Beam Off Research Articles

Dosimetric consequences of flap dose due to rapid beam off control for a high intensity carbon ion radiation therapy synchrotron.

In carbon ion radiation therapy (CIRT) the predominant method of irradiation is raster scanning, called dose driven continuous scanning (DDCS) by Hitachi, allowing for continuous synchrotron extraction. The reduction in irradiation time is highly beneficial in minimizing the impact of patient and target movement on dose distribution. The RF knock out (RFKO) slow-extraction method is commonly used for beam on/off control. When the Hitachi synchrotron receives a beam off signal the control system stops the RFKO and after some delay time (t-delay) during which the beam intensity declines, a high-speed steering magnet (HSST) is used to sweep the remaining beam from isocenter to a beam dump for safety reasons. Mayo Clinic Florida (MCF) will use a very short delay of the HSST operation from the RFKO beam OFF signal to minimize the delay time and delayed dose. MCF clinical beam intensity, a tenfold increase over HIMAK, is still less than 100 mMU/ms (approximately 4.9×109 pps for 430 MeV/u). The rapid beam off control (RBOC) proposed for MCF is associated with the occurrence of flap dose (FD), which refers to the asymmetric shoulder of the spot dose profile formed from the beam bent by HSST deviating from its planned spot position on the isocenter plane. In this study, we quantitatively assessed FD, proposed a treatment planning system (TPS) implementation using a flap spot (FS) and evaluated its impact on dose distribution. The experiments were conducted at the Osaka Heavy Ion Therapy Center (HIMAK) varying the t-delay from 0.01 to 1ms in a research environment to simulate the MCF RBOC. We studied the dependence of FD position on beam transport and its dependence on energy and beam intensity. FD was generated by delivering 10000 continuous spots on the central axis that are occasionally triggered by an external 10Hz gate signal. Measurements were conducted using an oscilloscope, and the nozzle's spot position monitor (SPM) and dose monitor (DM). All spot profile data were corrected for the gain of the SPM's beam intensity dependence. FD was determined by fitting the (SPM) Profile data to a double Gaussian. The position of the FS was found to be transport path dependent, with FS occurring on the opposite sides of the scanning x-direction for vertical and horizontal ports, respectively, as predicted by transport calculations. It was observed that the FD increases with beam intensity and did not exhibit a significant dependence on energy. The effect of FD on treatment planning is shown to have no significant dose impact on the organs at risk (OARs) near the target for clinical beam intensities and a modest increase for very high intensities. Using HIMAK in research mode the implications are that the FD has no clinical impact on the clinical CIRT beam intensities for MCF and maybe planned for higher intensities by incorporating FS into the TPS to predict the modest increased dose to OARs. A method for commissioning and quality assurance of FD has been proposed.

Efficient EPID-based quality assurance of beam time delay for respiratory-gated radiotherapy with validation on Catalyst™ and AlignRT™ systems.

To propose a straightforward and time-efficient quality assurance (QA) approach of beam time delay for respiratory-gated radiotherapy and validate the proposed method on typical respiratory gating systems, Catalyst™ and AlignRT™. The QA apparatus was composed of a motion platform and a Winston-Lutz cube phantom (WL3) embedded with metal balls. The apparatus was first scanned in CT-Sim and two types of QA plans specific for beam on and beam off time delay, respectively, were designed. Static reference images and motion testing images of the WL3 cube were acquired with EPID. By comparing the position differences of the embedded metal balls in the motion and reference images, beam time delays were determined. The proposed approach was validated on three linacs with either Catalyst™ or AlignRT™ respiratory gating systems. To investigate the impact of energy and dose rate on beam time delay, a range of QA plans with Eclipse (V15.7) were devised with varying energy and dose rates. For all energies, the beam on time delays in AlignRT™ V6.3.226, AlignRT™ V7.1.1, and Catalyst™ were 92.13 5.79ms, 123.11 6.44ms, and 303.44 4.28ms, respectively. The beam off time delays in AlignRT™ V6.3.226, AlignRT™ V7.1.1, and Catalyst™ were 121.87 1.34ms, 119.33 0.75ms, and 97.69 2.02ms, respectively. Furthermore, the beam on delays decreased slightly as dose rates increased for all gating systems, whereas the beam off delays remained unaffected. The validation results demonstrate the proposed QA approach of beam time delay for respiratory-gated radiotherapy was both reproducible and time-efficient to practice for institutions to customize accordingly.

Comprehensive beam delivery latency evaluation for gated proton therapy system using customized multi-channel signal acquisition platform.

Beam delivery latency in respiratory-gated particle therapy systems is a crucial issue to dose delivery accuracy. The aim of this study is to develop a multi-channel signal acquisition platform for investigating gating latencies occurring within RPM respiratory gating system (Varian, USA) and ProBeam proton treatment system (Varian, USA) individually. The multi-channel signal acquisition platform consisted of several electronic components, including a string position sensor for target motion detection, a photodiode for proton beam sensing, an interfacing board for accessing the trigger signal between the respiratory gating system and the proton treatment system, a signal acquisition device for sampling and synchronizing signals from the aforementioned components, and a laptop for controlling the signal acquisition device and data storage. RPM system latencies were determined by comparing the expected gating phases extracted from the motion signal with the trigger signal's state turning points. ProBeam system latencies were assessed by comparing the state turning points of the trigger signal with the beam signal. The total beam delivery latencies were calculated as the sum of delays in the respiratory gating system and the cyclotron proton treatment system. During latency measurements, simulated sinusoidal motion were applied at different amplitudes and periods for complete beam delivery latency evaluation under different breathing patterns. Each breathing pattern was repeated 30 times for statistical analysis. The measured gating ON/OFF latencies in the RPM system were found to be 104.20±13.64ms and 113.60±14.98ms, respectively. The measured gating ON/OFF delays in the ProBeam system were 108.29±0.85ms and 1.20±0.04ms, respectively. The total beam ON/OFF latencies were determined to be 212.50±13.64ms and 114.80±14.98ms. With the developed multi-channel signal acquisition platform, it was able to investigate the gating lags happened in both the respiratory gating system and the proton treatment system. The resolution of the platform is enough to distinguish the delays at the millisecond time level. Both the respiratory gating system and the proton treatment system made contributions to gating latency. Both systems contributed nearly equally to the total beam ON latency, with approximately 100ms. In contrast, the respiratory gating system was the dominant contributor to the total beam OFF latency.

Measurements in pulsed neutron fields.

Dosimetry in pulsed and mixed radiation fields represents an important challenge in radiation measurements, because in several accelerator technologies, the acceleration occurs in bunches of particles with short time duration, producing intense radiation pulses spaced by a relatively long time of beam off. The stray mixed radiation field generated around these installations maintains the same time structure as the primary beam and causes a problem in workplace fields' monitoring. Active neutron detectors normally used in steady neutron fields, specifically REM-counters and Bonner sphere spectrometers, can suffer pulsed fields because of the high dead time losses during the bursts and are often inadequate for pulsed field monitoring. This work reviews the efforts of European Radiation Dosimetry Group (EURADOS), and in particular of the Working Group 11 'High Energy Radiation Fields', to define the problem, characterize instrumentation and to propose solutions to the issue of pulsed and mixed radiation fields. Despite the EURADOS initiative, several open issues still remain. A metrological traceability for pulsed neutron fields is missing. There is still room for the optimization and better characterization of available instruments. Initiatives of education and training are required.

Large spatial shifts of reflected light beam off biaxial hyperbolic materials

Many optical systems that deal with polarization rely on the adaptability of controlling light reflection in the lithography-free nanostructure. In this study, we explore the Goos–Hänchen (GH) shift and Imbert–Fedorov (IF) shift in a biaxial hyperbolic film on a uniaxial hyperbolic substrate. This research statistically calculates and analyzes the GH shift and IF shift for the natural biaxial hyperbolic material (NBHM). We select the surface with the strongest anisotropy within the NBHM and obtain the complex beam-shift spectrum. By incorporating the NBHM film, the GH shift caused by a transversely magnetic incident-beam on the surface increases significantly compared with that on the uniaxial hyperbolic material. The maximum of GH shift can reach 86λ 0 at about 841 cm−1 when the thickness of NBHM is 90 nm, and the IF shift can approach 2.7λ 0 for a circularly-polarized beam incident on a 1700-nm-thick NBHM. It is found that the spatial-shift increases when a highly anisotropic hyperbolic polariton is excited in hyperbolic material, where the shift spectrum exhibits an oscillating behaviour accompanied with sharp shift peak (steep slope). This large spatial shift may provide an alternative strategy to develop novel sub-micrometric optical devices and biosensors.

ITER collective Thomson scattering-Preparing to diagnose fusion-born alpha particles (invited).

The ITER Collective Thomson scattering (CTS) diagnostic will measure the dynamics of fusion-born alpha particles in the burning ITER plasma by scattering a 1MW 60GHz gyrotron beam off fast-ion induced fluctuations in the plasma. The diagnostic will have seven measurement volumes across the ITER cross section and will resolve the alpha particle energies in the range from 300keV to 3.5MeV; importantly, the CTS diagnostic is the only diagnostic capable of measuring confined alpha particles for energies below ∼1.7MeV and will also be sensitive to the other fast-ion populations. The temporal resolution is 100ms, allowing the capture of dynamics on that timescale, and the typical spatial resolution is 10-50cm. The development and design of the in-vessel and primary parts of the CTS diagnostic has been completed. This marks the beginning of a new phase of preparation to maximize the scientific benefit of the diagnostic, e.g., by investigating the capability to contribute to the determination of the fuel-ion ratio and the bulk ion temperature as well as integrating data analysis with other fast-ion and bulk-ion diagnostics.

Treatment Time Optimization in Single Fraction Stereotactic Ablative Radiation Therapy: A 10-Year Institutional Experience

PurposeStereotactic ablative radiation therapy (SABR) delivered in a single fraction (SF) can be considered to have higher uncertainty given that the error probability is concentrated in a single session. This study aims to report the variation in technology and technique used and its effect on intrafraction motion based on a 10 years of experience in SF SABR. Methods and MaterialsRecords of patients receiving SF SABR delivered at our instruction between 2010 and 2019 were included. Treatment parameters were extracted from the patient management database by using an in-house script. Treatment time was defined as the time difference between the first image acquisition to the last beam off of a single session. The intrafraction variation was measured from the 3-dimensional couch displacement measured after the first cone beam computed tomography (CBCT) acquired during a treatment. ResultsThe number of SF SABR increased continuously from 2010 to 2019 and were mainly lung treatments. Treatment time was minimized by using volumetric modulated arc therapy, flattening filter-free dose rate, and coplanar field (24 ± 9 min). Treatment time increased as the number of CBCTs per session increased. The most common scenario involved both 2 and 3 CBCTs per session. On the average, a CBCT acquisition added 6 minutes to the treatment time. All treatments considered, the average intrafraction variation was 1.7 ± 1.6 mm. ConclusionsSF SABR usage increased with time in our institution. The intrafraction motion was acceptable and therefore a single fraction is an efficacious treatment option when considering SABR.

High-Resolution Optical Tweezers Combined with Multicolor Single-Molecule Microscopy.

We present an instrument that combines high-resolution optical tweezers and multicolor confocal fluorescence spectroscopy. Biological macromolecules exhibit complex conformation and stoichiometry changes in coordination with their motion and activity. To further our understanding of the complex machinery of life, we need methods that can simultaneously probe more than one degree of freedom of single molecules and complexes. Fluorescence optical tweezers, or "fleezers," combine the capabilities of optical tweezers and single-molecule fluorescence microscopy into a single instrument. Here we present the latest generation of a high-resolution fleezers instrument integrated with multicolor fluorescence spectroscopy. The tweezers portion of the instrument can manipulate biological macromolecules with pN scale forces while measuring subnanometer distances. Simultaneous with tweezers measurements, the multicolor fluorescence capability allows the direct observation of multiple molecules or multiple degrees of freedom which allows, for example, the observation of multiple proteins simultaneously within a complex. The instrument incorporates three fluorescence excitation lasers, all sourced from a single-mode optical fiber allowing a reliable alignment scheme, that allows, for example, three independent fluorescent probes or fluorescence resonance energy transfer (FRET) measurements and also increases flexibility in the choice of fluorescent probes. To avoid photobleaching and improve tweezers stability, the instrument implements a timesharing (using a single trap laser to produce a pair of traps via rapid switching between two locations) and interlacing (turning the trapping beam off when the fluorescence excitation beams are on and vice versa) scheme using acousto-optic modulators (AOM) to rapidly and precisely modulate lasers. Our latest "random phase" trap AOM control method obliterates previous residual trap positioning and bead position measurement errors. Here we present the general design principles and detailed construction and testing protocols for the instrument.

Using spin alignment of inelastically excited nuclei in fast beams to assign spins: The spectroscopy of O13 as a test case

Excited states in 13O were investigated using inelastic scattering of an E/A=69.5-MeV 13O beam off of a 9Be target. The excited states were identified in the invariant-mass spectra of the decay products. Both single proton and sequential two-proton decays of the excited states were examined. For a number of the excited states, the protons were emitted with strong anisotropy where emissions transverse to the beam axis are favored. The measured proton-decay angular distributions were compared to predictions from distorted-wave born-approximation (DWBA) calculations of the spin alignment which was shown to be largely independent of the excitation mechanism. The deduced $^{13}$O level scheme is compared to ab initio no-core shell model with continuum (NCSMC) predictions. The lowest-energy excited states decay isotropically consistent with predictions of strong proton 1s1/2 structure. Above these states in the level scheme, we observed a number of higher-spin states not predicted within the model. Possibly these are associated with rotational bands built on deformed cluster configurations predicted by antisymmetrized molecular dynamics (AMD) calculations. The spin alignment mechanism is shown to be useful for making spin assignments and may have widespread use.

Design of the HEBT components inside TIR room of the IFMIF DONES facility

The High Energy Beam Transport (HEBT) line components maintenance are to be conducted during twice yearly shutdown “beam off” periods, one 3-day shutdown and the main “beam off” shutdown period (annual preventive maintenance), which includes the necessary cooling and warming time, all totalling 20 days. Due to the radiation doses calculated and its subsequent radiation zone classification, technically challenging maintenance activities will need to be performed in the Accelerator Systems (AS) and particularly in the HEBT section located inside Target Interface Room (TIR). Thus, all HEBT components inside TIR must be designed to be maintained and replaced by Remote Handling (RH). In order to fulfil the RH requirements, a modularity approach intends to divide HEBT line section into independent large replacement units (LRUs), with localized interfaces. Splitting this section in three modules allows, first, the identification of faulty components more easily and secondly, reduces time needed for their replacement. In addition, the design of these modules has been performed to comply with beam dynamics, vacuum, building, RAMI and positioning requirements established for this section of the HEBT. As a result of the work done, the conclusions concerning the whole design process are summarized at the end of the paper.

Measurement of the proton spin structure at long distances

Measuring the spin structure of protons and neutrons tests our understanding of how they arise from quarks and gluons, the fundamental building blocks of nuclear matter. At long distances the coupling constant of the strong interaction becomes large, requiring non-perturbative methods to calculate quantum chromodynamics processes, such as lattice gauge theory or effective field theories. Here we report proton spin structure measurements from scattering a polarized electron beam off polarized protons. The spin-dependent cross-sections were measured at large distances, corresponding to the region of low momentum transfer squared between 0.012 and 1.0 GeV$^2$. This kinematic range provides unique tests of chiral effective field theory predictions. Our results show that a complete description of the nucleon spin remains elusive, and call for further theoretical works, e.g. in lattice quantum chromodynamics. Finally, our data extrapolated to the photon point agree with the Gerasimov-Drell-Hearn sum rule, a fundamental prediction of quantum field theory that relates the anomalous magnetic moment of the proton to its integrated spin-dependent cross-sections.

New Model Of Enhanced Plasticity For Reinforced Concrete Structural Elements That Take Into Account The Effects Of Lateral Loading And Gravity

Reinforced concrete structures are exposed to a progression of activities all through their life expectancy which may be the purpose behind damage. Subsequently, rehabilitation of existing structures is typically performed either to restore structural limit because of decay or damage or to broaden existing structural limit due to expanded loads. To fortify existing structures, numerous new creative materials like progressed fiber-reinforced polymers (FRPs) are discovered to be acceptable substitute for reinforcing materials like steel. They are actualized to fortify the presentation of structural components in flexure, pivotal, shear, and twist. In a RC outline, migrating plastic pivots in the beam off from the column face is normally prescribed to broaden pliability of the edge. This could be accomplished through rib reinforced FRP retrofit of the joint. Furthermore, to it, thus we execute an expanded pliancy for the concrete structural components like column, beam, chunk, dividers then on. The primary motivation behind a wide range of structural frameworks utilized in the structure type of structures is to transfer gravity and horizontal loads effectively.

Estimation of monitor unit through analytical method for dynamic IMRT using control points as an effective parameter

AbstractIntroduction:The control points (CP) play a significant role in the delivery of segmented based Intensity-Modulated Radiation Therapy (IMRT) delivery, particularly in dynamic mode. The number of segments is determined by control points and these segments will transfer from one to the other either during beam ON called dynamic delivery or during beam OFF called static delivery or step and shoot. This study was aimed at indirect estimation of the total monitor units (MU) to be delivered per field by exploiting the control points and also to find the MUs at any nth segment.Materials and methods:This study was performed in the Eclipse treatment planning software version 13.8.0. The details of control points, metre set weight per segment, leaf positions for each segment, field size, etc. were taken into consideration.Results:TPS calculated MU value and analytically estimated MU value were compared and the percentage of difference was estimated. The overall mean percentage of deviation was 1·03% between the TPS calculated method and the analytical method. The paired sample t-test was performed and, p-value <0·05, no significant difference was found. The analytical relationship determined to estimate the total number of MU delivered for any nth control point was also evaluated.Conclusion:The control points are a potential parameter in the conventional IMRT delivery. Through this study, we have addressed the indirect method to estimate the monitor units delivered per segment.

Time motion study to evaluate the impact of flattening filter free beam on overall treatment time for frameless intracranial radiosurgery using Varian TrueBeam® linear accelerator.

The aim was to study the impact of the flattening filter free (FFF) beam on overall treatment time for frameless intracranial radiosurgery using TrueBeam® LINAC.The development of frameless stereotactic radiosurgery (SRS) is possible due to the incorporation of image guidance in the delivery of treatment. It is important to analyze the cost and benefits of FFF beams for treating SRS by understanding the impact of FFF beams in reducing the treatment time. Dynamic conformal arc (DCA ) and volumetric arc therapy (VMAT) plans were generated using 6 MV with a flattening filter (FF) and FFF beams. Overall treatment time was divided into beam on time (BOT) and beam off time (BFT). Percentage beam on time reduction (PBOTR) and Percentage total time reduction (PTTR) factors were defined for the comparison. BOT reduction was observed to be significant for higher dose per fraction but subjected to the treatment technique and modulation differences. PBOTR values are much higher than PTTR values. The 39.9% of PBOTR resulted in only 8% PTTR for DCA and 65.3% resulted in 15.9% PTTR for VMAT. Major BFT was utilized for imaging and verification. FFF beam significantly reduced the beam on time and was found to be most effective if the fractional dose was as high as that for SRS. Newly defined PBOTR and PTTR factors are very useful indicators to evaluate the efficacy of FFF beams in terms of time reduction.

To the Bones by Valerie Nieman

To the Bones by Valerie Nieman Katherine Scott Crawford (bio) Valerie Nieman. To the Bones. Morgantown, W.Va.: West Virginia University Press, 2019. 220 pages. Softcover. $19.99. The images in Valerie Nieman's novel To the Bones—dank mine shafts rattling with skeletons, acidic rivers peeling the skin from human faces, gaping head wounds, and more—should make us all want to turn back. This was my first thought, upon reading the jacket copy: Are not the horrors coal mining inflicts upon the American landscape enough, without a hint of zombie? The answer is quick: No. Not nearly enough. Nieman does not take her readers gently into the West Virginia night. She plummets us down mine shafts, walks us through grand and terrifying old houses, sends our cars skidding over lonely mountain roads, hides us in dusty attics, makes us watch characters to whom we've become attached melt before our eyes. Hers is a heart-pounding, cinematic, and multi-layered story. It's the sort of rollercoaster ride you race back to the start of the line for, time and again, because despite a queasy [End Page 115] stomach and your heart in your throat, you're not ready for the thrill to end. From the moment Darrick Brehon, orphan, government auditor and unlikely hero, wakes in a mine shaft filled with dead bodies, to the story's very last line, I was in, too: a community member of hardscrabble Redbird, West Virginia, on the hunt for the truth. How did Darrick end up in that awful crack in the earth? Who were the skeleton dead, recent and otherwise? Did an evil more profligate than acid seep into the water from mining tunnels beneath the town? Why was he now possessed of a dangerous power? And what did the controlling and cryptic Kavanaugh family have to do with any of it? It is to Nieman's storytelling credit that she then introduces sharp and steady Louranna Taylor, a Redbird native and sweepstakes operator on the search for her missing daughter. Louranna is a fighter, tough as her mountain roots, and a well-drawn equal to Darrick and the novel's other central characters, including conflicted ex-Marine Marco DeLucca and persistent local journalist Zadie Person. Nieman mines the interiority of her characters to glance a flashlight's beam off their flinty layers. Characters who so easily could become stock—whether by trade or regional stereotype—are instead revealed to be deeply human. Put them on a quest—to unlock the secrets behind the poisoning of their town, save their family members, and usurp a dangerous, robber-baron-like ruling family—and give it a supernatural twist, and the novel becomes something entirely new and different. My favorite books are those which straddle the genre line, refusing to exist within publishing industry parameters. To the Bones does exactly this, and while one of its genres is certainly [End Page 116] Appalachian literature, it defies expected themes. Take frustrated outsider Darrick, who halfway through the story asks this internal question of his West Virginia compatriots: "How much misery could one place absorb? Disappearances, murders, mine disasters, people dying in a river that might have boiled right out of hell? Why don't people just leave?" This is the question, right? Most Appalachian, regional, and place-based literature in general concerns itself on some level with an unapologetic love of the land. But instead of offering us the land and its beauty, Nieman offers us its people. Like Louranna, who tells Darrick that, "… we still love these hills, more'n you can imagine. We make a home here because it is home, not because it's easy. We grow up learning to fish, hunt ramps, shake down apples. We build our homes in places that don't make economic sense. And we dig coal, because that's what we've done for generations, and there's pride in having the skill and guts to do that even when we know the cost." Louranna, however, is the only character who seems to voice why she stays. If the others have their reasons, they never fully emerge from the dark, and perhaps do...

Intrafraction Deviations and Tolerance Levels for a Surface-Guidance System

The importance of analyzing intrafraction movements in radiotherapy patients is widely acknowledged. In order to obtain this information, a surface-guidance system captures the external surface of the patients in real time when they are on the treatment table. This mechanism controls intrafraction movements by switching the beam on and off in case the deviation values become larger than the tolerance levels. In our institution the initial values used as tolerance were proposed by the manufacturer. Taking this into account, the aim of this project will be to optimize these tolerance levels. Data from a total of n=126 patients with different types of cancer were used in this work. Each of their radiotherapy sessions was classified depending on the localization of the lesion: cranial (n=12,170 sessions), head and neck (n=18, 436 sessions), thorax (n=20, 514 sessions), breast (n=39, 593 sessions), abdomen (n=11, 151 sessions), pelvis (n=20, 517 sessions) and extremities (n=6, 108 sessions), thus achieving a total of 2489 sessions which would be equivalent to more than 200 hours of monitoring. Tolerances were derived from a histogram for each localization. The histogram allows calculating the time spent by patients for each localization within different maximum deviations thus enabling the estimation of tolerance values at various levels. In this study we have chosen to pay attention to the 80%, 85%, 90%, 95%, 97%, 98% and 99% levels as possible tolerance values. In this context, a tolerance value of, say, 95% means that patients of a given localization spend 95% of the time within tolerance. Table 1 presents the obtained tolerances (in milimeters) and the corresponding figures provided by the manufacturer. Since it is necessary to reach a trade-off between very restraining tolerance values, only allowing very small movements but holding the beam off for long times, and very loosened tolerance values, that barely restrict patient movement but decrease treatment duration by letting the beam on almost all the time. We believe that a proper balance is obtained for tolerance values in the 90% to 95% range, reducing in 1 mm the tolerance level for all localizations, when compared with the initial values proposed by the manufacturer.Abstract 3764; Table 1ToleranceBreastThoraxAbdomenPelvisExtremitiesCranialHead & NeckAt 80%2.82.93.22.91.41.41.0At 85%3.23.23.73.32.21.61.3At 90%3.73.74.43.73.01.91.7At 95%4.54.75.24.33.72.52.3At 97%5.05.15.74.64.12.72.5At 98%5.65.46.04.84.42.92.7At 99%6.45.86.55.14.73.33.0Manufacturer5655533 Open table in a new tab

The comparison of spatial resolution of ion chamber, diode, and EBT3 film based on the dose profile

Background: It is essential for the physicist to quantify the dose of the radiation prior and during cancer treatment to ensure proper execution of the treatment plan. The most common way to measure the dose is utilizing Farmer chamber. The limitation of Farmer chamber is that it only provides dose of a specific point, while the beam dose profile is needed for the planning system. The Gafchromic EBT3 film can provide a quantitative dose profile in a 2D space. The EBT3 film has low energy dependence, similar effective atomic number to water, and self-developing; making it an ideal candidate for dose profile measurement. Methods: Dose profiles of EBT3 was measured, analyzed and compared to semiflex chamber and EDGE detector under same conditions. The EBT3 films were placed at the center of RW3 water phantom (30×30×30 cm 3 ) under flattening filter free (FFF) Mode of Linac. The EBT3 films were calibrated by additional RW3 with a Farmer chamber under the stacked RW3 water phantom. Percentage depth dose (PDD) and Matlab were used to fit the dose curve of EBT3 and the results are presented. Results: The penumbra of the measured dose profile through EBT3 film demonstrated little differences when comparing with that of the EDGE detector and noticeable differences when compared to that of the semiflex chamber. For a field size of 2×2 cm 2 , (b=0.08, depth of 5 cm, beam off central axis 0.8 cm), the measured difference of dose profile between EBT3 and EDGE detector is –2.24%. Under the same conditions, the dose profile difference between EBT3 and semiflex chamber is 10.59%. Conclusions: This study shows that EDGE detector has the highest spatial resolution to the dose profile. EBT3 film in combination with solid phantom can quickly sample dose profile in 2D. EBT3 film can be considered to be an excellent quality assurance (QA) tool with accurate dosimetry, a good spatial resolution and tolerable dose uncertainty.

Quality assurance of gating response times for surface guided motion management treatment delivery using an electronic portal imaging detector

Gating response times of monitoring system/LINAC combinations for gated radiotherapy treatments are notoriously difficult to measure. This difficulty may reflect why the incorporation of gating response times is not thoroughly considered when creating treatment margins for gated radiotherapy treatments, however ignoring the effect of gating response time could lead to significant treatment inaccuracies. This study shows a methodology which measured gating response times for AlignRT/Varian Truebeam combination which appears to be applicable to any surface guided monitoring/Linac combination as well as those combinations which incorporate extended lag times (>200 ms). Beam on lag time appears to be measurably greater than beam off lag time. Although these gating response times are slower than other gating systems on the market, the advantages surface guided radiotherapy (SGRT) could potentially provide for treatment accuracy is discussed as well as demonstrating the lack of guidance regarding SGRT with respect to gated treatments.

Characteristics of highly charged ions produced at Kobe EBIS under modulated operation

The electron beam ion source (Kobe EBIS) has been developed to perform modification of surfaces using highly charged ions (HCIs) at the Kobe University, Japan. Recent study revealed that periodic intermission of electron beam improves charge state distribution of extracted ions. The period of intermission is in the order of 100 ms, and the width of beam‐off time is 1 ms or less. This operational mode (pulse mode) makes it possible to produce Ar15+ to Ar17+ effectively, whereas the charge is limited less than 14+ under the ordinary operational mode with direct current (DC) electron beam. A spike of HCIs with a peak current in the order of nA is also observed at each moment of electron beam off. The measurement of the time evolution of Ar16+ intensity around the timing of mode change revealed that the intensity of extracted Ar16+ changes slowly after mode change with a time constant of few seconds.

SELECTION OF COINCIDENCE ELECTRON-PROTON EVENTS IN NUCLEI INTERACTION

The main goal of this analysis is to study momentum (or kinetic energy) distribution of the backward going protons using data from CLAS EG2 experiment at Jefferson Lab. In this experiment scattering of a 5.014 GeV electron beam off various nucleus targets, ranging from deuterium to lead, have been recorded. The analysis includes selection of events in the reaction $ A(e, e^{\prime}, P_{back}) X $, where $ P_{back} $ is a proton scattered above 90° either in the lab coordinate frame or with respect to the direction of the interacting virtual photon, then performing required corrections and studying the protons momentum distribution as a function of energy transfer. In this paper identification of electron-proton events is presented.