Uniform Radiation Field Research Articles

Defining functional changes in the brain caused by targeted stereotaxic radiosurgery.

Brain tumor patients routinely undergo cranial radiotherapy, and while beneficial, this treatment often results in debilitating cognitive dysfunction. This serious and unresolved problem has at present, no clinical recourse, and has driven our efforts to more clearly define the consequences of different brain irradiation paradigms on specific indices of cognitive performance and on the underlying cellular mechanisms believed to affect these processes. To accomplish this we have developed the capability to deliver highly focused X-ray beams to small and precisely defined volumes of the athymic rat brain, thereby providing more realistic simulations of clinical irradiation scenarios. Using this technique, termed stereotaxic radiosurgery, we evaluated the cognitive consequences of irradiation targeted to the hippocampus in one or both hemispheres of the brain, and compared that to whole brain irradiation. While whole brain irradiation was found to elicit significant deficits in novel place recognition and fear conditioning, standard platforms for quantifying hippocampal and non-hippocampal decrements, irradiation targeted to both hippocampi was only found to elicit deficits in fear conditioning. Cognitive decrements were more difficult to demonstrate in animals subjected to unilateral hippocampal ablation. Immunohistochemical staining for newly born immature (doublecortin positive) and mature (NeuN positive) neurons confirmed our capability to target irradiation to the neurogenic regions of the hippocampus. Stereotaxic radiosurgery (SRS) of the ipsilateral hemisphere reduced significantly the number of doublecortin and NeuN positive neurons by 80% and 27% respectively. Interestingly, neurogenesis on the contralateral side was upregulated in response to stereotaxic radiosurgery, where the number of doublecortin and NeuN positive neurons increased by 22% and 36% respectively. Neuroinflammation measured by immunostaining for activated microglia (ED1 positive cells) was significantly higher on the ipsilateral versus contralateral sides, as assessed throughout the various subfields of the hippocampus. These data suggest that certain cognitive decrements are linked to changes in neurogenesis, and that the unilaterally irradiated brain exhibits distinct neurogenic responses that may be regulated by regional differences in neuroinflammation. Compensatory upregulation of neurogenesis on the contralateral hemisphere may suffice to maintain cognition under certain dose limits. Our results demonstrate unique cognitive and neurogenic consequences as a result of targeted stereotaxic radiosurgery, and suggest that these irradiation paradigms elicit responses distinct from those found after exposing the whole brain to more uniform radiation fields.

MODELING THE ATOMIC-TO-MOLECULAR TRANSITION AND CHEMICAL DISTRIBUTIONS OF TURBULENT STAR-FORMING CLOUDS

We use 3D-PDR, a three-dimensional astrochemistry code for modeling photodissociation regions (PDRs), to post-process hydrodynamic simulations of turbulent, star-forming clouds. We focus on the transition from atomic to molecular gas, with specific attention to the formation and distribution of H, C+, C, H2 and CO. First, we demonstrate that the details of the cloud chemistry and our conclusions are insensitive to the simulation spatial resolution, to the resolution at the cloud edge, and to the ray angular resolution. We then investigate the effect of geometry and simulation parameters on chemical abundances and find weak dependence on cloud morphology as dictated by gravity and turbulent Mach number. For a uniform external radiation field, we find similar distributions to those derived using a one-dimensional PDR code. However, we demonstrate that a three-dimensional treatment is necessary for a spatially varying external field, and we caution against using one-dimensional treatments for non-symmetric problems. We compare our results with the work of Glover et al. (2010), who self-consistently followed the time evolution of molecule formation in hydrodynamic simulations using a reduced chemical network. In general, we find good agreement with this in situ approach for C and CO abundances. However, the temperature and H2 abundances are discrepant in the boundary regions (Av < 5), which is due to the different number of rays used by the two approaches.

Improving analysis of radiochromic films

An appropriate radiochromic film should respond uniformly throughout its surface after exposure to a uniform radiation field. The evaluation of radiochromic films may be carried out, for example, by measuring color intensities in film-based digitized images. Fluctuations in color intensity may be caused by many different factors such as optical structure of the film's active layer, defects in structure of the film, scratches and external agents, such as dust. The use of high spatial resolution during film scanning should also increase microscopic uniformity. Since the average is strongly influenced by extreme values, the use of other statistical tools, for which this problem becomes inconspicuous, optimizes the application of higher spatial resolution as well as reduces standard deviations. This paper compares the calibration curves of the XR-QA2 Gafchromic® radiochromic film based on three different methods: the average of all color intensity readings, the median of these same readings and the average of readings that fall between the first and third quartiles. Results indicate that a higher spatial resolution may be adopted whenever the calibration curve is based on tools less influenced by extreme values such as those generated by the factors mentioned above.

Proton beam scattering system optimization for clinical and research applications

To develop and test a method for optimizing and constructing a dual scattering system in passively scattered proton therapy. A beam optics optimization algorithm was developed to optimize the thickness of the first scatterer (S1) and the profile (of both the high-Z material and Lexan) of the second scatterer (S2) to deliver a proton beam matching a given set of parameters, including field diameter, fluence, flatness, and symmetry. A new manufacturing process was also tested that allows the contoured second scattering foil to be created much more economically and quickly using Cerrobend casting. Two application-specific scattering systems were developed and tested using both experimental and Monte Carlo techniques to validate the optimization process described. A scattering system was optimized and constructed to deliver large uniform irradiations of radiobiology samples at low dose rates. This system was successfully built and tested using film and ionization chambers. The system delivered a uniform radiation field of 50 cm diameter (to a dose of ± 7% of the central axis) while the depth dose profile could be tuned to match the specifications of the particular investigator using modulator wheels and range shifters. A second scattering system for intermediate field size (4 cm < diameter < 10 cm) stereotactic radiosurgery and radiation therapy (SRS and SRT) treatments was also developed and tested using GEANT4. This system improved beam efficiency by over 70% compared with existing scattering systems while maintaining field flatness and depth dose profile. In both cases the proton range uniformity across the radiation field was maintained, further indicating the accuracy of the energy loss formalism in the optimization algorithm. The methods described allow for rapid prototyping of scattering foils to meet the demands of both research and clinical beam delivery applications in proton therapy.

DNA Damage Responses following Exposure to Modulated Radiation Fields

During the delivery of advanced radiotherapy treatment techniques modulated beams are utilised to increase dose conformity across the target volume. Recent investigations have highlighted differential cellular responses to modulated radiation fields particularly in areas outside the primary treatment field that cannot be accounted for by scattered dose alone. In the present study, we determined the DNA damage response within the normal human fibroblast AG0-1522B and the prostate cancer cell line DU-145 utilising the DNA damage assay. Cells plated in slide flasks were exposed to 1 Gy uniform or modulated radiation fields. Modulated fields were delivered by shielding 25%, 50% or 75% of the flask during irradiation. The average number of 53BP1 or γH2AX foci was measured in 2 mm intervals across the slide area. Following 30 minutes after modulated radiation field exposure an increase in the average number of foci out-of-field was observed when compared to non-irradiated controls. In-field, a non-uniform response was observed with a significant decrease in the average number of foci compared to uniformly irradiated cells. Following 24 hrs after exposure there is evidence for two populations of responding cells to bystander signals in-and out-of-field. There was no significant difference in DNA damage response between 25%, 50% or 75% modulated fields. The response was dependent on cellular secreted intercellular signalling as physical inhibition of intercellular communication abrogated the observed response. Elevated residual DNA damage observed within out-of-field regions decreased following addition of an inducible nitric oxide synthase inhibitor (Aminoguanidine). These data show, for the first time, differential DNA damage responses in-and out-of-field following modulated radiation field delivery. This study provides further evidence for a role of intercellular communication in mediating cellular radiobiological response to modulated radiation fields and may inform the refinement of existing radiobiological models for the optimization of advanced radiotherapy treatment plans.

MO-F-213AB-06: Experimental Evaluation of Radiation Dose Effect by High Atomic Number Materials for Superficial Radiation Therapy.

High atomic number (Z) materials have been considered as a method for enhancing radiation dose in tumors. The dose enhancement due to interactions of kilovoltage x-rays with high-Z materials (i.e., gold or iodine) has been well demonstrated through computational works. This study is to experimentally quantify the effect using gold nanoparticles (AuNPs) and iodine solutions, respectively. Iodine and AuNPs (AuroVist, Nanoprobes, Yaphank NY) are uniformly distributed in each cylinder phantom (1.6 cm diameter and 2.0 cm depth) separately. Concentrations of Iodine and AuNPs were varied from 40 to 225 mg/ml and 16.0 mg/ml to 42.7 mg/ml, respectively. The Iodine solutions were irradiated with 75 to 150 kVp x-rays from a superficial x-ray therapy machine at doses of 250 to 400 cGy. The AuNPs solutions in the cylinder were irradiated with 40 to 150 kVp x-rays. The phantom was placed at the center of the cone to ensure a uniform radiation field. Radiation doses were measured using GafChromic EBT2 films (International Specialty Products, Wayne NJ). Dose enhancement factors (DEF), i.e., the ratio of dose to high-Z material versus dose to water, were calculated and plotted as functions of concentration and kVp. Experimental DEFs varied between 1.01 and 1.38. The DEFs increased with increasing concentration and varied with changing kVp. The maximum DEF measured for Iodine solution was 1.38 at 225 mg/ml and 150 kVp. The maximum DEF measured for AuNPs was 1.22 at 42.7 mg/ml and 40 kVp. The target volume covered by dose enhancement is larger with relatively lower concentrations. The magnitude of dose enhancement due to AuNPs and Iodine presence has a dependency with the concentration and kVp. In clinical applications, the concentration of the high-Z material and kVp should also be selected to suit the depth and volume of the target tumor.

Comparison of noise power spectrum methodologies in measurements by using megavoltage X-ray energies

The noise power spectrum (NPS) is one of the most general methods for measuring the noise amplitude and the quality of an image acquired from a uniform radiation field. The purpose of this study was to compare different NPS methodologies by using megavoltage X-ray energies. The NPS evaluation methods in diagnostic radiation were applied to therapy using the International Electrotechnical Commission standard (IEC 62220-1). In order to measure the region of interest (ROI) of the NPS, we used the following five factors: the overlapping impact, the non-overlapping impact, the penumbra, the flatness and different ROI sizes. We used NPS from four different types of detectors, the CR-IP (computed radiography image plate: photo-stimulable phosphor screen), the CR-IP-lead (hexalon lead screen), the CR-IP-back [lanex TM fast back screen: {terbium-doped gadolinium oxysulfide granular phosphor screen (Gd2O2S:Tb,133 mg/cm2)} + 1-mm-thick copper plate and the CR-IP-front (lanex TM fast front screen). A Kodak 2000 RT photo-stimulable phosphor-based computed radiographic (CR) system showed that the normalized noise power spectrum (NNPS) curve gradually decreased, in compliance with increasing spatial resolution. In addition, each detector showed a different reactivity of the NPS to megavoltage. The results of multivariate analysis of variance (MANOVA) test (methods × detectors) revealed significant main effects of the methods [F(1, 4) = 53.543, P = 0.001 and of the detectors [F(1, 4) = 17.556, P = 0.001]. The present study revealed that various factors could be employed to produce megavoltage imaging (MVI) of the NPS and as a baseline standard for NPS control in MVI.

A methodology for modeling photocatalytic reactors for indoor pollution control using previously estimated kinetic parameters

A methodology for modeling photocatalytic reactors for their application in indoor air pollution control is carried out. The methodology implies, firstly, the determination of intrinsic reaction kinetics for the removal of formaldehyde. This is achieved by means of a simple geometry, continuous reactor operating under kinetic control regime and steady state. The kinetic parameters were estimated from experimental data by means of a nonlinear optimization algorithm.The second step was the application of the obtained kinetic parameters to a very different photoreactor configuration. In this case, the reactor is a corrugated wall type using nanosize TiO2 as catalyst irradiated by UV lamps that provided a spatially uniform radiation field. The radiative transfer within the reactor was modeled through a superficial emission model for the lamps, the ray tracing method and the computation of view factors. The velocity and concentration fields were evaluated by means of a commercial CFD tool (Fluent 12) where the radiation model was introduced externally. The results of the model were compared experimentally in a corrugated wall, bench scale reactor constructed in the laboratory. The overall pollutant conversion showed good agreement between model predictions and experiments, with a root mean square error less than 4%.

Uniform Irradiation in a PEFP 100-MeV Beam Line with Octupole Magnets

One of the PEFP (Proton Engineering Frontier Project) 100-MeV beam lines requires a large and uniform irradiation field of ±10% uniformity in the target area of 300 mm ◊ 300 mm. We studied the nonlinear optics method by using two octupole magnets in order to achieve a large uniform field at the target. We found that the particles can be uniformly distributed within ±10% in a 300 mm ◊ 300 mm irradiation field at the target. We also studied the conditions of the quadrupole and the octupole magnets to meet the requirement of a large and uniform irradiation field.

Measurement of neutron ambient dose equivalent in passive carbon‐ion and proton radiotherapies

Secondary neutron ambient dose equivalents per the treatment absorbed dose in passive carbon-ion and proton radiotherapies were measured using a rem meter, WENDI-II at two carbon-ion radiotherapy facilities and four proton radiotherapy facilities in Japan. Our measured results showed that (1) neutron ambient dose equivalent in carbon-ion radiotherapy is lower than that in proton radiotherapy, and (2) the difference to the measured neutron ambient dose equivalents among the facilities is within a factor of 3 depending on the operational beam setting used at the facility and the arrangement of the beam line, regardless of the method for making a laterally uniform irradiation field: the double scattering method or the single-ring wobbling method. The reoptimization of the beam line in passive particle radiotherapy is an effective way to reduce the risk of secondary cancer because installing an adjustable precollimator and designing the beam line devices with consideration of their material, thickness and location, etc., can significantly reduce the neutron exposure. It was also found that the neutron ambient dose equivalent in passive particle radiotherapy is equal to or less than that in the photon radiotherapy. This result means that not only scanning particle radiotherapy but also passive particle radiotherapy can provide reduced exposure to normal tissues around the target volume without an accompanied increase in total body dose.

Evaluation of beam wobbling methods for heavy‐ion radiotherapy

The National Institute of Radiological Sciences (NIRS) has extensively studied carbon-ion radiotherapy at the Heavy-Ion Medical Accelerator in Chiba (HIMAC) with some positive outcomes, and has established its efficacy. Therefore, efforts to distribute the therapy to the general public should be made, for which it is essential to enable direct application of clinical and technological experiences obtained at NIRS. For widespread use, it is very important to reduce the cost through facility downsizing with minimal acceleration energy to deliver the HIMAC-equivalent clinical beams. For the beam delivery system, the requirement of miniaturization is translated to reduction in length while maintaining the clinically available field size and penetration range for range-modulated uniform broad beams of regular fields that are either circular or square for simplicity. In this paper, we evaluate the various wobbling methods including original improvements, especially for application to the compact facilities through the experimental and computational studies. The single-ring wobbling method used at HIMAC is the best one including a lot of experience at HIMAC but the residual range is a fatal problem in the case of a compact facility. On the other hand, uniform wobbling methods such as the spiral and zigzag wobbling methods are effective and suitable for a compact facility. Furthermore, these methods can be applied for treatment with passive range modulation including respiratory gated irradiation. In theory, the choice between the spiral and zigzag wobbling methods depends on the shape of the required irradiation field. However, we found that it is better to use the zigzag wobbling method with transformation of the wobbling pattern even when a circular uniform irradiation field is required, because it is difficult to maintain the stability of the wobbler magnet due to the rapid change of the wobbler current in the spiral wobbling method. The regulated wobbling method, which is our improvement, can well expand the uniform irradiation field and lead to reducing the power requirement of the wobbler magnets. Our evaluations showed that the regulated zigzag wobbling method is the most suitable method for use in currently designed compact carbon-therapy facilities.

The Effect of External Radiative Heating on Ignition Temperature of Diesel Fuel for DeNOx

The system considered in this model consists of a single, semi-transparent, diesel fuel droplet, which is immobile in the heating area and surround by a quiescent air. A uniform external radiation field surrounds the droplet. Results from mathematical simulation suggest that because of the higher surface temperature, the external radiative heating of the droplet can promote an earlier ignition of the fuel vapour/air mixture. The radiative heating of the droplet increases the mass transfer from the droplet to the surrounding gas-phase, thus decreasing the heterogeneity of the fuel droplet/air system.

Real-time tracking of tumor motions and deformations along the leaf travel direction with the aid of a synchronized dynamic MLC leaf sequencer

Advanced radiotherapeutical techniques like intensity-modulated radiation therapy (IMRT) are based on an accurate knowledge of the location of the radiation target. An accurate dose delivery, therefore, requires a method to account for the inter- and intrafractional target motion and the target deformation occurring during the course of treatment. A method to compensate in real time for changes in the position and shape of the target is the use of a dynamic multileaf collimator (MLC) technique which can be devised to automatically arrange the treatment field according to real-time image information. So far, various approaches proposed for leaf sequencers have had to rely on a priori known target motion data and have aimed to optimize the overall treatment time. Since for a real-time dose delivery the target motion is not known a priori, the velocity range of the leading leaves is restricted by a safety margin to c × vmax while the following leaves can travel with an additional maximum speed to compensate for the respective target movements. Another aspect to be considered is the tongue and groove effect. A uniform radiation field can only be achieved if the leaf movements are synchronized. The method presented in this note is the first to combine a synchronizing sequencer and real-time tracking with a dynamic MLC. The newly developed algorithm is capable of online optimizing the leaf velocities by minimizing the overall treatment time while at the same time it synchronizes the leaf trajectories in order to avoid the tongue and groove effect. The simultaneous synchronization is performed with the help of an online-calculated mid-time leaf trajectory which is common for all leaf pairs and which takes into account the real-time target motion and deformation information.

Heavy-ion conformal irradiation in the shallow-seated tumor therapy terminal at HIRFL

Basic research related to heavy-ion cancer therapy has been done at the Institute of Modern Physics (IMP), Chinese Academy of Sciences since 1995. Now a plan of clinical trial with heavy ions has been launched at IMP. First, superficially placed tumor treatment with heavy ions is expected in the therapy terminal at the Heavy Ion Research Facility in Lanzhou (HIRFL), where carbon ion beams with energy up to 100 MeV/u can be supplied. The shallow-seated tumor therapy terminal at HIRFL is equipped with a passive beam delivery system including two orthogonal dipole magnets, which continuously scan pencil beams laterally and generate a broad and uniform irradiation field, a motor-driven energy degrader and a multi-leaf collimator. Two different types of range modulator, ripple filter and ridge filter with which Guassian-shaped physical dose and uniform biological effective dose Bragg peaks can be shaped for therapeutic ion beams respectively, have been designed and manufactured. Therefore, two-dimensional and three-dimensional conformal irradiations to tumors can be performed with the passive beam delivery system at the earlier therapy terminal. Both the conformal irradiation methods have been verified experimentally and carbon-ion conformal irradiations to patients with superficially placed tumors have been carried out at HIRFL since November 2006.

Study of dose rate profile at sample disks in a Risø OSL single-grain attachment system

The spatial variation of dose rate from a 90Sr/ 90Y calibration source mounted on a Risø equipment TL-DA-15 was investigated. Six disks accommodating single grains of α - Al 2 O 3 :C were irradiated at the Secondary Standard Dosimetry Laboratory (SSDL) at GSF to a uniform photon radiation field. The corresponding single-grain OSL signals of each grain were then compared with those obtained after the irradiation of the disks with the built-in beta source of the equipment. Additionally, the irradiation system was modelled to perform a Monte Carlo calculation assuming a homogeneous source. A continuous drop of the beta dose rate with increasing radial distance from the centre of the disk was observed in the experiments, indicating that grains located in the central part of the disk absorbed a higher dose than those placed in the outer region of the hole matrix. This experimental dose profile pattern was also confirmed by the results of the Monte Carlo calculation. It can therefore be concluded that different calibration factors, depending on the grain location, should be applied in order to improve the reliability of equivalent dose assessment using single-grain OSL measurements.

The use of α-Al2O3:C in RISØ OSL single grains attachment system for assessing the spatial dose rate distribution due to incorporation of 90Sr in human teeth

The possibility of using a single grain OSL attachment system developed by the Risø National Laboratory (Roskilde, Denmark) for assessing the spatial distribution of radionuclides incorporated in human tissues was investigated. Detectors containing arrays of single grains of alpha-Al2O3)C powder (Landauer Inc., USA) were prepared using aluminium discs (diameter 9.7 mm), which can accommodate 100 single grains in 0.3 mm holes positioned in a 10 x 10 grid. The luminescence and dosimetric properties of each grain were investigated by exposing the detectors to uniform photon radiation fields. After the characterisation of the detectors, the systems were tested to assess the spatial dose rate distribution because of 90Sr incorporated in a tooth sample extracted from an inhabitant of the Techa River region.

Thermal characteristics of a thermosyphon heated enclosure

This work analyzes and compares the thermal characteristics of two enclosures heated using different methods: one is heated using two-phase thermosyphons and the other is heated with a more conventional approach; hot exhaustion gases flowing into the enclosure. The first type has been evaluated for application to baking ovens, while the second type is already commonly used for this application in some countries. The methodology used to compare the two enclosures was developed by the present authors and is presented in the literature. The results show that the enclosure heated using thermosyphons has more uniform temperature and radiative heat transfer coefficient distributions compared to the conventional approach. The conventional enclosure tends to present larger convective heat transfer coefficients than the thermosyphon assisted enclosure because of the exhaustion gases movement. The thermosyphon assisted enclosure present a very uniform temperature distribution, which causes the air to become stagnant and the heat transfer coefficients to be low. The radiation field inside the thermosyphon assisted enclosure is more uniform than the conventional enclosure. A more uniform radiation field is obviously better when applying the enclosure for cooking as it makes the process more even.

Dose distribution of carbon ions in air assessed using imaging plates and ionization chamber

A system to expose biological specimens to medium-energy (2.6–6.0 MeV/u) irradiation has been developed at the NIRS-HIMAC. In order to determine the beam energy or LET at the irradiation position in air, the dose distribution for 6.0 MeV/u carbon beam has been obtained using a secondary electron monitor and a flat-type ionization chamber by using air as the energy absorber. Imaging plates were applied to assess the beam profile distribution. The intensity of photo-stimulated luminescence (PSL) was found to be almost proportional to the energy deposited within the sensitive layer of the imaging plate. It has been confirmed that a uniform irradiation field can be produced (about ± 5 % within 20 mm in diameter) at low-intensity exposure from 10 1 to 10 4 ions / cm 2 / s . Long-term beam stability in the low-intensity condition has also been demonstrated. As a consequence, the methodology for uniform, stable and low-intensity beam exposure has been established, and the continuously variable linear energy transfer (LET) values have also been obtained by changing the distance from the endcap of beamport, for biological studies.

Biological effects of radioactive 9C-ion beams on cells

The distinguishing feature and current technique progress of tumor treatment with heavy-ion beams is introduced in the paper. Additional superiority to tumor treatment from a radioactive ion beam (RIB) is emphatically discussed. The experimental research of the radioactive 9C-ion beams aimed at tumor treatment at Heavy Ion Medical Accelerator in Chiba (HIMAC), National Institute of Radiological Sciences (NIRS), Japan is described in detail, including production of the beams, optimization of parameters, distribution of depth dose, survival effect of cell and comparison of RBE between 9C- and 12C-beams. Results show that under 40 mm thick Beryllium target and 10 mm thick aluminum degrader at full (5%) momentum acceptance, the production rate and purity of the produced 9C-beams are 9.07×l06 and 82.88% respectively with the primary 12Cbeams of 430 MeV/u and 1.8×l09 pps. A uniform irradiation field with homogeneity up to 89.6% inside central area 10 mm in diameter is obtained by using spot scanning. In this case, the dose rate at the entrance is 0.5 Gy/h. In survival experiment of cells, the average relative biological effectiveness (RBE) of 9C-beams is 5.28 and 2.93 for 12C-beams in the region around Bragg peak. The RBE of 9C-beams is 1.8 times higher than that of 12C-beams. It indicates that cell-killing efficiency of 9C-beams is stronger than that of {u12}C-beams. 9C-beams are more efficacious for tumor treatment than 12C-beams.

The production of 9C beam in the secondary beam line of the HIMAC facility and its potential application in cancer therapy

The emitted particles from a β -delayed particle decay beam must enhance biological effects in the region of interest and such a radioactive ion beam may be useful in cancer treatment. To test this therapeutic purpose of β -delayed particle decay beams, 9 C beams were produced in the secondary beam line at HIMAC for the first time. The thickness of production target and degrader to yield a 9 C beam with higher production rate and purity was optimized and the momentum distribution of the produced 9 C beam under the optimal condition was measured. For upcoming radiobiological experiments, a uniform irradiation field for the produced 9 C beam was made by means of wobbling magnets.