stripe in Si and Ge film on rolled flexible glass substrate by UV cw micro-chevron laser beam

NASA Astrophysics Data System (ADS)

Yeh, Wenchang

2017-08-01

Micro chevron laser beam annealing (μCLBA) of Si film and Ge film were introduced. Single crystal stripe with a dimension of several tens to hundreds μm in length and 3-8μm in width was formed in Si film or Ge film by scanning μCLBA over the film. Main boundaries in the c-Si stripe were Σ3 CSL twin boundary. Scanning speed of micro linear laser beam annealing (μLLBA) was varied from 0.05 m/s to 8m/s to investigate its influence to crystallinity. Even at 8m/s lateral growth taken place, however, crystal quality was better for slower lateral growth. Crystallization area per energy (APE) of μLLBA was evaluated and compared with other methods. It was found APE of μLLBA was larger than other method, especially for a display with low fill factor of TFT, APE can be several orders of magnitude larger.

Simulation results of corkscrew motion in DARHT-II

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chan, K. D.; Ekdahl, C. A.; Chen, Y. J.

2003-01-01

DARHT-II, the second axis of the Dual-Axis Radiographic Hydrodynamics Test Facility, is being commissioned. DARHT-II is a linear induction accelerator producing 2-microsecond electron beam pulses at 20 MeV and 2 kA. These 2-microsecond pulses will be chopped into four short pulses to produce time resolved x-ray images. Radiographic application requires the DARHT-II beam to have excellent beam quality, and it is important to study various beam effects that may cause quality degradation of a DARHT-II beam. One of the beam dynamic effects under study is 'corkscrew' motion. For corkscrew motion, the beam centroid is deflected off axis due to misalignmentsmore » of the solenoid magnets. The deflection depends on the beam energy variation, which is expected to vary by {+-}0.5% during the 'flat-top' part of a beam pulse. Such chromatic aberration will result in broadening of beam spot size. In this paper, we will report simulation results of our study of corkscrew motion in DARHT-II. Sensitivities of beam spot size to various accelerator parameters and the strategy for minimizing corkscrew motion will be described. Measured magnet misalignment is used in the simulation.« less

Laser Brazing with Beam Scanning: Experimental and Simulative Analysis

NASA Astrophysics Data System (ADS)

Heitmanek, M.; Dobler, M.; Graudenz, M.; Perret, W.; Göbel, G.; Schmidt, M.; Beyer, E.

Laser beam brazing with copper based filler wire is a widely established technology for joining zinc-coated steel plates in the body-shop. Successful applications are the divided tailgate or the zero-gap joint, which represents the joint between the side panel and the roof-top of the body-in-white. These joints are in direct view to the customer, and therefore have to fulfil highest optical quality requirements. For this reason a stable and efficient laser brazing process is essential. In this paper the current results on quality improvement due to one dimensional laser beam deflections in feed direction are presented. Additionally to the experimental results a transient three-dimensional simulation model for the laser beam brazing process is taken into account. With this model the influence of scanning parameters on filler wire temperature and melt pool characteristics is analyzed. The theoretical predictions are in good accordance with the experimental results. They show that the beam scanning approach is a very promising method to increase process stability and seam quality.

Effect of Zn and Te beam intensity upon the film quality of ZnTe layers on severely lattice mismatched sapphire substrates by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Nakasu, Taizo; Sun, W.; Kobayashi, M.; Asahi, T.

2017-06-01

Zinc telluride layers were grown on highly-lattice-mismatched sapphire substrates by molecular beam epitaxy, and their crystallographic properties were studied by means of X-ray diffraction pole figures. The crystal quality of the ZnTe thin film was further studied by scanning electron microscopy, X-ray rocking curves and low-temperature photoluminescence measurements. These methods show that high-crystallinity (111)-oriented single domain ZnTe layers with the flat surface and good optical properties are realized when the beam intensity ratio of Zn and Te beams is adjusted. The migration of Zn and Te was inhibited by excess surface material and cracks were appeared. In particular, excess Te inhibited the formation of a high-crystallinity ZnTe film. The optical properties of the ZnTe layer revealed that the exciton-related features were dominant, and therefore the film quality was reasonably high even though the lattice constants and the crystal structures were severely mismatched.

Beam quality improvement by population-dynamic-coupled combined guiding effect in end-pumped Nd:YVO4 laser oscillator

NASA Astrophysics Data System (ADS)

Shen, Yijie; Gong, Mali; Fu, Xing

2018-05-01

Beam quality improvement with pump power increasing in an end-pumped laser oscillator is experimentally realized for the first time, to the best of our knowledge. The phenomenon is caused by the population-dynamic-coupled combined guiding effect, a comprehensive theoretical model of which has been well established, in agreement with the experimental results. Based on an 888 nm in-band dual-end-pumped oscillator using four tandem Nd:YVO4 crystals, the output beam quality of M^2= 1.1/1.1 at the pump power of 25 W is degraded to M^2 = 2.5/1.8 at 75 W pumping and then improved to M^2= 1.8/1.3 at 150 W pumping. The near-TEM_{00} mode is obtained with the highest continuous-wave output power of 72.1 W and the optical-to-optical efficiency of 48.1%. This work demonstrates great potential to further scale the output power of end-pumped laser oscillator while keeping good beam quality.

The effects of TGG crystal length on output power and beam quality of a unidirectional ring Nd:YVO4 laser with and without second harmonic generation

NASA Astrophysics Data System (ADS)

Ahmadi, A.; Avazpour, A.; Nadgaran, H.; Mousavi, M.

2018-04-01

The effect of terbium gallium garnet (TGG ) crystal length on 1064 and 532 nm output powers and beam quality of a unidirectional ring Nd:YVO4 laser is investigated. In the case of 1064 nm (without nonlinear crystal), the laser output power without considerating the effect of TGG crystal was computed theoretically. Then three TGG crystals with different lengths were placed in the laser setup one by one. A systematic decrease in output power was observed by increasing the TGG crystal length. The experiment was repeated in the case of 532 nm. It was found that in a 532 nm laser, higher laser efficiency and small beam quality degradation can be achieved by increasing the TGG crystal length leading to a 5.7 W green laser with 27 W pump power. The power stability and beam quality were 0.8% for 30 min and less than 1.3, respectively.

Beam propagation factor based on the Rényi entropy.

PubMed

Vaveliuk, Pablo; da Silva, Marcone Lopes

2008-09-15

A beam width measure based on Rényi entropy was introduced by Luis [Opt. Lett 31, 3644 (2006)]. That one-dimensional analysis was limited to beam profiles with rectangular symmetry. In this Letter, we derive a general Rényi beam width measure that accounts for the diffraction properties of beams with profiles of arbitrary symmetry. We also show that the square of this measure has a quadratic dependence as a function of the propagation coordinate, so that it can be applied to propagation through arbitrary ABCD paraxial systems. The Rényi beam propagation factor, here introduced, is discussed in examples where the M(2) factor seems to have a limited effectiveness in describing the beam spreading.

Response analysis of TLD-300 dosimeters in heavy-particle beams.

PubMed

Loncol, T; Hamal, M; Denis, J M; Vynckier, S; Wambersie, A; Scalliet, P

1996-09-01

In vivo dosimetry is recommended as part of the quality control procedure for treatment verification in radiation therapy. Using thermoluminescence, such controls are planned in the p(65) + Be neutron and 85 MeV proton beams produced at the cyclotron at Louvain-La-Neuve and dedicated to therapy applications. A preliminary study of the peak 3 (150 degrees C) and peak 5 (250 degrees C) response of CaF2:Tm (TLD-300) to neutron and proton beams aimed to analyse the effect of different radiation qualities on the dosimetric behaviour of the detector irradiated in phantom. To broaden the range of investigation, the study was extended to an experimental 12C heavy ion beam (95 MeV/nucleon). The peak 3 and 5 sensitivities in the neutron beam, compared to 60Co, varied little with depth. A major change of peak 5 sensitivity was observed for samples positioned under five leaves of the multi-leaf collimator. While peak 3 sensitivity was constant with depth in the unmodulated proton beam, peak 5 sensitivity increased by 15%. Near the Bragg peak, peak 3 showed the highest decrease of sensitivity. In the modulated proton beam, the sensitivity values were not significantly smaller than those measured in the unmodulated beam far from the Bragg peak region. The ratio of the heights of peak 3 and peak 5 decreased by 70% from the 60Co reference radiation to the 12C heavy-ion beam. This parameter was strongly correlated with the change of radiation quality.

Stable generation of GeV-class electron beams from self-guided laser-plasma channels

NASA Astrophysics Data System (ADS)

Hafz, Nasr A. M.; Jeong, Tae Moon; Choi, Il Woo; Lee, Seong Ku; Pae, Ki Hong; Kulagin, Victor V.; Sung, Jae Hee; Yu, Tae Jun; Hong, Kyung-Han; Hosokai, Tomonao; Cary, John R.; Ko, Do-Kyeong; Lee, Jongmin

2008-09-01

Table-top laser-driven plasma accelerators are gaining attention for their potential use in miniaturizing future high-energy accelerators. By irradiating gas jet targets with ultrashort intense laser pulses, the generation of quasimonoenergetic electron beams was recently observed. Currently, the stability of beam generation and the ability to scale to higher electron beam energies are critical issues for practical laser acceleration. Here, we demonstrate the first generation of stable GeV-class electron beams from stable few-millimetre-long plasma channels in a self-guided wakefield acceleration process. As primary evidence of the laser wakefield acceleration in a bubble regime, we observed a boost of both the electron beam energy and quality by reducing the plasma density and increasing the plasma length in a 1-cm-long gas jet. Subsequent three-dimensional simulations show the possibility of achieving even higher electron beam energies by minimizing plasma bubble elongation, and we anticipate dramatic increases in beam energy and quality in the near future. This will pave the way towards ultracompact, all-optical electron beam accelerators and their applications in science, technology and medicine.

Laser beam delivery at ELI-NP

DOE PAGES

Ursescu, Daniel; Cheriaux, G.; Audebert, P.; ...

2017-01-01

The Laser Beam Delivery (LBD) system technical design report covers the interface between the High Power Laser System (HPLS) and the experiments, together with the pulse quality management. Here, the laser transport part of the LBD has a number of subsystems as follows: the beam transport lines for the six main outputs of HPLS, the additional short and long pulses and the synchronization system including the timing of the laser pulses with the Gamma Beam System (GBS) and the experiments on femtosecond timescale. Pulse quality management, discussed further here, consist in the generation and delivery of multiple HPLS pulses, coherentmore » combining of the HPLS arms, laser pulse diagnostics on target, laser beam dumps, shutters and output energy adaption.« less

High power far-infrared optical parametric oscillator with high beam quality

NASA Astrophysics Data System (ADS)

Qian, Chuan-Peng; Shen, Ying-Jie; Dai, Tong-Yu; Duan, Xiao-Ming; Yao, Bao-Quan

2016-11-01

A high power ZnGeP2 (ZGP) optical parametric oscillator (OPO) with good beam quality pumped by a Q-switched Ho:YAG laser was demonstrated. The maximum output power of the ZGP OPO with a four-mirror ring cavity was about 5.04 W around 8.1 μm with 83.9 W Ho incident pump power, corresponding to a slope efficiency of 9.2 %. The ZGP OPO produced 36.0 ns far-IR pulse laser in the 8.0-8.3 μm spectral regions. The beam quality was measured to be M2 1.6 at the highest output power.

IEC 61267: Feasibility of type 1100 aluminium and a copper/aluminium combination for RQA beam qualities.

PubMed

Leong, David L; Rainford, Louise; Zhao, Wei; Brennan, Patrick C

2016-01-01

In the course of performance acceptance testing, benchmarking or quality control of X-ray imaging systems, it is sometimes necessary to harden the X-ray beam spectrum. IEC 61267 specifies materials and methods to accomplish beam hardening and, unfortunately, requires the use of 99.9% pure aluminium (Alloy 1190) for the RQA beam quality, which is expensive and difficult to obtain. Less expensive and more readily available filters, such as Alloy 1100 (99.0% pure) aluminium and copper/aluminium combinations, have been used clinically to produce RQA series without rigorous scientific investigation to support their use. In this paper, simulation and experimental methods are developed to determine the differences in beam quality using Alloy 1190 and Alloy 1100. Additional simulation investigated copper/aluminium combinations to produce RQA5 and outputs from this simulation are verified with laboratory tests using different filter samples. The results of the study demonstrate that although Alloy 1100 produces a harder beam spectrum compared to Alloy 1190, it is a reasonable substitute. A combination filter of 0.5 mm copper and 2 mm aluminium produced a spectrum closer to that of Alloy 1190 than Alloy 1100 with the added benefits of lower exposures and lower batch variability. Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Comparison of the Diagnostic Image Quality of the Canine Maxillary Dentoalveolar Structures Obtained by Cone Beam Computed Tomography and 64-Multidetector Row Computed Tomography.

PubMed

Soukup, Jason W; Drees, Randi; Koenig, Lisa J; Snyder, Christopher J; Hetzel, Scott; Miles, Chanda R; Schwarz, Tobias

2015-01-01

The objective of this blinded study was to validate the use of cone beam computed tomography (C) for imaging of the canine maxillary dentoalveolar structures by comparing its diagnostic image quality with that of 64-multidetector row CT Sagittal slices of a tooth-bearing segment of the maxilla of a commercially purchased dog skull embedded in methylmethacrylate were obtained along a line parallel with the dental arch using a commercial histology diamond saw. The slice of tooth-bearing bone that best depicted the dentoalveolar structures was chosen and photographed. The maxillary segment was imaged with cone beam CT and 64-multidetector row CT. Four blinded evaluators compared the cone beam CT and 64-multidetector row CT images and image quality was scored as it related to the anatomy of dentoalveolar structures. Trabecular bone, enamel, dentin, pulp cavity, periodontal ligament space, and lamina dura were scored In addition, a score depicting the evaluators overall impression of the image was recorded. Images acquired with cone beam CT were found to be significantly superior in image quality to images acquired with 64-multidetector row CT overall, and in all scored categories. In our study setting cone beam CT was found to be a valid and clinically superior imaging modality for the canine maxillary dentoalveolar structures when compared to 64-multidetector row CT.

Comparison of the Diagnostic Image Quality of the Canine Maxillary Dentoalveolar Structures Obtained by Cone Beam Computed Tomography and 64-Multidetector Row Computed Tomography

PubMed Central

Soukup, Jason W.; Drees, Randi; Koenig, Lisa J.; Snyder, Christopher J.; Hetzel, Scott; Miles, Chanda R.; Schwarz, Tobias

2016-01-01

Summary The objective of this blinded study was to validate the use of cone beam computed tomography (CT) for imaging of the canine maxillary dentoalveolar structures by comparing its diagnostic image quality with that of 64-multidetector row CT. Sagittal slices of a tooth-bearing segment of the maxilla of a commercially purchased dog skull embedded in methyl methacrylate were obtained along a line parallel with the dental arch using a commercial histology diamond saw. The slice of tooth-bearing bone that best depicted the dentoalveolar structures was chosen and photographed. The maxilla segment was imaged with cone beam CT and 64-multidetector row CT. Four blinded evaluators compared the cone beam CT and 64-multidetector row CT images and image quality was scored as it related to the anatomy of dentoalveolar structures. Trabecular bone, enamel, dentin, pulp cavity, periodontal ligament space, and lamina dura were scored. In addition, a score depicting the evaluators overall impression of the image was recorded. Images acquired with cone beam CT were found to be significantly superior in image quality to images acquired with 64-multidetector row CT overall, and in all scored categories. In our study setting, cone beam CT was found to be a valid and clinically superior imaging modality for the canine maxillary dentoalveolar structures when compared to 64-multidetector row CT. PMID:26415384

Polarized millijoule fiber laser system with high beam quality and pulse shaping ability

NASA Astrophysics Data System (ADS)

Zhang, Rui; Tian, Xiaocheng; Xu, Dangpeng; Zhou, Dandan; Zong, Zhaoyu; Li, Hongxun; Fan, Mengqiu; Huang, Zhihua; Zhu, Na; Su, Jingqin; Zhu, Qihua; Jing, Feng

2017-05-01

The coherent amplification network (CAN) aims at developing a laser system based on the coherent combination of multiple laser beams, which are produced through a network of high beam quality optical fiber amplifiers. The scalability of the CAN laser facilitates the development of many novel applications, such as fiber-based acceleration, orbital debris removal and inertial confinement fusion energy. According to the requirements of CAN and the front end of high-power laser facilities, a millijoule polarized fiber laser system was studied in this paper. Using polarization maintaining Ytterbium-fiber laser system as the seed, and 10-μm core Yb-doped fiber amplifier as the first power amplifier and 40-μm core polarizing (PZ) photonic crystal fiber (PCF) as the second power amplifier, the all-fiber laser system outputs 1.06-mJ energy at 10 ns and diffraction limited mode quality. Using 85-μm rod-type PCF as the third power amplifiers, 2.5-mJ energy at 10-ns pulse width was obtained with better than 500:1 peak-to-foot pulse shaping ability and fundamental mode beam quality. The energy fluctuation of the system is 1.3% rms with 1-mJ output in one hour. When using phase-modulated pulse as the seed, the frequency modulation to amplitude modulation (FM-to-AM) conversion ratio of the system is better than 5%. This fiber laser system has the advantages of high beam quality, high beam shaping ability, good stability, small volume and free of maintenance, which can be used in many applications.

Response of LiF:Mg,Ti thermoluminescent dosimeters at photon energies relevant to the dosimetry of brachytherapy (<1 MeV)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tedgren, Aasa Carlsson; Hedman, Angelica; Grindborg, Jan-Erik

2011-10-15

Purpose: High energy photon beams are used in calibrating dosimeters for use in brachytherapy since absorbed dose to water can be determined accurately and with traceability to primary standards in such beams, using calibrated ion chambers and standard dosimetry protocols. For use in brachytherapy, beam quality correction factors are needed, which include corrections for differences in mass energy absorption properties between water and detector as well as variations in detector response (intrinsic efficiency) with radiation quality, caused by variations in the density of ionization (linear energy transfer (LET) -distributions) along the secondary electron tracks. The aim of this work wasmore » to investigate experimentally the detector response of LiF:Mg,Ti thermoluminescent dosimeters (TLD) for photon energies below 1 MeV relative to {sup 60}Co and to address discrepancies between the results found in recent publications of detector response. Methods: LiF:Mg,Ti dosimeters of formulation MTS-N Poland were irradiated to known values of air kerma free-in-air in x-ray beams at tube voltages 25-250 kV, in {sup 137}Cs- and {sup 60}Co-beams at the Swedish Secondary Standards Dosimetry Laboratory. Conversions from air kerma free-in-air into values of mean absorbed dose in the dosimeters in the actual irradiation geometries were made using EGSnrc Monte Carlo simulations. X-ray energy spectra were measured or calculated for the actual beams. Detector response relative to that for {sup 60}Co was determined at each beam quality. Results: An increase in relative response was seen for all beam qualities ranging from 8% at tube voltage 25 kV (effective energy 13 keV) to 3%-4% at 250 kV (122 keV effective energy) and {sup 137}Cs with a minimum at 80 keV effective energy (tube voltage 180 kV). The variation with effective energy was similar to that reported by Davis et al.[Radiat. Prot. Dosim. 106, 33-43 (2003)] with our values being systematically lower by 2%-4%. Compared to the results by Nunn et al.[Med. Phys. 35, 1861-1869 (2008)], the relative detector response as a function of effective energy differed in both shape and magnitude. This could be explained by the higher maximum read-out temperature (350 deg. C) used by Nunn et al.[Med. Phys. 35, 1861-1869 (2008)], allowing light emitted from high-temperature peaks with a strong LET dependence to be registered. Use of TLD-100 by Davis et al.[Radiat. Prot. Dosim. 106, 33-43 (2003)] with a stronger super-linear dose response compared to MTS-N was identified as causing the lower relative detector response in this work. Conclusions: Both careful dosimetry and strict protocols for handling the TLDs are required to reach solid experimental data on relative detector response. This work confirms older findings that an over-response relative to {sup 60}Co exists for photon energies below 200-300 keV. Comparison with the results from the literature indicates that using similar protocols for annealing and read-out, dosimeters of different makes (TLD-100, MTS-N) differ in relative detector response. Though universality of the results has not been proven and further investigation is needed, it is anticipated that with the use of strict protocols for annealing and read-out, it will be possible to determine correction factors that can be used to reduce uncertainties in dose measurements around brachytherapy sources at photon energies where primary standards for absorbed dose to water are not available.« less

Beam wander of dark hollow, flat-topped and annular beams

NASA Astrophysics Data System (ADS)

Eyyuboğlu, H. T.; Çil, C. Z.

2008-11-01

Benefiting from the earlier derivations for the Gaussian beam, we formulate beam wander for dark hollow (DH) and flat-topped (FT) beams, also covering the annular Gaussian (AG) beam as a special case. Via graphical illustrations, beam wander variations of these beams are analyzed and compared among themselves and to the fundamental Gaussian beam against changes in propagation length, amplitude factor, source size, wavelength of operation, inner and outer scales of turbulence. These comparisons show that in relation to the fundamental Gaussian beam, DH and FT beams will exhibit less beam wander, particularly at small primary beam source sizes, lower amplitude factors of the secondary beam and higher beam orders. Furthermore, DH and FT beams will continue to preserve this advantageous position all throughout the considered range of wavelengths, inner and outer scales of turbulence. FT beams, in particular, are observed to have the smallest beam wander values among all, up to certain source sizes.

Transmission of laser pulses with high output beam quality using step-index fibers having large cladding

DOEpatents

Yalin, Azer P; Joshi, Sachin

2014-06-03

An apparatus and method for transmission of laser pulses with high output beam quality using large core step-index silica optical fibers having thick cladding, are described. The thick cladding suppresses diffusion of modal power to higher order modes at the core-cladding interface, thereby enabling higher beam quality, M.sup.2, than are observed for large core, thin cladding optical fibers. For a given NA and core size, the thicker the cladding, the better the output beam quality. Mode coupling coefficients, D, has been found to scale approximately as the inverse square of the cladding dimension and the inverse square root of the wavelength. Output from a 2 m long silica optical fiber having a 100 .mu.m core and a 660 .mu.m cladding was found to be close to single mode, with an M.sup.2=1.6. Another thick cladding fiber (400 .mu.m core and 720 .mu.m clad) was used to transmit 1064 nm pulses of nanosecond duration with high beam quality to form gas sparks at the focused output (focused intensity of >100 GW/cm.sup.2), wherein the energy in the core was <6 mJ, and the duration of the laser pulses was about 6 ns. Extending the pulse duration provided the ability to increase the delivered pulse energy (>20 mJ delivered for 50 ns pulses) without damaging the silica fiber.

Beam brilliance investigation of high current ion beams at GSI heavy ion accelerator facility.

PubMed

Adonin, A A; Hollinger, R

2014-02-01

In this work the emittance measurements of high current Ta-beam provided by VARIS (Vacuum Arc Ion Source) ion source are presented. Beam brilliance as a function of beam aperture at various extraction conditions is investigated. Influence of electrostatic ion beam compression in post acceleration gap on the beam quality is discussed. Use of different extraction systems (single aperture, 7 holes, and 13 holes) in order to achieve more peaked beam core is considered. The possible ways to increase the beam brilliance are discussed.

Linear energy transfer in water phantom within SHIELD-HIT transport code

NASA Astrophysics Data System (ADS)

Ergun, A.; Sobolevsky, N.; Botvina, A. S.; Buyukcizmeci, N.; Latysheva, L.; Ogul, R.

2017-02-01

The effect of irradiation in tissue is important in hadron therapy for the dose measurement and treatment planning. This biological effect is defined by an equivalent dose H which depends on the Linear Energy Transfer (LET). Usually, H can be expressed in terms of the absorbed dose D and the quality factor K of the radiation under consideration. In literature, various types of transport codes have been used for modeling and simulation of the interaction of the beams of protons and heavier ions with tissue-equivalent materials. In this presentation we used SHIELD-HIT code to simulate decomposition of the absorbed dose by LET in water for 16O beams. A more detailed description of capabilities of the SHIELD-HIT code can be found in the literature.

Application of spherical diodes for megavoltage photon beams dosimetry.

PubMed

Barbés, Benigno; Azcona, Juan D; Burguete, Javier; Martí-Climent, Josep M

2014-01-01

External beam radiation therapy (EBRT) usually uses heterogeneous dose distributions in a given volume. Designing detectors for quality control of these treatments is still a developing subject. The size of the detectors should be small to enhance spatial resolution and ensure low perturbation of the beam. A high uniformity in angular response is also a very important feature in a detector, because it has to measure radiation coming from all the directions of the space. It is also convenient that detectors are inexpensive and robust, especially to perform in vivo measurements. The purpose of this work is to introduce a new detector for measuring megavoltage photon beams and to assess its performance to measure relative dose in EBRT. The detector studied in this work was designed as a spherical photodiode (1.8 mm in diameter). The change in response of the spherical diodes is measured regarding the angle of incidence, cumulated irradiation, and instantaneous dose rate (or dose per pulse). Additionally, total scatter factors for large and small fields (between 1 × 1 cm(2) and 20 × 20 cm(2)) are evaluated and compared with the results obtained from some commercially available ionization chambers and planar diodes. Additionally, the over-response to low energy scattered photons in large fields is investigated using a shielding layer. The spherical diode studied in this work produces a high signal (150 nC/Gy for photons of nominal energy of 15 MV and 160 for 6 MV, after 12 kGy) and its angular dependence is lower than that of planar diodes: less than 5% between maximum and minimum in all directions, and 2% around one of the axis. It also has a moderated variation with accumulated dose (about 1.5%/kGy for 15 MV photons and 0.7%/kGy for 6 MV, after 12 kGy) and a low variation with dose per pulse (± 0.4%), and its behavior is similar to commercial diodes in total scatter factor measurements. The measurements of relative dose using the spherical diode described in this work show its feasibility for the dosimetry of megavoltage photon beams. A particularly important feature is its good angular response in the MV range. They would be good candidates for in vivo dosimetry, and quality assurance of VMAT and tomotherapy, and other modalities with beams irradiating from multiple orientations, such as Cyberknife and ViewRay, with minor modifications.

A Projection Quality-Driven Tube Current Modulation Method in Cone-Beam CT for IGRT: Proof of Concept.

PubMed

Men, Kuo; Dai, Jianrong

2017-12-01

To develop a projection quality-driven tube current modulation method in cone-beam computed tomography for image-guided radiotherapy based on the prior attenuation information obtained by the planning computed tomography and then evaluate its effect on a reduction in the imaging dose. The QCKV-1 phantom with different thicknesses (0-400 mm) of solid water upon it was used to simulate different attenuation (μ). Projections were acquired with a series of tube current-exposure time product (mAs) settings, and a 2-dimensional contrast to noise ratio was analyzed for each projection to create a lookup table of mAs versus 2-dimensional contrast to noise ratio, μ. Before a patient underwent computed tomography, the maximum attenuation [Formula: see text] within the 95% range of each projection angle (θ) was estimated according to the planning computed tomography images. Then, a desired 2-dimensional contrast to noise ratio value was selected, and the mAs setting at θ was calculated with the lookup table of mAs versus 2-dimensional contrast to noise ratio,[Formula: see text]. Three-dimensional cone-beam computed tomography images were reconstructed using the projections acquired with the selected mAs. The imaging dose was evaluated with a polymethyl methacrylate dosimetry phantom in terms of volume computed tomography dose index. Image quality was analyzed using a Catphan 503 phantom with an oval body annulus and a pelvis phantom. For the Catphan 503 phantom, the cone-beam computed tomography image obtained by the projection quality-driven tube current modulation method had a similar quality to that of conventional cone-beam computed tomography . However, the proposed method could reduce the imaging dose by 16% to 33% to achieve an equivalent contrast to noise ratio value. For the pelvis phantom, the structural similarity index was 0.992 with a dose reduction of 39.7% for the projection quality-driven tube current modulation method. The proposed method could reduce the additional dose to the patient while not degrading the image quality for cone-beam computed tomography. The projection quality-driven tube current modulation method could be especially beneficial to patients who undergo cone-beam computed tomography frequently during a treatment course.

Beam Dynamics for ARIA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ekdahl, Carl August Jr.

2014-10-14

Beam dynamics issues are assessed for a new linear induction electron accelerator being designed for flash radiography of large explosively driven hydrodynamic experiments. Special attention is paid to equilibrium beam transport, possible emittance growth, and beam stability. It is concluded that a radiographic quality beam will be produced possible if engineering standards and construction details are equivalent to those on the present radiography accelerators at Los Alamos.

Beam control of high-power broad-area photonic crystal lasers using ladderlike groove structure

NASA Astrophysics Data System (ADS)

Wang, Tao; Wang, Lijie; Shu, Shili; Tian, Sicong; Lu, Zefeng; Hou, Guanyu; Lu, Huanyu; Tong, Cunzhu; Wang, Lijun

2017-06-01

The high-power broad-area (BA) photonic bandgap crystal (PBC) diode laser is promising as a high-brightness laser source, however, it suffers from poor lateral beam quality owing to the intrinsic drawback of BA lasers. In this paper, a ladderlike groove structure (LLGS) was proposed to improve both the lateral beam quality and emission power of BA PBC lasers. An approximately 15.4% improvement in output power and 25.2% decrease in the lateral beam parameter product (BPP) were realized and the underlying mechanism was discussed. On the basis of the one-dimensional PBC epitaxial structure, a stable vertical far field was demonstrated.

Characterization of a synthetic single crystal diamond detector for dosimetry in spatially fractionated synchrotron x-ray fields.

PubMed

Livingstone, Jayde; Stevenson, Andrew W; Butler, Duncan J; Häusermann, Daniel; Adam, Jean-François

2016-07-01

Modern radiotherapy modalities often use small or nonstandard fields to ensure highly localized and precise dose delivery, challenging conventional clinical dosimetry protocols. The emergence of preclinical spatially fractionated synchrotron radiotherapies with high dose-rate, sub-millimetric parallel kilovoltage x-ray beams, has pushed clinical dosimetry to its limit. A commercially available synthetic single crystal diamond detector designed for small field dosimetry has been characterized to assess its potential as a dosimeter for synchrotron microbeam and minibeam radiotherapy. Experiments were carried out using a synthetic diamond detector on the imaging and medical beamline (IMBL) at the Australian Synchrotron. The energy dependence of the detector was characterized by cross-referencing with a calibrated ionization chamber in monoenergetic beams in the energy range 30-120 keV. The dose-rate dependence was measured in the range 1-700 Gy/s. Dosimetric quantities were measured in filtered white beams, with a weighted mean energy of 95 keV, in broadbeam and spatially fractionated geometries, and compared to reference dosimeters. The detector exhibits an energy dependence; however, beam quality correction factors (kQ) have been measured for energies in the range 30-120 keV. The kQ factor for the weighted mean energy of the IMBL radiotherapy spectrum, 95 keV, is 1.05 ± 0.09. The detector response is independent of dose-rate in the range 1-700 Gy/s. The percentage depth dose curves measured by the diamond detector were compared to ionization chambers and agreed to within 2%. Profile measurements of microbeam and minibeam arrays were performed. The beams are well resolved and the full width at halfmaximum agrees with the nominal width of the beams. The peak to valley dose ratio (PVDR) calculated from the profiles at various depths in water agrees within experimental error with PVDR calculations from Gafchromic film data. The synthetic diamond detector is now well characterized and will be used to develop an experimental dosimetry protocol for spatially fractionated synchrotron radiotherapy.

SU-C-201-07: Towards Clinical Cherenkov Emission Dosimetry: Stopping Power-To-Cherenkov Power Ratios and Beam Quality Specification of Clinical Electron Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zlateva, Y; Seuntjens, J; El Naqa, I

Purpose: We propose a Cherenkov emission (CE)-based reference dosimetry method, which in contrast to ionization chamber-based dosimetry, employs spectrum-averaged electron restricted mass collision stopping power-to-Cherenkov power ratios (SCRs), and we examine Monte Carlo-calculated SCRs and beam quality specification of clinical electron beams. Methods: The EGSnrc user code SPRRZnrc was modified to compute SCRs instead of stopping-power ratios (single medium: water; cut-off: CE threshold (observing Spencer-Attix conditions); CE power: Frank-Tamm). SCRs are calculated with BEAMnrc for realistic electron beams with nominal energies of 6–22 MeV from three Varian accelerators (TrueBeam Clinac 21EX, Clinac 2100C/D) and for mono-energetic beams of energies equalmore » to the mean electron energy at the water surface. Sources of deviation between clinical and mono-energetic SCRs are analyzed quantitatively. A universal fit for the beam-quality index R{sub 50} in terms of the depth of 50% CE C{sub 50} is carried out. Results: SCRs at reference depth are overestimated by mono-energetic values by up to 0.2% for a 6-MeV beam and underestimated by up to 2.3% for a 22-MeV beam. The variation is mainly due to the clinical beam spectrum and photon contamination. Beam angular spread has a small effect across all depths and energies. The influence of the electron spectrum becomes increasingly significant at large depths, while at shallow depths and high beam energies photon contamination is predominant (up to 2.0%). The universal data fit reveals a strong linear correlation between R{sub 50} and C{sub 50} (ρ > 0.99999). Conclusion: CE is inherent to radiotherapy beams and can be detected outside the beam with available optical technologies, which makes it an ideal candidate for out-of-beam high-resolution 3D dosimetry. Successful clinical implementation of CE dosimetry hinges on the development of robust protocols for converting measured CE to radiation dose. Our findings constitute a key step towards clinical CE dosimetry.« less

Effect of idler absorption in pulsed optical parametric oscillators.

PubMed

Rustad, Gunnar; Arisholm, Gunnar; Farsund, Øystein

2011-01-31

Absorption at the idler wavelength in an optical parametric oscillator (OPO) is often considered detrimental. We show through simulations that pulsed OPOs with significant idler absorption can perform better than OPOs with low idler absorption both in terms of conversion efficiency and beam quality. The main reason for this is reduced back conversion. We also show how the beam quality depends on the beam width and pump pulse length, and present scaling relations to use the example simulations for other pulsed nanosecond OPOs.

Characteristics of optically stimulated luminescence dosimeters in the spread-out Bragg peak region of clinical proton beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kerns, James R.; Kry, Stephen F.; Sahoo, Narayan

Purpose: Optically stimulated luminescent detectors (OSLDs) have a number of advantages in radiation dosimetry making them excellent dosimeters for quality assurance and patient dose verification. Although the dosimeters have been investigated in several modalities, relatively little work has been done in examining the dosimeters for use in clinical proton beams. This study examined a number of characteristics of the response of the dosimeters in the spread-out Bragg peak (SOBP) region of clinical proton beams. Methods: Optically stimulated luminescence (OSL) dosimeters from Landauer, Inc., specifically the nanoDot dosimeter, were investigated. These dosimeters were placed in a special phantom with a recessmore » to fit the dosimeters without an air gap. Beams with nominal energies of 160, 200, and 250 MeV were used in the passively-scattered proton beam at the MD Anderson Cancer Center Proton Therapy Center. Dosimetric properties including linearity, field size dependence, energy dependence, residual signal as a function of cumulative dose, and postirradiation fading were investigated by taking measurements at the center of SOBPs. Results: The dosimeters showed 1% supralinearity at 200 cGy and 5% supralinearity at 1000 cGy. No noticeable field size dependence of the detector was found for field sizes from 2 x 2 cm{sup 2} to 18 x 18 cm{sup 2}. Residual signal as a function of cumulative dose showed a small increase for measurements up to 1000 cGy. Readout signal depletion of the dosimeters after consecutive readings showed a slightly larger depletion in protons for doses up to 500 cGy but not by a clinically significant amount. Within the center of various SOBP widths and proton energies the variation in response was less than 2%. An average beam quality factor of 1.089 with experimental standard deviation of 0.007 was determined and applied to the data such that the results were within 1.2% of ion chamber data. Conclusions: The nanoDot OSL dosimeter characteristics were studied in the SOBP region of clinical proton beams. To achieve accurate dosimetric readings, corrections to the dosimeter response were applied. Corrections tended to be minimal or broadly consistent. The nanoDot OSLD was found to be an acceptable dosimeter for measurement in the SOBP region for a range of clinical proton beams.« less

Characteristics of optically stimulated luminescence dosimeters in the spread-out Bragg peak region of clinical proton beams.

PubMed

Kerns, James R; Kry, Stephen F; Sahoo, Narayan

2012-04-01

Optically stimulated luminescent detectors (OSLDs) have a number of advantages in radiation dosimetry making them excellent dosimeters for quality assurance and patient dose verification. Although the dosimeters have been investigated in several modalities, relatively little work has been done in examining the dosimeters for use in clinical proton beams. This study examined a number of characteristics of the response of the dosimeters in the spread-out Bragg peak (SOBP) region of clinical proton beams. Optically stimulated luminescence (OSL) dosimeters from Landauer, Inc., specifically the nanoDot dosimeter, were investigated. These dosimeters were placed in a special phantom with a recess to fit the dosimeters without an air gap. Beams with nominal energies of 160, 200, and 250 MeV were used in the passively-scattered proton beam at the MD Anderson Cancer Center Proton Therapy Center. Dosimetric properties including linearity, field size dependence, energy dependence, residual signal as a function of cumulative dose, and postirradiation fading were investigated by taking measurements at the center of SOBPs. The dosimeters showed 1% supralinearity at 200 cGy and 5% supralinearity at 1000 cGy. No noticeable field size dependence of the detector was found for field sizes from 2 × 2 cm(2) to 18 × 18 cm(2). Residual signal as a function of cumulative dose showed a small increase for measurements up to 1000 cGy. Readout signal depletion of the dosimeters after consecutive readings showed a slightly larger depletion in protons for doses up to 500 cGy but not by a clinically significant amount. Within the center of various SOBP widths and proton energies the variation in response was less than 2%. An average beam quality factor of 1.089 with experimental standard deviation of 0.007 was determined and applied to the data such that the results were within 1.2% of ion chamber data. The nanoDot OSL dosimeter characteristics were studied in the SOBP region of clinical proton beams. To achieve accurate dosimetric readings, corrections to the dosimeter response were applied. Corrections tended to be minimal or broadly consistent. The nanoDot OSLD was found to be an acceptable dosimeter for measurement in the SOBP region for a range of clinical proton beams.

Individualized Selection of Beam Angles and Treatment Isocenter in Tangential Breast Intensity Modulated Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Penninkhof, Joan, E-mail: j.penninkhof@erasmusmc.nl; Spadola, Sara; Department of Physics and Astronomy, Alma Mater Studiorum, University of Bologna, Bologna

Purpose and Objective: Propose a novel method for individualized selection of beam angles and treatment isocenter in tangential breast intensity modulated radiation therapy (IMRT). Methods and Materials: For each patient, beam and isocenter selection starts with the fully automatic generation of a large database of IMRT plans (up to 847 in this study); each of these plans belongs to a unique combination of isocenter position, lateral beam angle, and medial beam angle. The imposed hard planning constraint on patient maximum dose may result in plans with unacceptable target dose delivery. Such plans are excluded from further analyses. Owing to differencesmore » in beam setup, database plans differ in mean doses to organs at risk (OARs). These mean doses are used to construct 2-dimensional graphs, showing relationships between: (1) contralateral breast dose and ipsilateral lung dose; and (2) contralateral breast dose and heart dose (analyzed only for left-sided). The graphs can be used for selection of the isocenter and beam angles with the optimal, patient-specific tradeoffs between the mean OAR doses. For 30 previously treated patients (15 left-sided and 15 right-sided tumors), graphs were generated considering only the clinically applied isocenter with 121 tangential beam angle pairs. For 20 of the 30 patients, 6 alternative isocenters were also investigated. Results: Computation time for automatic generation of 121 IMRT plans took on average 30 minutes. The generated graphs demonstrated large variations in tradeoffs between conflicting OAR objectives, depending on beam angles and patient anatomy. For patients with isocenter optimization, 847 IMRT plans were considered. Adding isocenter position optimization next to beam angle optimization had a small impact on the final plan quality. Conclusion: A method is proposed for individualized selection of beam angles in tangential breast IMRT. This may be especially important for patients with cardiac risk factors or an enhanced risk for the development of contralateral breast cancer.« less

Determination of output factor for 6 MV small photon beam: comparison between Monte Carlo simulation technique and microDiamond detector

NASA Astrophysics Data System (ADS)

Krongkietlearts, K.; Tangboonduangjit, P.; Paisangittisakul, N.

2016-03-01

In order to improve the life's quality for a cancer patient, the radiation techniques are constantly evolving. Especially, the two modern techniques which are intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) are quite promising. They comprise of many small beam sizes (beamlets) with various intensities to achieve the intended radiation dose to the tumor and minimal dose to the nearby normal tissue. The study investigates whether the microDiamond detector (PTW manufacturer), a synthetic single crystal diamond detector, is suitable for small field output factor measurement. The results were compared with those measured by the stereotactic field detector (SFD) and the Monte Carlo simulation (EGSnrc/BEAMnrc/DOSXYZ). The calibration of Monte Carlo simulation was done using the percentage depth dose and dose profile measured by the photon field detector (PFD) of the 10×10 cm2 field size with 100 cm SSD. Comparison of the values obtained from the calculations and measurements are consistent, no more than 1% difference. The output factors obtained from the microDiamond detector have been compared with those of SFD and Monte Carlo simulation, the results demonstrate the percentage difference of less than 2%.

Projection imaging of photon beams by the Cerenkov effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glaser, Adam K.; Davis, Scott C.; McClatchy, David M.

2013-01-15

Purpose: A novel technique for beam profiling of megavoltage photon beams was investigated for the first time by capturing images of the induced Cerenkov emission in water, as a potential surrogate for the imparted dose in irradiated media. Methods: A high-sensitivity, intensified CCD camera (ICCD) was configured to acquire 2D projection images of Cerenkov emission from a 4 Multiplication-Sign 4 cm{sup 2} 6 MV linear accelerator (LINAC) x-ray photon beam operating at a dose rate of 400 MU/min incident on a water tank with transparent walls. The ICCD acquisition was gated to the LINAC sync pulse to reduce background lightmore » artifacts, and the measurement quality was investigated by evaluating the signal to noise ratio and measurement repeatability as a function of delivered dose. Monte Carlo simulations were used to derive a calibration factor for differences between the optical images and deposited dose arising from the anisotropic angular dependence of Cerenkov emission. Finally, Cerenkov-based beam profiles were compared to a percent depth dose (PDD) and lateral dose profile at a depth of d{sub max} from a reference dose distribution generated from the clinical Varian ECLIPSE treatment planning system (TPS). Results: The signal to noise ratio was found to be 20 at a delivered dose of 66.6 cGy, and proportional to the square root of the delivered dose as expected from Poisson photon counting statistics. A 2.1% mean standard deviation and 5.6% maximum variation in successive measurements were observed, and the Monte Carlo derived calibration factor resulted in Cerenkov emission images which were directly correlated to deposited dose, with some spatial issues. The dose difference between the TPS and PDD predicted by Cerenkov measurements was within 20% in the buildup region with a distance to agreement (DTA) of 1.5-2 mm and {+-}3% at depths beyond d{sub max}. In the lateral profile, the dose difference at the beam penumbra was within {+-}13% with a DTA of 0-2 mm, {+-}5% in the central beam region, and 2%-3% in the beam umbra. Conclusions: The results from this initial study demonstrate the first documented use of Cerenkov emission imaging to profile x-ray photon LINAC beams in water. The proposed modality has several potential advantages over alternative methods, and upon future refinement may prove to be a robust and novel dosimetry method.« less

Improved performance of laser wakefield acceleration by tailored self-truncated ionization injection

NASA Astrophysics Data System (ADS)

Irman, A.; Couperus, J. P.; Debus, A.; Köhler, A.; Krämer, J. M.; Pausch, R.; Zarini, O.; Schramm, U.

2018-04-01

We report on tailoring ionization-induced injection in laser wakefield acceleration so that the electron injection process is self-truncating following the evolution of the plasma bubble. Robust generation of high-quality electron beams with shot-to-shot fluctuations of the beam parameters better than 10% is presented in detail. As a novelty, the scheme was found to enable well-controlled yet simple tuning of the injected charge while preserving acceleration conditions and beam quality. Quasi-monoenergetic electron beams at several 100 MeV energy and 15% relative energy spread were routinely demonstrated with a total charge of the monoenergetic feature reaching 0.5 nC. Finally these unique beam parameters, suggesting unprecedented peak currents of several 10 kA, are systematically related to published data on alternative injection schemes.

Magnetic field extraction of trap-based electron beams using a high-permeability grid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hurst, N. C.; Danielson, J. R.; Surko, C. M., E-mail: csurko@physics.ucsd.edu

2015-07-15

A method to form high quality electrostatically guided lepton beams is explored. Test electron beams are extracted from tailored plasmas confined in a Penning-Malmberg trap. The particles are then extracted from the confining axial magnetic field by passing them through a high magnetic permeability grid with radial tines (a so-called “magnetic spider”). An Einzel lens is used to focus and analyze the beam properties. Numerical simulations are used to model non-adiabatic effects due to the spider, and the predictions are compared with the experimental results. Improvements in beam quality are discussed relative to the use of a hole in amore » high permeability shield (i.e., in lieu of the spider), and areas for further improvement are described.« less

Beam collimation and focusing and error analysis of LD and fiber coupling system based on ZEMAX

NASA Astrophysics Data System (ADS)

Qiao, Lvlin; Zhou, Dejian; Xiao, Lei

2017-10-01

Laser diodde has many advantages, such as high efficiency, small volume, low cost and easy integration, so it is widely used. Because of its poor beam quality, the application of semiconductor laser has also been seriously hampered. In view of the poor beam quality, the ZEMAX optical design software is used to simulate the far field characteristics of the semiconductor laser beam, and the coupling module of the semiconductor laser and the optical fiber is designed and optimized. And the beam is coupled into the fiber core diameter d=200µm, the numerical aperture NA=0.22 optical fiber, the output power can reach 95%. Finally, the influence of the three docking errors on the coupling efficiency during the installation process is analyzed.

A specialized bioengineering ion beam line

NASA Astrophysics Data System (ADS)

Yu, L. D.; Sangyuenyongpipat, S.; Sriprom, C.; Thongleurm, C.; Suwanksum, R.; Tondee, N.; Prakrajang, K.; Vilaithong, T.; Brown, I. G.; Wiedemann, H.

2007-04-01

A specialized bioengineering ion beam line has recently been completed at Chiang Mai University to meet rapidly growing needs of research and application development in low-energy ion beam biotechnology. This beam line possesses special features: vertical main beam line, low-energy (30 keV) ion beams, double swerve of the beam, a fast pumped target chamber, and an in-situ atomic force microscope (AFM) system chamber. The whole beam line is situated in a bioclean environment, occupying two stories. The quality of the ion beam has been studied. It has proved that this beam line has significantly contributed to our research work on low-energy ion beam biotechnology.

Experimental Aspects in Beam Characterization

NASA Astrophysics Data System (ADS)

Sona, Alberto

2004-08-01

Beam characterization is the pre-requisite of any research exploiting light beams, especially in cases involving laser beams. One can rely on the beam parameters provided by the manufacturer but often they are inadequate and/or not sufficient for the experimental data analysis. The full characterization of a laser beam can require the determination of many parameters (about ten for a generic beam); however for symmetrical beams the significant ones can reduce to only to a few. The characterization can be performed with the accuracy requested by the application and limited to the relevant parameters. The main parameters of interest will be defined and the measurement procedures and equipment will be discussed. The ISO standards consider the following parameters mainly of interest for industrial applications: 1) Beam widths, divergence angle and beam propagation ratio. 2) Power, energy density distribution 3) Parameters for stigmatic and simple astigmatic beams 4) Parameters for general astigmatic beams 5) Geometrical laser beams classification and propagation 6) Power, energy and temporal characteristics 7) Beam positional stability 8) Beam polarization 9) Spectral characteristics 10) Shape of a laser wavefront: Phase distribution All the above points will be briefly discussed as regards the experimental problems involved. Special attention will be given to the methods for measuring the intensity distribution and to the related instrumentation to derive the Beam propagation ratio, the Beam Quality factor M2 or the Beam Parameters Product. Examples of the parameters relevance for specific applications will be given. Depending on the spectral range, specific detectors are used: CCD cameras with detector arrays in the visible and near infrared, thermocameras with a single detector and scanning system for the medium and far IR. The major problems in data collection and processing will be discussed. Another new and not yet fully investigated area is the characterization of laser beam by wavefront measuring instruments. One possible approach is the use of self-referencing interferometers such as the point diffraction interferometers. Alternatively wavefront gradient measuring instruments can be used such as the Hartmann-Shack sensors. Wavefront intensity and phase joint distributions can now be measured at the same time. This can provide in addition new methods to derive the modal content. A short review of the experimental problems in this area still looking for a practical solution will be given. Note from Publisher: This article contains the abstract and references only.

Real-time determination of laser beam quality by modal decomposition.

PubMed

Schmidt, Oliver A; Schulze, Christian; Flamm, Daniel; Brüning, Robert; Kaiser, Thomas; Schröter, Siegmund; Duparré, Michael

2011-03-28

We present a real-time method to determine the beam propagation ratio M2 of laser beams. The all-optical measurement of modal amplitudes yields M2 parameters conform to the ISO standard method. The experimental technique is simple and fast, which allows to investigate laser beams under conditions inaccessible to other methods.

Comparison of the NIST and BIPM Air-Kerma Standards for Measurements in the Low-Energy X-Ray Range

PubMed Central

Burns, D. T.; Lamperti, P.; O’Brien, M.

1999-01-01

A direct comparison was made between the air-kerma standards used for the measurement of low-energy x rays at the National Institute of Standards and Technology (NIST) and the Bureau International des Poids et Mesures (BIPM). The comparison was carried out at the BIPM using the BIPM reference beam qualities in the range from 10 kV to 100 kV. The results show the standards to be in agreement to around 0.5 % at reference beam qualities up to 50 kV and at 100 kV. The result at the 80 kV beam quality is less favorable, with agreement at the 1 % level.

SU-F-T-487: On-Site Beam Matching of An Elekta Infinity with Agility MLC with An Elekta Versa HD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nelson, C; Garcia, M; Mason, B

2016-06-15

Purpose: Historically, beam matching of similar Linear Accelerators has been accomplished by sending beam data to the manufacturer to match at their factory. The purpose of this work is to demonstrate that fine beam matching can be carried out on-site as part of the acceptance test, with similar or better results. Methods: Initial scans of a 10 × 10 Percent depth dose (PDD) and a 40 × 40 beam profile at the depth of Dmax, for 6MV and 10 MV were taken to compare with the standard beam data from the Versa. The energy was then adjusted and the beammore » steered to achieve agreement between the depth dose and the horns of the beam profile. This process was repeated until the best agreement between PDD and profiles was achieved. Upon completion, all other clinical data were measured to verify match. This included PDD, beam profiles, output factors and Wedge factors. For electron beams PDD’s were matched and the beam profiles verified for the final beam energy. Confirmatory PDD and beam profiles for clinical field sizes, as well as Output Factors were measured. Results: The average difference in PDD’s for 6MV and 10MV were within 0.4% for both wedged and open fields. Beam profile comparisons over the central 80% of the field, at multiple depths, show agreement of 0.8% or less for both wedged and open fields. Average output factor agreement over all field sizes was 0.4% for 6MV and 0.2 % for 10MV. Wedge factors agreement was less than 0.6% for both photon energies over all field sizes. Electron PDD agreed to 0.5mm. Cone ratios agreed to 1% or less. Conclusion: This work indicates that beam matching can be carried out on-site simply and quickly. The results of this beam matching can achieve similar or better results than factory matching.« less

Beam shaping by using small-aperture SLM and DM in a high power laser

NASA Astrophysics Data System (ADS)

Li, Sensen; Lu, Zhiwei; Du, Pengyuan; Wang, Yulei; Ding, Lei; Yan, Xiusheng

2018-03-01

High-power laser plays an important role in many fields, such as directed energy weapon, optoelectronic contermeasures, inertial confinement fusion, industrial processing and scientific research. The uniform nearfield and wavefront are the important part of the beam quality for high power lasers, which is conducive to maintaining the high spatial beam quality in propagation. We demonstrate experimentally that the spatial intensity and wavefront distribution at the output is well compensated in the complex high-power solid-state laser system by using the small-aperture spatial light modulator (SLM) and deformable mirror (DM) in the front stage. The experimental setup is a hundred-Joule-level Nd:glass laser system operating at three wavelengths at 1053 nm (1ω), 527 nm (2ω) and 351 nm (3ω) with 3 ns pulse duration with the final output beam aperture of 60 mm. While the clear arperture of the electrically addressable SLM is less than 20 mm and the effective diameter of the 52-actuators DM is about 15 mm. In the beam shaping system, the key point is that the two front-stage beam shaping devices needs to precompensate the gain nonuniform and wavefront distortion of the laser system. The details of the iterative algorithm for improving the beam quality are presented. Experimental results show that output nearfield and wavefont are both nearly flat-topped with the nearfield modulation of 1.26:1 and wavefront peak-to-valley value of 0.29 λ at 1053nm after beam shaping.

Tuning donut profile for spatial resolution in stimulated emission depletion microscopy.

PubMed

Neupane, Bhanu; Chen, Fang; Sun, Wei; Chiu, Daniel T; Wang, Gufeng

2013-04-01

In stimulated emission depletion (STED)-based or up-conversion depletion-based super-resolution optical microscopy, the donut-shaped depletion beam profile is of critical importance to its resolution. In this study, we investigate the transformation of the donut-shaped depletion beam focused by a high numerical aperture (NA) microscope objective, and model STED point spread function (PSF) as a function of donut beam profile. We show experimentally that the intensity profile of the dark kernel of the donut can be approximated as a parabolic function, whose slope is determined by the donut beam size before the objective back aperture, or the effective NA. Based on this, we derive the mathematical expression for continuous wave (CW) STED PSF as a function of focal plane donut and excitation beam profiles, as well as dye properties. We find that the effective NA and the residual intensity at the center are critical factors for STED imaging quality and the resolution. The effective NA is critical for STED resolution in that it not only determines the donut shape but also the area the depletion laser power is dispersed. An improperly expanded depletion beam will have negligible improvement in resolution. The polarization of the depletion beam also plays an important role as it affects the residual intensity in the center of the donut. Finally, we construct a CW STED microscope operating at 488 nm excitation and 592 nm depletion with a resolution of 70 nm. Our study provides detailed insight to the property of donut beam, and parameters that are important for the optimal performance of STED microscopes. This paper will provide a useful guide for the construction and future development of STED microscopes.

Evaluation of an empirical monitor output estimation in carbon ion radiotherapy.

PubMed

Matsumura, Akihiko; Yusa, Ken; Kanai, Tatsuaki; Mizota, Manabu; Ohno, Tatsuya; Nakano, Takashi

2015-09-01

A conventional broad beam method is applied to carbon ion radiotherapy at Gunma University Heavy Ion Medical Center. According to this method, accelerated carbon ions are scattered by various beam line devices to form 3D dose distribution. The physical dose per monitor unit (d/MU) at the isocenter, therefore, depends on beam line parameters and should be calibrated by a measurement in clinical practice. This study aims to develop a calculation algorithm for d/MU using beam line parameters. Two major factors, the range shifter dependence and the field aperture effect, are measured via PinPoint chamber in a water phantom, which is an identical setup as that used for monitor calibration in clinical practice. An empirical monitor calibration method based on measurement results is developed using a simple algorithm utilizing a linear function and a double Gaussian pencil beam distribution to express the range shifter dependence and the field aperture effect. The range shifter dependence and the field aperture effect are evaluated to have errors of 0.2% and 0.5%, respectively. The proposed method has successfully estimated d/MU with a difference of less than 1% with respect to the measurement results. Taking the measurement deviation of about 0.3% into account, this result is sufficiently accurate for clinical applications. An empirical procedure to estimate d/MU with a simple algorithm is established in this research. This procedure allows them to use the beam time for more treatments, quality assurances, and other research endeavors.

Improved Design of Beam Tunnel for 42 GHz Gyrotron

NASA Astrophysics Data System (ADS)

Singh, Udaybir; Kumar, Nitin; Purohit, L. P.; Sinha, A. K.

2011-04-01

In gyrotron, there is the chance of generation and excitation of unwanted RF modes (parasite oscillations). These modes may interact with electron beam and consequently degrade the beam quality. This paper presents the improved design of the beam tunnel to reduce the parasite oscillations and the effect of beam tunnel geometry on the electron beam parameters. The design optimization of the beam tunnel has been done with the help of 3-D simulation software CST-Microwave Studio and the effect of beam tunnel geometry on the electron beam parameters has been analyzed by EGUN code.

Average glandular dose in paired digital mammography and digital breast tomosynthesis acquisitions in a population based screening program: effects of measuring breast density, air kerma and beam quality

NASA Astrophysics Data System (ADS)

Helge Østerås, Bjørn; Skaane, Per; Gullien, Randi; Catrine Trægde Martinsen, Anne

2018-02-01

The main purpose was to compare average glandular dose (AGD) for same-compression digital mammography (DM) and digital breast tomosynthesis (DBT) acquisitions in a population based screening program, with and without breast density stratification, as determined by automatically calculated breast density (Quantra™). Secondary, to compare AGD estimates based on measured breast density, air kerma and half value layer (HVL) to DICOM metadata based estimates. AGD was estimated for 3819 women participating in the screening trial. All received craniocaudal and mediolateral oblique views of each breasts with paired DM and DBT acquisitions. Exposure parameters were extracted from DICOM metadata. Air kerma and HVL were measured for all beam qualities used to acquire the mammograms. Volumetric breast density was estimated using Quantra™. AGD was estimated using the Dance model. AGD reported directly from the DICOM metadata was also assessed. Mean AGD was 1.74 and 2.10 mGy for DM and DBT, respectively. Mean DBT/DM AGD ratio was 1.24. For fatty breasts: mean AGD was 1.74 and 2.27 mGy for DM and DBT, respectively. For dense breasts: mean AGD was 1.73 and 1.79 mGy, for DM and DBT, respectively. For breasts of similar thickness, dense breasts had higher AGD for DM and similar AGD for DBT. The DBT/DM dose ratio was substantially lower for dense compared to fatty breasts (1.08 versus 1.33). The average c-factor was 1.16. Using previously published polynomials to estimate glandularity from thickness underestimated the c-factor by 5.9% on average. Mean AGD error between estimates based on measurements (air kerma and HVL) versus DICOM header data was 3.8%, but for one mammography unit as high as 7.9%. Mean error of using the AGD value reported in the DICOM header was 10.7 and 13.3%, respectively. Thus, measurement of breast density, radiation dose and beam quality can substantially affect AGD estimates.

Average glandular dose in paired digital mammography and digital breast tomosynthesis acquisitions in a population based screening program: effects of measuring breast density, air kerma and beam quality.

PubMed

Østerås, Bjørn Helge; Skaane, Per; Gullien, Randi; Martinsen, Anne Catrine Trægde

2018-01-25

The main purpose was to compare average glandular dose (AGD) for same-compression digital mammography (DM) and digital breast tomosynthesis (DBT) acquisitions in a population based screening program, with and without breast density stratification, as determined by automatically calculated breast density (Quantra ™ ). Secondary, to compare AGD estimates based on measured breast density, air kerma and half value layer (HVL) to DICOM metadata based estimates. AGD was estimated for 3819 women participating in the screening trial. All received craniocaudal and mediolateral oblique views of each breasts with paired DM and DBT acquisitions. Exposure parameters were extracted from DICOM metadata. Air kerma and HVL were measured for all beam qualities used to acquire the mammograms. Volumetric breast density was estimated using Quantra ™ . AGD was estimated using the Dance model. AGD reported directly from the DICOM metadata was also assessed. Mean AGD was 1.74 and 2.10 mGy for DM and DBT, respectively. Mean DBT/DM AGD ratio was 1.24. For fatty breasts: mean AGD was 1.74 and 2.27 mGy for DM and DBT, respectively. For dense breasts: mean AGD was 1.73 and 1.79 mGy, for DM and DBT, respectively. For breasts of similar thickness, dense breasts had higher AGD for DM and similar AGD for DBT. The DBT/DM dose ratio was substantially lower for dense compared to fatty breasts (1.08 versus 1.33). The average c-factor was 1.16. Using previously published polynomials to estimate glandularity from thickness underestimated the c-factor by 5.9% on average. Mean AGD error between estimates based on measurements (air kerma and HVL) versus DICOM header data was 3.8%, but for one mammography unit as high as 7.9%. Mean error of using the AGD value reported in the DICOM header was 10.7 and 13.3%, respectively. Thus, measurement of breast density, radiation dose and beam quality can substantially affect AGD estimates.

Sci-Thur AM: YIS – 04: Stopping power-to-Cherenkov power ratios and beam quality specification for clinical Cherenkov emission dosimetry of electrons: beam-specific effects and experimental validation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zlateva, Yana; Seuntjens, Jan; El Naqa, Issam

Purpose: To advance towards clinical Cherenkov emission (CE)-based dosimetry by investigating beam-specific effects on Monte Carlo-calculated electron-beam stopping power-to-CE power ratios (SCRs), addressing electron beam quality specification in terms of CE, and validating simulations with measurements. Methods: The EGSnrc user code SPRRZnrc, used to calculate Spencer-Attix stopping-power ratios, was modified to instead calculate SCRs. SCRs were calculated for 6- to 22-MeV clinical electron beams from Varian TrueBeam, Clinac 21EX, and Clinac 2100C/D accelerators. Experiments were performed with a 20-MeV electron beam from a Varian TrueBeam accelerator, using a diffraction grating spectrometer with optical fiber input and a cooled back-illuminated CCD.more » A fluorophore was dissolved in the water to remove CE signal anisotropy. Results: It was found that angular spread of the incident beam has little effect on the SCR (≤ 0.3% at d{sub max}), while both the electron spectrum and photon contamination increase the SCR at shallow depths and decrease it at large depths. A universal data fit of R{sub 50} in terms of C{sub 50} (50% CE depth) revealed a strong linear dependence (R{sup 2} > 0.9999). The SCR was fit with a Burns-type equation (R{sup 2} = 0.9974, NRMSD = 0.5%). Below-threshold incident radiation was found to have minimal effect on beam quality specification (< 0.1%). Experiments and simulations were in good agreement. Conclusions: Our findings confirm the feasibility of the proposed CE dosimetry method, contingent on computation of SCRs from additional accelerators and on further experimental validation. This work constitutes an important step towards clinical high-resolution out-of-beam CE dosimetry.« less

Industrial 30-kW CO2 laser with fast axial gas flow and rf excitation

NASA Astrophysics Data System (ADS)

Habich, Uwe; Loosen, Peter; Hertzler, Christoph; Wollermann-Windgasse, Reinhard

1996-03-01

A CO2 laser with fast axial gas flow was set up and operated with a maximum cw output power above 30 kW. The laser makes use of 8 rf-excited discharges which were optimized regarding to the gas-flow, to the discharge homogeneity and to the optical properties of the gain medium. Results of experimental investigation of these topics are described as well as performance characteristics of the laser system equipped with a stable and an unstable resonator, respectively. With an unstable resonator and an aerodynamic window for the extraction of the beam the laser system gives a beam quality which is close to the diffraction limit for this type of resonator. Disregarding the difficulties which are related to the definition and measurement of beam quality for unstable resonators, the beam quality could be described as M2 equals 3. Measured far field intensity profiles in the focal plane of a focusing optics are presented as well as the beam propagation behavior near focus. First results of applications in materials processing are discussed.

Experimental investigation of the effect of the laser beam polarization state on the quality of steel sheet cutting

NASA Astrophysics Data System (ADS)

Golyshev, A. A.; Orishich, A. M.; Shulyatyev, V. B.

2017-10-01

The paper presents the results of experimental investigation of the effect of the beam polarization on the quality of the oxygen-assisted laser cutting of steel by a CO2-laser. Under consideration is the effect of the laser cutting parameters by the beam with the linear polarization on the cut surface roughness. It is founded that the minimal roughness is reached when the electric field vector is perpendicular to the cutting speed vector. It is concluded that the absorbed power distribution imposes the essential influence on the surface quality, and that the radiation heating of side walls is important to have lower roughness. Obtained results enabled to present probable reasons of the worse surface quality of the metals cut by a fiber laser than the ones cut by a CO2-laser.

Generation and Amplification of Tunable Multicolored Femtosecond Laser Pulses by Using Cascaded Four-Wave Mixing in Transparent Bulk Media

PubMed Central

Liu, Jun; Kobayashi, Takayoshi

2010-01-01

We have reviewed the generation and amplification of wavelength-tunable multicolored femtosecond laser pulses using cascaded four-wave mixing (CFWM) in transparent bulk media, mainly concentrating on our recent work. Theoretical analysis and calculations based on the phase-matching condition could explain well the process semi-quantitatively. The experimental studies showed: (1) as many as fifteen spectral up-shifted and two spectral down-shifted sidebands were obtained simultaneously with spectral bandwidth broader than 1.8 octaves from near ultraviolet (360 nm) to near infrared (1.2 μm); (2) the obtained sidebands were spatially separated well and had extremely high beam quality with M2 factor better than 1.1; (3) the wavelengths of the generated multicolor sidebands could be conveniently tuned by changing the crossing angle or simply replacing with different media; (4) as short as 15-fs negatively chirped or nearly transform limited 20-fs multicolored femtosecond pulses were obtained when one of the two input beams was negatively chirped and the other was positively chirped; (5) the pulse energy of the sideband can reach a μJ level with power stability better than 1% RMS; (6) broadband two-dimensional (2-D) multicolored arrays with more than ten periodic columns and more than ten rows were generated in a sapphire plate; (7) the obtained sidebands could be simultaneously spectra broadened and power amplified in another bulk medium by using cross-phase modulation (XPM) in conjunction with four-wave optical parametric amplification (FOPA). The characterization showed that this is interesting and the CFWM sidebands generated by this novel method have good enough qualities in terms of power stability, beam quality, and temporal features suited to various experiments such as ultrafast multicolor time-resolved spectroscopy and multicolor-excitation nonlinear microscopy. PMID:22399882

Characterization of Scattered X-Ray Photons in Dental Cone-Beam Computed Tomography.

PubMed

Yang, Ching-Ching

2016-01-01

Scatter is a very important artifact causing factor in dental cone-beam CT (CBCT), which has a major influence on the detectability of details within images. This work aimed to improve the image quality of dental CBCT through scatter correction. Scatter was estimated in the projection domain from the low frequency component of the difference between the raw CBCT projection and the projection obtained by extrapolating the model fitted to the raw projections acquired with 2 different sizes of axial field-of-view (FOV). The function for curve fitting was optimized by using Monte Carlo simulation. To validate the proposed method, an anthropomorphic phantom and a water-filled cylindrical phantom with rod inserts simulating different tissue materials were scanned using 120 kVp, 5 mA and 9-second scanning time covering an axial FOV of 4 cm and 13 cm. The detectability of the CT image was evaluated by calculating the contrast-to-noise ratio (CNR). Beam hardening and cupping artifacts were observed in CBCT images without scatter correction, especially in those acquired with 13 cm FOV. These artifacts were reduced in CBCT images corrected by the proposed method, demonstrating its efficacy on scatter correction. After scatter correction, the image quality of CBCT was improved in terms of target detectability which was quantified as the CNR for rod inserts in the cylindrical phantom. Hopefully the calculations performed in this work can provide a route to reach a high level of diagnostic image quality for CBCT imaging used in oral and maxillofacial structures whilst ensuring patient dose as low as reasonably achievable, which may ultimately make CBCT scan a reliable and safe tool in clinical practice.

High quality single shot diffraction patterns using ultrashort megaelectron volt electron beams from a radio frequency photoinjector.

PubMed

Musumeci, P; Moody, J T; Scoby, C M; Gutierrez, M S; Bender, H A; Wilcox, N S

2010-01-01

Single shot diffraction patterns using a 250-fs-long electron beam have been obtained at the UCLA Pegasus laboratory. High quality images with spatial resolution sufficient to distinguish closely spaced peaks in the Debye-Scherrer ring pattern have been recorded by scattering the 1.6 pC 3.5 MeV electron beam generated in the rf photoinjector off a 100-nm-thick Au foil. Dark current and high emittance particles are removed from the beam before sending it onto the diffraction target using a 1 mm diameter collimating hole. These results open the door to the study of irreversible phase transformations by single shot MeV electron diffraction.

Characterization of a MOSkin detector for in vivo skin dose measurements during interventional radiology procedures.

PubMed

Safari, M J; Wong, J H D; Ng, K H; Jong, W L; Cutajar, D L; Rosenfeld, A B

2015-05-01

The MOSkin is a MOSFET detector designed especially for skin dose measurements. This detector has been characterized for various factors affecting its response for megavoltage photon beams and has been used for patient dose measurements during radiotherapy procedures. However, the characteristics of this detector in kilovoltage photon beams and low dose ranges have not been studied. The purpose of this study was to characterize the MOSkin detector to determine its suitability for in vivo entrance skin dose measurements during interventional radiology procedures. The calibration and reproducibility of the MOSkin detector and its dependency on different radiation beam qualities were carried out using RQR standard radiation qualities in free-in-air geometry. Studies of the other characterization parameters, such as the dose linearity and dependency on exposure angle, field size, frame rate, depth-dose, and source-to-surface distance (SSD), were carried out using a solid water phantom under a clinical x-ray unit. The MOSkin detector showed good reproducibility (94%) and dose linearity (99%) for the dose range of 2 to 213 cGy. The sensitivity did not significantly change with the variation of SSD (± 1%), field size (± 1%), frame rate (± 3%), or beam energy (± 5%). The detector angular dependence was within ± 5% over 360° and the dose recorded by the MOSkin detector in different depths of a solid water phantom was in good agreement with the Markus parallel plate ionization chamber to within ± 3%. The MOSkin detector proved to be reliable when exposed to different field sizes, SSDs, depths in solid water, dose rates, frame rates, and radiation incident angles within a clinical x-ray beam. The MOSkin detector with water equivalent depth equal to 0.07 mm is a suitable detector for in vivo skin dosimetry during interventional radiology procedures.

Physics and material science of ultra-high quality factor superconducting resonator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vostrikov, Alexander

2015-08-01

The nitrogen doping into niobium superconducting radio frequency cavity walls aiming to improve the fundamental mode quality factor is the subject of the research in the given work. Quantitative nitrogen diffusion into niobium model calculating the concentration profile was developed. The model estimations were confirmed with secondary ion mass spectrometry technique measurements. The model made controlled nitrogen doping recipe optimization possible. As a result the robust reproducible recipe for SRF cavity walls treatment with nitrogen doping was developed. The cavities produced with optimized recipe met LCLS–II requirements on quality factor of 2.7 ∙ 10 10 at acceleration field of 16more » MV/m. The microscopic effects of nitrogen doping on superconducting niobium properties were studied with low energy muon spin rotation technique and magnetometer measurements. No significant effect of nitrogen on the following features was found: electron mean free path, magnetic field penetration depth, and upper and surface critical magnetic fields. It was detected that for nitrogen doped niobium samples magnetic flux starts to penetrate inside the superconductor at lower external magnetic field value compared to the low temperature baked niobium ones. This explains lower quench field of SRF cavities treated with nitrogen. Quality factor improvement of fundamental mode forced to analyze the high order mode (HOM) impact on the particle beam dynamics. Both resonant and cumulative effects caused by monopole and dipole HOMs respectively are found to be negligible within the requirements for LCLS–II.« less

Implementation of a dose gradient method into optimization of dose distribution in prostate cancer 3D-CRT plans

PubMed Central

Giżyńska, Marta K.; Kukołowicz, Paweł F.; Kordowski, Paweł

2014-01-01

Aim The aim of this work is to present a method of beam weight and wedge angle optimization for patients with prostate cancer. Background 3D-CRT is usually realized with forward planning based on a trial and error method. Several authors have published a few methods of beam weight optimization applicable to the 3D-CRT. Still, none on these methods is in common use. Materials and methods Optimization is based on the assumption that the best plan is achieved if dose gradient at ICRU point is equal to zero. Our optimization algorithm requires beam quality index, depth of maximum dose, profiles of wedged fields and maximum dose to femoral heads. The method was tested for 10 patients with prostate cancer, treated with the 3-field technique. Optimized plans were compared with plans prepared by 12 experienced planners. Dose standard deviation in target volume, and minimum and maximum doses were analyzed. Results The quality of plans obtained with the proposed optimization algorithms was comparable to that prepared by experienced planners. Mean difference in target dose standard deviation was 0.1% in favor of the plans prepared by planners for optimization of beam weights and wedge angles. Introducing a correction factor for patient body outline for dose gradient at ICRU point improved dose distribution homogeneity. On average, a 0.1% lower standard deviation was achieved with the optimization algorithm. No significant difference in mean dose–volume histogram for the rectum was observed. Conclusions Optimization shortens very much time planning. The average planning time was 5 min and less than a minute for forward and computer optimization, respectively. PMID:25337411

Wavelength stabilized high pulse power laser diodes for automotive LiDAR

NASA Astrophysics Data System (ADS)

Knigge, A.; Klehr, A.; Wenzel, H.; Zeghuzi, A.; Fricke, J.; Maaßdorf, A.; Liero, A.; Tränkle, G.

2018-03-01

Diode lasers generating optical pulses with high peak power and lengths in the nanosecond range are key components of systems for free-space communication, metrology, material processing, spectroscopy, and light detection and ranging (LiDAR) as needed for object detection and autonomous driving. Automotive LiDAR systems demand additionally a good beam quality and low wavelength shift with temperature due to the wide operating temperature span. We present here internally wavelength stabilized lasers emitting ns optical pulses from an emission aperture between 30 μm and 100 μm with peak powers of tens of Watts at wavelengths around 905 nm. The vertical structure based on AlGaAs (confinement and cladding layers) and InGaAs (active quantum well) is especially optimized for pulsed operation with respect to the implementation of a surface Bragg grating with a high reflectivity. The fabricated 6 mm long distributed Bragg reflector (DBR) broad area (BA) lasers are electrically driven by an in-house developed high-speed unit generating 3 to 10 ns long nearly rectangular shaped current pulses with amplitudes of up to 250 A. Such lasers emit optical pulses with a peak power of more than 30 W at 95 A pulse current up to a temperature of 85°C with a wavelength shift as low as 65 pm/K and a lateral beam propagation factor less than 10. The influence of the lateral aperture width and the pulse length on the beam quality will be shown. A monolithic integration of 3 DBR BA lasers on a single chip whose emission can be combined into a single beam raises the output power to more than 100 W.

A dual-end-pumped Ho:YAG laser with a high energy output

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, X M; Cui, Zh; Dai, T Y

2015-08-31

We report a high energy output from a Ho:YAG oscillator resonantly double-end pumped by Tm:YLF lasers at room temperature. The maximum pulse energy of 52.5 mJ was achieved at a pulse repetition rate of 100Hz and a pulse duration of 35.2 ns, corresponding to a peak power of approximately 1.5 MW. The output wavelength was 2090.7 nm with beam quality factor M{sup 2} ∼ 1.2. (lasers)

Is the PTW 60019 microDiamond a suitable candidate for small field reference dosimetry?

NASA Astrophysics Data System (ADS)

De Coste, Vanessa; Francescon, Paolo; Marinelli, Marco; Masi, Laura; Paganini, Lucia; Pimpinella, Maria; Prestopino, Giuseppe; Russo, Serenella; Stravato, Antonella; Verona, Claudio; Verona-Rinati, Gianluca

2017-09-01

A systematic study of the PTW microDiamond (MD) output factors (OF) is reported, aimed at clarifying its response in small fields and investigating its suitability for small field reference dosimetry. Ten MDs were calibrated under 60Co irradiation. OF measurements were performed in 6 MV photon beams by a CyberKnife M6, a Varian DHX and an Elekta Synergy linacs. Two PTW silicon diodes E (Si-D) were used for comparison. The results obtained by the MDs were evaluated in terms of absorbed dose to water determination in reference conditions and OF measurements, and compared to the results reported in the recent literature. To this purpose, the Monte Carlo (MC) beam-quality correction factor, kQMD , was calculated for the MD, and the small field output correction factors, k{{Qclin},{{Q}msr}}{{fclin},{{f}msr}} , were calculated for both the MD and the Si-D by two different research groups. An empirical function was also derived, providing output correction factors within 0.5% from the MC values calculated for all of the three linacs. A high reproducibility of the dosimetric properties was observed among the ten MDs. The experimental kQMD values are in agreement within 1% with the MC calculated ones. Output correction factors within  +0.7% and  -1.4% were obtained down to field sizes as narrow as 5 mm. The resulting MD and Si-D field factors are in agreement within 0.2% in the case of CyberKnife measurements and 1.6% in the other cases. This latter higher spread of the data was demonstrated to be due to a lower reproducibility of small beam sizes defined by jaws or multi leaf collimators. The results of the present study demonstrate the reproducibility of the MD response and provide a validation of the MC modelling of this device. In principle, accurate reference dosimetry is thus feasible by using the microDiamond dosimeter for field sizes down to 5 mm.

Comparison of k Q factors measured with a water calorimeter in flattening filter free (FFF) and conventional flattening filter (cFF) photon beams

NASA Astrophysics Data System (ADS)

de Prez, Leon; de Pooter, Jacco; Jansen, Bartel; Perik, Thijs; Wittkämper, Frits

2018-02-01

Recently flattening filter free (FFF) beams became available for application in modern radiotherapy. There are several advantages of FFF beams over conventional flattening filtered (cFF) beams, however differences in beam spectra at the point of interest in a phantom potentially affect the ion chamber response. Beams are also non-uniform over the length of a typical reference ion chamber and recombination is usually larger. Despite several studies describing FFF beam characteristics, only a limited number of studies investigated their effect on k Q factors. Some of those studies predicted significant discrepancies in k Q factors (0.4% up to 1.0%) if TPR20,10 based codes of practice (CoPs) were to be used. This study addresses the question to which extent k Q factors, based on a TPR20,10 CoP, can be applied in clinical reference dosimetry. It is the first study that compares k Q factors measured directly with an absorbed dose to water primary standard in FFF-cFF pairs of clinical photon beams. This was done with a transportable water calorimeter described elsewhere. The measurements corrected for recombination and beam radial non-uniformity were performed in FFF-cFF beam pairs at 6 MV and 10 MV of an Elekta Versa HD for a selection of three different Farmer-type ion chambers (eight serial numbers). The ratio of measured k Q factors of the FFF-cFF beam pairs were compared with the TPR20,10 CoPs of the NCS and IAEA and the %dd(10) x CoP of the AAPM. For the TPR20,10 based CoPs differences less than 0.23% were found in k Q factors between the corresponding FFF-cFF beams with standard uncertainties smaller than 0.35%, while for the %dd(10) x these differences were smaller than 0.46% and within the expanded uncertainty of the measurements. Based on the measurements made with the equipment described in this study the authors conclude that the k Q factors provided by the NCS-18 and IAEA TRS-398 codes of practice can be applied for flattening filter free beams without additional correction. However, existing codes of practice cannot be applied ignoring the significant volume averaging effect of the FFF beams over the ion chamber cavity. For this a corresponding volume averaging correction must be applied.

SU-E-T-592: OSL Response of Al2O3:C Detectors Exposed to Therapeutic Proton Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Granville, DA; Flint, DB; Sawakuchi, GO

Purpose: To characterize the response of Al{sub 2}O{sub 3}:C optically stimulated luminescence (OSL) detectors (OSLDs) exposed to therapeutic proton beams of differing beam quality. Methods: We prepared Al{sub 2}O{sub 3}:C OSLDs from the same material as commercially available nanoDot dosimeters (Landauer, Inc). We irradiated the OSLDs in modulated proton beams of varying quality, as defined by the residual range. An absorbed dose to water of 0.2 Gy was delivered to all OSLDs with the residual range values varying from 0.5 to 23.5 cm (average LET in water from ∼0.5 to 2.5 keV/µm). To investigate the beam quality dependence of differentmore » emission bands within the OSL spectrum, we performed OSLD readouts using both continuous-wave stimulation (CW-OSL) and pulsed stimulation (P-OSL) with two sets of optical filters (Hoya U-340 and Kopp 5113). For all readout modes, the relative absorbed dose sensitivity ( S{sub rel}) for each beam quality was calculated using OSLDs irradiated in a 6 MV photon beam as a reference. Results: We found that the relative absorbed dose sensitivity was highly dependent on both readout mode and integration time of the OSL signal. For CW-OSL signals containing only the blue emission band, S{sub rel} was between 0.85 and 0.94 for 1 s readouts and between 0.82 and 0.93 for 10 s readouts. Similarly, for P-OSL readouts containing only the blue emission band S{sub rel} ranged from 0.86 to 0.91, and 0.82 to 0.93 for 1 s and 10 s readouts, respectively. For OSLD signals containing only the UV emission band, S{sub rel} ranged from 1.00 to 1.46, and 0.97 to 1.30 for P-OSL readouts of 1 s and 10 s, respectively. Conclusion: For measurements of absorbed dose using Al{sub 2}O{sub 3}:C OSLDs in therapeutic proton beams, dependence on beam quality was smallest for readout protocols that selected the blue emission band with small integration times. DA Granville received financial support from the Natural Sciences and Engineering Research Council of Canada.« less

Beam and tissue factors affecting Cherenkov image intensity for quantitative entrance and exit dosimetry on human tissue

PubMed Central

Zhang, Rongxiao; Glaser, Adam K.; Andreozzi, Jacqueline; Jiang, Shudong; Jarvis, Lesley A.; Gladstone, David J.; Pogue, Brian W.

2017-01-01

This study’s goal was to determine how Cherenkov radiation emission observed in radiotherapy is affected by predictable factors expected in patient imaging. Factors such as tissue optical properties, radiation beam properties, thickness of tissues, entrance/exit geometry, curved surface effects, curvature and imaging angles were investigated through Monte Carlo simulations. The largest physical cause of variation of the correlation factor between of Cherenkov emission and dose was the entrance/exit geometry (~50%). The largest human tissue effect was from different optical properties (~45%). Beyond these, clinical beam energy varies the correlation factor significantly (~20% for x-ray beams), followed by curved surfaces (~15% for x-ray beams and ~8% for electron beams), and finally, the effect of field size (~5% for x-ray beams). Other investigated factors which caused variations less than 5% were tissue thicknesses and source to surface distance. The effect of non-Lambertian emission was negligible for imaging angles smaller than 60 degrees. The spectrum of Cherenkov emission tends to blue-shift along the curved surface. A simple normalization approach based on the reflectance image was experimentally validated by imaging a range of tissue phantoms, as a first order correction for different tissue optical properties. PMID:27507213

In-line quality control of moving objects by means of spectral-domain OCT

NASA Astrophysics Data System (ADS)

Markl, Daniel; Hannesschläger, Günther; Buchsbaum, Andreas; Sacher, Stephan; Khinast, Johannes G.; Leitner, Michael

2014-08-01

In-line quality control of intermediate and final products is essential in various industries. This may imply determining the thickness of a foil or evaluating the homogeneity of coating applied to a pharmaceutical tablet. Such a qualitative and quantitative monitoring in a depth-resolved manner can be accomplished using optical coherence tomography (OCT). In-line quality control based on OCT requires additional consideration of motion effects for the system design as well as for data interpretation. This study focuses on transverse motion effects that can arise in spectral-domain (SD-) OCT systems. The impact of a transverse movement is analyzed for a constant relative speed difference up to 0.7 m/s between sample and sensor head. In particular, transverse motion is affecting OCT system properties such as the beam displacement (distance between adjacent A-scans) and transverse resolution. These properties were evaluated theoretically and experimentally for OCT images of a resolution target and pharmaceutical film-coated tablets. Both theoretical and experimental analyses highlight the shift of the transverse resolution limiting factor from the optics to the beam displacement above a relative speed difference between sensor head and sample of 0.42 m/s (for the presented SD-OCT setup). Speeds above 0.4 m/s are often demanded when monitoring industrial processes, such as a coating process when producing film-coated tablets. This emphasizes the importance of a fast data acquisition when using OCT as in-line quality control tool.

High-molecular-weight glutenin subunit-deficient mutants induced by ion beam and the effects of Glu-1 loci deletion on wheat quality properties.

PubMed

Zhang, Lujun; Chen, Qiufang; Su, Mingjie; Yan, Biao; Zhang, Xiangqi; Jiao, Zhen

2016-03-15

High-molecular-weight glutenin subunits (HMW-GSs) play a critical role in determining the viscoelastic properties of wheat. Mutations induced by ion beam radiation have been applied to improve the yield and quality of crop. In this study, HMW-GS-deficient mutant lines were selected and the effects of Glu-1 loci deletion on wheat quality properties were illustrated according to the analysis of dry seeds of common wheat (Triticum aestivum L.) Xiaoyan 81 treated with a nitrogen ion beam. Three HMW-GS-deficient mutant lines were obtained and then detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Large-chromosome-fragment deletion resulted in specific deficiencies, and the deleted region sizes were determined using molecular markers. Agronomic characters, quantity and proportion of glutenins and dough microstructure of the deletion lines all proved to be quite different from those of wild-type Xiaoyan 81. Analysis of quality properties suggested that GluA1(-) had superior property parameters, while GluB1(-) and GluD1(-) both showed a significant decrease in quality properties compared with Xiaoyan 81. The effects of the three Glu-1 loci on flour and dough quality-related parameters should be Glu-D1 > Glu-B1 > Glu-A1. Ion beam radiation can be used as a mutagen to create new crop mutants. © 2015 Society of Chemical Industry.

Dynamic intensity-weighted region of interest imaging for conebeam CT

PubMed Central

Pearson, Erik; Pan, Xiaochuan; Pelizzari, Charles

2017-01-01

BACKGROUND Patient dose from image guidance in radiotherapy is small compared to the treatment dose. However, the imaging beam is untargeted and deposits dose equally in tumor and healthy tissues. It is desirable to minimize imaging dose while maintaining efficacy. OBJECTIVE Image guidance typically does not require full image quality throughout the patient. Dynamic filtration of the kV beam allows local control of CT image noise for high quality around the target volume and lower quality elsewhere, with substantial dose sparing and reduced scatter fluence on the detector. METHODS The dynamic Intensity-Weighted Region of Interest (dIWROI) technique spatially varies beam intensity during acquisition with copper filter collimation. Fluence is reduced by 95% under the filters with the aperture conformed dynamically to the ROI during cone-beam CT scanning. Preprocessing to account for physical effects of the collimator before reconstruction is described. RESULTS Reconstructions show image quality comparable to a standard scan in the ROI, with higher noise and streak artifacts in the outer region but still adequate quality for patient localization. Monte Carlo modeling shows dose reduction by 10–15% in the ROI due to reduced scatter, and up to 75% outside. CONCLUSIONS The presented technique offers a method to reduce imaging dose by accepting increased image noise outside the ROI, while maintaining full image quality inside the ROI. PMID:27257875

Image quality improvement in megavoltage cone beam CT using an imaging beam line and a sintered pixelated array system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Breitbach, Elizabeth K.; Maltz, Jonathan S.; Gangadharan, Bijumon

2011-11-15

Purpose: To quantify the improvement in megavoltage cone beam computed tomography (MVCBCT) image quality enabled by the combination of a 4.2 MV imaging beam line (IBL) with a carbon electron target and a detector system equipped with a novel sintered pixelated array (SPA) of translucent Gd{sub 2}O{sub 2}S ceramic scintillator. Clinical MVCBCT images are traditionally acquired with the same 6 MV treatment beam line (TBL) that is used for cancer treatment, a standard amorphous Si (a-Si) flat panel imager, and the Kodak Lanex Fast-B (LFB) scintillator. The IBL produces a greater fluence of keV-range photons than the TBL, to whichmore » the detector response is more optimal, and the SPA is a more efficient scintillator than the LFB. Methods: A prototype IBL + SPA system was installed on a Siemens Oncor linear accelerator equipped with the MVision{sup TM} image guided radiation therapy (IGRT) system. A SPA strip consisting of four neighboring tiles and measuring 40 cm by 10.96 cm in the crossplane and inplane directions, respectively, was installed in the flat panel imager. Head- and pelvis-sized phantom images were acquired at doses ranging from 3 to 60 cGy with three MVCBCT configurations: TBL + LFB, IBL + LFB, and IBL + SPA. Phantom image quality at each dose was quantified using the contrast-to-noise ratio (CNR) and modulation transfer function (MTF) metrics. Head and neck, thoracic, and pelvic (prostate) cancer patients were imaged with the three imaging system configurations at multiple doses ranging from 3 to 15 cGy. The systems were assessed qualitatively from the patient image data. Results: For head and neck and pelvis-sized phantom images, imaging doses of 3 cGy or greater, and relative electron densities of 1.09 and 1.48, the CNR average improvement factors for imaging system change of TBL + LFB to IBL + LFB, IBL + LFB to IBL + SPA, and TBL + LFB to IBL + SPA were 1.63 (p < 10{sup -8}), 1.64 (p < 10{sup -13}), 2.66 (p < 10{sup -9}), respectively. For all imaging doses, soft tissue contrast was more easily differentiated on IBL + SPA head and neck and pelvic images than TBL + LFB and IBL + LFB. IBL + SPA thoracic images were comparable to IBL + LFB images, but less noisy than TBL + LFB images at all imaging doses considered. The mean MTFs over all imaging doses were comparable, at within 3%, for all imaging system configurations for both the head- and pelvis-sized phantoms. Conclusions: Since CNR scales with the square root of imaging dose, changing from TBL + LFB to IBL + LFB and IBL + LFB to IBL + SPA reduces the imaging dose required to obtain a given CNR by factors of 0.38 and 0.37, respectively. MTFs were comparable between imaging system configurations. IBL + SPA patient image quality was always better than that of the TBL + LFB system and as good as or better than that of the IBL + LFB system, for a given dose.« less

Technical Note: Evaluation of the latency and the beam characteristics of a respiratory gating system using an Elekta linear accelerator and a respiratory indicator device, Abches.

PubMed

Saito, Masahide; Sano, Naoki; Ueda, Koji; Shibata, Yuki; Kuriyama, Kengo; Komiyama, Takafumi; Marino, Kan; Aoki, Shinichi; Onishi, Hiroshi

2018-01-01

To evaluate the basic performance of a respiratory gating system using an Elekta linac and an Abches respiratory-monitoring device. The gating system was comprised of an Elekta Synergy linac equipped with a Response TM gating interface module and an Abches respiratory-monitoring device. The latencies from a reference respiratory signal to the resulting Abches gating output signal and the resulting monitor-ion-chamber output signal were measured. Then, the flatness and symmetry of the gated beams were measured using a two-dimensional ionization chamber array for fixed and arc beams, respectively. Furthermore, the beam quality, TPR 20,10 , and the output of the fixed gated beams were also measured using a Farmer chamber. Each of the beam characteristics was compared with each of those for nongated irradiation. The full latencies at beam-on and beam-off for 6-MV gated beams were 336.4 ± 23.4 ms and 87.6 ± 7.1 ms, respectively. The differences in flatness between the gated and nongated beams were within 0.91% and 0.87% for the gun-target and left-right directions, respectively. In the same manner, the beam symmetries were within 0.68% and 0.82%, respectively. The percentage differences in beam quality and beam output were below 1% for a beam-on time range of 1.1-7 s. The latency of the Elekta gating system combined with Abches was found to be acceptable using our measurement method. Furthermore, we demonstrated that the beam characteristics of the gating system using our respiratory indicator were comparable with the nongated beams for a single-arc gated beam delivery. © 2017 American Association of Physicists in Medicine.

The judgment of the All-melted-moment during using electron beam melting equipment to purify silicon

NASA Astrophysics Data System (ADS)

Han, Xiaojie; Meng, Jianxiong; Wang, Shuaiye; Jiang, Tonghao; Wang, Feng; Tan, Yi; Jiang, Dachuan

2017-06-01

Experiment has proved that the rate of impurity removal depends on the pressure and the temperature of the vacuum chamber during using electron beam to smelt silicon, and the amount of removed-impurity depends on time when other conditions are the same. In the actual production process, smelting time is a decisive factor of impurity removal amount while pressure and temperature of the vacuum chamber is certain due to a certain melting power. To avoiding the influence of human control and improving the quality of production, thinking of using cooling water temperature to estimate the state of material during metal smelting is considered. We try to use the change of cooling water temperature to judge that when silicon is all melted and to evaluate the effectiveness of this method.

Effect of Annealing Temperature and Oxygen Flow in the Properties of Ion Beam Sputtered SnO-₂x Thin Films.

PubMed

Wang, Chun-Min; Huang, Chun-Chieh; Kuo, Jui-Chao; Sahu, Dipti Ranjan; Huang, Jow-Lay

2015-08-14

Tin oxide (SnO 2-x ) thin films were prepared under various flow ratios of O₂/(O₂ + Ar) on unheated glass substrate using the ion beam sputtering (IBS) deposition technique. This work studied the effects of the flow ratio of O₂/(O₂ + Ar), chamber pressures and post-annealing treatment on the physical properties of SnO₂ thin films. It was found that annealing affects the crystal quality of the films as seen from both X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. In addition, the surface RMS roughness was measured with atomic force microscopy (AFM). Auger electron spectroscopy (AES) analysis was used to obtain the changes of elemental distribution between tin and oxygen atomic concentration. The electrical property is discussed with attention to the structure factor.

Modeling laser brightness from cross Porro prism resonators

NASA Astrophysics Data System (ADS)

Forbes, Andrew; Burger, Liesl; Litvin, Igor Anatolievich

2006-08-01

Laser brightness is a parameter often used to compare high power laser beam delivery from various sources, and incorporates both the power contained in the particular mode, as well as the propagation of that mode through the beam quality factor, M2. In this study a cross Porro prism resonator is considered; crossed Porro prism resonators have been known for some time, but until recently have not been modeled as a complete physical optics system that allows the modal output to be determined as a function of the rotation angle of the prisms. In this paper we consider the diffraction losses as a function of the prism rotation angle relative to one another, and combine this with the propagation of the specific modes to determine the laser output brightness as a function of the prism orientation.

Absolute calibration of sniffer probes on Wendelstein 7-X

NASA Astrophysics Data System (ADS)

Moseev, D.; Laqua, H. P.; Marsen, S.; Stange, T.; Braune, H.; Erckmann, V.; Gellert, F.; Oosterbeek, J. W.

2016-08-01

Here we report the first measurements of the power levels of stray radiation in the vacuum vessel of Wendelstein 7-X using absolutely calibrated sniffer probes. The absolute calibration is achieved by using calibrated sources of stray radiation and the implicit measurement of the quality factor of the Wendelstein 7-X empty vacuum vessel. Normalized absolute calibration coefficients agree with the cross-calibration coefficients that are obtained by the direct measurements, indicating that the measured absolute calibration coefficients and stray radiation levels in the vessel are valid. Close to the launcher, the stray radiation in the empty vessel reaches power levels up to 340 kW/m2 per MW injected beam power. Furthest away from the launcher, i.e., half a toroidal turn, still 90 kW/m2 per MW injected beam power is measured.

Absolute calibration of sniffer probes on Wendelstein 7-X.

PubMed

Moseev, D; Laqua, H P; Marsen, S; Stange, T; Braune, H; Erckmann, V; Gellert, F; Oosterbeek, J W

2016-08-01

Here we report the first measurements of the power levels of stray radiation in the vacuum vessel of Wendelstein 7-X using absolutely calibrated sniffer probes. The absolute calibration is achieved by using calibrated sources of stray radiation and the implicit measurement of the quality factor of the Wendelstein 7-X empty vacuum vessel. Normalized absolute calibration coefficients agree with the cross-calibration coefficients that are obtained by the direct measurements, indicating that the measured absolute calibration coefficients and stray radiation levels in the vessel are valid. Close to the launcher, the stray radiation in the empty vessel reaches power levels up to 340 kW/m(2) per MW injected beam power. Furthest away from the launcher, i.e., half a toroidal turn, still 90 kW/m(2) per MW injected beam power is measured.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moseev, D., E-mail: dmitry.moseev@ipp.mpg.de; Laqua, H. P.; Marsen, S.

Here we report the first measurements of the power levels of stray radiation in the vacuum vessel of Wendelstein 7-X using absolutely calibrated sniffer probes. The absolute calibration is achieved by using calibrated sources of stray radiation and the implicit measurement of the quality factor of the Wendelstein 7-X empty vacuum vessel. Normalized absolute calibration coefficients agree with the cross-calibration coefficients that are obtained by the direct measurements, indicating that the measured absolute calibration coefficients and stray radiation levels in the vessel are valid. Close to the launcher, the stray radiation in the empty vessel reaches power levels up tomore » 340 kW/m{sup 2} per MW injected beam power. Furthest away from the launcher, i.e., half a toroidal turn, still 90 kW/m{sup 2} per MW injected beam power is measured.« less

Practical use of a plastic scintillator for quality assurance of electron beam therapy.

PubMed

Yogo, Katsunori; Tatsuno, Yuya; Tsuneda, Masato; Aono, Yuki; Mochizuki, Daiki; Fujisawa, Yoshiki; Matsushita, Akihiro; Ishigami, Minoru; Ishiyama, Hiromichi; Hayakawa, Kazushige

2017-06-07

Quality assurance (QA) of clinical electron beams is essential for performing accurate and safe radiation therapy. However, with advances in radiation therapy, QA has become increasingly labor-intensive and time-consuming. In this paper, we propose a tissue-equivalent plastic scintillator for quick and easy QA of clinical electron beams. The proposed tool comprises a plastic scintillator plate and a charge-coupled device camera that enable the scintillation light by electron beams to be recorded with high sensitivity and high spatial resolution. Further, the Cerenkov image is directly subtracted from the scintillation image to discriminate Cerenkov emissions and accurately measure the dose profiles of electron beams with high spatial resolution. Compared with conventional methods, discrepancies in the depth profile improved from 7% to 2% in the buildup region via subtractive corrections. Further, the output brightness showed good linearity with dose, good reproducibility (deviations below 1%), and dose rate independence (within 0.5%). The depth of 50% dose measured with the tool, an index of electron beam quality, was within  ±0.5 mm of that obtained with an ionization chamber. Lateral brightness profiles agreed with the lateral dose profiles to within 4% and no significant improvement was obtained using Cerenkov corrections. Field size agreed to within 0.5 mm with those obtained with ionization chamber. For clinical QA of electron boost treatment, a disk scintillator that mimics the shape of a patient's breast is applied. The brightness distribution and dose, calculated using a treatment planning system, was generally acceptable for clinical use, except in limited zones. Overall, the proposed plastic scintillator plate tool efficiently performs QA for electron beam therapy and enables simultaneous verification of output constancy, beam quality, depth, and lateral dose profiles during monthly QAs at lower doses of irradiation (small monitor units, MUs).

Yb3+-doped rod-type amplifiers with local adiabatic tapers for peak power scaling and beam quality improvement

NASA Astrophysics Data System (ADS)

Zhu, Yuan; Eschrich, Tina; Leich, Martin; Grimm, Stephan; Kobelke, Jens; Lorenz, Martin; Bartelt, Hartmut; Jäger, Matthias

2017-10-01

The use of short local tapers in large mode area fiber amplifiers is proposed for peak power scaling while maintaining good beam quality. To avoid modal distortions, the powder-sintering (REPUSIL) method was employed to obtain core materials with excellent refractive index homogeneity. First experiments with Yb3+-doped rod-type amplifiers delivered 2 ns pulses with peak powers of 540 kW and energies of 1.4 mJ for the untapered rod and 230 kW for the tapered rod (limited by facet damage). The beam quality improved from an M 2 value of approximately 10 to 3.5. The investigation of the taper structure indicates room for further improvement.

A trichrome beam model for biological dose calculation in scanned carbon-ion radiotherapy treatment planning.

PubMed

Inaniwa, T; Kanematsu, N

2015-01-07

In scanned carbon-ion (C-ion) radiotherapy, some primary C-ions undergo nuclear reactions before reaching the target and the resulting particles deliver doses to regions at a significant distance from the central axis of the beam. The effects of these particles on physical dose distribution are accounted for in treatment planning by representing the transverse profile of the scanned C-ion beam as the superposition of three Gaussian distributions. In the calculation of biological dose distribution, however, the radiation quality of the scanned C-ion beam has been assumed to be uniform over its cross-section, taking the average value over the plane at a given depth (monochrome model). Since these particles, which have relatively low radiation quality, spread widely compared to the primary C-ions, the radiation quality of the beam should vary with radial distance from the central beam axis. To represent its transverse distribution, we propose a trichrome beam model in which primary C-ions, heavy fragments with atomic number Z ≥ 3, and light fragments with Z ≤ 2 are assigned to the first, second, and third Gaussian components, respectively. Assuming a realistic beam-delivery system, we performed computer simulations using Geant4 Monte Carlo code for analytical beam modeling of the monochrome and trichrome models. The analytical beam models were integrated into a treatment planning system for scanned C-ion radiotherapy. A target volume of 20  ×  20  ×  40 mm(3) was defined within a water phantom. A uniform biological dose of 2.65 Gy (RBE) was planned for the target with the two beam models based on the microdosimetric kinetic model (MKM). The plans were recalculated with Geant4, and the recalculated biological dose distributions were compared with the planned distributions. The mean target dose of the recalculated distribution with the monochrome model was 2.72 Gy (RBE), while the dose with the trichrome model was 2.64 Gy (RBE). The monochrome model underestimated the RBE within the target due to the assumption of no radial variations in radiation quality. Conversely, the trichrome model accurately predicted the RBE even in a small target. Our results verify the applicability of the trichrome model for clinical use in C-ion radiotherapy treatment planning.

A trichrome beam model for biological dose calculation in scanned carbon-ion radiotherapy treatment planning

NASA Astrophysics Data System (ADS)

Inaniwa, T.; Kanematsu, N.

2015-01-01

In scanned carbon-ion (C-ion) radiotherapy, some primary C-ions undergo nuclear reactions before reaching the target and the resulting particles deliver doses to regions at a significant distance from the central axis of the beam. The effects of these particles on physical dose distribution are accounted for in treatment planning by representing the transverse profile of the scanned C-ion beam as the superposition of three Gaussian distributions. In the calculation of biological dose distribution, however, the radiation quality of the scanned C-ion beam has been assumed to be uniform over its cross-section, taking the average value over the plane at a given depth (monochrome model). Since these particles, which have relatively low radiation quality, spread widely compared to the primary C-ions, the radiation quality of the beam should vary with radial distance from the central beam axis. To represent its transverse distribution, we propose a trichrome beam model in which primary C-ions, heavy fragments with atomic number Z ≥ 3, and light fragments with Z ≤ 2 are assigned to the first, second, and third Gaussian components, respectively. Assuming a realistic beam-delivery system, we performed computer simulations using Geant4 Monte Carlo code for analytical beam modeling of the monochrome and trichrome models. The analytical beam models were integrated into a treatment planning system for scanned C-ion radiotherapy. A target volume of 20  ×  20  ×  40 mm3 was defined within a water phantom. A uniform biological dose of 2.65 Gy (RBE) was planned for the target with the two beam models based on the microdosimetric kinetic model (MKM). The plans were recalculated with Geant4, and the recalculated biological dose distributions were compared with the planned distributions. The mean target dose of the recalculated distribution with the monochrome model was 2.72 Gy (RBE), while the dose with the trichrome model was 2.64 Gy (RBE). The monochrome model underestimated the RBE within the target due to the assumption of no radial variations in radiation quality. Conversely, the trichrome model accurately predicted the RBE even in a small target. Our results verify the applicability of the trichrome model for clinical use in C-ion radiotherapy treatment planning.

Response analysis of TLD-300 dosimeters in heavy-particle beams

NASA Astrophysics Data System (ADS)

Loncol, Th; Hamal, M.; Denis, J. M.; Vynckier, S.; Wambersie, A.; Scalliet, P.

1996-09-01

In vivo dosimetry is recommended as part of the quality control procedure for treatment verification in radiation therapy. Using thermoluminescence, such controls are planned in the p(65)+Be neutron and 85 MeV proton beams produced at the cyclotron at Louvain-La-Neuve and dedicated to therapy applications. A preliminary study of the peak 3 (C) and peak 5 (C) response of :Tm (TLD-300) to neutron and proton beams aimed to analyse the effect of different radiation qualities on the dosimetric behaviour of the detector irradiated in phantom. To broaden the range of investigation, the study was extended to an experimental C-12 heavy ion beam (95 MeV/nucleon). The peak 3 and 5 sensitivities in the neutron beam, compared to Co-60, varied little with depth. A major change of peak 5 sensitivity was observed for samples positioned under five leaves of the multi-leaf collimator. While peak 3 sensitivity was constant with depth in the unmodulated proton beam, peak 5 sensitivity increased by 15%. Near the Bragg peak, peak 3 showed the highest decrease of sensitivity. In the modulated proton beam, the sensitivity values were not significantly smaller than those measured in the unmodulated beam far from the Bragg peak region. The ratio of the heights of peak 3 and peak 5 decreased by 70% from the Co-60 reference radiation to the C-12 heavy-ion beam. This parameter was strongly correlated with the change of radiation quality.

On the p(dis) correction factor for cylindrical chambers.

PubMed

Andreo, Pedro

2010-03-07

The authors of a recent paper (Wang and Rogers 2009 Phys. Med. Biol. 54 1609) have used the Monte Carlo method to simulate the 'classical' experiment made more than 30 years ago by Johansson et al (1978 National and International Standardization of Radiation Dosimetry (Atlanta 1977) vol 2 (Vienna: IAEA) pp 243-70) on the displacement (or replacement) perturbation correction factor p(dis) for cylindrical chambers in 60Co and high-energy photon beams. They conclude that an 'unreasonable normalization at dmax' of the ionization chambers response led to incorrect results, and for the IAEA TRS-398 Code of Practice, which uses ratios of those results, 'the difference in the correction factors can lead to a beam calibration deviation of more than 0.5% for Farmer-like chambers'. The present work critically examines and questions some of the claims and generalized conclusions of the paper. It is demonstrated that for real, commercial Farmer-like chambers, the possible deviations in absorbed dose would be much smaller (typically 0.13%) than those stated by Wang and Rogers, making the impact of their proposed values negligible on practical high-energy photon dosimetry. Differences of the order of 0.4% would only appear at the upper extreme of the energies potentially available for clinical use (around 25 MV) and, because lower energies are more frequently used, the number of radiotherapy photon beams for which the deviations would be larger than say 0.2% is extremely small. This work also raises concerns on the proposed value of pdis for Farmer chambers at the reference quality of 60Co in relation to their impact on electron beam dosimetry, both for direct dose determination using these chambers and for the cross-calibration of plane-parallel chambers. The proposed increase of about 1% in p(dis) (compared with TRS-398) would lower the kQ factors and therefore Dw in electron beams by the same amount. This would yield a severe discrepancy with the current good agreement between electron dosimetry based on an electron cross-calibrated plane-parallel chamber (against a Farmer) or on a directly 60Co calibrated plane-parallel chamber, which is not likely to be in error by 1%. It is suggested that the influence of the 60Co source spectrum used in the simulations may not be negligible for calculations aimed at an uncertainty level of 0.1%.

LETTER TO THE EDITOR: On the pdis correction factor for cylindrical chambers

NASA Astrophysics Data System (ADS)

Andreo, Pedro

2010-03-01

The authors of a recent paper (Wang and Rogers 2009 Phys. Med. Biol. 54 1609) have used the Monte Carlo method to simulate the 'classical' experiment made more than 30 years ago by Johansson et al (1978 National and International Standardization of Radiation Dosimetry (Atlanta 1977) vol 2 (Vienna: IAEA) pp 243-70) on the displacement (or replacement) perturbation correction factor pdis for cylindrical chambers in 60Co and high-energy photon beams. They conclude that an 'unreasonable normalization at dmax' of the ionization chambers response led to incorrect results, and for the IAEA TRS-398 Code of Practice, which uses ratios of those results, 'the difference in the correction factors can lead to a beam calibration deviation of more than 0.5% for Farmer-like chambers'. The present work critically examines and questions some of the claims and generalized conclusions of the paper. It is demonstrated that for real, commercial Farmer-like chambers, the possible deviations in absorbed dose would be much smaller (typically 0.13%) than those stated by Wang and Rogers, making the impact of their proposed values negligible on practical high-energy photon dosimetry. Differences of the order of 0.4% would only appear at the upper extreme of the energies potentially available for clinical use (around 25 MV) and, because lower energies are more frequently used, the number of radiotherapy photon beams for which the deviations would be larger than say 0.2% is extremely small. This work also raises concerns on the proposed value of pdis for Farmer chambers at the reference quality of 60Co in relation to their impact on electron beam dosimetry, both for direct dose determination using these chambers and for the cross-calibration of plane-parallel chambers. The proposed increase of about 1% in pdis (compared with TRS-398) would lower the kQ factors and therefore Dw in electron beams by the same amount. This would yield a severe discrepancy with the current good agreement between electron dosimetry based on an electron cross-calibrated plane-parallel chamber (against a Farmer) or on a directly 60Co calibrated plane-parallel chamber, which is not likely to be in error by 1%. It is suggested that the influence of the 60Co source spectrum used in the simulations may not be negligible for calculations aimed at an uncertainty level of 0.1%.

A Z-Axis Quartz Cross-Fork Micromachined Gyroscope Based on Shear Stress Detection

PubMed Central

Xie, Liqiang; Wu, Xuezhong; Li, Shengyi; Wang, Haoxu; Su, Jianbin; Dong, Peitao

2010-01-01

Here we propose a novel quartz micromachined gyroscope. The sensor has a simple cross-fork structure in the x-y plane of quartz crystal. Shear stress rather than normal stress is utilized to sense Coriolis’ force generated by the input angular rate signal. Compared to traditional quartz gyroscopes, which have two separate sense electrodes on each sidewall, there is only one electrode on each sidewall of the sense beam. As a result, the fabrication of the electrodes is simplified and the structure can be easily miniaturized. In order to increase sensitivity, a pair of proof masses is attached to the ends of the drive beam, and the sense beam has a tapered design. The structure is etched from a z-cut quartz wafer and the electrodes are realized by direct evaporation using the aperture mask method. The drive mode frequency of the prototype is 13.38 kHz, and the quality factor is approximately 1,000 in air. Therefore, the gyroscope can work properly without a vacuum package. The measurement ability of the shear stress detection design scheme is validated by the Coriolis’ force test. The performance of the sensor is characterized on a precision rate table using a specially designed readout circuit. The experimentally obtained scale factor is 1.45 mV/°/s and the nonlinearity is 3.6% in range of ±200 °/s. PMID:22294887

Physics Design Considerations for Diagnostic X Electron Beam Transport System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Y-J

2000-04-10

The Diagnostic X (D-X) beamlines will transport the DARHT-II beam from the end of the accelerator to the Diagnostic X firing point providing four lines of sight for x-ray radiography. The design goal for the Diagnostic X beamline is to deliver four x-ray pulses with the DARHT-II dose format and time integrated spot size on each line of sight. The D-X beamline's final focus should be compatible with a range of first conjugates from 1 m-5 m. Furthermore, the D-X beamline operational parameters and the beamline layout should not preclude a possible upgrade to additional lines of sight. The DARHT-IImore » accelerator is designed to deliver beams at a rate of 1 pulse per minute or less. Tuning the D-X beamline with several hundred optical elements would be time consuming. Therefore, minimizing the required number of tuning shots for the D-X beamline is also an important design goal. Many different beamline configurations may be able to accomplish these design objectives, and high beam quality (i.e., high current and low emittance) must be maintained throughout the chosen beamline configuration in order to achieve the DARHT-II x-ray dose format. In general, the longer the distance a beam travels, the harder it is to preserve the beam quality. Therefore, from the point of view of maintaining beam quality, it is highly desirable to minimize the beamline length. Lastly, modification to the DARHT-II building and the downstream transport should be minimized. Several processes can degrade beam quality by increasing the beam emittance, increasing the time-varying transverse beam motion, creating a beam halo, or creating a time-varying beam envelope. In this report, we consider those processes in the passive magnet lattice beamline and indicate how they constrain the beamline design. The physics design considerations for the active components such as the kicker system will be discussed in Ref. 2. In Sec. I, we discuss how beam emittance affects the x-ray forward dose. We also establish a physics design goal for the emittance growth budget. In Sec. II, we discuss how the conductivity and size of the beam pipe affects the transverse beam motion. We also discuss the emittance growth arise from the beam centroid offset. In Sec. III, we discuss the background gas focusing effects and establish the vacuum requirements. In Sec. IV, we consider the emittance growth in a bend. In Sec. V, we discuss the misalignment and corkscrew motion. The design specifications for misalignment are established. In Secs. VI and VII, we discuss the design objectives on how to extract beams from the DARHT-II beamline and how to minimize the tuning shots. The integrated spot size and final focusing are discussed in Sec. VIII. A conclusion will be presented in Sec. IX.« less

Beam wander of coherent and partially coherent Airy beam arrays in a turbulent atmosphere

NASA Astrophysics Data System (ADS)

Wen, Wei; Jin, Ying; Hu, Mingjun; Liu, Xianlong; Cai, Yangjian; Zou, Chenjuan; Luo, Mi; Zhou, Liwang; Chu, Xiuxiang

2018-05-01

The beam wander properties of coherent and partially coherent Airy beam arrays in a turbulent atmosphere are investigated. Based on the analytical results, we find that the beam wander of partially coherent Airy beam arrays is significantly reduced compared with the wander of a partially coherent Airy beam by numerical simulation. Moreover, the beam wander of a 2 × 2 partially coherent Airy beam arrays is significantly reduced compared with the wander of a 2 × 2 partially coherent Gaussian beam arrays. By using the definition of beam wander arrays factor which is used to characterize the capability of beam arrays for reducing the beam wander effect compared with a single beam, we find that the arrays factor of partially coherent Airy beam arrays is significantly less than that of partially coherent Gaussian beam arrays with the same arrays order. We also find that an artificial reduction of the initial coherence of laser arrays can be used to decrease the beam wander effect. These results indicate that the partially coherent Airy beam arrays have potential applications in long-distance free-space optical communications.

High-power direct diode laser output by spectral beam combining

NASA Astrophysics Data System (ADS)

Tan, Hao; Meng, Huicheng; Ruan, Xu; Du, Weichuan; Wang, Zhao

2018-03-01

We demonstrate a spectral beam combining scheme based on multiple mini-bar stacks, which have more diode laser combining elements, to increase the combined diode laser power and realize equal beam quality in both the fast and slow axes. A spectral beam combining diode laser output of 1130 W is achieved with an operating current of 75 A. When a 9.6 X de-magnifying telescope is introduced between the output mirror and the diffraction grating, to restrain cross-talk among diode laser emitters, a 710 W spectral beam combining diode laser output is achieved at the operating current of 70 A, and the beam quality on the fast and slow axes of the combined beam is about 7.5 mm mrad and 7.3 mm mrad respectively. The power reduction is caused by the existence of a couple resonator between the rear facet of the diode laser and the fast axis collimation lens, and it should be eliminated by using diode laser chips with higher front facet transmission efficiency and a fast axis collimation lens with lower residual reflectivity.

Tailored laser beam shaping for efficient and accurate microstructuring

NASA Astrophysics Data System (ADS)

Häfner, T.; Strauß, J.; Roider, C.; Heberle, J.; Schmidt, M.

2018-02-01

Large-area processing with high material removal rates by ultrashort pulsed (USP) lasers is coming into focus by the development of high-power USP laser systems. However, currently the bottleneck for high-rate production is given by slow and inefficient beam manipulation. On the one hand, slow beam deflection with regard to high pulse repetition rates leads to heat accumulation and shielding effects, on the other hand, a conventional focus cannot provide the optimum fluence due to the Gaussian intensity profile. In this paper, we emphasize on two approaches of dynamic laser beam shaping with liquid crystal on silicon spatial light modulation and acousto-optic beam shaping. Advantages and limitations of dynamic laser beam shaping with regard to USP laser material processing and methods for reducing the influence of speckle are discussed. Additionally, the influence of optics induced aberrations on speckle characteristics is evaluated. Laser material processing results are presented correlating the achieved structure quality with the simulated and measured beam quality. Experimental and analytical investigations show a certain fluence dependence of the necessary number of alternative holograms to realize homogeneous microstructures.

Beam uniformity of flat top lasers

NASA Astrophysics Data System (ADS)

Chang, Chao; Cramer, Larry; Danielson, Don; Norby, James

2015-03-01

Many beams that output from standard commercial lasers are multi-mode, with each mode having a different shape and width. They show an overall non-homogeneous energy distribution across the spot size. There may be satellite structures, halos and other deviations from beam uniformity. However, many scientific, industrial and medical applications require flat top spatial energy distribution, high uniformity in the plateau region, and complete absence of hot spots. Reliable standard methods for the evaluation of beam quality are of great importance. Standard methods are required for correct characterization of the laser for its intended application and for tight quality control in laser manufacturing. The International Organization for Standardization (ISO) has published standard procedures and definitions for this purpose. These procedures have not been widely adopted by commercial laser manufacturers. This is due to the fact that they are unreliable because an unrepresentative single-pixel value can seriously distort the result. We hereby propose a metric of beam uniformity, a way of beam profile visualization, procedures to automatically detect hot spots and beam structures, and application examples in our high energy laser production.

Optical parametric osicllators with improved beam quality

DOEpatents

Smith, Arlee V.; Alford, William J.

2003-11-11

An optical parametric oscillator (OPO) having an optical pump, which generates a pump beam at a pump frequency greater than a desired signal frequency, a nonlinear optical medium oriented so that a signal wave at the desired signal frequency and a corresponding idler wave are produced when the pump beam (wave) propagates through the nonlinear optical medium, resulting in beam walk off of the signal and idler waves, and an optical cavity which directs the signal wave to repeatedly pass through the nonlinear optical medium, said optical cavity comprising an equivalently even number of non-planar mirrors that produce image rotation on each pass through the nonlinear optical medium. Utilizing beam walk off where the signal wave and said idler wave have nonparallel Poynting vectors in the nonlinear medium and image rotation, a correlation zone of distance equal to approximately .rho.L.sub.crystal is created which, through multiple passes through the nonlinear medium, improves the beam quality of the OPO output.

Storage-ring Electron Cooler for Relativistic Ion Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Fanglei; Derbenev, Yaroslav; Douglas, David R.

Application of electron cooling at ion energies above a few GeV has been limited due to reduction of electron cooling efficiency with energy and difficulty in producing and accelerating a high-current high-quality electron beam. A high-current storage-ring electron cooler offers a solution to both of these problems by maintaining high cooling beam quality through naturally-occurring synchrotron radiation damping of the electron beam. However, the range of ion energies where storage-ring electron cooling can be used has been limited by low electron beam damping rates at low ion energies and high equilibrium electron energy spread at high ion energies. This papermore » reports a development of a storage ring based cooler consisting of two sections with significantly different energies: the cooling and damping sections. The electron energy and other parameters in the cooling section are adjusted for optimum cooling of a stored ion beam. The beam parameters in the damping section are adjusted for optimum damping of the electron beam. The necessary energy difference is provided by an energy recovering SRF structure. A prototype linear optics of such storage-ring cooler is presented.« less

Gaussian beam profile shaping apparatus, method therefor and evaluation thereof

DOEpatents

Dickey, Fred M.; Holswade, Scott C.; Romero, Louis A.

1999-01-01

A method and apparatus maps a Gaussian beam into a beam with a uniform irradiance profile by exploiting the Fourier transform properties of lenses. A phase element imparts a design phase onto an input beam and the output optical field from a lens is then the Fourier transform of the input beam and the phase function from the phase element. The phase element is selected in accordance with a dimensionless parameter which is dependent upon the radius of the incoming beam, the desired spot shape, the focal length of the lens and the wavelength of the input beam. This dimensionless parameter can also be used to evaluate the quality of a system. In order to control the radius of the incoming beam, optics such as a telescope can be employed. The size of the target spot and the focal length can be altered by exchanging the transform lens, but the dimensionless parameter will remain the same. The quality of the system, and hence the value of the dimensionless parameter, can be altered by exchanging the phase element. The dimensionless parameter provides design guidance, system evaluation, and indication as to how to improve a given system.

Gaussian beam profile shaping apparatus, method therefore and evaluation thereof

DOEpatents

Dickey, F.M.; Holswade, S.C.; Romero, L.A.

1999-01-26

A method and apparatus maps a Gaussian beam into a beam with a uniform irradiance profile by exploiting the Fourier transform properties of lenses. A phase element imparts a design phase onto an input beam and the output optical field from a lens is then the Fourier transform of the input beam and the phase function from the phase element. The phase element is selected in accordance with a dimensionless parameter which is dependent upon the radius of the incoming beam, the desired spot shape, the focal length of the lens and the wavelength of the input beam. This dimensionless parameter can also be used to evaluate the quality of a system. In order to control the radius of the incoming beam, optics such as a telescope can be employed. The size of the target spot and the focal length can be altered by exchanging the transform lens, but the dimensionless parameter will remain the same. The quality of the system, and hence the value of the dimensionless parameter, can be altered by exchanging the phase element. The dimensionless parameter provides design guidance, system evaluation, and indication as to how to improve a given system. 27 figs.

Nanophotonic photon echo memory based on rare-earth-doped crystals

NASA Astrophysics Data System (ADS)

Zhong, Tian; Kindem, Jonathan; Miyazono, Evan; Faraon, Andrei; Caltech nano quantum optics Team

2015-03-01

Rare earth ions (REIs) are promising candidates for implementing solid-state quantum memories and quantum repeater devices. Their high spectral stability and long coherence times make REIs a good choice for integration in an on-chip quantum nano-photonic platform. We report the coupling of the 883 nm transition of Neodymium (Nd) to a Yttrium orthosilicate (YSO) photonic crystal nano-beam resonator, achieving Purcell enhanced spontaneous emission by 21 times and increased optical absorption. Photon echoes were observed in nano-beams of different doping concentrations, yielding optical coherence times T2 up to 80 μs that are comparable to unprocessed bulk samples. This indicates the remarkable coherence properties of Nd are preserved during nanofabrication, therefore opening the possibility of efficient on-chip optical quantum memories. The nano-resonator with mode volume of 1 . 6(λ / n) 3 was fabricated using focused ion beam, and a quality factor of 3200 was measured. Purcell enhanced absorption of 80% by an ensemble of ~ 1 × 106 ions in the resonator was measured, which fulfills the cavity impedance matching condition that is necessary to achieve quantum storage of photons with unity efficiency.

Simulations of the temporal and spatial resolution for a compact time-resolved electron diffractometer

NASA Astrophysics Data System (ADS)

Robinson, Matthew S.; Lane, Paul D.; Wann, Derek A.

2016-02-01

A novel compact electron gun for use in time-resolved gas electron diffraction experiments has recently been designed and commissioned. In this paper we present and discuss the extensive simulations that were performed to underpin the design in terms of the spatial and temporal qualities of the pulsed electron beam created by the ionisation of a gold photocathode using a femtosecond laser. The response of the electron pulses to a solenoid lens used to focus the electron beam has also been studied. The simulated results show that focussing the electron beam affects the overall spatial and temporal resolution of the experiment in a variety of ways, and that factors that improve the resolution of one parameter can often have a negative effect on the other. A balance must, therefore, be achieved between spatial and temporal resolution. The optimal experimental time resolution for the apparatus is predicted to be 416 fs for studies of gas-phase species, while the predicted spatial resolution of better than 2 nm-1 compares well with traditional time-averaged electron diffraction set-ups.

Measurement and validation of benchmark-quality thick-target tungsten X-ray spectra below 150 kVp.

PubMed

Mercier, J R; Kopp, D T; McDavid, W D; Dove, S B; Lancaster, J L; Tucker, D M

2000-11-01

Pulse-height distributions of two constant potential X-ray tubes with fixed anode tungsten targets were measured and unfolded. The measurements employed quantitative alignment of the beam, the use of two different semiconductor detectors (high-purity germanium and cadmium-zinc-telluride), two different ion chamber systems with beam-specific calibration factors, and various filter and tube potential combinations. Monte Carlo response matrices were generated for each detector for unfolding the pulse-height distributions into spectra incident on the detectors. These response matrices were validated for the low error bars assigned to the data. A significant aspect of the validation of spectra, and a detailed characterization of the X-ray tubes, involved measuring filtered and unfiltered beams at multiple tube potentials (30-150 kVp). Full corrections to ion chamber readings were employed to convert normalized fluence spectra into absolute fluence spectra. The characterization of fixed anode pitting and its dominance over exit window plating and/or detector dead layer was determined. An Appendix of tabulated benchmark spectra with assigned error ranges was developed for future reference.

Mechanically coupled CMOS-MEMS free-free beam resonator arrays with enhanced power handling capability.

PubMed

Li, Ming-Huang; Chen, Wen-Chien; Li, Sheng-Shian

2012-03-01

Integrated CMOS-MEMS free-free beam resonator arrays operated in a standard two-port electrical configuration with low motional impedance and high power handling capability, centered at 10.5 MHz, have been demonstrated using the combination of pull-in gap reduction mechanism and mechanically coupled array design. The mechanical links (i.e., coupling elements) using short stubs connect each constituent resonator of an array to its adjacent ones at the high-velocity vibrating locations to accentuate the desired mode and reject all other spurious modes. A single second-mode free-free beam resonator with quality factor Q > 2200 and motional impedance R(m) < 150 kΩ has been used to achieve mechanically coupled resonator arrays in this work. In array design, a 9-resonator array has been experimentally characterized to have performance improvement of approximately 10× on motional impedance and power handling as compared with that of a single resonator. In addition, the two-port electrical configuration is much preferred over a one-port configuration because of its low-feedthrough and high design flexibility for future oscillator and filter implementation.

SU-E-I-42: Measurement of X-Ray Beam Width and Geometric Efficiency in MDCT Using Radiochromic Films.

PubMed

Liillau, T; Liebmann, M; von Boetticher, H; Poppe, B

2012-06-01

The purpose of this work was to measure the x-ray beam width and geometric efficiency (GE) of a multi detector computed tomography scanner (MDCT) for different beam collimations using radiochromic films. In MDCT, the primary beam width extends the nominal beam collimation to irradiate the active detector elements uniformly (called 'over-beaming') which contributes to increased radiation dose to the patient compared to single detector CT. Therefore, the precise determination of the primary beam width and GE is of value for any CT dose calculation using Monte Carlo or analytical methods. Single axial dose profiles free in air were measured for 6 different beam collimations nT for a Siemens SOMATOM Sensation 64 Scanner with Gafchromic XR-QA2 films. The films were calibrated relative to the measured charge of a PTW semiflex ionization chamber (type: 31010) for a single rotation in the CT scanner at the largest available beam collimation of 28.8 mm. The beam energy for all measurements in this work was set to 120 kVp. For every measured dose profile and beam collimation the GEin-air and the full-width-at-half- maximum value (FWHM) as a value for the x-ray beam width was determined. Over-beaming factors FWHM / nT were calculated accordingly. For MDCT beam collimations from 7.2 (12×0.6 mm) to 28.8 (24×1.2 mm) the geometric efficiency was between 58 and 85 %. The over- beaming factor ranged from 1.43 to 1.11. For beam collimations of 1×5 mm and 1×10 mm the GE was 77 % and 84 % respectively. The over-beaming factors were close to 1, as expected. This work has shown that radiochromic films can be used for accurate x-ray beam width and geometric efficiency measurements due to their high spatial resolution. The measured free-in-air geometric efficiency and the over-beaming factor depend strongly on beam collimation. © 2012 American Association of Physicists in Medicine.

Lasers for industrial production processing: tailored tools with increasing flexibility

NASA Astrophysics Data System (ADS)

Rath, Wolfram

2012-03-01

High-power fiber lasers are the newest generation of diode-pumped solid-state lasers. Due to their all-fiber design they are compact, efficient and robust. Rofin's Fiber lasers are available with highest beam qualities but the use of different process fiber core sizes enables the user additionally to adapt the beam quality, focus size and Rayleigh length to his requirements for best processing results. Multi-mode fibers from 50μm to 600μm with corresponding beam qualities of 2.5 mm.mrad to 25 mm.mrad are typically used. The integrated beam switching modules can make the laser power available to 4 different manufacturing systems or can share the power to two processing heads for parallel processing. Also CO2 Slab lasers combine high power with either "single-mode" beam quality or higher order modes. The wellestablished technique is in use for a large number of industrial applications, processing either metals or non-metallic materials. For many of these applications CO2 lasers remain the best choice of possible laser sources either driven by the specific requirements of the application or because of the cost structure of the application. The actual technical properties of these lasers will be presented including an overview over the wavelength driven differences of application results, examples of current industrial practice as cutting, welding, surface processing including the flexible use of scanners and classical optics processing heads.

Generation and propagation of a sine-azimuthal wavefront modulated Gaussian beam

PubMed Central

Lao, Guanming; Zhang, Zhaohui; Luo, Meilan; Zhao, Daomu

2016-01-01

We introduce a method for modulating the Gaussian beam by means of sine-azimuthal wavefront and carry out the experimental generation. The analytical propagation formula of such a beam passing through a paraxial ABCD optical system is derived, by which the intensity properties of the sine-azimuthal wavefront modulated Gaussian (SWMG) beam are examined both theoretically and experimentally. Both of the experimental and theoretical results show that the SWMG beam goes through the process from beam splitting to a Gaussian-like profile, which is closely determined by the phase factor and the propagation distance. Appropriate phase factor and short distance are helpful for the splitting of beam. However, in the cases of large phase factor and focal plane, the intensity distributions tend to take a Gaussian form. Such unique features may be of importance in particle trapping and medical applications. PMID:27443798

Spectral and spatial characterisation of laser-driven positron beams

DOE PAGES

Sarri, G.; Warwick, J.; Schumaker, W.; ...

2016-10-18

The generation of high-quality relativistic positron beams is a central area of research in experimental physics, due to their potential relevance in a wide range of scientific and engineering areas, ranging from fundamental science to practical applications. There is now growing interest in developing hybrid machines that will combine plasma-based acceleration techniques with more conventional radio-frequency accelerators, in order to minimise the size and cost of these machines. Here we report on recent experiments on laser-driven generation of high-quality positron beams using a relatively low energy and potentially table-top laser system. Lastly, the results obtained indicate that current technology allowsmore » to create, in a compact setup, positron beams suitable for injection in radio-frequency accelerators.« less

Generalized M-factor of hollow Gaussian beams through a hard-edge circular aperture

NASA Astrophysics Data System (ADS)

Deng, Dongmei

2005-06-01

Based on the generalized truncated second-order moments, the generalized M-factor (MG2-factor) of three-dimensional hollow Gaussian beams (HGBs) through a hard-edge circular aperture is studied in cylindrical coordinate system analytically and numerically. The closed-form expression for the MG2-factor of the truncated HGBs, which is dependent on the truncation parameter β and the beam order n, can be simplified to that of the truncated, the untruncated Gaussian beams and the untruncated HGBs. Also, the power fraction is demonstrated analytically and numerically, which shows that the area of the dark region across the HGBs increases as n increasing.

High-quality electron beam generation in a proton-driven hollow plasma wakefield accelerator

NASA Astrophysics Data System (ADS)

Li, Y.; Xia, G.; Lotov, K. V.; Sosedkin, A. P.; Hanahoe, K.; Mete-Apsimon, O.

2017-10-01

Simulations of proton-driven plasma wakefield accelerators have demonstrated substantially higher accelerating gradients compared to conventional accelerators and the viability of accelerating electrons to the energy frontier in a single plasma stage. However, due to the strong intrinsic transverse fields varying both radially and in time, the witness beam quality is still far from suitable for practical application in future colliders. Here we demonstrate the efficient acceleration of electrons in proton-driven wakefields in a hollow plasma channel. In this regime, the witness bunch is positioned in the region with a strong accelerating field, free from plasma electrons and ions. We show that the electron beam carrying the charge of about 10% of 1 TeV proton driver charge can be accelerated to 0.6 TeV with a preserved normalized emittance in a single channel of 700 m. This high-quality and high-charge beam may pave the way for the development of future plasma-based energy frontier colliders.

Compact compressive arc and beam switchyard for energy recovery linac-driven ultraviolet free electron lasers

NASA Astrophysics Data System (ADS)

Akkermans, J. A. G.; Di Mitri, S.; Douglas, D.; Setija, I. D.

2017-08-01

High gain free electron lasers (FELs) driven by high repetition rate recirculating accelerators have received considerable attention in the scientific and industrial communities in recent years. Cost-performance optimization of such facilities encourages limiting machine size and complexity, and a compact machine can be realized by combining bending and bunch length compression during the last stage of recirculation, just before lasing. The impact of coherent synchrotron radiation (CSR) on electron beam quality during compression can, however, limit FEL output power. When methods to counteract CSR are implemented, appropriate beam diagnostics become critical to ensure that the target beam parameters are met before lasing, as well as to guarantee reliable, predictable performance and rapid machine setup and recovery. This article describes a beam line for bunch compression and recirculation, and beam switchyard accessing a diagnostic line for EUV lasing at 1 GeV beam energy. The footprint is modest, with 12 m compressive arc diameter and ˜20 m diagnostic line length. The design limits beam quality degradation due to CSR both in the compressor and in the switchyard. Advantages and drawbacks of two switchyard lines providing, respectively, off-line and on-line measurements are discussed. The entire design is scalable to different beam energies and charges.

Dual-Energy Contrast-Enhanced Breast Tomosynthesis: Optimization of Beam Quality for Dose and Image Quality

PubMed Central

Samei, Ehsan; Saunders, Robert S.

2014-01-01

Dual-energy contrast-enhanced breast tomosynthesis is a promising technique to obtain three-dimensional functional information from the breast with high resolution and speed. To optimize this new method, this study searched for the beam quality that maximized image quality in terms of mass detection performance. A digital tomosynthesis system was modeled using a fast ray-tracing algorithm, which created simulated projection images by tracking photons through a voxelized anatomical breast phantom containing iodinated lesions. The single-energy images were combined into dual-energy images through a weighted log subtraction process. The weighting factor was optimized to minimize anatomical noise, while the dose distribution was chosen to minimize quantum noise. The dual-energy images were analyzed for the signal difference to noise ratio (SdNR) of iodinated masses. The fast ray-tracing explored 523,776 dual-energy combinations to identify which yields optimum mass SdNR. The ray-tracing results were verified using a Monte Carlo model for a breast tomosynthesis system with a selenium-based flat-panel detector. The projection images from our voxelized breast phantom were obtained at a constant total glandular dose. The projections were combined using weighted log subtraction and reconstructed using commercial reconstruction software. The lesion SdNR was measured in the central reconstructed slice. The SdNR performance varied markedly across the kVp and filtration space. Ray-tracing results indicated that the mass SdNR was maximized with a high-energy tungsten beam at 49 kVp with 92.5 μm of copper filtration and a low-energy tungsten beam at 49 kVp with 95 μm of tin filtration. This result was consistent with Monte Carlo findings. This mammographic technique led to a mass SdNR of 0.92 ± 0.03 in the projections and 3.68 ± 0.19 in the reconstructed slices. These values were markedly higher than those for non-optimized techniques. Our findings indicate that dual-energy breast tomosynthesis can be performed optimally at 49 kVp with alternative copper and tin filters, with reconstruction following weighted subtraction. The optimum technique provides best visibility of iodine against structured breast background in dual-energy contrast-enhanced breast tomosynthesis. PMID:21908902

Back-streaming ion emission and beam focusing on high power linear induction accelerator

NASA Astrophysics Data System (ADS)

Zhu, Jun; Chen, Nan; Yu, Haijun; Jiang, Xiaoguo; Wang, Yuan; Dai, Wenhua; Gao, Feng; Wang, Minhong; Li, Jin; Shi, Jinshui

2011-08-01

Ions released from target surfaces by impact of a high intensity and current electron beam can be accelerated and trapped in the beam potential, and further destroy the beam focus. By solving the 2D Poisson equation, we found that the charge neutralization factor of the ions to the beam under space charge limited condition is 1/3, which is large enough to disrupt the spot size. Therefore, the ion emission at the target in a single-pulse beam/target system must be source limited. Experimental results on the time-resolved beam profile measurement have also proven that. A new focus scheme is proposed in this paper to focus the beam to a small spot size with the existence of back-streaming ions. We found that the focal spot will move upstream as the charge neutralization factor increases. By comparing the theoretical and experimental focal length of the Dragon-I accelerator (20 MeV, 2.5 kA, 60 ns flattop), we found that the average neutralization factor is about 5% in the beam/target system.

Demonstration of cathode emittance dominated high bunch charge beams in a DC gun-based photoinjector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gulliford, Colwyn, E-mail: cg248@cornell.edu; Bartnik, Adam, E-mail: acb20@cornell.edu; Bazarov, Ivan

We present the results of transverse emittance and longitudinal current profile measurements of high bunch charge (≥100 pC) beams produced in the DC gun-based Cornell energy recovery linac photoinjector. In particular, we show that the cathode thermal and core beam emittances dominate the final 95% and core emittances measured at 9–9.5 MeV. Additionally, we demonstrate excellent agreement between optimized 3D space charge simulations and measurement, and show that the quality of the transverse laser distribution limits the optimal simulated and measured emittances. These results, previously thought achievable only with RF guns, demonstrate that DC gun based photoinjectors are capable of deliveringmore » beams with sufficient single bunch charge and beam quality suitable for many current and next generation accelerator projects such as Energy Recovery Linacs and Free Electron Lasers.« less

Preparation and comparative testing of advanced diamond-like carbon foils for tandem accelerators and time-of-flight spectrometers

NASA Astrophysics Data System (ADS)

Liechtenstein, V. Kh.; Ivkova, T. M.; Olshanski, E. D.; Baranov, A. M.; Repnow, R.; Hellborg, R.; Weller, R. A.; Wirth, H. L.

1999-12-01

The sputter preparation technique for thin diamond-like carbon (DLC) foils, advantageously used for ion-beam stripping and timing in accelerator experiments, has been optimized to improve the quality and the performance of the foils. Irradiation lifetimes of 5 μg/cm 2 DLC foils prepared by this technique have been compared with those for foils of approximately the same thickness, prepared by laser plasma ablation and for ethylene cracked foils when bombarded by 11 MeV Cu - - and Au --ion beams of ˜1 μA beam current at the Heidelberg MP-tandem. Standard carbon arc-evaporated foils were used as references. In these experiments, DLC stripper foils appeared to have a mean lifetime approximately two times longer than ethylene-cracked foils regardless of ion species, and compared favorably with foils prepared by laser ablation method. All these foils lasted at least, 10 times longer than standard carbon foils, when irradiated in the MP terminal. Approximately, the same improvement factor was confirmed with 3 μg/cm 2 DLC stripper foils irradiated with 2.3 MeV Ni-beams at the Pelletron accelerator in Lund. Unlike standard carbon foils, most of the advanced lifetime foils exhibited thinning during long irradiation, under clean vacuum. This suggests that sputtering of the foil by the heavy-ion beam might be a dominant process, responsible for the observed failure of these long-lived strippers. Along with specifically corrugated self-supporting DLC beam strippers, we succeeded in the fabrication of very smooth and ultra thin (˜0.5 μg/cm 2) DLC foils, mounted on grids and used as start foils for the ToF spectrometers applied in ion beam analysis.

Influences of thermal deformation of cavity mirrors induced by high energy DF laser to beam quality under the simulated real physical circumstances

NASA Astrophysics Data System (ADS)

Deng, Shaoyong; Zhang, Shiqiang; He, Minbo; Zhang, Zheng; Guan, Xiaowei

2017-05-01

The positive-branch confocal unstable resonator with inhomogeneous gain medium was studied for the normal used high energy DF laser system. The fast changing process of the resonator's eigenmodes was coupled with the slow changing process of the thermal deformation of cavity mirrors. Influences of the thermal deformation of cavity mirrors to the outcoupled beam quality and transmission loss of high frequency components of high energy laser were computed. The simulations are done through programs compiled by MATLAB and GLAD software and the method of combination of finite elements and Fox-li iteration algorithm was used. Effects of thermal distortion, misaligned of cavity mirrors and inhomogeneous distribution of gain medium were introduced to simulate the real physical circumstances of laser cavity. The wavefront distribution and beam quality (including RMS of wavefront, power in the bucket, Strehl ratio, diffraction limit β, position of the beam spot center, spot size and intensity distribution in far-field ) of the distorted outcoupled beam were studied. The conclusions of the simulation agree with the experimental results. This work would supply references of wavefront correction range to the adaptive optics system of interior alleyway.

On Solutions for the Transient Response of Beams

NASA Technical Reports Server (NTRS)

Leonard, Robert W.

1959-01-01

Williams type modal solutions of the elementary and Timoshenko beam equations are presented for the response of several uniform beams to a general applied load. Example computations are shown for a free-free beam subject to various concentrated loads at its center. Discussion includes factors influencing the convergence of modal solutions and factors to be considered in a choice of beam theory. Results obtained by two numerical procedures, the traveling-wave method and Houbolt's method, are also presented and discussed.

Modified hollow Gaussian beam and its paraxial propagation

NASA Astrophysics Data System (ADS)

Cai, Yangjian; Chen, Chiyi; Wang, Fei

2007-10-01

A model named modified hollow Gaussian beam (HGB) is proposed to describe a dark hollow beam with adjustable beam spot size, central dark size and darkness factor. In this modified model, both the beam spot size and the central dark size will be convergent to finite constants as the beam order approaches infinity, which are much different from that of the previous unmodified model, where the beam spot size and the central dark size will not be convergent as the beam order approaches infinity. The dependences of the propagation factor of modified and unmodified HGBs on the beam order are found to be the same. Based on the Collins integral, analytical formulas for the modified HGB propagating through aligned and misaligned optical system are derived. Some numerical examples are given.

Plasma mirrors for short pulse KrF lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gilicze, Barnabás; Szatmári, Sándor; Barna, Angéla

2016-08-15

It is demonstrated for the first time that plasma mirrors can be successfully applied for KrF laser systems. High reflectivity up to 70% is achieved by optimization of the beam quality on the plasma mirror. The modest spectral shift and the good reflected beam quality allow its applicability for high power laser systems for which a new arrangement is suggested.

[Diagnostic possibilities of digital volume tomography].

PubMed

Lemkamp, Michael; Filippi, Andreas; Berndt, Dorothea; Lambrecht, J Thomas

2006-01-01

Cone beam computed tomography allows high quality 3D images of cranio-facial structures. Although detail resolution is increased, x-ray exposition is reduced compared to classic computer tomography. The volume is analysed in three orthogonal plains, which can be rotated independently without quality loss. Cone beam computed tomography seems to be a less expensive and less x-ray exposing alternative to classic computer tomography.

The use of ion beam cleaning to obtain high quality cold welds with minimal deformation

NASA Technical Reports Server (NTRS)

Sater, B. L.; Moore, T. J.

1978-01-01

This paper describes a variation of cold welding which utilizes an ion beam to clean mating surfaces prior to joining in a vacuum environment. High quality solid state welds were produced with minimal deformation. Due to experimental fixture limitation in applying pressure work has been limited to a few low yield strength materials.

Fiber optic diffraction grating maker

DOEpatents

Deason, V.A.; Ward, M.B.

1991-05-21

A compact and portable diffraction grating maker is comprised of a laser beam, optical and fiber optics devices coupling the beam to one or more evanescent beam splitters, and collimating lenses or mirrors directing the split beam at an appropriate photosensitive material. The collimating optics, the output ends of the fiber optic coupler and the photosensitive plate holder are all mounted on an articulated framework so that the angle of intersection of the beams can be altered at will without disturbing the spatial filter, collimation or beam quality, and assuring that the beams will always intersect at the position of the plate. 4 figures.

Fiber optic diffraction grating maker

DOEpatents

Deason, Vance A.; Ward, Michael B.

1991-01-01

A compact and portable diffraction grating maker comprised of a laser beam, optical and fiber optics devices coupling the beam to one or more evanescent beam splitters, and collimating lenses or mirrors directing the split beam at an appropriate photosensitive material. The collimating optics, the output ends of the fiber optic coupler and the photosensitive plate holder are all mounted on an articulated framework so that the angle of intersection of the beams can be altered at will without disturbing the spatial filter, collimation or beam quality, and assuring that the beams will always intersect at the position of the plate.

Spatial control of photoemitted electron beams using a microlens-array transverse-shaping technique

DOE PAGES

Halavanau, A.; Qiang, G.; Ha, G.; ...

2017-10-26

A transversely inhomogeneous laser distribution on the photocathode surface generally produces electron beams with degraded beam quality. In this paper, we explore the use of microlens arrays to dramatically improve the transverse uniformity of an ultraviolet drive-laser pulse used in a photoinjector. Here, we also demonstrate a capability of microlens arrays to generate transversely modulated electron beams and present an application of such a feature to diagnose the properties of a magnetized beam.

Final report on LDRD project : narrow-linewidth VCSELs for atomic microsystems.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chow, Weng Wah; Geib, Kent Martin; Peake, Gregory Merwin

2011-09-01

Vertical-cavity surface-emitting lasers (VCSELs) are well suited for emerging photonic microsystems due to their low power consumption, ease of integration with other optical components, and single frequency operation. However, the typical VCSEL linewidth of 100 MHz is approximately ten times wider than the natural linewidth of atoms used in atomic beam clocks and trapped atom research, which degrades or completely destroys performance in those systems. This report documents our efforts to reduce VCSEL linewidths below 10 MHz to meet the needs of advanced sub-Doppler atomic microsystems, such as cold-atom traps. We have investigated two complementary approaches to reduce VCSEL linewidth:more » (A) increasing the laser-cavity quality factor, and (B) decreasing the linewidth enhancement factor (alpha) of the optical gain medium. We have developed two new VCSEL devices that achieved increased cavity quality factors: (1) all-semiconductor extended-cavity VCSELs, and (2) micro-external-cavity surface-emitting lasers (MECSELs). These new VCSEL devices have demonstrated linewidths below 10 MHz, and linewidths below 1 MHz seem feasible with further optimization.« less

Coupling efficiency of laser beam to multimode fiber

NASA Astrophysics Data System (ADS)

Niu, Jinfu; Xu, Jianqiu

2007-06-01

The coupling efficiency of laser beam to multimode fiber is given by geometrical optics, and the relation between the maximum coupling efficiency and the beam propagation factor M2 is analyzed. An equivalent factor MF2 for the multimode fiber is introduced to characterize the fiber coupling capability. The coupling efficiency of laser beam to multimode fiber is calculated in respect of the ratio M2/MF2 by the overlapping integral theory. The optimal coupling efficiency can be roughly estimated by the ratio of M2 to MF2 but with a large error range. The deviation comes from the lacks of information on the detail of phase and intensity profile in the beam factor M2.

Effect of Axial Force on the Performance of Micromachined Vibratory Rate Gyroscopes

PubMed Central

Hou, Zhanqiang; Xiao, Dingbang; Wu, Xuezhong; Dong, Peitao; Chen, Zhihua; Niu, Zhengyi; Zhang, Xu

2011-01-01

It is reported in the published literature that the resonant frequency of a silicon micromachined gyroscope decreases linearly with increasing temperature. However, when the axial force is considerable, the resonant frequency might increase as the temperature increases. The axial force is mainly induced by thermal stress due to the mismatch between the thermal expansion coefficients of the structure and substrate. In this paper, two types of micromachined suspended vibratory gyroscopes with slanted beams were proposed to evaluate the effect of the axial force. One type was suspended with a clamped-free (C-F) beam and the other one was suspended with a clamped-clamped (C-C) beam. Their drive modes are the bending of the slanted beam, and their sense modes are the torsion of the slanted beam. The relationships between the resonant frequencies of the two types were developed. The prototypes were packaged by vacuum under 0.1 mbar and an analytical solution for the axial force effect on the resonant frequency was obtained. The temperature dependent performances of the operated mode responses of the micromachined gyroscopes were measured. The experimental values of the temperature coefficients of resonant frequencies (TCF) due to axial force were 101.5 ppm/°C for the drive mode and 21.6 ppm/°C for the sense mode. The axial force has a great influence on the modal frequency of the micromachined gyroscopes suspended with a C-C beam, especially for the flexure mode. The quality factors of the operated modes decreased with increasing temperature, and changed drastically when the micromachined gyroscopes worked at higher temperatures. PMID:22346578

A rapid communication from the AAPM Task Group 201: recommendations for the QA of external beam radiotherapy data transfer. AAPM TG 201: quality assurance of external beam radiotherapy data transfer.

PubMed

Siochi, R Alfredo; Balter, Peter; Bloch, Charles D; Santanam, Lakshmi; Blodgett, Kurt; Curran, Bruce H; Engelsman, Martijn; Feng, Wenzheng; Mechalakos, Jim; Pavord, Dan; Simon, Tom; Sutlieff, Steven; Zhu, X Ronald

2010-12-04

The transfer of radiation therapy data among the various subsystems required for external beam treatments is subject to error. Hence, the establishment and management of a data transfer quality assurance program is strongly recommended. It should cover the QA of data transfers of patient specific treatments, imaging data, manually handled data and historical treatment records. QA of the database state (logical consistency and information integrity) is also addressed to ensure that accurate data are transferred.

SU-E-T-410: Evaluation of Treatment Modalities for Stereotactic Lung Radiation Therapy: A Phantom Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohatt, D; Malhotra, H

Purpose: To evaluate and verify the accuracy of alternative treatment modalities for stereotactic lung therapy with end-to-end testing. We compared three dimensional conformal therapy (3DCRT), dynamic conformal arc therapy (DCAT), intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) treatment using 6 MV, 6 MV flattening filter free (FFF) and 10 MV FFF photons. Methods: A QUASAR respiratory motion phantom was utilized with custom ion chamber and gafchromatic EBT2 film inserts. The phantom contained a low density lung medium with a cylindrical polystyrene tumor (35 cc). Pseudo representative structures for various organs at risk (OAR) were created. Allmore » treatment plans were created using Eclipse ver. 11 using the same image and structure sets, and delivered via Varian TrueBeam STx linear accelerator equipped with high definition MLC. Evaluation of plan quality followed ROTG 0813 criterion for conformity index (CI100%), high dose spillage, D2cm, and R50%. Results: All treatment plans met the OAR dose constraints per protocol and could be delivered without any beam hold offs or other interlocks and hence were deemed clinically safe. For equivalent beam energies, target conformity was improved for all modalities when switching to FFF mode. Treatment efficiency increased for VMAT FFF by a factor of 3–4 over IMRT, and up to factor of 7 when compared to 3DCRT. Pass rates were > 97% for all treatment using gamma criteria of 3%, 3mm. Absolute dose at iso-center was verified with ion chamber, and found to be within 2% of the treatment planning system. Conclusion: The higher dose rate associated with FFF not only reduces delivery times, but in most cases enhances plan quality. The one modality with succeeding best results for all RTOG criterions was VMAT 6 MV FFF. This end-to-end testing provides necessary confidence in the entire dose delivery chain for lung SBRT patients.« less

First and Second Order Stokes Generation by SRS in Methane: Influence of Rep-Rate, Beam Quality and Astigmatism (Opwekking van Eerste en Tweede Orde Stokes d.m.v. SRS in Methaan: Invloed van de Pulsfrequentie, de Bundelkwaliteit en Astigmatisme)

DTIC Science & Technology

1992-09-01

omzettings rendementen van circa 75% gehaad bij een ingangs- energie van 280 mJ. De mogelijkheden tot bet halen van een hoger rendement lijken...of rep-rate, beam quality and astigmatism DImi-Thu-B~mO ITA1EiM-tT-h lF I~~ ~~’ IAPR2 8 1993~ I ~Xtbai Uiitdw FJ.M. van Putten J.C. van den Heuvel RJ.L...Influence of rep-rate. beam quality and astigmatism author(s) : F.J.M. van Putten, I.C. van den Heuvel, R.J.L. Lerou institute : TNO Physics and

An experimental study of recombination and polarity effect in a set of customized plane parallel ionization chambers.

PubMed

Kron, T; McNiven, A; Witruk, B; Kenny, M; Battista, J

2006-12-01

Plane parallel ionization chambers are an important tool for dosimetry and absolute calibration of electron beams used for radiotherapy. Most dosimetric protocols require corrections for recombination and polarity effects, which are to be determined experimentally as they depend on chamber design and radiation quality. Both effects were investigated in electron beams from a linear accelerator (Varian 21CD) for a set of four tissue equivalent plane parallel ionization chambers customized for the present research by Standard Imaging (Madison WI). All four chambers share the same design and air cavity dimensions, differing only in the diameter of their collecting electrode and the corresponding width of the guard ring. The diameters of the collecting electrodes were 2 mm, 4 mm, 10 mm and 20 mm. Measurements were taken using electron beams of nominal energy 6 to 20 MeV in a 10 cm x 10 cm field size with a SSD of 100 cm at various depths in a Solid Water slab phantom. No significant variation of recombination effect was found with radiation quality, depth of measurement or chamber design. However, the polarity effect exceeded 5% for the chambers with small collecting electrode for an effective electron energy below 4 MeV at the point of measurement. The magnitude of the effect increased with decreasing electron energy in the phantom. The polarity correction factor calculated following AAPM protocol TG51 ranged from approximately 1.00 for the 20.0 mm chamber to less than 0.95 for the 2 mm chamber at 4.1 cm depth in a electron beam of nominally 12 MeV. By inverting the chamber it could be shown that the polarity effect did not depend on the polarity of the electrode first traversed by the electron beam. Similarly, the introduction of an air gap between the overlying phantom layer and the chambers demonstrated that the angular distribution of the electrons at the point of measurement had a lesser effect on the polarity correction than the electron energy itself. The magnitude of the absolute difference between charge collected at positive and negative polarity was found to correlate with the area of the collecting electrode which is consistent with the explanation that differences in thickness of the collecting electrodes and the number of electrons stopped in them contribute significantly to the polarity effect. Overall, the polarity effects found in the present study would have a negligible effect on electron beam calibration at a measurement depth recommended by most calibration protocols. However, the present work tested the corrections under extreme conditions thereby aiming at greater understanding of the mechanism underlying the correction factors for these chambers. This may lead to better chamber design for absolute dosimetry and electron beam characterization with less reliance on empirical corrections.

Dosimetric commissioning and quality assurance of scanned ion beams at the Italian National Center for Oncological Hadrontherapy.

PubMed

Mirandola, Alfredo; Molinelli, S; Vilches Freixas, G; Mairani, A; Gallio, E; Panizza, D; Russo, S; Ciocca, M; Donetti, M; Magro, G; Giordanengo, S; Orecchia, R

2015-09-01

To describe the dosimetric commissioning and quality assurance (QA) of the actively scanned proton and carbon ion beams at the Italian National Center for Oncological Hadrontherapy. The laterally integrated depth-dose-distributions (IDDs) were acquired with the PTW Peakfinder, a variable depth water column, equipped with two Bragg peak ionization chambers. fluka Monte Carlo code was used to generate the energy libraries, the IDDs in water, and the fragment spectra for carbon beams. EBT3 films were used for spot size measurements, beam position over the scan field, and homogeneity in 2D-fields. Beam monitor calibration was performed in terms of number of particles per monitor unit using both a Farmer-type and an Advanced Markus ionization chamber. The beam position at the isocenter, beam monitor calibration curve, dose constancy in the center of the spread-out-Bragg-peak, dose homogeneity in 2D-fields, beam energy, spot size, and spot position over the scan field are all checked on a daily basis for both protons and carbon ions and on all beam lines. The simulated IDDs showed an excellent agreement with the measured experimental curves. The measured full width at half maximum (FWHM) of the pencil beam in air at the isocenter was energy-dependent for both particle species: in particular, for protons, the spot size ranged from 0.7 to 2.2 cm. For carbon ions, two sets of spot size are available: FWHM ranged from 0.4 to 0.8 cm (for the smaller spot size) and from 0.8 to 1.1 cm (for the larger one). The spot position was accurate to within ± 1 mm over the whole 20 × 20 cm(2) scan field; homogeneity in a uniform squared field was within ± 5% for both particle types at any energy. QA results exceeding tolerance levels were rarely found. In the reporting period, the machine downtime was around 6%, of which 4.5% was due to planned maintenance shutdowns. After successful dosimetric beam commissioning, quality assurance measurements performed during a 24-month period show very stable beam characteristics, which are therefore suitable for performing safe and accurate patient treatments.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hussain, A

Purpose: Novel linac machines, TrueBeam (TB) and Elekta Versa have updated head designing and software control system, include flattening-filter-free (FFF) photon and electron beams. Later on FFF beams were also introduced on C-Series machines. In this work FFF beams for same energy 6MV but from different machine versions were studied with reference to beam data parameters. Methods: The 6MV-FFF percent depth doses, profile symmetry and flatness, dose rate tables, and multi-leaf collimator (MLC) transmission factors were measured during commissioning process of both C-series and Truebeam machines. The scanning and dosimetric data for 6MV-FFF beam from Truebeam and C-Series linacs wasmore » compared. A correlation of 6MV-FFF beam from Elekta Versa with that of Varian linacs was also found. Results: The scanning files were plotted for both qualitative and quantitative analysis. The dosimetric leaf gap (DLG) for C-Series 6MV-FFF beam is 1.1 mm. Published values for Truebeam dosimetric leaf gap is 1.16 mm. 6MV MLC transmission factor varies between 1.3 % and 1.4 % in two separate measurements and measured DLG values vary between 1.32 mm and 1.33 mm on C-Series machine. MLC transmission factor from C-Series machine varies between 1.5 % and 1.6 %. Some of the measured data values from C-Series FFF beam are compared with Truebeam representative data. 6MV-FFF beam parameter values like dmax, OP factors, beam symmetry and flatness and additional parameters for C-Series and Truebeam liancs will be presented and compared in graphical form and tabular data form if selected. Conclusion: The 6MV flattening filter (FF) beam data from C-Series & Truebeam and 6MV-FFF beam data from Truebeam has already presented. This particular analysis to compare 6MV-FFF beam from C-Series and Truebeam provides opportunity to better elaborate FFF mode on novel machines. It was found that C-Series and Truebeam 6MV-FFF dosimetric and beam data was quite similar.« less

2000W high beam quality diode laser for direct materials processing

NASA Astrophysics Data System (ADS)

Qin, Wen-bin; Liu, You-qiang; Cao, Yin-hua; Gao, Jing; Pan, Fei; Wang, Zhi-yong

2011-11-01

This article describes high beam quality and kilowatt-class diode laser system for direct materials processing, using optical design software ZEMAX® to simulate the diode laser optical path, including the beam shaping, collimation, coupling, focus, etc.. In the experiment, the diode laser stack of 808nm and the diode laser stack of 915nm were used for the wavelength coupling, which were built vertical stacks up to 16 bars. The threshold current of the stack is 6.4A, the operating current is 85A and the output power is 1280W. Through experiments, after collimating the diode laser beam with micro-lenses, the fast axis BPP of the stack is less than 60mm.mrad, and the slow-axis BPP of the stack is less than 75mm.mrad. After shaping the laser beam and improving the beam quality, the fast axis BPP of the stack is still 60mm.mrad, and the slow-axis BPP of the stack is less than 19mm.mrad. After wavelength coupling and focusing, ultimately the power of 2150W was obtained, focal spot size of 1.5mm * 1.2mm with focal length 300mm. The laser power density is 1.2×105W/cm2, and that can be used for metal remelting, alloying, cladding and welding. The total optical coupling conversion efficiency is 84%, and the total electrical - optical conversion efficiency is 50%.

Beam shaping optics to enhance performance of interferometry techniques in grating manufacture

NASA Astrophysics Data System (ADS)

Laskin, Alexander; Laskin, Vadim; Ostrun, Aleksei

2018-02-01

Improving of industrial holographic and interferometry techniques is of great importance in interference lithography, computer-generated holography, holographic data storage, interferometry recording of Bragg gratings as well as gratings of various types in semiconductor industry. Performance of mentioned techniques is essentially enhanced by providing a light beam with flat phase front and flat-top irradiance distribution. Therefore, transformation of Gaussian distribution of a TEM00 laser to flat-top (top hat, uniform) distribution is an important optical task. There are different refractive and diffractive beam shaping approaches used in laser industrial and scientific applications, but only few of them are capable to fulfil the optimum conditions for beam quality demanding holography and interferometry. As a solution it is suggested to apply refractive field mapping beam shaping optics πShaper, which operational principle presumes almost lossless transformation of Gaussian to flat-top beam with flatness of output wavefront, conserving of beam consistency, providing collimated low divergent output beam, high transmittance, extended depth of field, negligible wave aberration, and achromatic design provides capability to work with several lasers with different wavelengths simultaneously. High optical quality of resulting flat-top beam allows applying additional optical components to build various imaging optical systems for variation of beam size and shape to fulfil requirements of a particular application. This paper will describe design basics of refractive beam shapers and optical layouts of their applying in holography and laser interference lithography. Examples of real implementations and experimental results will be presented as well.

SU-E-T-586: Field Size Dependence of Output Factor for Uniform Scanning Proton Beams: A Comparison of TPS Calculation, Measurement and Monte Carlo Simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Y; Singh, H; Islam, M

2014-06-01

Purpose: Output dependence on field size for uniform scanning beams, and the accuracy of treatment planning system (TPS) calculation are not well studied. The purpose of this work is to investigate the dependence of output on field size for uniform scanning beams and compare it among TPS calculation, measurements and Monte Carlo simulations. Methods: Field size dependence was studied using various field sizes between 2.5 cm diameter to 10 cm diameter. The field size factor was studied for a number of proton range and modulation combinations based on output at the center of spread out Bragg peak normalized to amore » 10 cm diameter field. Three methods were used and compared in this study: 1) TPS calculation, 2) ionization chamber measurement, and 3) Monte Carlos simulation. The XiO TPS (Electa, St. Louis) was used to calculate the output factor using a pencil beam algorithm; a pinpoint ionization chamber was used for measurements; and the Fluka code was used for Monte Carlo simulations. Results: The field size factor varied with proton beam parameters, such as range, modulation, and calibration depth, and could decrease over 10% from a 10 cm to 3 cm diameter field for a large range proton beam. The XiO TPS predicted the field size factor relatively well at large field size, but could differ from measurements by 5% or more for small field and large range beams. Monte Carlo simulations predicted the field size factor within 1.5% of measurements. Conclusion: Output factor can vary largely with field size, and needs to be accounted for accurate proton beam delivery. This is especially important for small field beams such as in stereotactic proton therapy, where the field size dependence is large and TPS calculation is inaccurate. Measurements or Monte Carlo simulations are recommended for output determination for such cases.« less

Electron Beam/Optical Hybrid Lithography For The Production Of Gallium Arsenide Monolithic Microwave Integrated Circuits (Mimics)

NASA Astrophysics Data System (ADS)

Nagarajan, Rao M.; Rask, Steven D.

1988-06-01

A hybrid lithography technique is described in which selected levels are fabricated by high resolution direct write electron beam lithography and all other levels are fabricated optically. This technique permits subhalf micron geometries and the site-by-site alignment for each field written by electron beam lithography while still maintaining the high throughput possible with optical lithography. The goal is to improve throughput and reduce overall cost of fabricating MIMIC GaAS chips without compromising device performance. The lithography equipment used for these experiments is the Cambridge Electron beam vector scan system EBMF 6.4 capable of achieving ultra high current densities with a beam of circular cross section and a gaussian intensity profile operated at 20 kev. The optical aligner is a Karl Suss Contact aligner. The flexibility of the Cambridge electron beam system is matched to the less flexible Karl Suss contact aligner. The lithography related factors, such as image placement, exposure and process related analyses, which influence overlay, pattern quality and performance, are discussed. A process chip containing 3.2768mm fields in an eleven by eleven array was used for alignment evaluation on a 3" semi-insulating GaAS wafer. Each test chip contained five optical verniers and four Prometrix registration marks per field along with metal bumps for alignment marks. The process parameters for these chips are identical to those of HEMT/epi-MESFET ohmic contact and gate layer processes. These layers were used to evaluate the overlay accuracy because of their critical alignment and dimensional control requirements. Two cases were examined: (1) Electron beam written gate layers aligned to optically imaged ohmic contact layers and (2) Electron beam written gate layers aligned to electron beam written ohmic contact layers. The effect of substrate charging by the electron beam is also investigated. The resulting peak overlay error accuracies are: (1) Electron beam to optical with t 0.2μm (2 sigma) and (2) Electron beam to electron beam with f 0.lμm (2 sigma). These results suggest that the electron beam/optical hybrid lithography techniques could be used for MIMIC volume production as alignment tolerances required by GaAS chips are met in both cases. These results are discussed in detail.

Towards the clinical implementation of iterative low-dose cone-beam CT reconstruction in image-guided radiation therapy: Cone/ring artifact correction and multiple GPU implementation

PubMed Central

Yan, Hao; Wang, Xiaoyu; Shi, Feng; Bai, Ti; Folkerts, Michael; Cervino, Laura; Jiang, Steve B.; Jia, Xun

2014-01-01

Purpose: Compressed sensing (CS)-based iterative reconstruction (IR) techniques are able to reconstruct cone-beam CT (CBCT) images from undersampled noisy data, allowing for imaging dose reduction. However, there are a few practical concerns preventing the clinical implementation of these techniques. On the image quality side, data truncation along the superior–inferior direction under the cone-beam geometry produces severe cone artifacts in the reconstructed images. Ring artifacts are also seen in the half-fan scan mode. On the reconstruction efficiency side, the long computation time hinders clinical use in image-guided radiation therapy (IGRT). Methods: Image quality improvement methods are proposed to mitigate the cone and ring image artifacts in IR. The basic idea is to use weighting factors in the IR data fidelity term to improve projection data consistency with the reconstructed volume. In order to improve the computational efficiency, a multiple graphics processing units (GPUs)-based CS-IR system was developed. The parallelization scheme, detailed analyses of computation time at each step, their relationship with image resolution, and the acceleration factors were studied. The whole system was evaluated in various phantom and patient cases. Results: Ring artifacts can be mitigated by properly designing a weighting factor as a function of the spatial location on the detector. As for the cone artifact, without applying a correction method, it contaminated 13 out of 80 slices in a head-neck case (full-fan). Contamination was even more severe in a pelvis case under half-fan mode, where 36 out of 80 slices were affected, leading to poorer soft tissue delineation and reduced superior–inferior coverage. The proposed method effectively corrects those contaminated slices with mean intensity differences compared to FDK results decreasing from ∼497 and ∼293 HU to ∼39 and ∼27 HU for the full-fan and half-fan cases, respectively. In terms of efficiency boost, an overall 3.1 × speedup factor has been achieved with four GPU cards compared to a single GPU-based reconstruction. The total computation time is ∼30 s for typical clinical cases. Conclusions: The authors have developed a low-dose CBCT IR system for IGRT. By incorporating data consistency-based weighting factors in the IR model, cone/ring artifacts can be mitigated. A boost in computational efficiency is achieved by multi-GPU implementation. PMID:25370645

Towards the clinical implementation of iterative low-dose cone-beam CT reconstruction in image-guided radiation therapy: Cone/ring artifact correction and multiple GPU implementation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Hao, E-mail: steve.jiang@utsouthwestern.edu, E-mail: xun.jia@utsouthwestern.edu; Shi, Feng; Jiang, Steve B.

Purpose: Compressed sensing (CS)-based iterative reconstruction (IR) techniques are able to reconstruct cone-beam CT (CBCT) images from undersampled noisy data, allowing for imaging dose reduction. However, there are a few practical concerns preventing the clinical implementation of these techniques. On the image quality side, data truncation along the superior–inferior direction under the cone-beam geometry produces severe cone artifacts in the reconstructed images. Ring artifacts are also seen in the half-fan scan mode. On the reconstruction efficiency side, the long computation time hinders clinical use in image-guided radiation therapy (IGRT). Methods: Image quality improvement methods are proposed to mitigate the conemore » and ring image artifacts in IR. The basic idea is to use weighting factors in the IR data fidelity term to improve projection data consistency with the reconstructed volume. In order to improve the computational efficiency, a multiple graphics processing units (GPUs)-based CS-IR system was developed. The parallelization scheme, detailed analyses of computation time at each step, their relationship with image resolution, and the acceleration factors were studied. The whole system was evaluated in various phantom and patient cases. Results: Ring artifacts can be mitigated by properly designing a weighting factor as a function of the spatial location on the detector. As for the cone artifact, without applying a correction method, it contaminated 13 out of 80 slices in a head-neck case (full-fan). Contamination was even more severe in a pelvis case under half-fan mode, where 36 out of 80 slices were affected, leading to poorer soft tissue delineation and reduced superior–inferior coverage. The proposed method effectively corrects those contaminated slices with mean intensity differences compared to FDK results decreasing from ∼497 and ∼293 HU to ∼39 and ∼27 HU for the full-fan and half-fan cases, respectively. In terms of efficiency boost, an overall 3.1 × speedup factor has been achieved with four GPU cards compared to a single GPU-based reconstruction. The total computation time is ∼30 s for typical clinical cases. Conclusions: The authors have developed a low-dose CBCT IR system for IGRT. By incorporating data consistency-based weighting factors in the IR model, cone/ring artifacts can be mitigated. A boost in computational efficiency is achieved by multi-GPU implementation.« less

Free Electron Laser Analysis For the Innovative Navy Prototype

DTIC Science & Technology

2008-03-01

important measure of electron beam quality is transverse emittance, which is the product of the RMS width and the angular spread of the beam, as measured...respect to s . This is possible because the electron’s position in s is uniquely defined for any given time by s = vst ≈ ct , therefore d 2 dt 2...Longitudinal emittance (keV ps) 70 dgog Beam energy spread (%) 0.37 dthetax Beam angular spread, x rms (mrad) 0.17 dthetay Beam angular spread, y rms (mrad

In silico carbon molecular beam epitaxial growth of graphene on the h-BN substrate: carbon source effect on van der Waals epitaxy

NASA Astrophysics Data System (ADS)

Lee, Jonghoon; Varshney, Vikas; Park, Jeongho; Farmer, Barry L.; Roy, Ajit K.

2016-05-01

Against the presumption that hexagonal boron-nitride (h-BN) should provide an ideal substrate for van der Waals (vdW) epitaxy to grow high quality graphene films, carbon molecular beam epitaxy (CMBE) techniques using solid carbon sublimation have reported relatively poor quality of the graphene. In this article, the CMBE growth of graphene on the h-BN substrate is numerically studied in order to identify the effect of the carbon source on the quality of the graphene film. The carbon molecular beam generated by the sublimation of solid carbon source materials such as graphite and glassy carbon is mostly composed of atomic carbon, carbon dimers and carbon trimers. Therefore, the graphene film growth becomes a complex process involving various deposition characteristics of a multitude of carbon entities. Based on the study of surface adsorption and film growth characteristics of these three major carbon entities comprising graphite vapour, we report that carbon trimers convey strong traits of vdW epitaxy prone to high quality graphene growth, while atomic carbon deposition is a surface-reaction limited process accompanied by strong chemisorption. The vdW epitaxial behaviour of carbon trimers is found to be substantial enough to nucleate and develop into graphene like planar films within a nanosecond of high flux growth simulation, while reactive atomic carbons tend to impair the structural integrity of the crystalline h-BN substrate upon deposition to form an amorphous interface between the substrate and the growing carbon film. The content of reactive atomic carbons in the molecular beam is suspected to be the primary cause of low quality graphene reported in the literature. A possible optimization of the molecular beam composition towards the synthesis of better quality graphene films is suggested.Against the presumption that hexagonal boron-nitride (h-BN) should provide an ideal substrate for van der Waals (vdW) epitaxy to grow high quality graphene films, carbon molecular beam epitaxy (CMBE) techniques using solid carbon sublimation have reported relatively poor quality of the graphene. In this article, the CMBE growth of graphene on the h-BN substrate is numerically studied in order to identify the effect of the carbon source on the quality of the graphene film. The carbon molecular beam generated by the sublimation of solid carbon source materials such as graphite and glassy carbon is mostly composed of atomic carbon, carbon dimers and carbon trimers. Therefore, the graphene film growth becomes a complex process involving various deposition characteristics of a multitude of carbon entities. Based on the study of surface adsorption and film growth characteristics of these three major carbon entities comprising graphite vapour, we report that carbon trimers convey strong traits of vdW epitaxy prone to high quality graphene growth, while atomic carbon deposition is a surface-reaction limited process accompanied by strong chemisorption. The vdW epitaxial behaviour of carbon trimers is found to be substantial enough to nucleate and develop into graphene like planar films within a nanosecond of high flux growth simulation, while reactive atomic carbons tend to impair the structural integrity of the crystalline h-BN substrate upon deposition to form an amorphous interface between the substrate and the growing carbon film. The content of reactive atomic carbons in the molecular beam is suspected to be the primary cause of low quality graphene reported in the literature. A possible optimization of the molecular beam composition towards the synthesis of better quality graphene films is suggested. Electronic supplementary information (ESI) available: Three movie files: 3mer-physorption.mpg and 3mer-chemisorption.mpg feature examples of the adsorption state sampling of a carbon trimer on the heated h-BN substrate as mentioned in the ``Single Molecule Adsorption Study'' section. In 3mer-film-growth.mpg, an instance of honey comb formation during the initial phase of graphene growth simulation using a carbon trimer beam is captured. An initially sp hybridized carbon atom (red colored) becomes sp2 hybridized as a result of additional covalent bonding with the impinging carbon trimer. As the bond angle around the red carbon changes from 180 degree (sp) to 120 degree (sp2), nearby carbon atoms enclose to form a hexagon structure composed of 6 carbon atoms. See DOI: 10.1039/c6nr01396a

M2-factor of coherent and partially coherent dark hollow beams propagating in turbulent atmosphere.

PubMed

Yuan, Yangsheng; Cai, Yangjian; Qu, Jun; Eyyuboğlu, Halil T; Baykal, Yahya; Korotkova, Olga

2009-09-28

Analytical formula is derived for the M(2)-factor of coherent and partially coherent dark hollow beams (DHB) in turbulent atmosphere based on the extended Huygens-Fresnel integral and the second-order moments of the Wigner distribution function. Our numerical results show that the M(2)- factor of a DHB in turbulent atmosphere increases on propagation, which is much different from its invariant properties in free-space, and is mainly determined by the parameters of the beam and the atmosphere. The relative M(2)-factor of a DHB increases slower than that of Gaussian and flat-topped beams on propagation, which means a DHB is less affected by the atmospheric turbulence than Gaussian and flat-topped beams. Furthermore, the relative M(2)-factor of a DHB with lower coherence, longer wavelength and larger dark size is less affected by the atmospheric turbulence. Our results will be useful in long-distance free-space optical communications.

Propagation characteristics of partially coherent anomalous elliptical hollow Gaussian beam propagating through atmospheric turbulence along a slant path

NASA Astrophysics Data System (ADS)

Tian, Huanhuan; Xu, Yonggen; Yang, Ting; Ma, Zairu; Wang, Shijian; Dan, Youquan

2017-02-01

Based on the extended Huygens-Fresnel principal and the Wigner distribution function, the root mean square (rms) angular width and propagation factor (M2-factor) of partially coherent anomalous elliptical hollow Gaussian (PCAEHG) beam propagating through atmospheric turbulence along a slant path are studied in detail. Analytical formulae of the rms angular width and M2-factor of PCAEHG beam are derived. Our results show that the rms angular width increases with increasing of wavelength and zenith angle and with decreasing of transverse coherence length, beam waist sizes and inner scale. The M2-factor increases with increasing of zenith angle and with decreasing of wavelength, transverse coherence length, beam waist sizes and inner scale. The saturation propagation distances (SPDs) increase as zenith angle increases. The numerical calculations also indicate that the SPDs of rms angular width and M2-factor for uplink slant paths with zenith angle of π/12 are about 0.2 and 20 km, respectively.

Development of chip passivated monolithic complementary MISFET circuits with beam leads

NASA Technical Reports Server (NTRS)

Ragonese, L. J.; Kim, M. J.; Corrie, B. L.; Brouillette, J. W.; Warr, R. E.

1972-01-01

The results are presented of a program to demonstrate the processes for fabricating complementary MISFET beam-leaded circuits, which, potentially, are comparable in quality to available bipolar beam-lead chips that use silicon nitride passivation in conjunction with a platinum-titanium-gold metal system. Materials and techniques, different from the bipolar case, were used in order to be more compatible with the special requirements of fully passivated complementary MISFET devices. Two types of circuits were designed and fabricated, a D-flip-flop and a three-input NOR/NAND gate. Fifty beam-leaded chips of each type were constructed. A quality and reliability assurance program was performed to identify failure mechanisms. Sample tests and inspections (including destructive) were developed to measure the physical characteristics of the circuits.

Cluster Beam Studies.

DTIC Science & Technology

1988-04-01

Continue on reverse if necessary and identify by block number) Cluster beams offer a means of depositing high-quality thin films at low...either directly inclustered vapors of nonvolatile materials or Indirectly by bombarding the film duringdeposition with clusters of inert gases. When a...electron volt energy per atom. The suprathermal energy of thej depositing atoms is thought to produce unique thin films (either in quality, or in the ability

Comparing four volumetric modulated arc therapy beam arrangements for the treatment of early-stage prostate cancer

PubMed Central

Elith, Craig A; Dempsey, Shane E; Warren-Forward, Helen M

2014-01-01

Introduction This study compared four different volumetric modulated arc therapy (VMAT) beam arrangements for the treatment of early-stage prostate cancer examining plan quality and the impact on a radiotherapy department's resources. Methods Twenty prostate cases were retrospectively planned using four VMAT beam arrangements (1) a partial arc (PA), (2) one arc (1A), (3) one arc plus a partial arc (1A + PA) and (4) two arcs (2A). The quality of the dose distributions generated were compared by examining the overall plan quality, the homogeneity and conformity to the planning target volume (PTV), the number of monitor units and the dose delivered to the organs at risk. Departmental resources were considered by recording the planning time and beam delivery time. Results Each technique produced a plan of similar quality that was considered adequate for treatment; though some differences were noted. The 1A, 1A + PA and 2A plans demonstrated a better conformity to the PTV which correlated to improved sparing of the rectum in the 60–70 Gy range for the 1A + PA and 2A techniques. The time needed to generate the plans was different for each technique ranging from 13.1 min for 1A + PA to 17.8 min for 1A. The PA beam delivery time was fastest with a mean time of 0.9 min. Beam-on times then increased with an increase in the number of arcs up to an average of 2.2 min for the 2A technique. Conclusion Which VMAT technique is best suited for clinical implementation for the treatment of prostate cancer may be dictated by the individual patient and the availability of departmental resources. PMID:26229643

Odontological light-emitting diode light-curing unit beam quality.

PubMed

de Magalhães Filho, Thales Ribeiro; Weig, Karin de Mello; Werneck, Marcelo Martins; da Costa Neto, Célio Albano; da Costa, Marysilvia Ferreira

2015-05-01

The distribution of light intensity of three light-curing units (LCUs) to cure the resin-based composite for dental fillings was analyzed, and a homogeneity index [flat-top factor (FTF)] was calculated. The index is based on the M2 index, which is used for laser beams. An optical spectrum analyzer was used with an optical fiber to produce an x-y power profile of each LCU light guide. The FTF-calculated values were 0.51 for LCU1 and 0.55 for LCU2, which was the best FTF, although it still differed greatly from the perfect FTF = 1, and 0.27 for LCU3, which was the poorest value and even lower than the Gaussian FTF = 0.5. All LCUs presented notably heterogeneous light distribution, which can lead professionals and researchers to produce samples with irregular polymerization and poor mechanical properties.

25  W/m² collection efficiency solar-pumped Nd:YAG laser by a heliostat-parabolic mirror system.

PubMed

Liang, D; Almeida, J; Vistas, C R

2016-09-20

A large aspheric fused silica lens was used to couple efficiently the concentrated solar radiation from the focal zone of a 1.5-m-diameter primary concentrator into a 4-mm-diameter, 35-mm-long Nd:YAG single-crystal rod within a conical pump cavity. Continuous-wave laser power of 29.3 W was measured, attaining 25.0  W/m² solar laser collection efficiency, corresponding to a 19% increase over the previous record. Its laser beam figure of merit-the ratio between laser power and the product of Mx2, My2 beam quality factors-of 0.01 W is 1.6 times higher than that of a direct tracking solar laser with 30  W/m² collection efficiency. A strong dependency of solar laser power on laser resonator cavity length was found.

Odontological light-emitting diode light-curing unit beam quality

NASA Astrophysics Data System (ADS)

de Magalhães Filho, Thales Ribeiro; Weig, Karin de Mello; Werneck, Marcelo Martins; da Costa Neto, Célio Albano; da Costa, Marysilvia Ferreira

2015-05-01

The distribution of light intensity of three light-curing units (LCUs) to cure the resin-based composite for dental fillings was analyzed, and a homogeneity index [flat-top factor (FTF)] was calculated. The index is based on the M2 index, which is used for laser beams. An optical spectrum analyzer was used with an optical fiber to produce an x-y power profile of each LCU light guide. The FTF-calculated values were 0.51 for LCU1 and 0.55 for LCU2, which was the best FTF, although it still differed greatly from the perfect FTF=1, and 0.27 for LCU3, which was the poorest value and even lower than the Gaussian FTF=0.5. All LCUs presented notably heterogeneous light distribution, which can lead professionals and researchers to produce samples with irregular polymerization and poor mechanical properties.

Design and test of SX-FEL cavity BPM

NASA Astrophysics Data System (ADS)

Yuan, Ren-Xian; Zhou, Wei-Min; Chen, Zhi-Chu; Yu, Lu-Yang; Wang, Bao-Pen; Leng, Yong-Bin

2013-11-01

This paper reports the design and cold test of the cavity beam position monitor (CBPM) for SX-FEL to fulfill the requirement of beam position measurement resolution of less than 1 μm, even 0.1 μm. The CBPM was optimized by using a coupling slot to damp the TM010 mode in the output signal. The isolation of TM010 mode is about 117 dB, and the shunt impedance is about 200 Ω@4.65 GHz with the quality factor 80 from MAFIA simulation and test result. A special antenna was designed to load power for reducing excitation of other modes in the cavity. The resulting output power of TM110 mode was about 90 mV/mm when the source was 6 dBm, and the accomplishable minimum voltage was about 200 μV. The resolution of the CBPM was about 0.1 μm from the linear fitting result based on the cold test.

Journal of Air Transportation, Volume 8, No. 2. Volume 8, No. 2

NASA Technical Reports Server (NTRS)

Bowen, Brent (Editor); Kabashkin, Igor (Editor); Nickerson, Jocelyn (Editor)

2003-01-01

The mission of the Journal of Air Transportation (JAT) is to provide the global community immediate key resource information in all areas of air transportation. This journal contains articles on the following:Fuel Consumption Modeling of a Transport Category Aircraft: A FlightOperationsQualityAssurance (F0QA) Analysis;Demand for Air Travel in the United States: Bottom-Up Econometric Estimation and Implications for Forecasts by Origin and Destination Pairs;Blind Flying on the Beam: Aeronautical Communication, Navigation and Surveillance: Its Origins and the Politics of Technology: Part I1 Political Oversight and Promotion;Blind Flying on the Beam: Aeronautical Communication, Navigation and Surveillance: Its Origins and the Politics of Technology: Part 111: Emerging Technologies;Ethics Education in University Aviation Management Programs in the US: Part Two B-Statistical Analysis of Current Practice;Integrating Human Factors into the Human-computer Interface: and How Best to Display Meteorological Information for Critical Aviation Decision-making and Performance.

Characterization of a synthetic single crystal diamond detector for dosimetry in spatially fractionated synchrotron x-ray fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Livingstone, Jayde, E-mail: Jayde.Livingstone@sync

Purpose: Modern radiotherapy modalities often use small or nonstandard fields to ensure highly localized and precise dose delivery, challenging conventional clinical dosimetry protocols. The emergence of preclinical spatially fractionated synchrotron radiotherapies with high dose-rate, sub-millimetric parallel kilovoltage x-ray beams, has pushed clinical dosimetry to its limit. A commercially available synthetic single crystal diamond detector designed for small field dosimetry has been characterized to assess its potential as a dosimeter for synchrotron microbeam and minibeam radiotherapy. Methods: Experiments were carried out using a synthetic diamond detector on the imaging and medical beamline (IMBL) at the Australian Synchrotron. The energy dependence ofmore » the detector was characterized by cross-referencing with a calibrated ionization chamber in monoenergetic beams in the energy range 30–120 keV. The dose-rate dependence was measured in the range 1–700 Gy/s. Dosimetric quantities were measured in filtered white beams, with a weighted mean energy of 95 keV, in broadbeam and spatially fractionated geometries, and compared to reference dosimeters. Results: The detector exhibits an energy dependence; however, beam quality correction factors (k{sub Q}) have been measured for energies in the range 30–120 keV. The k{sub Q} factor for the weighted mean energy of the IMBL radiotherapy spectrum, 95 keV, is 1.05 ± 0.09. The detector response is independent of dose-rate in the range 1–700 Gy/s. The percentage depth dose curves measured by the diamond detector were compared to ionization chambers and agreed to within 2%. Profile measurements of microbeam and minibeam arrays were performed. The beams are well resolved and the full width at halfmaximum agrees with the nominal width of the beams. The peak to valley dose ratio (PVDR) calculated from the profiles at various depths in water agrees within experimental error with PVDR calculations from Gafchromic film data. Conclusions: The synthetic diamond detector is now well characterized and will be used to develop an experimental dosimetry protocol for spatially fractionated synchrotron radiotherapy.« less

Effect of comfort pads and incubator design on neonatal radiography.

PubMed

Jiang, Xia; Baad, Michael; Reiser, Ingrid; Feinstein, Kate A; Lu, Zhengfeng

2016-01-01

There has been increasing interest in patient dose reduction in neonatal intensive care units. Removing comfort pads for radiography has been identified as a potential means to decrease patient dose. To assess the effect of comfort pads and support trays on detector entrance exposure (DEE) and image quality for neonatal radiography, and its implication for patient dose. Comfort pads and support trays from three incubator and warmer systems were examined. The attenuation of the primary beam by these structures was measured using a narrow beam geometry. Their effect on DEE and image quality was then assessed using typical neonatal chest radiography techniques with three configurations: 1) both the comfort pad and support included in the beam, 2) only the support tray included and 3) both the comfort pad and support tray removed. Comfort pads and support trays were found to attenuate the primary beam by 6-15%. Eliminating these structures from the X-ray beam's path was found to increase the detector entrance exposure by 28-36% and increase contrast-to-noise ratio by more than 21%, suggesting room for patient dose reduction when the same image quality is maintained. Comfort pads and tray support devices can have a considerable effect on DEE and image quality, with large variations among different incubator designs. Positioning the image detector directly underneath neonatal patients for radiography is a potential means for patient dose reduction. However, such benefit should be weighed against the risks of moving the patient.

Diode-pumped solid state green laser for ophthalmologic application

NASA Astrophysics Data System (ADS)

Eno, Taizo; Goto, Yoshiaki; Momiuchi, Masayuki

2002-10-01

We have developed diode pumped solid state green laser suitable for ophthalmologic applications. Beam parameters were designed by considering the coagulation system. We have lowered the beam quality to multi transverse and longitudinal mode on purpose to improve the speckle noise of the slit lamp output beam. The beam profile shows homogeneous intensity and it is very useful for ophthalmologic application. End pumping and short cavity configuration made it possible.

Effect of electron beam cooling on transversal and longitudinal emittance of an external proton beam

NASA Astrophysics Data System (ADS)

Kilian, K.; Machner, H.; Magiera, A.; Prasuhn, D.; von Rossen, P.; Siudak, R.; Stein, H. J.; Stockhorst, H.

2018-02-01

Benefits of electron cooling to the quality of extracted ion beams from storage rings are discussed. The transversal emittances of an external proton beam with and without electron cooling at injection energy are measured with the GEM detector assembly. While the horizontal emittance remains the vertical emittance shrinks by the cooling process. The longitudinal momentum variance is also reduced by cooling.

The g factor of the 21+ state in 126Sn

NASA Astrophysics Data System (ADS)

Kumbartzki, G. J.; Benczer-Koller, N.; Torres, D. A.; Gürdal, G.; Gross, C. J.; Galindo-Uribarri, A.; Bingham, C.; Stone, N.; Stuchberry, A. E.; Speidel, K.-H.

2011-10-01

In the quest to develop the necessary tools and gather experience in using the transient field technique to measure g factors of low-lying short-lived nuclear states in radioactive beam experiments, the 126Sn (t1/2 = 2 . 3 .105 years) will be measured at the HRIBF, ORNL. Each radioactive beam experiment presents its own set of problems and challenges due to the radioactive background from the beam and beam contaminants and their life times, and the low beam intensity. This experiment is a test with a very long lived, nearly stable beam. The target is designed to stop the reaction products in the backing of the target but to allow the bulk of the beam to pass through and stop in a foil placed between the target and the particle detector. This foil can be changed in the course of the experiment, should it become too radioactive. The experiment is scheduled to run in July 2011. Success or failure will provide a wealth of information on working in different radioactive environments and will extend the spectroscopic information on g factors of 21+states in Sn isotopes. The transient field measurement will provide the sign of the g factor.

Microdosimetric intercomparison of BNCT beams at BNL and MIT.

PubMed

Burmeister, Jay; Riley, Kent; Coderre, Jeffrey A; Harling, Otto K; Ma, Ruimei; Wielopolski, Lucian; Kota, Chandrasekhar; Maughan, Richard L

2003-08-01

Microdosimetric measurements have been performed at the clinical beam intensities in two epithermal neutron beams, the Brookhaven Medical Research Reactor and the M67 beam at the Massachusetts Institute of Technology Research Reactor, which have been used to treat patients with Boron Neutron Capture Therapy (BNCT). These measurements offer an independent assessment of the dosimetry used at these two facilities, as well as provide information about the radiation quality not obtainable from conventional macrodosimetric techniques. Moreover, they provide a direct measurement of the absorbed dose resulting from the BNC reaction. BNC absorbed doses measured within this study are approximately 15% lower than those estimated using foil activation at both MIT and BNL. Finally, an intercomparison of the characteristics and radiation quality of these two clinical beams is presented. The techniques described here allow an accurate quantitative comparison of the physical absorbed dose as well as a measure of the biological effectiveness of the absorbed dose delivered by different epithermal beams. No statistically significant differences were observed in the predicted RBEs of these two beams. The methodology presented here can help to facilitate the effective sharing of clinical results in an effort to demonstrate the clinical utility of BNCT.

SU-D-209-02: Percent Depth Dose Curves for Fluoroscopic X-Ray Beam Qualities Incorporating Copper Filtration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wunderle, K; Wayne State University School of Medicine, Detroit, MI; Godley, A

Purpose: The purpose of this investigation was to quantify percent depth dose (PDD) curves for fluoroscopic x-ray beam qualities incorporating added copper filtration. Methods: A PTW (Freiburg, Germany) MP3 water tank was used with a Standard Imaging (Middleton, WI) Exradin Model 11 Spokas Chamber to measure PDD curves for 60, 80, 100 and 120 kVp x-ray beams with copper filtration ranging from 0.0–0.9 mm at 22cm and 42cm fields of view from 0 to 150 mm of water. A free-in-air monitor chamber was used to normalize the water tank data to fluctuations in output from the fluoroscope. The measurements weremore » acquired on a Siemens (Erlangen, Germany) Artis ZeeGo fluoroscope. The fluoroscope was inverted from the typical orientation providing an x-ray beam originating from above the water tank. The water tank was positioned so that the water level was located at 60cm from the focal spot; which also represents the focal spot to interventional reference plane distance for that fluoroscope. Results: PDDs for 60, 80, 100, and 120 kVp with 0 mm of copper filtration compared well to previously published data by Fetterly et al. [Med Phys, 28, 205 (2001)] for those beam qualities given differences in fluoroscopes, geometric orientation, type of ionization chamber, and the water tank used for data collection. PDDs for 60, 80, 100, and 120 kVp with copper filtration were obtained and are presented, which have not been previously investigated and published. Conclusion: The equipment and processes used to acquire the reported data were sound and compared well with previously published data for PDDs without copper filtration. PDD data for the fluoroscopic x-ray beams incorporating copper filtration can be used as reference data for estimating organ or soft tissue dose at depth involving similar beam qualities or for comparison with mathematical models.« less

Accurate Monte Carlo simulations for nozzle design, commissioning and quality assurance for a proton radiation therapy facility.

PubMed

Paganetti, H; Jiang, H; Lee, S Y; Kooy, H M

2004-07-01

Monte Carlo dosimetry calculations are essential methods in radiation therapy. To take full advantage of this tool, the beam delivery system has to be simulated in detail and the initial beam parameters have to be known accurately. The modeling of the beam delivery system itself opens various areas where Monte Carlo calculations prove extremely helpful, such as for design and commissioning of a therapy facility as well as for quality assurance verification. The gantry treatment nozzles at the Northeast Proton Therapy Center (NPTC) at Massachusetts General Hospital (MGH) were modeled in detail using the GEANT4.5.2 Monte Carlo code. For this purpose, various novel solutions for simulating irregular shaped objects in the beam path, like contoured scatterers, patient apertures or patient compensators, were found. The four-dimensional, in time and space, simulation of moving parts, such as the modulator wheel, was implemented. Further, the appropriate physics models and cross sections for proton therapy applications were defined. We present comparisons between measured data and simulations. These show that by modeling the treatment nozzle with millimeter accuracy, it is possible to reproduce measured dose distributions with an accuracy in range and modulation width, in the case of a spread-out Bragg peak (SOBP), of better than 1 mm. The excellent agreement demonstrates that the simulations can even be used to generate beam data for commissioning treatment planning systems. The Monte Carlo nozzle model was used to study mechanical optimization in terms of scattered radiation and secondary radiation in the design of the nozzles. We present simulations on the neutron background. Further, the Monte Carlo calculations supported commissioning efforts in understanding the sensitivity of beam characteristics and how these influence the dose delivered. We present the sensitivity of dose distributions in water with respect to various beam parameters and geometrical misalignments. This allows the definition of tolerances for quality assurance and the design of quality assurance procedures.

A special ionisation chamber for quality control of diagnostic and mammography X ray equipment.

PubMed

Costa, A M; Caldas, L V E

2003-01-01

A quality control program for X ray equipment used for conventional radiography and mammography requires the constancy check of the beam qualities in terms of the half-value layers. In this work, a special double-faced parallel-plate ionisation chamber was developed with inner electrodes of different materials, in a tandem system. Its application will be in quality control programs of diagnostic and mammography X ray equipment for confirmation of half-value layers previously determined by the conventional method. Moreover, the chamber also may be utilised for measurements of air kerma values (and air kerma rates) in X radiation fields used for conventional radiography and mammography. The chamber was studied in relation to the characteristics of saturation, ion collection efficiency, polarity effects, leakage current, and short-term stability. The energy dependence in response of each of the two faces of the chamber was determined over the conventional radiography and mammography X ray ranges (unattenuated beams). The different energy response of the two faces of the chamber allowed the formation of a tandem system useful for the constancy check of beam qualities.

Investigation of the practical aspects of an additional 0.1 mm copper x-ray spectral filter for cine acquisition mode imaging in a clinical care setting.

PubMed

Fetterly, Kenneth A

2010-11-01

Minimizing the x-ray radiation dose is an important aspect of patient safety during interventional fluoroscopy procedures. This work investigates the practical aspects of an additional 0.1 mm Cu x-ray beam spectral filter applied to cine acquisition mode imaging on patient dose and image quality. Measurements were acquired using clinical interventional imaging systems. Acquisition images of Solid Water phantoms (15-40 cm) were acquired using x-ray beams with the x-ray tube inherent filtration and using an additional 0.1 mm Cu x-ray beam spectral filter. The skin entrance air kerma (dose) rate was measured and the signal difference to noise ratio (SDNR) of an iodine target embedded into the phantom was calculated to assess image quality. X-ray beam parameters were recorded and analyzed and a primary x-ray beam simulation was performed to assess additional x-ray tube burden attributable to the Cu filter. For all phantom thicknesses, the 0.1 mm Cu filter resulted in a 40% reduction in the entrance air kerma rate to the phantoms and a 9% reduction in the SDNR of the iodine phantom. The expected additional tube load required by the 0.1 mm Cu filter ranged from 11% for a 120 kVp x-ray beam to 43% for a 60 kVp beam. For these clinical systems, use of the 0.1 mm Cu filter resulted in a favorable compromise between reduced skin dose rate and image quality and increased x-ray tube burden.

A comparison of phantom scatter from flattened and flattening filter free high-energy photon beams.

PubMed

Richmond, Neil; Allen, Vince; Daniel, Jim; Dacey, Rob; Walker, Chris

2015-01-01

Flattening filter free (FFF) photon beams have different dosimetric properties from those of flattened beams. The aim of this work was to characterize the collimator scatter (Sc) and total scatter (Scp) from 3 FFF beams of differing quality indices and use the resulting mathematical fits to generate phantom scatter (Sp) data. The similarities and differences between Sp of flattened and FFF beams are described. Sc and Scp data were measured for 3 flattened and 3 FFF high-energy photon beams (Varian 6 and 10MV and Elekta 6MV). These data were fitted to logarithmic power law functions with 4 numerical coefficients. The agreement between our experimentally determined flattened beam Sp and published data was within ± 1.2% for all 3 beams investigated and all field sizes from 4 × 4 to 40 × 40cm(2). For the FFF beams, Sp was only within 1% of the same flattened beam published data for field sizes between 6 × 6 and 14 × 14cm(2). Outside this range, the differences were much greater, reaching - 3.2%, - 4.5%, and - 4.3% for the fields of 40 × 40cm(2) for the Varian 6-MV, Varian 10-MV, and Elekta 6-MV FFF beams, respectively. The FFF beam Sp increased more slowly with increasing field size than that of the published and measured flattened beam of a similar reference field size quality index, i.e., there is less Phantom Scatter than that found with flattened beams for a given field size. This difference can be explained when the fluence profiles of the flattened and FFF beams are considered. The FFF beam has greatly reduced fluence off axis, especially as field size increases, compared with the flattened beam profile; hence, less scatter is generated in the phantom reaching the central axis. Copyright © 2015 American Association of Medical Dosimetrists. Published by Elsevier Inc. All rights reserved.

650-nJ pulses from a cavity-dumped Yb:fiber-pumped ultrafast optical parametric oscillator

NASA Astrophysics Data System (ADS)

Lamour, Tobias P.; Reid, Derryck T.

2011-08-01

Sub-250-fs pulses with energies of up to 650 nJ and peak powers up to 2.07 MW were generated from a cavity-dumped optical parametric oscillator, synchronously-pumped at 15.3 MHz with sub-400-fs pulses from an Yb:fiber laser. The average beam quality factor of the dumped output was M2 ~1.2 and the total relative-intensity noise was 8 mdBc, making the system a promising candidate for ultrafast laser inscription of infrared materials.

Progress in performance enhancement methods for capacitive silicon resonators

NASA Astrophysics Data System (ADS)

Van Toan, Nguyen; Ono, Takahito

2017-11-01

In this paper, we review the progress in recent studies on the performance enhancement methods for capacitive silicon resonators. We provide information on various fabrication technologies and design considerations that can be employed to improve the performance of capacitive silicon resonators, including low motional resistance, small insertion loss, and high quality factor (Q). This paper contains an overview of device structures and working principles, fabrication technologies consisting of hermetic packaging, deep reactive-ion etching and neutral beam etching, and design considerations including mechanically coupled, movable electrode structures and piezoresistive heat engines.

Large-mode-area single-mode-output Neodymium-doped silicate glass all-solid photonic crystal fiber

PubMed Central

Li, Wentao; Chen, Danping; Qinling, Zhou; Hu, Lili

2015-01-01

We have demonstrated a 45 μm core diameter Neodymium-doped all-solid silicate glass photonic crystal fiber laser with a single mode laser output. The structure parameters and modes information of the fiber are both demonstrated by theoretical calculations using Finite Difference Time Domain (FDTD) method and experimental measurements. Maximum 0.8 W output power limited by launched pump power has been generated in 1064 nm with laser beam quality factor M2 1.18. PMID:26205850

Hollow vortex Gaussian beams

NASA Astrophysics Data System (ADS)

Zhou, GuoQuan; Cai, YangJian; Dai, ChaoQing

2013-05-01

A kind of hollow vortex Gaussian beam is introduced. Based on the Collins integral, an analytical propagation formula of a hollow vortex Gaussian beam through a paraxial ABCD optical system is derived. Due to the special distribution of the optical field, which is caused by the initial vortex phase, the dark region of a hollow vortex Gaussian beam will not disappear upon propagation. The analytical expressions for the beam propagation factor, the kurtosis parameter, and the orbital angular momentum density of a hollow vortex Gaussian beam passing through a paraxial ABCD optical system are also derived, respectively. The beam propagation factor is determined by the beam order and the topological charge. The kurtosis parameter and the orbital angular momentum density depend on beam order n, topological charge m, parameter γ, and transfer matrix elements A and D. As a numerical example, the propagation properties of a hollow vortex Gaussian beam in free space are demonstrated. The hollow vortex Gaussian beam has eminent propagation stability and has crucial application prospects in optical micromanipulation.

Experimental Observations of Microwave Emission from a 35 GHz Cyclotron Autoresonant Maser

DTIC Science & Technology

1990-07-27

available graphite products) with a density of p =1.84 gm/cm 3 . The electron beam in the diode is generated through the process of explosive field emission...introduction to the physics of intense charge particle beams. Plenum Press, 1982. [331 D. Prosnitz %... .. T. Scharlemann. Beam quality definitions

Evaluation of resonating Si cantilevers sputter-deposited with AlN piezoelectric thin films for mass sensing applications

NASA Astrophysics Data System (ADS)

Sökmen, Ü.; Stranz, A.; Waag, A.; Ababneh, A.; Seidel, H.; Schmid, U.; Peiner, E.

2010-06-01

We report on a micro-machined resonator for mass sensing applications which is based on a silicon cantilever excited with a sputter-deposited piezoelectric aluminium nitride (AlN) thin film actuator. An inductively coupled plasma (ICP) cryogenic dry etching process was applied for the micro-machining of the silicon substrate. A shift in resonance frequency was observed, which was proportional to a mass deposited in an e-beam evaporation process on top. We had a mass sensing limit of 5.2 ng. The measurements from the cantilevers of the two arrays revealed a quality factor of 155-298 and a mass sensitivity of 120.34 ng Hz-1 for the first array, and a quality factor of 130-137 and a mass sensitivity of 104.38 ng Hz-1 for the second array. Furthermore, we managed to fabricate silicon cantilevers, which can be improved for the detection in the picogram range due to a reduction of the geometrical dimensions.

High energy micro electron beam generation using chirped laser pulse in the presence of an axial magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akou, H., E-mail: h.akou@nit.ac.ir; Hamedi, M.

2015-10-15

In this paper, the generation of high-quality and high-energy micro electron beam in vacuum by a chirped Gaussian laser pulse in the presence of an axial magnetic field is numerically investigated. The features of energy and angular spectra, emittances, and position distribution of electron beam are compared in two cases, i.e., in the presence and absence of an external magnetic field. The electron beam is accelerated with higher energy and qualified in spatial distribution in the presence of the magnetic field. The presence of an axial magnetic field improves electron beam spatial quality as well as its gained energy throughmore » keeping the electron motion parallel to the direction of propagation for longer distances. It has been found that a 64 μm electron bunch with about MeV initial energy becomes a 20 μm electron beam with high energy of the order of GeV, after interacting with a laser pulse in the presence of an external magnetic field.« less

Electron beam irradiation of Matricaria chamomilla L. for microbial decontamination

NASA Astrophysics Data System (ADS)

Nemţanu, Monica R.; Kikuchi, Irene Satiko; de Jesus Andreoli Pinto, Terezinha; Mazilu, Elena; Setnic, Silvia; Bucur, Marcela; Duliu, Octavian G.; Meltzer, Viorica; Pincu, Elena

2008-05-01

Wild chamomile (Matricaria chamomilla L.) is one of the most popular herbal materials with both internal and external use to cure different health disturbances. As a consequence of its origin, chamomile could carry various microbial contaminants which offer different hazards to the final consumer. Reduction of the microbial load to the in force regulation limits represents an important phase in the technological process of vegetal materials, and the electron beam treatment might be an efficient alternative to the classical methods of hygienic quality assurance. The purpose of the study was to analyze the potential application of the electron beam treatment in order to assure the microbial safety of the wild chamomile. Samples of chamomile dry inflorescences were treated in electron beam (e-beam) of 6 MeV mean energy, at room temperature and ambient pressure. Some loss of the chemical compounds with bioactive role could be noticed, but the number of microorganisms decreased as a function on the absorbed dose. Consequently, the microbial quality of studied vegetal material inflorescences was improved by e-beam irradiation.

Design of collimating and rearrangement systems of laser diode array beam

NASA Astrophysics Data System (ADS)

Gao, Runmei; Fang, Tao; Fu, Rulian; Yao, Jianquan

2015-10-01

To improve the laser diode output beam quality, micro-cylindrical lens and the step-type lens combination are designed. The former is used to collimate beam in fast-axis direction, while the latter plays a role in the slow-axis of splitting and the rearrangement. The micro-column semi-elliptical lens is made with the drops of spherical zoom lensin electric field and with the help of the material properties of light-cured production, which can reduce the reflection of the front surface and total reflection loss of the after. The divergence angle in the fast axis is compressed to roughly the same as that in the slow-axis direction; Stepped lens splits compressed long strip beam in the slow axis, with parallelogram style of level equidistant and rearrange in the fast axis direction. The spot in the slow axis gets smaller and the spot becomes larger in the fast axis. At last divergence angle and the beam spot achieve balanced in the fast axis and slow axis, optical parameters BPP integrates approximate the same, and beam quality can be improved.

Automated generation of IMRT treatment plans for prostate cancer patients with metal hip prostheses: Comparison of different planning strategies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Voet, Peter W. J.; Dirkx, Maarten L. P.; Breedveld, Sebastiaan

2013-07-15

Purpose: To compare IMRT planning strategies for prostate cancer patients with metal hip prostheses.Methods: All plans were generated fully automatically (i.e., no human trial-and-error interactions) using iCycle, the authors' in-house developed algorithm for multicriterial selection of beam angles and optimization of fluence profiles, allowing objective comparison of planning strategies. For 18 prostate cancer patients (eight with bilateral hip prostheses, ten with a right-sided unilateral prosthesis), two planning strategies were evaluated: (i) full exclusion of beams containing beamlets that would deliver dose to the target after passing a prosthesis (IMRT{sub remove}) and (ii) exclusion of those beamlets only (IMRT{sub cut}). Plansmore » with optimized coplanar and noncoplanar beam arrangements were generated. Differences in PTV coverage and sparing of organs at risk (OARs) were quantified. The impact of beam number on plan quality was evaluated.Results: Especially for patients with bilateral hip prostheses, IMRT{sub cut} significantly improved rectum and bladder sparing compared to IMRT{sub remove}. For 9-beam coplanar plans, rectum V{sub 60Gy} reduced by 17.5%{+-} 15.0% (maximum 37.4%, p= 0.036) and rectum D{sub mean} by 9.4%{+-} 7.8% (maximum 19.8%, p= 0.036). Further improvements in OAR sparing were achievable by using noncoplanar beam setups, reducing rectum V{sub 60Gy} by another 4.6%{+-} 4.9% (p= 0.012) for noncoplanar 9-beam IMRT{sub cut} plans. Large reductions in rectum dose delivery were also observed when increasing the number of beam directions in the plans. For bilateral implants, the rectum V{sub 60Gy} was 37.3%{+-} 12.1% for coplanar 7-beam plans and reduced on average by 13.5% (maximum 30.1%, p= 0.012) for 15 directions.Conclusions: iCycle was able to automatically generate high quality plans for prostate cancer patients with prostheses. Excluding only beamlets that passed through the prostheses (IMRT{sub cut} strategy) significantly improved OAR sparing. Noncoplanar beam arrangements and, to a larger extent, increasing the number of treatment beams further improved plan quality.« less

Inverse compton light source: a compact design proposal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deitrick, Kirsten Elizabeth

In the last decade, there has been an increasing demand for a compact Inverse Compton Light Source (ICLS) which is capable of producing high-quality X-rays by colliding an electron beam and a high-quality laser. It is only in recent years when both SRF and laser technology have advanced enough that compact sources can approach the quality found at large installations such as the Advanced Photon Source at Argonne National Laboratory. Previously, X-ray sources were either high flux and brilliance at a large facility or many orders of magnitude lesser when produced by a bremsstrahlung source. A recent compact source wasmore » constructed by Lyncean Technologies using a storage ring to produce the electron beam used to scatter the incident laser beam. By instead using a linear accelerator system for the electron beam, a significant increase in X-ray beam quality is possible, though even subsequent designs also featuring a storage ring offer improvement. Preceding the linear accelerator with an SRF reentrant gun allows for an extremely small transverse emittance, increasing the brilliance of the resulting X-ray source. In order to achieve sufficiently small emittances, optimization was done regarding both the geometry of the gun and the initial electron bunch distribution produced off the cathode. Using double-spoke SRF cavities to comprise the linear accelerator allows for an electron beam of reasonable size to be focused at the interaction point, while preserving the low emittance that was generated by the gun. An aggressive final focusing section following the electron beam's exit from the accelerator produces the small spot size at the interaction point which results in an X-ray beam of high flux and brilliance. Taking all of these advancements together, a world class compact X-ray source has been designed. It is anticipated that this source would far outperform the conventional bremsstrahlung and many other compact ICLSs, while coming closer to performing at the levels found at large facilities than ever before. The design process, including the development between subsequent iterations, is presented here in detail, with the simulation results for this groundbreaking X-ray source.« less

The Australian radiation protection and nuclear safety agency megavoltage photon thermoluminescence dosimetry postal audit service 2007-2010.

PubMed

Oliver, C P; Butler, D J; Webb, D V

2012-03-01

The Australian radiation protection and nuclear safety agency (ARPANSA) has continuously provided a level 1 mailed thermoluminescence dosimetry audit service for megavoltage photons since 2007. The purpose of the audit is to provide an independent verification of the reference dose output of a radiotherapy linear accelerator in a clinical environment. Photon beam quality measurements can also be made as part of the audit in addition to the output measurements. The results of all audits performed between 2007 and 2010 are presented. The average of all reference beam output measurements calculated as a clinically stated dose divided by an ARPANSA measured dose is 0.9993. The results of all beam quality measurements calculated as a clinically stated quality divided by an ARPANSA measured quality is 1.0087. Since 2011 the provision of all auditing services has been transferred from the Ionizing Radiation Standards section to the Australian Clinical Dosimetry Service (ACDS) which is currently housed within ARPANSA.

Development of high-average-power DPSSL with high beam quality

NASA Astrophysics Data System (ADS)

Nakai, Sadao; Kanabe, Tadashi; Kawashima, Toshiyuki; Yamanaka, Masanobu; Izawa, Yasukazu; Nakatuka, Masahiro; Kandasamy, Ranganathan; Kan, Hirofumi; Hiruma, Teruo; Niino, Masayuki

2000-08-01

The recent progress of high power diode laser is opening new fields of laser and its application. We are developing high average power diode pumped solid state laser DPSSL for laser fusion power plant, for space propulsion and for various applications in industry. The common features or requirements of our High Average-power Laser for Nuclear-fusion Application (HALNA) are large pulse energy with relatively low repetition of few tens Hz, good beam quality of order of diffraction limit and high efficiency more than 10%. We constructed HALNA 10 (10J X 10 Hz) and tested the performance to clarify the scalability to higher power system. We have obtained in a preliminary experiment a 8.5 J output energy at 0.5 Hz with beam quality of 2 times diffraction limited far-field pattern.

Acceleration and stability of a high-current ion beam in induction fields

NASA Astrophysics Data System (ADS)

Karas', V. I.; Manuilenko, O. V.; Tarakanov, V. P.; Federovskaya, O. V.

2013-03-01

A one-dimensional nonlinear analytic theory of the filamentation instability of a high-current ion beam is formulated. The results of 2.5-dimensional numerical particle-in-cell simulations of acceleration and stability of an annular compensated ion beam (CIB) in a linear induction particle accelerator are presented. It is shown that additional transverse injection of electron beams in magnetically insulated gaps (cusps) improves the quality of the ion-beam distribution function and provides uniform beam acceleration along the accelerator. The CIB filamentation instability in both the presence and the absence of an external magnetic field is considered.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Q.

In memory of the significant contribution of Dr. Jacques Ovadia to electron beam techniques, this session will review recent, advanced techniques which are reinvigorating the science of electron beam radiation therapy. Recent research efforts in improving both the applicability and quality of the electron beam therapy will be discussed, including modulated electron beam radiotherapy (MERT) and dynamic electron arc radiotherapy (DEAR). Learning Objectives: To learn about recent advances in electron beam therapy, including modulated electron beam therapy and dynamic electron arc therapy (DEAR). Put recent advances in the context of work that Dr. Ovadia pursued during his career in medicalmore » physics.« less

Quantitative comparison of self-healing ability between Bessel–Gaussian beam and Airy beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wen, Wei; Chu, Xiuxiang, E-mail: xiuxiangchu@yahoo.com

The self-healing ability during propagation process is one of the most important properties of non-diffracting beams. This ability has crucial advantages to light sheet-based microscopy to reduce scattering artefacts, increase the quality of the image and enhance the resolution of microscopy. Based on similarity between two infinite-dimensional complex vectors in Hilbert space, the ability to a Bessel–Gaussian beam and an Airy beam have been studied and compared. Comparing the evolution of the similarity of Bessel–Gaussian beam with Airy beam under the same conditions, we find that Bessel–Gaussian beam has stronger self-healing ability and is more stable than that of Airymore » beam. To confirm this result, the intensity profiles of Bessel–Gaussian beam and Airy beam with different similarities are numerically calculated and compared.« less