Beams Of Different Energies Research Articles

Moving GPU-OpenCL-based Monte Carlo dose calculation toward clinical use: Automatic beam commissioning and source sampling for treatment plan dose calculation.

We have previously developed a GPU‐based Monte Carlo (MC) dose engine on the OpenCL platform, named goMC, with a built‐in analytical linear accelerator (linac) beam model. In this paper, we report our recent improvement on goMC to move it toward clinical use. First, we have adapted a previously developed automatic beam commissioning approach to our beam model. The commissioning was conducted through an optimization process, minimizing the discrepancies between calculated dose and measurement. We successfully commissioned six beam models built for Varian TrueBeam linac photon beams, including four beams of different energies (6 MV, 10 MV, 15 MV, and 18 MV) and two flattening‐filter‐free (FFF) beams of 6 MV and 10 MV. Second, to facilitate the use of goMC for treatment plan dose calculations, we have developed an efficient source particle sampling strategy. It uses the pre‐generated fluence maps (FMs) to bias the sampling of the control point for source particles already sampled from our beam model. It could effectively reduce the number of source particles required to reach a statistical uncertainty level in the calculated dose, as compared to the conventional FM weighting method. For a head‐and‐neck patient treated with volumetric modulated arc therapy (VMAT), a reduction factor of ~2.8 was achieved, accelerating dose calculation from 150.9 s to 51.5 s. The overall accuracy of goMC was investigated on a VMAT prostate patient case treated with 10 MV FFF beam. 3D gamma index test was conducted to evaluate the discrepancy between our calculated dose and the dose calculated in Varian Eclipse treatment planning system. The passing rate was 99.82% for 2%/2 mm criterion and 95.71% for 1%/1 mm criterion. Our studies have demonstrated the effectiveness and feasibility of our auto‐commissioning approach and new source sampling strategy for fast and accurate MC dose calculations for treatment plans.

Secondary radiation measurements for particle therapy applications: prompt photons produced by 4He, 12C and 16O ion beams in a PMMA target

Charged particle beams are used in particle therapy (PT) to treat oncological patients due to their selective dose deposition in tissues with respect to the photons and electrons used in conventional radiotherapy. Heavy (Z > 1) PT beams can additionally be exploited for their high biological effectiveness in killing cancer cells. Nowadays, protons and carbon ions are used in PT clinical routines. Recently, interest in the potential application of helium and oxygen beams has been growing. With respect to protons, such beams are characterized by their reduced multiple scattering inside the body, increased linear energy transfer, relative biological effectiveness and oxygen enhancement ratio.The precision of PT demands online dose monitoring techniques, crucial to improving the quality assurance of any treatment: possible patient mis-positioning and biological tissue changes with respect to the planning CT scan could negatively affect the outcome of the therapy. The beam range confined in the irradiated target can be monitored thanks to the neutral or charged secondary radiation emitted by the interactions of hadron beams with matter. Among these secondary products, prompt photons are produced by nuclear de-excitation processes, and at present, different dose monitoring and beam range verification techniques based on prompt-γ detection are being proposed. It is hence of importance to perform γ yield measurement in therapeutic-like conditions.In this paper we report on the yields of prompt photons produced by the interaction of helium, carbon and oxygen ion beams with a poly-methyl methacrylate (PMMA) beam stopping target. The measurements were performed at the Heidelberg Ion-Beam Therapy Center (HIT) with beams of different energies. An LYSO scintillator, placed at and with respect to the beam direction, was used as the photon detector. The obtained γ yields for the carbon ion beams are compared with results from the literature, while no other results from helium and oxygen beams have been published yet. A discussion on the expected resolution of a slit camera detector is presented, demonstrating the feasibility of a prompt-γ-based monitoring technique for PT treatments using helium, carbon and oxygen ion beams.

Monte Carlo modeling of cavity imaging in pure iron using back-scatter electron scanning microscopy

Backscattered electrons (BSE) in a scanning electron microscope (SEM) can produce images of subsurface cavity distributions as a nondestructive characterization technique. Monte Carlo simulations were performed to understand the mechanism of void imaging and to identify key parameters in optimizing void resolution. The modeling explores an iron target of different thicknesses, electron beams of different energies, beam sizes, and scan pitch, evaluated for voids of different sizes and depths below the surface. The results show that the void image contrast is primarily caused by discontinuity of energy spectra of backscattered electrons, due to increased outward path lengths for those electrons which penetrate voids and are backscattered at deeper depths. Size resolution of voids at specific depths, and maximum detection depth of specific voids sizes are derived as a function of electron beam energy. The results are important for image optimization and data extraction.

Determination of Tungsten Target Parameters for Transmission X-ray Tube: A Simulation Study Using Geant4

Abstract Transmission X-ray tubes based on carbon nanotube have attracted significant attention recently. In most of these tubes, tungsten is used as the target material. In this article, the well-known simulator Geant4 was used to obtain some of the tungsten target parameters. The optimal thickness for maximum production of usable X-rays when the target is exposed to electron beams of different energies was obtained. The linear variation of optimal thickness of the target for different electron energies was also obtained. The data obtained in this study can be used to design X-ray tubes. A beryllium window was considered for the X-ray tube. The X-ray energy spectra at the moment of production and after passing through the target and window for different electron energies in the 30–110 keV range were also obtained. The results obtained show that with a specific thickness, the target material itself can act as filter, which enables generation of X-rays with a limited energy.

Effects of the interstrip gap on the efficiency and response of Double Sided Silicon Strip Detectors

In this work the effects of the segmentation of the electrodes of Double Sided Silicon Strip Detectors (DSSSDs) are investigated. In order to characterize the response of the DSSSDs we perform a first experiment by using tandem beams of different energies directly sent on the detector and a second experiment by mean of a proton microbeam. Results show that the effective width of the inter-strip region and the efficiency for full energy detection, varies with both detected energy and bias voltage. The experimental results are qualitatively reproduced by a simplified model based on the Shockley-Ramo-Gunn framework.

Theoretical detection threshold of the proton-acoustic range verification technique.

Range verification in proton therapy using the proton-acoustic signal induced in the Bragg peak was investigated for typical clinical scenarios. The signal generation and detection processes were simulated in order to determine the signal-to-noise limits. An analytical model was used to calculate the dose distribution and local pressure rise (per proton) for beams of different energy (100 and 160 MeV) and spot widths (1, 5, and 10 mm) in a water phantom. In this method, the acoustic waves propagating from the Bragg peak were generated by the general 3D pressure wave equation implemented using a finite element method. Various beam pulse widths (0.1-10 μs) were simulated by convolving the acoustic waves with Gaussian kernels. A realistic PZT ultrasound transducer (5 cm diameter) was simulated with a Butterworth bandpass filter with consideration of random noise based on a model of thermal noise in the transducer. The signal-to-noise ratio on a per-proton basis was calculated, determining the minimum number of protons required to generate a detectable pulse. The maximum spatial resolution of the proton-acoustic imaging modality was also estimated from the signal spectrum. The calculated noise in the transducer was 12-28 mPa, depending on the transducer central frequency (70-380 kHz). The minimum number of protons detectable by the technique was on the order of 3-30 × 10(6) per pulse, with 30-800 mGy dose per pulse at the Bragg peak. Wider pulses produced signal with lower acoustic frequencies, with 10 μs pulses producing signals with frequency less than 100 kHz. The proton-acoustic process was simulated using a realistic model and the minimal detection limit was established for proton-acoustic range validation. These limits correspond to a best case scenario with a single large detector with no losses and detector thermal noise as the sensitivity limiting factor. Our study indicated practical proton-acoustic range verification may be feasible with approximately 5 × 10(6) protons/pulse and beam current.

Beam test results for a tungsten-cerium fluoride sampling calorimeter with wavelength-shifting fiber readout

A sampling calorimeter using cerium fluoride scintillating crystals as active material, interleaved with heavy absorber plates, and read out by wavelength-shifting (WLS) fibers is being studied as a calorimeter option for detectors at the upgraded High-Luminosity LHC (HL-LHC) collider at CERN. A prototype has been exposed to electron beams of different energies at the INFN Frascati (Italy) Beam Test Facility. This paper presents results from the studies performed on the prototype, such as signal amplitudes, light yield and energy resolution.

SU-D-213-06: Dosimetry of Modulated Electron Radiation Therapy Using Fricke Gel Dosimeter

Purpose: Modulated electron radiation therapy (MERT) has been proposed as an effective modality for treatment of superficial targets. MERT utilizes multiple beams of different energies which are intensity modulated to deliver optimized dose distribution. Energy independent dosimeters are thus needed for quantitative evaluations of MERT dose distributions and measurements of absolute doses delivered to patients. Thus in the current work we study the feasibility of Fricke gel dosimeters in MERT dosimetry. Methods: Batches of radiation sensitive Fricke gel is fabricated and poured into polymethyl methacrylate cuvettes. The samples were irradiated in solid water phantom and a thick layer of bolus was used as a buildup. A spectrophotometer system was used for measuring the color changes (the absorbance) before and after irradiation and then we calculate net absorbance. We constructed calibration curves to relate the measured absorbance in terms of absorbed dose for all available electron energies. Dosimetric measurements were performed for mixed electron beam delivery and we also performed measurement for segmented field delivery with the dosimeter placed at the junction of two adjacent electron beams of different energies. Dose measured by our gel dosimetry is compared to that calculation from our precise treatment planning system. We also initiated a Monte Carlo study to evaluate the water equivalence of our dosimeters. MCBEAM and MCSIM codes were used for treatment head simulation and phantom dose calculation. PDDs and profiles were calculated for electron beams incident on a phantom designed with 1cm slab of Fricke gel. Results: The calibration curves showed no observed energy dependence with all studied electron beam energies. Good agreement was obtained between dose calculated and that obtained by gel dosimetry. Monte Carlo results illustrated the tissue equivalency of our Gel dosimeters. Conclusion: Fricke Gel dosimeters represent a good option for the dosimetric quality assurance prior to MERT application.

WE‐EF‐303‐09: Proton‐Acoustic Range Verification in Proton Therapy

Purpose:We investigated proton‐acoustic signals detection for range verification with current ultrasound instruments in typical clinical scenarios. Using simulations that included a realistic noise model, we determined the theoretical minimum dose required to generate detectable proton‐acoustic signals.Methods:An analytical model was used to calculate the dose distributions and local pressure rise (per proton) for beams of different energy (100 and 160 MeV) and spot widths (1, 5, and 10 mm) in a water phantom. The acoustic waves propagating from the Bragg peak were modeled by the general 3D pressure wave equation and convolved with Gaussian kernels to simulate various proton pulse widths (0.1 – 10 ms). A realistic PZT ultrasound transducer (5 cm diameter) was simulated with a Butterworth band‐pass filter, and ii) randomly generated noise based on a model of thermal noise in the transducer. The signal‐to‐noise ratio was calculated, determining the minimum number of protons and dose required per pulse. The maximum spatial resolution was also estimated from the signal spectrum.Results:The calculated noise in the transducer was 12–28 mPa, depending on the transducer center frequency (70–380 kHz). The minimum number of protons were on the order of 0.6–6 million per pulse, leading to 3–110 mGy dose per pulse at the Bragg peak, depending on the spot size. The acoustic signal consisted of lower frequencies for wider pulses, leading to lower noise levels, but also worse spatial resolution. The resolution was 1‐mm for a 0.1‐µs pulse width, but increased to 5‐mm for a 10‐µs pulse width.Conclusion:We have established minimum dose detection limits for proton‐acoustic range validation. These limits correspond to a best case scenario with a large detector with no losses and only detector thermal noise. Feasible proton‐acoustic range detection will require at least 10⁷ protons per pulse and pulse widths ≤ 1‐µs.

Sc-47 production from titanium targets using electron linacs

In this work we have studied the feasibility of photonuclear production of 47Sc from 48Ti via 48Ti(γ,p)47Sc reaction. Photon flux distribution for electron beams of different energies incident on tungsten converter was calculated using MCNPX radiation transport code. 47Sc production rate dependence on electron beam energy was found and 47Sc yields were estimated. It was shown that irradiating a natural Ti target results in numerous scandium isotopes which can reduce the specific activity of 47Sc. Irradiating enriched 48Ti targets with a 22MeV 1mA beam will result in hundreds of MBq/g activity of 47Sc and no other isotopes of scandium. Decreasing the size of the target will result in much higher average photon flux through the target and tens of GBq/g levels of specific activity of 47Sc. Increasing the beam energy will also result in higher yields, but as soon as the electron energy exceeds the 48Ti(γ,np)46Sc reaction threshold, 46Sc starts being produced and its fraction in total scandium atoms grows as beam energy increases. The results of the simulations were benchmarked by irradiating natural titanium foil with 22MeV electron beam incident on the tungsten converter. Measured 47Sc activities were found to be in very good agreement with the predictions.

Transverse effects in a free-electron laser oscillator with two electron beams

We have analyzed the transverse effects in a free-electron laser (FEL) oscillator using two electron beams of different energies referring to a proposed FEL facility operated in the far-infrared and infrared regions. The transverse effects in a free-electron laser oscillator were studied taking into account the electron beam’s emittance, offset misalignment errors, energy spreads, and higher-order modes using an extended two-dimensional (2D) FEL code with two electron beams that we developed. The variation in the radiation amplitude depending on the electron beam emittance, offset misalignment errors, and energy spreads was also calculated in the case of betatron oscillations for multiparticles and multipass numbers using a new 2D code. The mode construction was studied for higher-order modes of the wiggler with and without offset misalignment errors for FEL operation with a high-quality electron beam.

Effects of a tapered undulator in a free-electron laser oscillator with two electron beams

We have analyzed the effects for a tapered undulator in a free-electron laser (FEL) oscillator by using two electron beams of different energies based on the proposed FEL facility that is to be operated in the far-infrared and infrared regions. The effects of the tapered undulator in a free-electron laser oscillator with two electron beams on the electron beam’s emittance, the offset misalignment errors, the energy spreads, and the higher-order modes were studied using a twodimensional (2D) FEL code with two electron beams that we had developed. The effects of the variations in the radiation amplitude on the electron beam’s emittance, the offset misalignment errors, and the energy spreads with a tapered undulator and with an untapered undulator were also calculated for the multi-particle and the multi-pass number by using a 2D code. The results for the gains of a higher energy beam with and without a tapered undulator in the two-beam system were compared to the results obtained using a single electron beam with and without tapering. The mode construction was studied for higher-order modes with a tapered undulator, and the results for the emittance and the offset misalignment errors were compared to those of an untapered undulator.

47Ca production for 47Ca/47Sc generator system using electron linacs

In this work we have studied the feasibility of photonuclear production of 47Ca from 48Ca for 47Ca/47Sc generators. Photon flux distribution for electron beams of different energies incident on a tungsten converter was calculated using the MCNPX radiation transport code. The 47Ca production rate dependence on electron beam energy was found and 47Ca/47Sc yields were estimated for a 40MeV electron beam. It was shown that irradiating enriched targets with a 40MeV, 1mA beam will result in tens of MBq g−1 (few mCi g−1) activity of 47Sc. The results of the simulations were benchmarked by irradiating 22.5g of CaCl2 powder with a 39MeV electron beam incident on a tungsten converter. Measured 47Ca/47Sc activities were found to be in very good agreement with the predictions.

Output trends, characteristics, and measurements of three megavoltage radiotherapy linear accelerators

The purpose of this study is to characterize and understand the long‐term behavior of the output from megavoltage radiotherapy linear accelerators. Output trends of nine beams from three linear accelerators over a period of more than three years are reported and analyzed. Output, taken during daily warm‐up, forms the basis of this study. The output is measured using devices having ion chambers. These are not calibrated by accredited dosimetry laboratory, but are baseline‐compared against monthly output which is measured using calibrated ion chambers. We consider the output from the daily check devices as it is, and sometimes normalized it by the actual output measured during the monthly calibration of the linacs. The data show noisy quasi‐periodic behavior. The output variation, if normalized by monthly measured “real’ output, is bounded between ± 3%. Beams of different energies from the same linac are correlated with a correlation coefficient as high as 0.97, for one particular linac, and as low as 0.44 for another. These maximum and minimum correlations drop to 0.78 and 0.25 when daily output is normalized by the monthly measurements. These results suggest that the origin of these correlations is both the linacs and the daily output check devices. Beams from different linacs, independent of their energies, have lower correlation coefficient, with a maximum of about 0.50 and a minimum of almost zero. The maximum correlation drops to almost zero if the output is normalized by the monthly measured output. Some scatter plots of pairs of beam output from the same linac show band‐like structures. These structures are blurred when the output is normalized by the monthly calibrated output. Fourier decomposition of the quasi‐periodic output is consistent with a 1/f power law. The output variation appears to come from a distorted normal distribution with a mean of slightly greater than unity. The quasi‐periodic behavior is manifested in the seasonally averaged output, showing annual variability with negative variations in the winter and positive in the summer. This trend is weakened when the daily output is normalized by the monthly calibrated output, indicating that the variation of the periodic component may be intrinsic to both the linacs and the daily measurement devices. Actual linac output was measured monthly. It needs to be adjusted once every three to six months for our tolerance and action levels. If these adjustments are artificially removed, then there is an increase in output of about 2%–4% per year.PACS numbers: 87.56bd, 87.56Fc, 87.55Qr

The effects of two electron beams on a free-electron laser oscillator

We have analyzed the characteristics of a free-electron laser (FEL) oscillator by using two electron beams of different energies. The evolution of the harmonic output intensity of the two-beam oscillator, the harmonic radiation field intensity relative to the beam’s current ratio, the harmonic field obtained by using both the lower and the higher electron energy beams, and the harmonic field for the higher energy electron beam alone were studied by using an extended 2D simulation code that described the effects of two electron beams with different energies. The 2D effects of the energy spread, higher-order modes, and the transverse mode construction of the optical field were also studied in the two electron beam oscillator model for the low-energy region.

Energy calibration of a CdTe X-ray pixel sensor hybridized to a Timepix chip

The X-ray energy response of a CdTe pixel sensor was investigated in view of applications for synchrotron experiments at high energy. We performed an energy calibration of a 1 mm thick CdTe pixel sensor of 55 μm pixel pitch bump-bonded to a Timepix chip in the 6–120 keV range. Calibration data were acquired in time-over-threshold (TOT) mode with monochromatic synchrotron beams of different energies and with gamma ray sources. Charge sharing in the raw TOT X-ray images was on-line corrected with a cluster summing algorithm implemented in the acquisition software. Variation of the TOT signal with respect to incident X-ray energy was found to be linear from 8 keV to 120 keV. A raw energy resolution of 43% FWHM was achieved at 59.5 keV without prior per-pixel TOT calibration. Fluorescence of the CdTe material was identified as the main drawback of fine pitch CdTe pixel sensors if considering spectral X-ray imaging applications at high energy.

Calibration of CR-39 with atomic force microscope for the measurement of short range tracks from proton-induced target fragmentation reactions

Abstract We studied the track response of CR-39 plastic nuclear track detectors (PNTD) for low ( 100 MeV/n) energy heavy ions using the atomic force microscope (AFM). CR-39 PNTD was exposed to several heavy ion beams of different energy at HIMAC (Heavy Ion Medical Accelerator in Chiba). For AFM measurement, the amount of bulk etch was controlled to be ∼2 μm in order to avoid etching away of short range tracks. The response data obtained by AFM for ∼2 μm bulk etch was in good agreement with data obtained by the conventional optical microscope analysis for larger bulk etch. The response data from low energy beams (stopping near the surface) was also consistent with the data from high energy beams (penetrating the detector) as a function of REL (restricted energy loss) with the δ-ray cut off energy of ω 0 = 200 eV. We experimentally verified that REL ( ω 0 = 200 eV) gives a universal function for wide energy range in CR-39 PNTD. This work has been done as part of a basic study in the measurement of secondary short range tracks produced by target fragmentation reactions in proton cancer therapy fields.

Evaluation of Single-Field Electron Beams for Postmastectomy Radiotherapy

Introduction:electron beams have been extensively used in postmastectomy radiotherapy due to its homogenous dose at the surface followed by sharp fall-off sparing the underlying tissue. Multiple electron fields or electron photon mix were the techniques commonly used. An old study reported the successful use of single-field electron beams with beam energy of 20 MeV. Yet the potential risks of the organs at risk were not clearly shown. Objectives:the objectives of this study were to assess the possibility of applying single-field electron beams in postmastectomy radiotherapy in terms of: the dose distribution in the target, the volume of organs that receive a certain threshold dose and the volume of organs that receive low doses of radiation. Materials and Methods: the Monte Carlo codes of EGSnrc were used to simulate electron beams of different energies and gantry angles. The resulting dose files were used by XSTING to generate dose volume histograms, which were used for evaluation. Results and Discussions: the target coverage was quite poor in most of the studied scenarios. Improving the target coverage was at the expense of irradiating the lung and heart with unacceptable dose values. Conclusion and Recommendations: Single field electron beams cannot be used for postmastectomy radiotherapy. Multiple electron fields or photon electron mix are necessary and need to be assessed.

Depth profiling of NbxO/W multilayers: effect of primary ion beam species (O2+, Ar+ and Cs+)

Depth profiling of NbxO/W multilayered samples was carried out using O2+, Cs+ or Ar+ beams of different energies (2 keV, 1 keV and 0.5 keV). The obtained depth profiles showed that sputtering with O2+ or Ar+ beams can reveal the distribution of light elements, while sputtering with Cs+ cannot show correctly their distribution if lower energy of 0.5 keV is applied. SRIM simulations show that changes in primary energy of sputter ions have much stronger effect on deposited energy incl. vacancy/ion and sputter yields than for oxygen and argon ion beam etching. It is suggested that O2+ or Ar+ sputter sources should be used when both light and heavy species are present in nano‐scale multilayered targets. Copyright © 2012 John Wiley & Sons, Ltd.

Gafchromic® EBT films for ion dosimetry

Abstract For dose delivery to patients, scanning ion beams are going to be increasingly used in the upcoming ion beam therapy facilities. Especially carbon ion beams are able to produce steep dose gradients. However, the currently used method for patient dose verification, employing ionization chamber arrays, provides a spatial resolution of 1 cm only. As continuous media, EBT films, widely used in photon therapy, are interesting candidates to be used for this purpose. The EBT film is the ancestor of the currently available EBT2 film. In our contribution two dimensional dosimetry and film response quenching in ion beams were investigated. For a real 12 C patient plan a good qualitative agreement with the planned dose distribution including a high signal-to-noise ratio and a good resolution in the measured photon-equivalent dose was found. The depth-dose response of EBT films for a 12 C ion beam shows response quenching, which rises towards the Bragg peak. It was quantified by the relative efficiency determined at different depths. Furthermore, the relative efficiency was measured in monoenergetic proton and carbon ion beams. All the measured efficiencies show no significant dependency on the dose up to the highest measured doses of 6 Gy. However, differences between proton and carbon ions as well as between carbon ion beams of different energies were observed. The measurements reveal, that the use of EBT films for absolute dose verification measurements requires to take the relative efficiency into account, dependent on the ion type and energy.