Pulsed Linear Accelerator Research Articles

Study of structural, surface energies, and tribomechanical properties of thermoplastics irradiated by electron beam

This study investigates the effects of electron irradiation on the structural, surface energy, and tribomechanical properties of two key thermoplastics: polyetheretherketone (PEEK) and polytetrafluoroethylene (PTFE). The experimental methods included electron beam irradiation using the ILU-10 pulsed linear accelerator, Fourier transform infrared spectroscopy (FT-IR), x-ray diffraction (XRD), microhardness testing, surface roughness assessment, tribology tests, and contact angle measurements.The FT-IR analysis revealed significant chemical changes on the surfaces of the polymers, including oxidation processes and the breaking of molecular bonds. XRD analysis showed an increase in the crystallinity of PTFE after irradiation, while the structure of PEEK remained stable. Microhardness testing indicated a notable increase in hardness for both polymers, particularly for PTFE, suggesting cross-linking of molecular chains. Surface roughness measurements demonstrated a decrease in roughness for both irradiated polymers. Tribology tests revealed that electron irradiation increased the coefficient of friction for PTFE and PEEK under various loads, which can be attributed to the alterations in their surface properties. Contact angle measurements indicated improved wettability of the irradiated surfaces, especially for PEEK, due to the formation of new functional groups. The total surface energy increased for both polymers post-irradiation, as determined using the Owens-Wendt-Rabel-Kaeble method. Electron irradiation leads to significant modifications in the surface and bulk properties of PEEK and PTFE, enhancing their tribomechanical and adhesive properties. These changes open new opportunities for the application of these materials in various engineering fields where specific performance characteristics are required.

Method of hyaluronidase immobilization to produce an oral dosage form

Hyaluronidase is an enzyme that helps maintain an optimal balance of hyaluronic acid in connective tissue and ensures full tissue regeneration. Currently, hyaluronidase drugs are used in various fields of medicine. Meanwhile, there are no oral preparations based on hyaluronidase on the pharmaceutical market due to its low bioavailability in this method of administration. One of the options to increase enzyme bioavailability is electron-beam pegylation, which involves obtaining drugs with a modified pharmacokinetic profile in the direction of increasing enteral bioavailability, as well as having additional protection from the action of proteolytic enzymes. Aim of the study was using the electron beam pegylation method to obtain a laboratory batch of a preparation based on highly purified hyaluronidase, which can be further used in the development of an oral drug product. Material and methods. Hyaluronidase, which was isolated from bovine testicular hyaluronidase and polyethylene glycols of different molecular weight, was used in the experimental study. Experiments were carried out using a pulsed linear accelerator ILU-10 for enzyme electron beam immobilization on a water-soluble polymer matrix of polyethylene glycol molecules. The formation of hyaluronidase and polyethylene glycols conjugates was confirmed by exclusion chromatography. Results. As a result of accelerated electron irradiation of hyaluronidase and polyethylene glycol of molecular mass 1500 Da conjugates of enzyme and polymer matrix were formed. After electron-beam pegylation, the specific activity of the enzyme was retained. Conclusions. A laboratory batch of prototype pharmaceutical substance based on immobilised hyaluronidase on polyethylene glycol was obtained.

Comparing the effects of irradiation with protons or photons on neonatal mouse brain: Apoptosis, oncogenesis and hippocampal alterations

Background and PurposeMedulloblastoma (MB) is a common primary brain cancer in children. Proton therapy in pediatric MB is intensively studied and widely adopted. Compared to photon, proton radiations offer potential for reduced toxicity due to the characteristic Bragg Peak at the end of their path in tissue. The aim of this study was to compare the effects of irradiation with the same dose of protons or photons in Patched1 heterozygous knockout mice, a murine model predisposed to cancer and non-cancer radiogenic pathologies, including MB and lens opacity. Materials and MethodsTOP-IMPLART is a pulsed linear proton accelerator for proton therapy applications. We compared the long-term health effects of 3 Gy of protons or photons in neonatal mice exposed at postnatal day 2, during a peculiarly susceptible developmental phase of the cerebellum, lens, and hippocampus, to genotoxic stress. ResultsExperimental testing of the 5 mm Spread-Out Bragg Peak (SOBP) proton beam, through evaluation of apoptotic response, confirmed that both cerebellum and hippocampus were within the SOBP irradiation field. While no differences in MB induction were observed after irradiation with protons or photons, lens opacity examination confirmed sparing of the lens after proton exposure. Marked differences in expression of neurogenesis-related genes and in neuroinflammation, but not in hippocampal neurogenesis, were observed after irradiation of wild-type mice with both radiation types.Conclusion.In-vivo experiments with radiosensitive mouse models improve our mechanistic understanding of the dependence of brain damage on radiation quality, thus having important implications in translational research.

Analytical solutions for the sliding displacement of model slopes simulating both the frictional and rotational effects under piecewise linear acceleration pulses

AbstractSimplified methods predicting earthquake‐induced displacement of slopes are based on the Newmark sliding‐block model. This model does not consider the decrease in inclination of the sliding mass as a result of its downward motion and this effect is usually modeled by improving the above model by assuming that the critical acceleration value for relative motion of the block increases linearly with the distance moved. This work, for the first time, derives analytical solutions predicting the sliding displacement under idealized acceleration pulses of the model described above simulating both the frictional and rotational effects. First, a general solution is derived in dimensionless form for the motion of the sliding mass under a piecewise linearly varying pulse for the cases of both static stability and instability. The solution is obtained in each interval by (a) solving for the displacement and velocity in terms of these quantities at the end of the previous interval, (b) estimating the time corresponding to a sliding velocity equal to zero, and (c) investigating if the estimated time solution is consistent with the time interval and thus if it can be considered as the global solution. Then, based on this solution and the conditions where downward and upward motion starts, a procedure predicting the final displacement of the sliding mass for a piecewise linearly varying pulse is proposed. Finally, analytical solutions are derived, given in graphical form, partly validated, and discussed for the particular cases of half and full cycle pulses of rectangular, triangular, and trapezoidal shapes.

PO-632-06 REAL-TIME EX-VIVO RADIOTHERAPY IMPACTS ON PACEMAKER FUNCTION ARE MINIMAL

There is a paucity of data regarding the safety of radiotherapy in patients with pacemakers and the impact of linear accelerator parameters is unclear. To assess the function of pacemakers when exposed to different linear accelerator parameters. Pacemakers (2 single, 1 dual chamber) were exposed to radiation at dose rates 0.2-11.8Gy/min. Dose rate was modulated by adjusting the distance from the beam edge, linear accelerator pulse repetition rate (rep rate) and distance from source. Noise amplitude, pacemaker output, and device behavior during irradiation were assessed in VVI or DDD modes. Each device was irradiated 28 times for 10 seconds. Noise amplitude on bipolar (Bi) channel increased with dose rate (r2=0.3611, p<0.0001, B) and on unipolar (Uni) channel decreased with rep rate (r2 = 0.09, p<0.01; C). On both channels noise amplitude decreased with distance from field edge (Bi r2 = 0.53, p<0.01; Uni r2 = 0.42, p<0.01; D). No over-sensed events occurred in response to radiation induced background noise. Low frequency signals on the Uni and Bi channels were observed with beam on and off (E), resulting in over-sensed events only when directly in the radiation beam and sensing Uni. When directly in the beam, oversensing of A pacing on the V sensing Uni channel was observed leading to pacing inhibition (F). Post-radiation exposure interrogation was unremarkable revealing no evidence of device malfunction. Pacemaker malfunctions when directly in photon radiation beam are related to oversensing and crosstalk phenomena preferentially affecting the unipolar sensing channel. There was no evidence of long-term device malfunction upon repeated interrogations despite multiple exposures.

Implementation and validation of a beam-current transformer on a medical pulsed electron beam LINAC for FLASH-RT beam monitoring.

PurposeTo implement and validate a beam current transformer as a passive monitoring device on a pulsed electron beam medical linear accelerator (LINAC) for ultra‐high dose rate (UHDR) irradiations in the operational range of at least 3 Gy to improve dosimetric procedures currently in use for FLASH radiotherapy (FLASH‐RT) studies.MethodsTwo beam current transformers (BCTs) were placed at the exit of a medical LINAC capable of UHDR irradiations. The BCTs were validated as monitoring devices by verifying beam parameters consistency between nominal values and measured values, determining the relationship between the charge measured and the absorbed dose, and checking the short‐ and long‐term stability of the charge‐absorbed dose ratio.ResultsThe beam parameters measured by the BCTs coincide with the nominal values. The charge‐dose relationship was found to be linear and independent of pulse width and frequency. Short‐ and long‐term stabilities were measured to be within acceptable limits.ConclusionsThe BCTs were implemented and validated on a pulsed electron beam medical LINAC, thus improving current dosimetric procedures and allowing for a more complete analysis of beam characteristics. BCTs were shown to be a valid method for beam monitoring for UHDR (and therefore FLASH) experiments.

Spatial and temporal dosimetry of individual electron FLASH beam pulses using radioluminescence imaging

Purpose. In this study, spatio-temporal beam profiling for electron ultra-high dose rate (UHDR; >40 Gy s−1) radiation via Cherenkov emission and radioluminescence imaging was investigated using intensified complementary metal–oxide–semiconductor cameras. Methods. The cameras, gated to FLASH optimized linear accelerator pulses, imaged radioluminescence and Cherenkov emission incited by single pulses of a UHDR (>40 Gy s−1) 10 MeV electron beam delivered to the isocenter. Surface dosimetry was investigated via imaging Cherenkov emission or scintillation from a solid water phantom or Gd2O2S:Tb screen positioned on top of the phantom, respectively. Projected depth–dose profiles were imaged from a tank filled with water (Cherenkov emission) and a 1 g l−1 quinine sulfate solution (scintillation). These optical results were compared with projected lateral dose profiles measured by Gafchromic film at different depths, including the surface. Results. The per-pulse beam output from Cherenkov imaging agreed with the photomultiplier tube Cherenkov output to within 3% after about the first five to seven ramp-up pulses. Cherenkov emission and scintillation were linear with dose (R 2 = 0.987 and 0.995, respectively) and independent of dose rate from ∼50 to 300 Gy s−1 (0.18–0.91 Gy/pulse). The surface dose distribution from film agreed better with scintillation than with Cherenkov emission imaging (3%/3 mm gamma pass rates of 98.9% and 88.8%, respectively). Using a 450 nm bandpass filter, the quinine sulfate-based water imaging of the projected depth optical profiles agreed with the projected film dose to within 5%. Conclusion. The agreement of surface dosimetry using scintillation screen imaging and Gafchromic film suggests it can verify the consistency of daily beam quality assurance parameters with an accuracy of around 2% or 2 mm. Cherenkov-based surface dosimetry was affected by the target’s optical properties, prompting additional calibration. In projected depth–dose profiling, scintillation imaging via spectral suppression of Cherenkov emission provided the best match to film. Both camera-based imaging modalities resolved dose from single UHDR beam pulses of up to 60 Hz repetition rate and 1 mm spatial resolution.

A Pulsed Power Supply for Accelerators of the ILU Series Based on Capacitive Storage

Abstract—A pulsed power supply based on capacitive storage with a partial discharge for high-frequency pulsed linear electron accelerators of the ILU type is described. The maximum output pulse voltage of the source is 36 kV at a load current of up to 250 A and a pulse duration of up to 1 ms, and a pulse repetition rate of up to 100 Hz. The source is built according to a relatively simple modular scheme and consists of ten modules connected in series. It was assembled and tested with a load connection in one module. The circuit provides uniform current consumption in all phases of a 380 V three-phase supply network.

An ionizing radiation acoustic imaging (iRAI) technique for real-time dosimetric measurements for FLASH radiotherapy.

FLASH radiotherapy (FLASH-RT) is a novel irradiation modality with ultra-high dose rates (>40Gy/s) that have shown tremendous promise for its ability to enhance normal tissue sparing while maintaining comparable tumor cell eradication toconventional radiotherapy (CONV-RT). Due to its extremely high dose rates, clinical translation of FLASH-RT is hampered by risky delivery and current limitations in dosimetric devices, which cannot accurately measure, in real time, dose at deeper tissue. This work aims to investigate ionizing radiation acoustic imaging (iRAI) as a promising image-guidance modality for real-time deep tissue dose measurements during FLASH-RT. The underlying hypothesis is that iRAI can enable mapping of dose deposition with respect to surrounding tissue with a single linear accelerator (linac) pulse precision in real time. In this work, the relationship between iRAI signal response and deposited dose was investigated as well as the feasibility of using a proof-of-concept dual-modality imaging system of ultrasound and iRAI for treatment beam co-localization with respect to underlying anatomy. Two experimental setups were used to study the feasibility of iRAI for FLASH-RT using 6MeV electrons from a modified Varian Clinac. First, experiments were conducted using a single element focused transducer to take a series of point measurements in a gelatin phantom, which was compared with independent dose measurements using GAFchromic film. Secondly, an ultrasound and iRAI dual-modality imaging system utilizing a phased array transducer was used to take coregistered two-dimensional (2D) iRAI signal amplitude images as well as ultrasound B-mode images, to map the dose deposition with respect to surrounding anatomy in an ex vivo rabbit liver model with a single linac pulse precision. Using a single element transducer, iRAI measurements showed a highly linear relationship between the iRAI signal amplitude and the linac dose per pulse (r2 =0.9998) with a repeatability precision of 1% and a dose resolution error <2.5% in a homogenous phantom when compared to GAFchromic film dose measurements. These phantom results were used to develop a calibration curve between the iRAI signal response and the delivered dose per pulse. Subsequently, a normalized depth dose curve was generated that agreed with film measurements with an RMSE of 0.0243, using correction factors to account for deviations in measurement conditions with respect to calibration. Experiments on the ex-vivo rabbit liver model demonstrated that a 2D iRAI image could be generated successfully from a single linac pulse, which was fused with the B-mode ultrasound image to provide information about the beam position with respect to surrounding anatomy in real time. This work demonstrates the potential of using iRAI for real-time deep tissue dosimetry in FLASH-RT. Our results show that iRAI signals are linear with dose and can accurately map the delivered radiation dose with respect to soft tissue anatomy. With its ability to measure dose for individual linac pulses at any location within surrounding soft tissue while identifying where that dose is being delivered anatomically in real time, iRAI can be an indispensable tool to enable safe and efficient clinical translation of FLASH-RT.

Scintillator Target Imaging: A Novel Surface Dosimetry Method

The hypothesis of this work was that remote imaging of surface dose from small scintillators would be possible, suitable for clinical needs in soft tissue radiotherapy, and would minimize workflow of on-patient dosimetry due to automation of data analysis. An intensified, time-gated, camera synchronized to linear accelerator (linac) pulses was used to capture scintillation light from plastic discs directly attached to the skin surface of patients and phantoms undergoing whole breast (WB), head-neck (HN), and total skin electron (TSE) treatment. Scintillators were painted with reflective paint on the rear face and edges, coated with a protective film, and an adhesive strip was attached to the rear face. Optically stimulated luminescence detectors (OSLDs) were placed adjacent to the scintillators to provide reference surface dose measurements during all imaging. Two types of imaging apparatus were evaluated in this study: 1) a camera sensitive to both Cherenkov and scintillation emission, and 2) a camera with improved sensitivity to scintillation. Both of the scintillator dosimeter imaging systems were able to determine surface dose with <3% error compared to OSLDs during TSE, HN, and WB therapy. Furthermore, analysis of a human pilot study involving 242 instances of surface dose measured by scintillator and OSLD were linearly correlated with an R2 = 0.95. The 2nd version of the imaging system, tuned to maximize sensitivity to scintillation emission, was able to enhance scintillation intensity detection by 7x and suppress Cherenkov detection by 25x. Scintillator dosimeters were able to accurately track cumulative surface dose at a given anatomical site over the course of a full cycle of TSET. In the context of HN treatment, feasibility testing has shown that scintillation emission can be imaged through an optically-clear bolus and gaps of an immobilization mask. Application of a protective clear coating and adhesive backing had no significant effect on scintillator light output, allows for easy application of the dosimeter to the skin surface, and enables dosimeter re-use by standard clinical cleaning methods. Imaging scintillator dosimeters has been shown to be a viable method to obtain surface dose measurements in clinical radiotherapy. Improvements to the spectral sensitivity of the camera system permit reduction in dosimeter size and geometry for potential use in smaller-field treatment or for improved signal to noise. Since this technique requires simplified attachment, features a streamlined readout process, and automatically saves data to an electronic record – with capture of the anatomical position of dosimeter placement on the patient – error and time related to dosimeter readout and dose recording is minimized.

Time-resolved dose measurements of linear accelerator pulses using a fibre optic sensor: Applications and challenges

We present time-resolved radioluminescence (RL) measurements from P-doped silica optical fibre, demonstrating potential utility in pulsed source dosimetry. When subjected to 140 MU/min from a 6 MV photon linac source, a 220 µm-core fibre has produced a RL response of 720 ± 20 photon counts/pulse from a saw-tooth ~ 40 µs duration return-to-baseline waveform. Conversely, the Cerenkov stem signal within the radiation insensitive carrier fibre is observed to offer an amplitude amounting to a little less than 3% of that of the P-doped fibre, the sharply spiked response being of ~ 2 µs duration. On the basis of these results, the practical applications and the challenges in the establishment of an effective dosimetry system are discussed.

Technical Note: Time-gating to medical linear accelerator pulses: Stray radiation detector.

CCD cameras are employed to image scintillation and Cherenkov radiation in external beam radiotherapy. This is achieved by gating the camera to the linear accelerator (Linac) output. A direct output signal line from the linac is not always accessible and even in cases where such a signal is accessible, a physical wire connected to the output port can potentially alter Linac performance through electrical feedback. A scintillating detector for stray radiation inside the Linac room was developed to remotely time-gate to linac pulses for camera-based dosimetry. A scintillator coupled silicon photomultiplier detector was optimized and systematically tested for location sensitivity and for use with both x rays and electron beams, at different energies and field sizes. Cherenkov radiation emitted due to static photon beams was captured using the remote trigger and compared to the images captured using a wired trigger. The issue of false-positive event detection, due to additional neutron activated products with high energy beams, was addressed. The designed circuit provided voltage >2.5V even for distances up to 3m from the isocenter with a 6MV, 5×5cm beam, using a Ø3×20mm3 Bi4 Ge3 O12 (BGO) crystal. With a larger scintillator size, the detector could be placed even beyond 3m distance. False-positive triggering was reduced by a coincidence detection scheme. Negligible fluctuations were observed in time-gated imaging of Cherenkov intensity emitted from a water phantom, when comparing directly connected vs this remote triggering approach. The remote detector provides untethered synchronization to linac pulses. It is especially useful for remote Cherenkov imaging or remote scintillator dosimetry imaging during radiotherapeutic procedures when a direct line signal is not accessible.

Comparative Analysis on Traumatic Brain Injury Risk Due to Primary and Secondary Impacts in a Pedestrian Sideswipe Accident

A series of pedestrian sideswipe impacts were computationally reconstructed; a fast-walking pedestrian was collided laterally with the side of a moving vehicle at 25 km/h or 40 km/h, which resulted in rotating the pedestrian's body axially. Potential severity of traumatic brain injury (TBI) was assessed using linear and rotational acceleration pulses applied to the head and by measuring intracranial brain tissue deformation. We found that TBI risk due to secondary head strike with the ground can be much greater than that due to primary head strike with the vehicle. Further, an “effective” head mass, meff, was computed based upon the impulse and vertical velocity change involved in the secondary head strike, which mostly exceeded the mass of the adult head-form impactor (4.5 kg) commonly used for a current regulatory impact test for pedestrian safety assessment. Our results demonstrated that a sport utility vehicle (SUV) is more aggressive than a sedan due to the differences in frontal shape. Additionally, it was highlighted that a striking vehicle velocity should be lower than 25 km/h at the moment of impact to exclude the potential risk of sustaining TBI, which would be mitigated by actively controlling meff, because meff is closely associated with a rotational acceleration pulse applied to the head involved in the final event of ground contact.

Recent advances in photonic dosimeters for medical radiation therapy

Radiation therapy, which uses X-rays to destroy or injure cancer cells, has become one of the most important modalities to treat the primary cancer or advanced cancer. High resolution, water equivalent and passive X-ray dosimeters are highly desirable for developing quality assurance (QA) systems for novel cancer therapy like microbeam radiation therapy (MRT) which is currently under development. Here we present the latest developments of high spatial resolution scintillator based photonic dosimeters, and their applications to clinical external radiation beam therapies: specifically high energy linear accelerator (LINAC) photon beams and low energy synchrotron photon beams. We have developed optical fiber dosimeters with spatial resolutions ranging from 50 to 500 mm and tested them with LINAC beams and synchrotron microbeams. For LINAC beams, the fiberoptic probes were exposed to a 6 MV, 10 cm by 10 cm Xray field and, the beam profiles as well as the depth dose profiles were measured at a source-to-surface distance (SSD) of 100 cm. We have also demonstrated the possibility for temporally separating Cherenkov light from the pulsed LINAC scintillation signals. Using the 50 mm fiber probes, we have successfully resolved the microstructures of the microbeams generated by the imaging and medical beamline (IMBL) at the Australian Synchrotron and measured the peak-to-valley dose ratios (PVDRs). In this paper, we summarize the results we have achieved so far, and discuss the possible solutions to the issues and challenges we have faced, also highlight the future work to further enhance the performances of the photonic dosimeters.

Investigating the performances of a 1 MV high pulsed power linear transformer driver: from beam dynamics to x radiation

The performance of a 1 MV pulsed high-power linear transformer driver accelerator were extensively investigated based on a numerical approach which utilizes both electromagnetic and Monte Carlo simulations. Particle-in-cell calculations were employed to examine the beam dynamics throughout the magnetically insulated transmission line which governs the coupling between the generator and the electron diode. Based on the information provided by the study of the beam dynamics, and using Monte Carlo methods, the main properties of the resulting x radiation were predicted. Good agreement was found between these simulations and experimental results. This work provides a detailed understanding of mechanisms affecting the performances of this type of high current, high-voltage pulsed accelerator, which are very promising for a growing number of applications.

Transmission dosimetry via MAPS‐based event discrimination in a medical linear accelerator

Transmission dosimetry, which places a detector upstream of the patient, is a promising method of dosimetry for intensity‐modulated radiotherapy. Dose‐predicted downstream of the patient is affected by attenuation and scattering. Changes in the radiation field are difficult to separate from changes in the beam that might indicate an erroneous treatment. Monolithic active pixel sensor (MAPS) technology offers a potentially cost‐effective method for measuring the beam profile in transmission geometry. MAPS detectors can be made very thin (interacting with less than 1% of photons), while offering high spatial and temporal resolution, and therefore event shape and energy discrimination. This study examines event discrimination with MAPS detectors in the high dose‐rate environment associated with a medical linear accelerator (LINAC), as a method of distinguishing between therapeutic and contaminant components of the radiation. Monte Carlo modeling of the LINAC and MAPS detector has been used to predict the spectrum of events in the panel, including an evaluation of the occupancy associated with individual LINAC pulses, occurring at rates of up to 40 Hz. It is shown via modeling and experimental measurements that there is sufficiently low occupancy to allow event discrimination. Identifiable signatures, including the dominance of photon events at low and high energy deposition limits, and features peculiar to contaminating charged‐particles, suggest fruitful avenues. Loss of resolution, because of charge sharing in the detector observed in measurements of the LINAC beam, and increasingly higher dose‐rates used in practice imply further challenges. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Effects of ground impact on traumatic brain injury in a fender vault pedestrian crash

The present study replicated a series of vehicle–to–pedestrian crashes involved in a right–corner frontal impact up to a secondary or ground impact. The results showed that post–impact pedestrian kinematics and subsequent kinetics are not easily predictable and are considerably affected by the vehicle front structure and impact speed. The Head Injury Criterion (HIC), calculated with a resultant linear acceleration of the head, reached around 1000 or higher because of secondary head strike even at 25 km/h. Similarly, the maximum rotational acceleration of the head resulted in higher values owing to ground impact rather than primary head strike. This study has also suggested the importance of accounting for both linear and angular acceleration pulses applied to the head to assess the potential risk of sustaining Traumatic Brain Injury (TBI) due to eventual contact with the ground even at low impact speeds, and this should be a focus of future research.

Does Vestibular End-Organ Function Recover after Gentamicin-Induced Trauma in Guinea Pigs?

Until 1993 it was commonly accepted that regeneration of vestibular hair cells was not possible in mammals. Two histological studies then showed structural evidence for spontaneous regeneration of vestibular hair cells after gentamicin treatment. There is less evidence for functional recovery going along with this regenerative process; in other words, do regenerated hair cells function adequately? This study aims to address this question, and in general evaluates whether spontaneous functional recovery may occur, in the short or long term, in mammals after ototoxic insult. Guinea pigs were treated with gentamicin for 10 consecutive days at a daily dose of 125 mg/kg body weight. Survival times varied from 1 day to 16 weeks. Vestibular short-latency evoked potentials (VsEPs) to linear acceleration pulses were recorded longitudinally to assess otolith function. After the final functional measurements we performed immunofluorescence histology for hair cell counts. Auditory brainstem responses (ABRs) to click stimuli were recorded to assess cochlear function. As intended, gentamicin treatment resulted in significant loss of utricular hair cells and accompanying declines in VsEPs. Hair cell counts 8 or 16 weeks after treatment did not significantly differ from counts after shorter survival periods. Maximal functional loss was achieved 1-4 weeks after treatment. After this period, only 2 animals showed recovery of VsEP amplitude - all other animals did not reveal signs of regeneration or recovery. In contrast, after initial ABR threshold shifts there was a small but significant recovery. We conclude that spontaneous recovery of otolith function, in contrast to cochlear function, is very limited in guinea pigs. These results support the concept of intratympanic gentamicin treatment where gentamicin is used for chemoablation of the vestibular sensory epithelia.

The influence of acceleration loading curve characteristics on traumatic brain injury

To prevent brain trauma, understanding the mechanism of injury is essential. Once the mechanism of brain injury has been identified, prevention technologies could then be developed to aid in their prevention. The incidence of brain injury is linked to how the kinematics of a brain injury event affects the internal structures of the brain. As a result it is essential that an attempt be made to describe how the characteristics of the linear and rotational acceleration influence specific traumatic brain injury lesions. As a result, the purpose of this study was to examine the influence of the characteristics of linear and rotational acceleration pulses and how they account for the variance in predicting the outcome of TBI lesions, namely contusion, subdural hematoma (SDH), subarachnoid hemorrhage (SAH), and epidural hematoma (EDH) using a principal components analysis (PCA). Monorail impacts were conducted which simulated falls which caused the TBI lesions. From these reconstructions, the characteristics of the linear and rotational acceleration were determined and used for a PCA analysis. The results indicated that peak resultant acceleration variables did not account for any of the variance in predicting TBI lesions. The majority of the variance was accounted for by duration of the resultant and component linear and rotational acceleration. In addition, the components of linear and rotational acceleration characteristics on the x, y, and z axes accounted for the majority of the remainder of the variance after duration.

Simulation and measurement of delayed γ-rays after photon-induced fission

Photon-induced fission has been investigated as a method to detect and identify nuclear materials. Although high-energy delayed-fission γ-rays have been considered as a reliable signature for detection of fissionable materials, interference from γ-rays produced as secondary effects from other photonuclear reactions is inevitable. This effect has been studied in distinguishing fissionable materials from non-fissionable materials based on differential delayed γ-ray yields via both simulation and measurements. The energy spectra of delayed-photofission γ-rays carry isotopic information of the target materials. The feasibility of accurate spectrometry measurements in between intense linear accelerator pulses has been demonstrated using three independent spectroscopy systems. The measured delayed γ-rays spectra were then compared with MCNPX simulation results. Through the comparison, this article intends to show the capabilities of the current version of MCNPX in applications of simulating the photofission process.