bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of glial and neuronal glycine transporters in the control of glycinergic and glutamatergic synaptic transmission in lamina X of the rat spinal cord
Authors: Bradaïa Amyaouch , Schlichter Rémy , Trouslard Jérôme
Published: July 2004

Using whole cell voltage clamp recordings from lamina X neurones in rat spinal cord slices, we investigated the effect of glycine transporter (GlyT) antagonists on both glycinergic inhibitory postsynaptic current (IPSCs) and glutamatergic excitatory postsynaptic current (EPSCs). We used ORG 24598 and ORG 25543, selective antagonists of the glial GlyT (GlyT1) and neuronal GlyT (GlyT2), respectively. In rats (P12–P16) and in the presence of kynurenic acid, 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) and bicuculline, ORG 24598 and ORG 25543 applied individually at a concentration of 10 μm induced a mean inward current of −10/−50 pA at −60 mV and increased significantly the decay time constants of miniature (mIPSCs), spontaneous (sIPSCs) and electrically evoked glycinergic (eIPSCs) inhibitory postsynaptic currents. ORG 25543, but not ORG 24598, decreased the frequency of mIPSCs and sIPSCs. Replacing extracellular sodium with N‐methyl‐d‐glucamine or superfusing the slice with micromolar concentrations of glycine also increased the decay time constant of glycinergic IPSCs. By contrast, the decay time constant, amplitude and frequency of miniature GABAergic IPSCs recorded in the presence of strychnine were not affected by ORG 24598 and ORG 25543. In the presence of strychnine, bicuculline and CNQX, we recorded electrically evoked NMDA receptor‐mediated EPSCs (eEPSCs). eEPSCs were suppressed by 30 μmd‐2‐amino‐5‐phosphonovalerate (APV), an antagonist of the NMDA receptor, and by 30 μm dichlorokynurenic acid (DCKA), an antagonist of the glycine site of the NMDA receptor. Glycine (1–5 μm) and d‐serine (10 μm) increased the amplitude of eEPSCs whereas l‐serine had no effect. ORG 24598 and ORG 25543 increased significantly the amplitude of NMDA receptor‐mediated eEPSCs without affecting the amplitude of non‐NMDA receptor‐mediated eEPSCs. We conclude that blocking glial and/or neuronal glycine transporters increased the level of glycine in spinal cord slices, which in turn prolonged the duration of glycinergic synaptic current and potentiated the NMDA‐mediated synaptic response.
Activation of Na+–H+ exchange and stretch‐activated channels underlies the slow inotropic response to stretch in myocytes and muscle from the rat heart
Authors: Calaghan Sarah , White Ed
Published: July 2004

We present the first direct comparison of the major candidates proposed to underlie the slow phase of the force increase seen following myocardial stretch: (i) the Na+–H+ exchanger (NHE) (ii) nitric oxide (NO) and the ryanodine receptor (RyR) and (iii) the stretch‐activated channel (SAC) in both single myocytes and multicellular muscle preparations from the rat heart. Ventricular myocytes were stretched by approximately 7% using carbon fibres. Papillary muscles were stretched from 88 to 98% of the length at which maximum tension is generated (Lmax). Inhibition of NHE with HOE 642 (5 μm) significantly reduced (P < 0.05) the magnitude of the slow force response in both muscle and myocytes. Neither inhibition of phosphatidylinositol‐3‐OH kinase (PtdIns‐3‐OH kinase) with LY294002 (10 μm) nor NO synthase with l‐NAME (1 mm) reduced the slow force response in muscle or myocytes (P > 0.05), and the slow response was still present in the single myocyte when the sarcoplasmic reticulum was rigorously inhibited with 1 μm ryanodine and 1 μm thapsigargin. We saw a significant reduction (P < 0.05) in the slow force response in the presence of the SAC blocker streptomycin in both muscle (80 μm) and myocytes (40 μm). In fura 2‐loaded myocytes, HOE 642 and streptomycin, but not l‐NAME, ablated the stretch‐induced increase in [Ca2+]i transient amplitude. Our data suggest that in the rat, under our experimental conditions, there are two mechanisms that underlie the slow inotropic response to stretch: activation of NHE; and of activation of SACs. Both these mechanisms are intrinsic to the myocyte.
Developmental segregation of spinal networks driving axial‐ and hindlimb‐based locomotion in metamorphosing Xenopus laevis
Authors: Combes D. , Merrywest S. D. , Simmers J. , Sillar K. T.
Published: July 2004

Amphibian metamorphosis includes a complete reorganization of an organism's locomotory system from axial‐based swimming in larvae to limbed propulsion in the young adult. At critical stages during this behavioural switch, larval and adult motor systems operate in the same animal, commensurate with a gradual and dynamic reconfiguration of spinal locomotor circuitry. To study this plasticity, we have developed isolated preparations of the spinal cord and brainstem from pre‐ to post‐metamorphic stages of the amphibian Xenopus laevis, in which spinal motor output patterns expressed spontaneously or in the presence of NMDA correlate with locomotor behaviour in the freely swimming animal. Extracellular ventral root recordings along the spinal cord of pre‐metamorphic tadpoles revealed motor output corresponding to larval axial swimming, whereas postmetamorphic animals expressed motor patterns appropriate for bilaterally synchronous hindlimb flexion–extension kicks. However, in vitro recordings from metamorphic climax stages, with the tail and the limbs both functional, revealed two distinct motor patterns that could occur either independently or simultaneously, albeit at very different frequencies. Activity at 0.5–1 Hz in lumbar ventral roots corresponded to bipedal extension–flexion cycles, while the second, faster pattern (2–5 Hz) recorded from tail ventral roots corresponded to larval‐like swimming. These data indicate that at intermediate stages during metamorphosis separate networks, one responsible for segmentally organized axial locomotion and another for more localized appendicular rhythm generation, coexist in the spinal cord and remain functional after isolation in vitro. These preparations now afford the opportunity to explore the cellular basis of locomotor network plasticity and reconfiguration necessary for behavioural changes during development.
Direct effect of Ca2+–calmodulin on cGMP‐activated Ca2+‐dependent Cl−channels in rat mesenteric artery myocytes
Authors: Piper A. S. , Large W. A.
Published: July 2004

Recently a novel cGMP‐activated Ca2+‐dependent Cl−channel has been described in rat mesenteric artery smooth muscle cells. In the present work we have investigated the actions of calmodulin (CaM) on single channel cGMP‐activated Ca2+‐dependent Cl−current (ICl(cGMP,Ca)) in inside‐out patches. When 1 μm CaM was applied to the intracellular surface of inside‐out patches bathed with 10 μm cGMP and 100 nm[Ca2+]i there was approximately a 10‐fold increase in channel open probability (NPo). This effect of CaM was not observed with lower [Ca2+]i and 100 nm[Ca2+]i with 1 μm CaM did not activate Cl−channels in the absence of cGMP. The unitary conductance, reversal potential and mean open time of the single‐channel currents were similar in the absence or presence of CaM. With 10 μm cGMP and 100 nm[Ca2+]i the relationship between NPo and CaM concentration was well fitted by the Hill equation yielding an equilibrium constant for CaM of about 1.9 nm and a Hill coefficient of 1.7. With 1 μm CaM (+10 μm cGMP) the relationship between [Ca2+]i and NPo was also fitted by the Hill equation which yielded an apparent equilibrium constant of 74 nm[Ca2+]i and a Hill coefficient of 4.8. When [Ca2+]i was increased from 300 nm to 1 μm there was a decrease in NPo. The potentiating effect of CaM was markedly reduced by the selective CaM binding peptide Trp (5 nm) but not by the Ca2+/CaM‐dependent protein kinase II (CaMKII) inhibitor autocamtide II related inhibitory peptide (AIP). It is concluded that CaM potentiates the activity of single channel ICl(cGMP,Ca) by increasing the probability of channel opening via a CaMKII‐independent mechanism.
Dose properties of a laser accelerated electron beam and prospects for clinical application
Authors: Kainz K. K. , Hogstrom K. R. , Antolak J. A. , Almond P. R. , Bloch C. D. , Chiu C. , Fomytskyi M. , Raischel F. , Downer M. , Tajima T.
Published: July 2004

Laser wakefield acceleration (LWFA) technology has evolved to where it should be evaluated for its potential as a future competitor to existing technology that produces electron and x‐ray beams. The purpose of the present work is to investigate the dosimetric properties of an electron beam that should be achievable using existing LWFA technology, and to document the necessary improvements to make radiotherapy application for LWFA viable. This paper first qualitatively reviews the fundamental principles of LWFA and describes a potential design for a 30 cm accelerator chamber containing a gas target. Electron beam energy spectra, upon which our dose calculations are based, were obtained from a uniform energy distribution and from two‐dimensional particle‐in‐cell (2D PIC) simulations. The 2D PIC simulation parameters are consistent with those reported by a previous LWFA experiment. According to the 2D PIC simulations, only approximately 0.3% of the LWFA electrons are emitted with an energy greater than 1 MeV. We studied only the high‐energy electrons to determine their potential for clinical electron beams of central energy from 9 to 21 MeV. Each electron beam was broadened and flattened by designing a dual scattering foil system to produce a uniform beam (103%>off‐axis ratio>95%) over a 25×25 cm2field. An energy windowranging from 0.5 to 6.5 MeV was selected to study central‐axis depth dose, beam flatness, and dose rate. Dose was calculated in water at a 100 cm source‐to‐surface distance using theEGS/BEAMMonte Carlo algorithm. Calculations showed that the beam flatness was fairly insensitive toHowever, since the falloff of the depth–dose curveand the dose rate both increase witha tradeoff between minimizingand maximizing dose rate is implied. Ifis constrained so thatis within 0.5 cm of its value for a monoenergetic beam, the maximum practical dose rate based on 2D PIC is approximately 0.1 Gy min−1for a 9 MeV beam and 0.03 Gy min−1for a 15 MeV beam. It was concluded that current LWFA technology should allow a table‐top terawattlaser to produce therapeutic electron beams that have acceptable flatness, penetration, and falloff of depth dose; however, the dose rate is still 1%–3% of that which would be acceptable, especially for higher‐energy electron beams. Further progress in laser technology, e.g., increasing the pulse repetition rate or number of high energy electrons generated per pulse, is necessary to give dose rates acceptable for electron beams. Future measurements confirming dosimetric calculations are required to substantiate our results. In addition to achieving adequate dose rate, significant engineering developments are needed for this technology to compete with current electron acceleration technology. Also, the functional benefits of LWFA electron beams require further study and evaluation.
Laser electron accelerators for radiation medicine: A feasibility study
Authors: Chiu Charles , Fomytskyi Mykhailo , Grigsby Franklin , Raischel Frank , Downer Michael C. , Tajima Toshiki
Published: July 2004

Table‐top laser wakefield accelerators (LWFAs), proposed theoretically in 1979, have now generated individual electron bunches in the laboratory with a significant number of electrons having energies up to 10 MeV and beyond with the maximum energy reaching tens of MeV and charge per laser pulse ofThe attained electron beam properties have stimulated a discussion about the possible applications of LWFAs to medical radiation treatment, either directly or via conversion to x‐rays. Our purpose in this paper is to analyze whether or not such applications are feasible, or can be made feasible with existing laser technology. Clinical electron beam applications require the selection of specific electron energies in the range of 6–25 MeV with a narrow energy binfor depth control, and a beam expansion to as much asfor various tumor radiation treatments. As a result, we show that present LWFA sources provide a dose rate that falls short of the requirements for clinical application by at least an order of magnitude. We then use particle simulations to evaluate the feasibility of developing an improved LWFA‐based medical accelerator. Current LWFA sources require such high peak intensity that laser repetition rate is restricted toA scheme to lower the threshold and increase the repetition rate of efficient LWFA thus appears essential. We analyze one such scheme. We show that by “seeding” the primary laser pulse with a second, hundred‐fold less intense pulse that is shifted downward in frequency by approximately the plasma frequencyLWFA produces a yield of clinically useful electrons per pulse comparable to that provided by an unseeded source, except that the primary pulse energy is now more than one order of magnitude lower than that in current LWFAs. This enables a repetition rate ofor more using existing laser technology, and thus dose rates (several Gy/min) in the range required for medical radiation applications.
Dosimetric properties of radiophotoluminescent glass rod detector in high‐energy photon beams from a linear accelerator and Cyber‐Knife
Authors: Araki Fujio , Moribe Nobuyuki , Shimonobou Toshiaki , Yamashita Yasuyuki
Published: July 2004

A fully automatic radiophotoluminescent glass rod dosimeter (GRD) system has recently become commercially available. This article discusses the dosimetric properties of the GRD including uniformity and reproducibility of signal, dose linearity, and energy and directional dependence in high‐energy photon beams. In addition, energy response is measured in electron beams. The uniformity and reproducibility of the signal from 50 GRDs using a beam are both (one standard deviation). Good dose linearity of the GRD is maintained for doses ranging from 0.5 to 30 Gy, the lower and upper limits of this study, respectively. The GRD response is found to show little energy dependence in photon energies of a beam, 4 MV and 10 MV x‐ray beams. However, the GRD responses for 9 MeV (mean energy, and 16 MeV electron beams are 4%–5% lower than that for a beam in the beam quality dependence. The measured angular dependence of GRD, ranging from (along the long axis of GRD) to is within 1.5% for a 4 MV x‐ray beam. As applications, a linear accelerator‐based radiosurgery system and Cyber‐Knife output factors are measured by a GRD and compared with those from various detectors including a ‐type silicon diode detector, a diamond detector, and an ion chamber. It is found that the GRD is a very useful detector for small field dosimetry, in particular, below 10 mm circular fields.
On the noise variance of a digital mammography system
Authors: Burgess Arthur
Published: July 2004

A recent paper by Cooper et al. [Med. Phys. 30, 2614–2621 (2003)] contains some apparently anomalous results concerning the relationship between pixel variance and x‐ray exposure for a digital mammography system. They found an unexpected peak in a display domain pixel variance plot as a function of 1/mAs (their Fig. 5) with a decrease in the range corresponding to high display data values, corresponding to low x‐ray exposures. As they pointed out, if the detector response is linear in exposure and the transformation from raw to display data scales is logarithmic, then pixel variance should be a monotonically increasing function in the figure. They concluded that the total system transfer curve, between input exposure and display image data values, is not logarithmic over the full exposure range. They separated data analysis into two regions and plotted the logarithm of display image pixel variance as a function of the logarithm of the mAs used to produce the phantom images. They found a slope of minus one for high mAs values and concluded that the transfer function is logarithmic in this region. They found a slope of 0.6 for the low mAs region and concluded that the transfer curve was neither linear nor logarithmic for low exposure values. It is known that the digital mammography system investigated by Cooper et al. has a linear relationship between exposure and raw data values [Vedantham et al., Med. Phys. 27, 558–567 (2000)]. The purpose of this paper is to show that the variance effect found by Cooper et al. (their Fig. 5) arises because the transformation from the raw data scale (14 bits) to the display scale (12 bits), for the digital mammography system they investigated, is not logarithmic for raw data values less than about 300 (display data values greater than about 3300). At low raw data values the transformation is linear and prevents over‐ranging of the display data scale. Parametric models for the two transformations will be presented. Results of pixel variance measurements made on raw data images will be presented. The experimental data are in good agreement with those of Cooper et al. It will be shown that the slope of 0.6 found by Cooper et al. for the log‐log plot at low exposure is not due to transfer function nonlinearity, it occurs because of an additive variance term—possibly due to electronic noise. It will also be shown, using population statistics from clinical images, that raw data values below 300 are rare in tissue areas. Those tissue areas with very low raw data values are within about a millimeter of the chest wall or in very dense muscle at corners of images.
Phantom size in brachytherapy source dosimetric studies
Authors: Pérez‐Calatayud J. , Granero D. , Ballester F.
Published: July 2004

An important point to consider in a brachytherapy dosimetry study is the phantom size involved in calculations or experimental measurements. As pointed out by Williamson [Med. Phys. 18, 776–786 (1991)] this topic has a relevant influence on final dosimetric results. Presently, one‐dimensional (1‐D) algorithms and newly‐developed 3‐D correction algorithms are based on physics data that are obtained under full scatter conditions, i.e., assumed infinite phantom size. One can then assume that reference dose distributions in source dosimetry for photon brachytherapy should use an unbounded phantom size rather than phantom‐like dimensions. Our aim in this paper is to study the effect of phantom size on brachytherapy for radionuclide and mainly used for clinical purposes. Using the GEANT4 Monte Carlo code, we can ascertain effects on derived dosimetry parameters and functions to establish a distance dependent difference due to the absence of full scatter conditions. We have found that for and a spherical phantom with a 40 cm radius is the equivalent of an unbounded phantom up to a distance of 20 cm from the source, as this size ensures full scatter conditions at this distance. For and the required radius for the spherical phantom in order to ensure full scatter conditions at 10 cm from the source is A simple expression based on fits of the dose distributions for various phantom sizes has been developed for and in order to compare the dose rate distributions published for different phantom sizes. Using these relations it is possible to obtain radial dose functions for unbounded medium from bounded phantom ones.
Elimination of ghost markers during dual sensor‐based infrared tracking of multiple individual reflective markers
Authors: Stroian G. , Falco T. , Seuntjens J. P.
Published: July 2004

The accuracy of dose delivery in radiotherapy is affected by the uncertainty in tumor localization. Motion of internal anatomy due to physiological processes such as respiration may lead to significant displacements which compromise tumor coverage and generate irradiation of healthy tissue. Real‐time tracking with infrared‐based systems is often used for tracking thoracic motion in radiation therapy. We studied the origin of ghost markers (“crosstalk”) which may appear during dual sensor‐based infrared tracking of independent reflective markers. Ghost markers occur when two or more reflective markers are coplanar with each other and with the sensors of the two camera‐based infrared tracking system. Analysis shows that sensors are not points but they have a finite extent and this extent determines for each marker a “ghost volume.” If one reflective marker enters the ghost volume of another marker, ghost markers will be reported by the tracking system; if the reflective markers belong to a surface their “ghost volume” is reduced to a “ghost surface” (ghost zone). Appearance of ghost markers is predicted for markers taped on the torso of an anthropomorphic phantom. This study illustrates the dependence of the shape, extent, and location of the ghost zones on the shape of the anthropomorphic phantom, the angle of view of the tracking system, and the distance between the tracking system and the anthropomorphic phantom. It is concluded that the appearance of ghost markers can be avoided by positioning the markers outside the ghost zones of the other markers. However, if this is not possible and the initial marker configuration is ghost marker‐free, ghost markers can be eliminated during real‐time tracking by virtue of the fact that they appear in the coordinate data sequence only temporarily.
Hemoglobin oxygen saturations in phantoms and in vivo from measurements of steady‐state diffuse reflectance at a single, short source‐detector separation
Authors: Finlay Jarod C. , Foster Thomas H.
Published: July 2004

We present a method for the analysis of steady state diffuse reflectance spectra obtained from vascularized tissue or from tissue simulating phantoms at a single, short source‐detector separation. This method uses reasonable assumptions about the structure of the reduced scattering spectrum and basis absorption spectra for oxy‐ and deoxyhemoglobin, which dominate tissue absorption in the visible region of the spectrum. Using a hybrid ‐diffusion description of light propagation, described originally by Hull and Foster [J. Opt. Soc. Am. A 18, 584–599 (2001)] and suitable for short (∼1 mm) source‐detector separations and optical properties of tissue at visible wavelengths, we create a forward model of the diffuse reflectance with four free parameters. We demonstrate that this model is able to recover accurately the hemoglobin concentrations and scattering properties from synthetic data generated by Monte Carlo simulation and from reflectance spectra acquired from tissue‐simulating phantoms containing intact human erythrocytes. We show also that the method is capable of monitoring carbogen‐induced changes in murine tumor oxygenation in vivo. The successful implementation of single, short detector separations enables the measurement of intratumor heterogeneities in hemoglobin oxygen saturation and responses to carbogen using a simple fiber‐based probe design.
EDR2 film dosimetry for IMRT verification using low‐energy photon filters
Authors: Yeo Inhwan Jason , Beiki‐Ardakani Akbar , Cho Young‐bin , Heydarian Mostafa , Zhang Ting , Islam Mohammad
Published: July 2004

Recently the EDR2 (extended dose range) film has been introduced commercially for applications in radiation therapy dosimetry. In addition to characterizing the wide dynamic range, several authors have reported a reduced energy dependence of this film compared to that of X‐Omatic Verification (XV) films for megavoltage photon beams. However, those investigations were performed under limited geometrical conditions. We have investigated the dosimetric performance of EDR2 film for the verification of IMRT fields at more clinically relevant conditions by comparing the film doses with the doses measured with an ion chamber and XV films. The effects of using a low energy scattered photon filter on EDR2 film dosimetry was also studied. In contrast to previous reports our results show that EDR2 film still exhibits considerable energy dependence (a maximum discrepancy of 9%, compared with an ion chamber) at clinically relevant conditions (10 cm depth for IMRT fields). However, by using the low‐energy filters the discrepancy is reduced to within 3%. Therefore, EDR2 film, in combination with the filters, is found to be a promising two‐dimensional dosimeter for verification of IMRT treatment fields.
A new approach in dose measurement and error analysis for narrow photon beams (beamlets) shaped by different multileaf collimators using a small detector
Authors: Li Shidong , Rashid Abdul , He Shanjin , Djajaputra David
Published: July 2004

Dose measurement for narrow stereotactic beams and intensity modulation radiotherapy beamlets is difficult and error‐prone due to the lack of lateral electron equilibrium. A small detector position error and finite sensitive volume as well as the nonfocus collimation could result in considerable (>10%) measurement errors. A new method is introduced here to measure the dose and error components so that the accuracy and precision of the dose measurement can be improved. Based on superposition principle, we can create exactly the small field of interest by subtraction of a reference open field (O‐field) and two strip fields (S‐fields) from the sum of four quadrant fields (Q‐fields). The position effect on the dose measurement is determined by the standard deviation of the four Q‐field readings. The collimator leaf‐edge effect (LEE) is quantified by the difference between the readings of the two S‐fields using a detector that has very small sensitive volume. The detector‐volume effect can be analytically estimated from the integrals of the dose distributions of the two S‐fields over the detector volume. Using a pinpoint ion chamber (PTW N31006) and a stereotactic silicon diode detector (Scanditronix, DEB050), we have measured scatter factors (SF) and tissue‐maximum ratios for 6‐MV x‐ray fields with sizes of 3×3 and 6×6 mm2 shaped by a BrainLAB micromultileaf collimator (microMLC) (M3), 4.4×4.4 and 8.8×8.8 mm2 shaped by a 3DLine double‐focus MLC, and 5×5 and 10×10 mm2 by a Varian Millennium MLC. Our experimental results demonstrate that the large errors are often caused by a small setup error or measuring point displacement from the central ray of the beam. The LEE is almost independent of the depth but closely related to the field size and the type of MLC. The volume effect becomes significant when the detector diameter is comparable to the half size of the small fields. Application of the new method using different detectors had achieved less than 8.3% total experiment error for all of the small fields of interest except for the SF of the 3×3 mm2 field from the pinpoint ion chamber that has 15% volume effect. Importantly, the new method using a solid water phantom is clinically convenient and highly reproducible.
Attenuation of intracavitary applicators in ‐HDR brachytherapy
Authors: Ye Sung‐Joon , Brezovich Ivan A. , Shen Sui , Duan Jun , Popple Richard A. , Pareek Prem N.
Published: July 2004

Unlike the penetrating monoenergetic 662 keV gamma rays emitted by LDR sources, the spectrum of used in HDR brachytherapy contains low‐energy components. Since these are selectively absorbed by the high‐atomic number materials of which intracavitary applicators are made, the traditional neglect of applicator attenuation can lead to appreciable dose errors. We investigated the attenuation effects of a uterine applicator, and of a set of commonly used vaginal cylinders. The uterine applicator consists of a stainless steel source guide tube with a wall thickness of 0.5 mm and a density of whereas the vaginal cylinders consist of the same stainless steel tube plus concentric polysulfone cylinders with a radius of 1 or 2 cm and a density of Monte Carlo simulations were performed to compute dose distributions for a bare ‐HDR source, and for the same source located within the applicators. Relative measurements of applicator attenuation using ion‐chambers confirmed the Monte Carlo results within 0.5%. We found that the neglect of the applicator attenuation overestimates the dose along the transverse plane by up to 3.5%. At oblique angles, the longer photon path within applicators worsens the error. We defined attenuation‐corrected radial dose and anisotropy functions, and applied them to a treatment having multiple dwell positions inside a vaginal cylinder.
Accurate Monte Carlo simulations for nozzle design, commissioning and quality assurance for a proton radiation therapy facility
Authors: Paganetti H. , Jiang H. , Lee S.‐Y. , Kooy H. M.
Published: July 2004

Monte Carlo dosimetry calculations are essential methods in radiation therapy. To take full advantage of this tool, the beam delivery system has to be simulated in detail and the initial beam parameters have to be known accurately. The modeling of the beam delivery system itself opens various areas where Monte Carlo calculations prove extremely helpful, such as for design and commissioning of a therapy facility as well as for quality assurance verification. The gantry treatment nozzles at the Northeast Proton Therapy Center (NPTC) at Massachusetts General Hospital (MGH) were modeled in detail using the GEANT4.5.2 Monte Carlo code. For this purpose, various novel solutions for simulating irregular shaped objects in the beam path, like contoured scatterers, patient apertures or patient compensators, were found. The four‐dimensional, in time and space, simulation of moving parts, such as the modulator wheel, was implemented. Further, the appropriate physics models and cross sections for proton therapy applications were defined. We present comparisons between measured data and simulations. These show that by modeling the treatment nozzle with millimeter accuracy, it is possible to reproduce measured dose distributions with an accuracy in range and modulation width, in the case of a spread‐out Bragg peak (SOBP), of better than 1 mm. The excellent agreement demonstrates that the simulations can even be used to generate beam data for commissioning treatment planning systems. The Monte Carlo nozzle model was used to study mechanical optimization in terms of scattered radiation and secondary radiation in the design of the nozzles. We present simulations on the neutron background. Further, the Monte Carlo calculations supported commissioning efforts in understanding the sensitivity of beam characteristics and how these influence the dose delivered. We present the sensitivity of dose distributions in water with respect to various beam parameters and geometrical misalignments. This allows the definition of tolerances for quality assurance and the design of quality assurance procedures.
Contrast effects on dosimetry of a partial breast irradiation system
Authors: Kassas Bassel , Mourtada Firas , Horton John L. , Lane Richard G.
Published: July 2004

MammoSite® is a high‐dose rate brachytherapy procedure for partial breast irradiation, which uses a balloon filled with radiopaque iodine‐based contrast solution and catheter for insertion of high‐dose‐rate source. The radiopaque material helps visualizing the balloon contour, catheter, and source position within the balloon, which is essential for computerized tomography‐based treatment planning and for daily QA using x‐ray radiographs. Because of the high content of iodine in contrast media, increased absorption and attenuation of photons may take place within the balloon, which would affect the resultant dose rates outside the balloon. The impact of the concentration of the radiopaque solution on the physical dosimetry of this brachytherapy procedure is investigated in this study using MCNPX (version 2.4) Monte Carlo simulation. Calculations were based on a 30 cm diameter water sphere phantom. The source geometry was that of the Nucletron microSelectron HDR v2 source. Concentration of the iodine‐based radiopaque solution was varied from 5% to 25% by volume, a range recommended by the balloon's manufacturer. Balloon diameters of 4, 5, and 6 cm were simulated. Dose rate per unit air‐kerma strength was calculated in 1 mm scoring bin steps. The dose rate reduction at the typical prescription line of 1 cm away from the balloon surface ranged from for the smallest balloon diameter and contrast concentration to a maximum of for the largest balloon diameter and contrast concentration, relative to a water‐filled balloon. Limiting the contrast concentration to 10% would insure less than 3% reduction in the prescription dose, regardless of balloon diameter.
A dosimetric approach to patient‐specific radioiodine treatment of Graves' disease with incorporation of treatment‐induced changes in thyroid mass
Authors: Traino A. Claudio , Di Martino Fabio , Lazzeri Mauro
Published: July 2004

The traditional algorithms (Marinelli–Quimby and MIRD) used for the absorbed dose calculation in radionuclide therapy generally assume that the mass of the target organs does not change with time. In radioiodine therapy for Graves' disease this approximation may not be valid. In this paper a mathematical model of thyroid mass reduction during the clearance phase (30–35 days) after administration to patients with Graves' disease is presented. A new algorithm for the absorbed dose calculation is derived, taking into account the reduction of the mass of the gland resulting from the therapy. It is demonstrated that thyroid mass reduction has a considerable effect on the calculated radiation dose. Either the model of the thyroid mass reduction or the new equation for the absorbed dose calculation depend on a parameter k for each patient. This parameter can be calculated after the administration of a diagnostic amount of radioiodine activity (0.37–1.85 MBq). Thus, thyroid absorbed dose and thyroid mass reduction during the first month after therapy can be predicted before therapy administration. The absorbed dose values calculated by the new algorithm are compared to those calculated by the traditional Marinelli–Quimby and MIRD algorithms.
A practical approach to prevent gantry–couch collision for linac‐based radiosurgery
Authors: Hua Chiaho , Chang Jenghwa , Yenice Kamil , Chan Maria , Amols Howard
Published: July 2004

Gantry–couch collision is a serious concern for treatment planning of the linear accelerator (linac) based stereotactic radiosurgery (SRS). The ability to detect collision at the time of planning eliminates the need for backup plans and preserves the useful beam angles that would be deemed unsafe and discarded otherwise. Most collision‐detection schemes embedded in commercial planning software guard only against the most apparent collisions. On the other hand, a fool‐proof collision‐map or lookup table often requires detailed measurement of machine geometry and complex graphic operations. In this study, we have developed a simple analytical method for collision detection with the use of quick machine‐specific measurements. The collision detection is mathematically solved by determining whether two facets in three‐dimensional space, representing gantry and couch surfaces, intersect with each other. A computer code was implemented and tested on a Varian Clinac 600C linac equipped with a BrainLab micromultileaf collimator (MLC) device. To measure machine‐specific parameters, the lesion isocenter was set to the origin of the stereotactic coordinate system. The reference coordinates of couch bracket corners and micro‐MLC to the linac isocenter were measured only once in the treatment room before they were incorporated into the computer program. Couch, gantry, and collimator were subsequently translated and rotated to study the clearance of various beam arrangements and lesion locations. Predicted results were verified at the machine. Our method correctly confirmed clearance for a retrospective study of 54 previously treated SRS plans (76 isocenters). It also accurately predicted the collisions for all ten artificially created cases. In conclusion, we have developed an analytical method for SRS collision detection that is accurate, easy to implement, and computationally inexpensive.
The effect of unrealistic thyroid vertical position on thyroid dose in the MIRD phantom
Authors: Lee Choonsik , Lee Jaiki , Lee Choonik
Published: July 2004

Anatomically, the thyroid gland is placed in the lower neck, extending from the level of the fifth cervical vertebra down to the first thoracic vertebra. However, the thyroid of the Medical Internal Radiation Dose (MIRD) phantom, which has been widely used for dosimetric calculation, is located right above the top of the torso and is completely included in the neck region. To investigate the effect of the unrealistic position of the thyroid in the MIRD phantom on dose calculation, thyroid absorbed doses at various vertical positions were calculated for the idealized external broad parallel photon beam from anterior‐posterior, posterior‐anterior, right lateral (RLAT), and left lateral (LLAT) direction using the Monte Carlo method. The thyroid absorbed dose decreased by as much as about 60% for 0.05 MeV photon in both RLAT and LLAT irradiations when the thyroid was relocated to realistic position (inserted into the torso). The effective dose also decreased by 10%, consequently. The thyroid dose of the widely accepted stylized model, the MIRD phantom, is overestimated in RLAT and LLAT irradiation geometries.
Assessment of flat panel LCD primary class display performance based on AAPM TG 18 acceptance protocol
Authors: Jung Haijo , Kim Hee‐Joung , Kang Won‐Suk , Yoo Sun Kook , Fujioka Kiyoto , Hasegawa Mikio , Samei Ehsan
Published: July 2004

The image display is an important component of the Picture Archiving and Communication System (PACS) and of digital imaging in general. In this paper, we assess the display performance of 32 different flat panel LCD devices, in terms of their reflection, luminance response, luminance uniformity, resolution, noise, veiling glare and color uniformity included in the tentative guidelines of the AAPM TG18 document version 8.1. We also report on the angular dependencies of luminance and contrast, which constitute one of the miscellaneous tests. The tools used included a telescopic photometer, which was also used as a colorimeter, an illuminance meter, light sources for the reflection assessment, light‐blocking devices, and digital TG18 test patterns. The luminance ratio (LR), maximum luminance difference and deviation of contrast response with respect to that of DICOM GSDF were and respectively. The maximum luminance nonuniformity was for the 10% luminance of the TG18‐UNL10 test pattern. In the luminance‐based resolution test, the percent luminance difference at the center was In all cases of noise testing, the rectangular target in each square in the three quadrants was visible, as were all 15 targets, except for the smallest one, in each corner pattern and the center pattern. The glare ratio (GR) was The average color uniformity parameter, across the display area of each display device was Nevertheless, not all of the color uniformity parameters of the display devices associated with a workstation met the acceptance criteria. For 7 selected flat panel displays, the mean specular and diffuse reflection coefficients were and per lux, respectively. All of the test results conformed to the criteria recommended by AAPM TG18, indicating that the displays were fully acceptable for diagnostic image interpretation. The maximum viewing angle conforming to the DICOM 3.14 standard luminance responses with a 10% tolerance was found to be approximately 50° in both directions along the vertical axis, 10° in the upper direction and 20° in the lower direction along the horizontal axis, and 20° in the upper direction and 10° in the lower direction along the diagonal axis. Therefore, a radiologist should interpret a displayed image by considering the physical characteristics of the narrow viewing angle of the AMLCD displays. The acceptance testing protocol described herein demonstrates the successful clinical implementation of the guidelines for the viewing conditions of medical displays, and if implemented with a QC program, can be used to determine when LCD devices used for diagnostic interpretation need to be upgraded.
Specific Response of a Novel and Abundant
Lactobacillus amylovorus
-Like Phylotype to Dietary Prebiotics in the Guts of Weaning Piglets
Authors: Konstantinov Sergey R. , Awati Ajay , Smidt Hauke , Williams Barbara A. , Akkermans Antoon D. L. , de Vos Willem M.
Published: July 2004

Using 16S rRNA gene-based approaches, we analyzed the responses of ileal and colonic bacterial communities of weaning piglets to dietary addition of four fermentable carbohydrates (inulin, lactulose, wheat starch, and sugar beet pulp). An enriched diet and a control diet lacking these fermentable carbohydrates were fed to piglets for 4 days (
n
= 48), and 10 days (
n
= 48), and the lumen-associated microbiota were compared using denaturing gradient gel electrophoresis (DGGE) analysis of amplified 16S rRNA genes. Bacterial diversities in the ileal and colonic samples were measured by assessing the number of DGGE bands and the Shannon index of diversity. A higher number of DGGE bands in the colon (24.2 ± 5.5) than in the ileum (9.7 ± 4.2) was observed in all samples. In addition, significantly higher diversity, as measured by DGGE fingerprint analysis, was detected in the colonic microbial community of weaning piglets fed the fermentable-carbohydrate-enriched diet for 10 days than in the control. Selected samples from the ileal and colonic lumens were also investigated using fluorescent in situ hybridization (FISH) and cloning and sequencing of the 16S rRNA gene. This revealed a prevalence of
Lactobacillus reuteri
in the ileum and
Lactobacillus amylovorus
-like populations in the ileum and the colon in the piglets fed with fermentable carbohydrates. Newly developed oligonucleotide probes targeting these phylotypes allowed their rapid detection and quantification in the ileum and colon by FISH. The results indicate that addition of fermentable carbohydrates supports the growth of specific lactobacilli in the ilea and colons of weaning piglets.
Purification and Characterization of Two Distinct Metalloproteases Secreted by the Entomopathogenic Bacterium
Photorhabdus
sp. Strain Az29
Authors: Cabral C. M. , Cherqui A. , Pereira A. , Simões N.
Published: July 2004

Photorhabdus
sp. strain Az29 is symbiotic with an Azorean nematode of the genus
Heterorhabditis
in a complex that is highly virulent to insects even at low temperatures. The virulence of the bacteria is mainly attributed to toxins and bacterial enzymes secreted during parasitism. The bacteria secrete proteases during growth, with a peak at the end of the exponential growth phase. Protease secretion was higher in cultures growing at lower temperatures. At 10°C the activity was highest and remained constant for over 7 days, whereas at 23 and 28°C it showed a steady decrease. Two proteases, PrtA and PrtS, that are produced in the growth medium were purified by liquid chromatography. PrtA was inhibited by 1,10-phenantroline and by EDTA and had a molecular mass of 56 kDa and an optimal activity at pH 9 and 50°C. Sequences of three peptides of PrtA showed strong homologies with alkaline metalloproteases from
Photorhabdus temperata
K122 and
Photorhabdus luminescens
W14. Peptide PrtA-36 contained the residues characteristic of metzincins, known to be involved in bacterial virulence. In vitro, PrtA inhibited antibacterial factors of inoculated Lepidoptera and of cecropins A and B. PrtS had a molecular mass of 38 kDa and was inhibited by 1,10-phenanthroline but not by EDTA. Its activity ranged between 10 and 80°C and was optimal at pH 7 and 50°C. PrtS also destroyed insect antibacterial factors. Three fragments of PrtS showed homology with a putative metalloprotease of
P. luminescens
TTO1. Polyclonal antibody raised against PrtA did not recognize PrtS, showing they are distinct molecules.
The front-form Hamiltonian and BRST formulations of the NielsenOlesen model in the broken symmetry phase
Authors: Kulshreshtha Usha , Kulshreshtha D S
Published: July 2004

The front-form Hamiltonian and BRST formulations of the NielsenOlesen model are investigated in two-space one-time dimension in the broken (frozen) symmetry phase, where the phase ϕ(xμ) of the complex matter field Φ(xμ) carries the charge degree of freedom of the complex matter field and is, in fact, akin to the Goldstone Boson.PACS No.: 11.15.q
Inequivalent Lagrangians for the damped harmonic oscillator
Authors: Ghosh S , Shamanna J , Talukdar B
Published: July 2004

A constant of the motion, in addition to what exists in the literature, is presented for the damped harmonic oscillator and its dynamical origin is investigated. These two constants of motion are used to construct expressions for a hierarchy of inequivalent Lagrangians. It is shown that each inequivalent Lagrangian may be related to a higher order degenerate Lagrangian. The hierarchical Lagrangians tend to pose some characteristic problems for discussing the corresponding phase-space structure. PACS Nos.: 47.20.Ky, 42.81.Dp
Coefficients of radial integral in the electrostatic interaction and their applications
Authors: Chen Z , Msezane A Z
Published: July 2004

We have derived the equations to calculate the electrostatic interaction energy and the coefficients of radial integrals between electrons ln or l1m and l′ of the atomic state |ln[S1L1]l1m[S2L2][ScLc]l′ SL >, where ln[S1L1], l1m[S2L2], and l′ are three open shells. The expressions have been checked against the formulas in the literature by reducing them to those for the case of atoms having two open shells. We demonstrate our formulas by evaluating the coefficients of the radial integrals in the interaction between the 2s or 2p4 and 3p electrons of the 2s2p4(2,4P)3p(3S,3P,3D) state of oxygen. Using these coefficients the wave functions and photoionization cross sections of oxygen 2s has been evaluated and compared with previous results. PACS Nos.: 31.15.Ne, 31.10.+z, 32.80.Fb
CLUSTERING-NEURAL NETWORK MODELS FOR FREEWAY WORK ZONE CAPACITY ESTIMATION
Authors: JIANG XIAOMO , ADELI HOJJAT
Published: July 2004

Two neural network models, called clustering-RBFNN and clustering-BPNN models, are created for estimating the work zone capacity in a freeway work zone as a function of seventeen different factors through judicious integration of the subtractive clustering approach with the radial basis function (RBF) and the backpropagation (BP) neural network models. The clustering-RBFNN model has the attractive characteristics of training stability, accuracy, and quick convergence. The results of validation indicate that the work zone capacity can be estimated by clustering-neural network models in general with an error of less than 10%, even with limited data available to train the models. The clustering-RBFNN model is used to study several main factors affecting work zone capacity. The results of such parametric studies can assist work zone engineers and highway agencies to create effective traffic management plans (TMP) for work zones quantitatively and objectively.
SOFTWARE RELIABILITY PREDICTION USING RECURRENT NEURAL NETWORK WITH BAYESIAN REGULARIZATION
Authors: TIAN LIANG , NOORE AFZEL
Published: July 2004

A recurrent neural network modeling approach for software reliability prediction with respect to cumulative failure time is proposed. Our proposed network structure has the capability of learning and recognizing the inherent internal temporal property of cumulative failure time sequence. Further, by adding a penalty term of sum of network connection weights, Bayesian regularization is applied to our network training scheme to improve the generalization capability and lower the susceptibility of overfitting. The performance of our proposed approach has been tested using four real-time control and flight dynamic application data sets. Numerical results show that our proposed approach is robust across different software projects, and has a better performance with respect to both goodness-of-fit and next-step-predictability compared to existing neural network models for failure time prediction.