A fast neutron source for cultured cell irradiation.

Because of recent interest in the use of neutrons for radiotherapy, there has been an increased interest in the radiology of neutrons. In this irradiated cell study, a 1.3 MeV accelerator produced beam currents over 100 muA on the water-cooled 3-mm thick beryllium disk target. The monolayer of irradiated cells was neutron-shielded by about 700 kg of paraffin. The neutron energy spectrum for the 9Be(d,n)10B reaction was obtained, with an average neutron energy calculated to be between 3.3 and 3.5 MeV, and an average linear energy transfer calculated at more than 30 keV/micron.     

Mean neutron energy and the neutron spectra from T(d,n)4He reaction

The mean neutron energy and energy spread of neutrons from the T(d,n)⁴He reaction have been calculated for deuteron beams of energy from 50 keV to 1 MeV incident on a thick tritiated titanium target. This has been done over the angular range from 0° to 180° and the results are presented graphically as a function of deuteron energy and neutron emission angle and are also tabulated.     

A review of boron neutron capture therapy (BNCT) and the design and dosimetry of a high-intensity, 24 keV, neutron beam for BNCT research

This paper reviews the development of boron neutron capture therapy (BNCT) and describes the design and dosimetry of an intermediate energy neutron beam, developed at the Harwell Laboratory, principally for BNCT research. Boron neutron capture therapy is a technique for the treatment of gliomas (a fatal form of brain tumour). The technique involves preferentially attaching 10B atoms to tumour cells and irradiating them with thermal neutrons. The thermal neutron capture products of 10B are short range and highly damaging, so they kill the tumour cells, but healthy tissue is relatively undamaged. Early trials required extensive neurosurgery to exposure the tumour to the thermal neutrons used and were unsuccessful. It is thought that intermediate-energy neutrons will overcome many of the problems encountered in the early trials, because they have greater penetration prior to thermalization, so that surgery will not be required. An intermediate-energy neutron beam has been developed at the Harwell Laboratory for research into BNCT. Neutrons from the core of a high-flux nuclear reactor are filtered with a combination of iron, aluminium and sulphur. Dosimetry measurements have been made to determine the neutron and gamma-ray characteristics of this beam, and to monitor them throughout the four cycles used for BNCT research. The beam is of high intensity (approximately 2 x 10(7) neutrons cm-2 s-1, equivalent to a neutron kerma rate in water of 205 mGy h-1) and nearly monoenergetic (93% of the neutrons have energies approximately 24 keV, corresponding to 79% of the neutron kerma rate).     

Characterization of ultra high energy neutron beam generated by 500 MeV proton beam

An ultra high energy neutron facility was constructed at PARMS, University of Tsukuba, to produce a neutron beam superior to an X-ray beam generated by a modern linac in terms of dose distribution. This has been achieved using the reaction on a thick uranium target struck by 500 MeV proton beam from the booster-synchrotron of High Energy Physics Laboratory. The percentage depth dose of this neutron beam is nearly equivalent to that of X-rays at around 20 MV and the dose rate of 15 cGy per minute. Relative biological effectiveness of this neutron beam has been estimated on the cell killing effect by the use of HMV-I cell line. Resultant survival curve of cells after the neutron irradiation shows the shoulder with n and Dq of 8 and 2.3 Gy, respectively. RBE value at 10(-2) survival level for the present neutron, compared with 137Cs gamma-rays is 1.24. The result suggests that the biological effects of high energy neutrons are not practically large enough whenever the depth dose distribution of neutrons becomes superior to high energy linac X-rays.     

Reducing the effects of metal artefact using high keV monoenergetic reconstruction of dual energy CT (DECT) in hip replacements

Purpose

The aim of this study was to determine whether high keV monoenergetic reconstruction of dual energy computed tomography (DECT) could be used to overcome the effects of beam hardening artefact that arise from preferential deflection of low energy photons.

Materials and Methods

Two phantoms were used: a Charnley total hip replacement set in gelatine and a Catphan 500. DECT datasets were acquired at 100, 200 and 400 mA (Siemens Definition Flash, 100 and 140 kVp) and reconstructed using a standard combined algorithm (1:1) and then as monoenergetic reconstructions at 10 keV intervals from 40 to 190 keV. Semi-automated segmentation with threshold inpainting was used to obtain the attenuation values and standard deviation (SD) of the streak artefact. High contrast line pair resolution and background noise were assessed using the Catphan 500.

Results

Streak artefact is progressively reduced with increasing keV monoenergetic reconstructions. Reconstruction of a 400 mA acquisition at 150 keV results in reduction in the volume of streak artefact from 65 cm³ to 17 cm³ (74 %). There was a decrease in the contrast to noise ratio (CNR) at higher tube voltages, with the peak CNR seen at 70–80 keV. High contrast spatial resolution was maintained at high keV values.

Conclusion

Monoenergetic reconstruction of dual energy CT at increasing theoretical kilovoltages reduces the streak artefact produced by beam hardening from orthopaedic prostheses, accompanied by a modest increase in heterogeneity of background image attenuation, and decrease in contrast to noise ratio, but no deterioration in high contrast line pair resolution.     

Development of a low-level background gamma-ray spectrometer by KRISS

A new low-level background and high-efficiency gamma-ray spectrometric system, to be used mainly for the activity certification of natural-matrix certified reference materials (CRMs) and environmental reference materials (RMs) that has been developed on the grounds of the Korea Research Institute of Standards and Science (KRISS). The spectrometer consists of a low-background high-purity germanium detector with a relative efficiency of 120% and various shielding devices to reduce radiation background. The cabinet-shaped device made of 10 ton of shielding materials encloses the germanium detector for protection against background from natural radioactivity and neutrons. Three plates of 50-mm-thick plastic scintillation detectors on top of the passive shielding cabinet suppress cosmogenic background by detecting high-energetic cosmic muons bombarding the germanium detector. The measured background rate of the spectrometer for the energy range 50–3000 keV was 1.72 s^–1.     

The Production of Chromosome Aberration in Chinese Hamster Fibroblasts Exposed to 24 keV Neutrons

Summary

A filtered reactor beam, consisting mainly of 24 keV neutrons, was used to study the induction of chromosome aberrations in the V79/4(AH1) Chinese hamster cell line. The yields of both dicentrics and acentrics were linear with dose and the value of relative biological effectiveness (RBE) for dicentrics at low doses was 6·5 ± 1·4. This value was similar to that found previously for a neutron spectrum with mean energy 2·1 MeV, and suggests that the RBE of neutrons does not increase to very high values in the energy region below 100 keV. This result does not support the suggestions of Davy (1969) and Key (1971) that the neutron RBE rises to very high values in the intermediate energy range.     

Analysis of neutron and gamma-ray streaming along the maze of NRCAM thallium production target room.

Study of the shield performance of a thallium-203 production target room has been investigated in this work. Neutron and gamma-ray equivalent dose rates at various points of the maze are calculated by simulating the transport of streaming neutrons, and photons using Monte Carlo method. For determination of neutron and gamma-ray source intensities and their energy spectrum, we have applied SRIM 2003 and ALICE91 computer codes to Tl target and its Cu substrate for a 145 microA of 28.5 MeV protons beam. The MCNP/4C code has been applied with neutron source term in mode n p to consider both prompt neutrons and secondary gamma-rays. Then the code is applied for the prompt gamma-rays as the source term. The neutron-flux energy spectrum and equivalent dose rates for neutron and gamma-rays in various positions in the maze have been calculated. It has been found that the deviation between calculated and measured dose values along the maze is less than 20%.     

Monoenergetic computed tomography reconstructions reduce beam hardening artifacts from dental restorations

The aim of this study was to assess the potential of monoenergetic computed tomography (CT) images to reduce beam hardening artifacts in comparison to standard CT images of dental restoration on dental post-mortem CT (PMCT). Thirty human decedents (15 male, 58 ± 22 years) with dental restorations were examined using standard single-energy CT (SECT) and dual-energy CT (DECT). DECT data were used to generate monoenergetic CT images, reflecting the X-ray attenuation at energy levels of 64, 69, 88 keV, and at an individually adjusted optimal energy level called OPTkeV. Artifact reduction and image quality of SECT and monoenergetic CT were assessed objectively and subjectively by two blinded readers. Subjectively, beam artifacts decreased visibly in 28/30 cases after monoenergetic CT reconstruction. Inter- and intra-reader agreement was good (k = 0.72, and k = 0.73 respectively). Beam hardening artifacts decreased significantly with increasing monoenergies (repeated-measures ANOVA p < 0.001). Artifact reduction was greatest on monoenergetic CT images at OPTkeV. Mean OPTkeV was 108 ± 17 keV. OPTkeV yielded the lowest difference between CT numbers of streak artifacts and reference tissues (?163 HU). Monoenergetic CT reconstructions significantly reduce beam hardening artifacts from dental restorations and improve image quality of post-mortem dental CT.     

High energy fast neutrons from the Harwell variable energy cyclotron. I. Physical characteristics.

A high energy fast neutron beam potentially suitable for radiotherapy was built at the Harwell variable energy cyclotron. The beam line is described and results are given of physical measurements on the fast neutron beams produced by 42 MeV deuterons on thick (4 mm) and thin (2 mm) beryllium targets. With 20 muA beam current the entrance dose rate in a phantom 150 cm from the target was about 130 rad min-1 with the thick target and about 60 rad min-1 with the thin target. Therefore, it is possible to use both the thin target and the relatively large target-skin distance of 150 cm to improve depth dose for radiotherapy or radiobiology. With this arrangement the dose rate decreased to 50% at depths in the phantom of 11.3-15.4 cm, depending on the field size. The use of primarily hydrogenous materials for shielding and collimation provided beam edge definition similar to that of 60Co teletherapy units, and off-axis radiation levels of approximately 1% which compare favorably with 14 MeV deuteron-tritium generators. The copper backing of the thin target became highly radioactive and an alterative material may be preferable. Biologic characteristics of the beam are described in a companion paper.     

Response of PIN diodes as room temperature photon detectors

In this work we have studied the direct detection and spectrometric capabilities of low-cost commercial silicon photodiodes for X- and γ-rays (energies from 10 up to 80 keV) envisaging their use in characterization of porous microstructures by X-ray microtomography. The best values of the energy resolution for the 59.5 keV ²⁴¹Am γ-ray line, measured at room temperature, were found to be 2.1 and 1.8 keV for SFH00206 K (Siemens) and S2506-04 (Hamamatsu) PIN diodes, respectively.     

Absolute Doubly Differential Cross Section for Bremsstrahlung Spectra Produced in 7.0 keV e<formula>^-</formula>--Ag and Au Collisions

The first experimental data are presented for the absolute doubly differential cross section (DDCS) for non-characteristics (bremsstrahlung) X-ray spectra produced by 7.0 keV electron bombardment of (semi-thick) targets of silver and gold at a photon detection angle of 90 degree. The bremsstrahlung spectra are corrected for detector's efficiency as well as for target effects; namely, electron energy loss, backscattering and photon-attenuation in the target. The DDCS values so obtained are compared with the predictions of a thin target bremsstrahlung theory. The agreement between experiment and theory for DDCS both in magnitude and shape is found to be satisfactory within the systematic experimental uncertainty of about 27%. penetrating electrons into the thick targets and the depth distribution of photons generated inside the targets are expected to be also present in the interaction. However, the contributions of these effects to the DDCS have not been taken into consideration. Various possible reasons for the existing discrepancy between experiment and theory are pointed out.     

The Effect of 238Pu α-particles on the Mouse Fibroblast Cell Line C3H 10T1/2: Characterization of Source and RBE for Cell Survival

Summary

Considerable interest has been aroused in recent years by reports that the transforming and carcinogenic effectiveness of low doses of high LET radiations can be increased by reducing the dose rate, especially for transformation of 10T1/2 cells in vitro by fission-spectrum neutrons. We report on conditions which have been established for irradiation of 10T1/2 cells with high LET monoenergetic α-particles (energy of 3·2 MeV, LET of 124 keV μm^?1) from ²³⁸Pu. The α-particle irradiator allows convenient irradiation of multiple dishes of cells at selectable high or low dose rates and temperatures. The survival curves of irradiated cells showed that the mean lethal dose of α-particles was 0·6 Gy and corresponded to an RBE, at high dose rates, of 7·9 at 80 per cent survival and 4·6 at 5 per cent survival, relative to ⁶⁰Co γ-rays. The mean areas of the 10T1/2 nuclei, perpendicular to the incident α-particles, was measured as 201 μm², from which it follows that, on average, only one in six of the α-particle traversals through a cell nucleus is lethal. Under the well-characterized conditions of these experiments the event frequency of α-particle traversals through cell nuclei is 9·8 Gy^?1.     

Dual energy computed tomography: simulated monoenergetic and material-selective imaging

A dual beam-quality technique was used to reduce the beam hardening artifact in CT and to obtain separate images of osseous and soft-tissue structures in phantom and clinical CT studies. Recordings were made with pulsed low and high kVp spectra with the Somatom DR2. Conventional polyenergetic and simulated monoenergetic images were reconstructed from the measurements. In the monoenergetic images the beam hardening artifacts were 60-90% lower than in the high kVp polyenergetic images whereas the noise was of the same order of magnitude in the two types. Noise in the monoenergetic images was lowest around 70-80 keV both in body and skull examinations although the contrast in the monoenergetic image was rather independent of energy.     

The interpretation of dose calculations and cell-survival measurements for the boron neutron capture therapy of brain tumours with 24 keV neurons

Monte-Carlo computer codes have been used to estimate the distribution of doses to borated and unborated tissues in head-sized phantoms when exposed to beams of 2 keV and 24 keV neutrons. For the application of such beams to boron neutron capture therapy (BNCT) these calculations show the superiority of 2 keV neutrons over 24 keV neutrons and the importance of using large-area beams. A 24 keV neutron beam has been used to irradiate HeLa cell cultures in vitro, with and without the addition of 10B, at various depths within a narrow polyethylene phantom. Survival data obtained from these experiments have been used to estimate depth-damage profiles for normal (unboronated) and tumour (boronated) brain tissues when exposed to 24 keV neutrons. A good differential between damage to normal and tumorous tissue is obtained under suitable irradiation conditions. Although lower-energy neutrons are probably preferable, these results demonstrate the possibility of using beams of 24 keV neutrons for the BNCT of brain tumours.     

The feasibility of accelerator-based in vivo neutron activation analysis of nitrogen

The feasibility of accelerator-based in vivo neutron activation analysis of nitrogen has been investigated. It was found that a moderated neutron flux from 10 μA of 2.5 MeV protons on a ⁹Be target performed as well as, and possibly slightly better than the existing isotope-based approach in terms of net counts per unit subject dose. Such a system may be an attractive alternative to the widespread use of ^238,239Pu/Be or ²⁵²Cf neutron sources, since there is more flexibility in the energy spectrum generated by accelerator-based neutron sources. From a radiation safety standpoint, accelerators have the advantage in that they only produce radiation when in operation. Furthermore, an accelerator beam can be pulsed, to reduce background detected in the prompt-γ measurement, and such a device has a wide range of additional biological and medical applications.     

High-power electron beam tests of a liquid-lithium target and characterization study of 7Li(p,n) near-threshold neutrons for accelerator-based boron neutron capture therapy

A compact Liquid-Lithium Target (LiLiT) was built and tested with a high-power electron gun at Soreq Nuclear Research Center (SNRC). The target is intended to demonstrate liquid-lithium target capabilities to constitute an accelerator-based intense neutron source for Boron Neutron Capture Therapy (BNCT) in hospitals. The lithium target will produce neutrons through the ⁷Li(p,n)⁷Be reaction and it will overcome the major problem of removing the thermal power >5 kW generated by high-intensity proton beams, necessary for sufficient therapeutic neutron flux.In preliminary experiments liquid lithium was flown through the target loop and generated a stable jet on the concave supporting wall. Electron beam irradiation demonstrated that the liquid-lithium target can dissipate electron power densities of more than 4 kW/cm² and volumetric power density around 2 MW/cm³ at a lithium flow of ~4 m/s, while maintaining stable temperature and vacuum conditions. These power densities correspond to a narrow (σ=~2 mm) 1.91 MeV, 3 mA proton beam. A high-intensity proton beam irradiation (1.91–2.5 MeV, 2 mA) is being commissioned at the SARAF (Soreq Applied Research Accelerator Facility) superconducting linear accelerator.In order to determine the conditions of LiLiT proton irradiation for BNCT and to tailor the neutron energy spectrum, a characterization of near threshold (~1.91 MeV) ⁷Li(p,n) neutrons is in progress based on Monte-Carlo (MCNP and Geant4) simulation and on low-intensity experiments with solid LiF targets. In-phantom dosimetry measurements are performed using special designed dosimeters based on CR-39 track detectors.     

Optimized energy of spectral coronary CT angiography for coronary plaque detection and quantification

BackgroundTo optimize spectral coronary computed tomography angiography (CTA) for quantification of coronary artery plaque components.Materials and methodsFifty-one subjects were prospectively enrolled (88.2% male) (NCT02740699). Dual energy coronary CTA was performed at 90/Sn150 kVp using a 3rd generation dual-source CT scanner (SOMATOM Force, Siemens Healthcare). Dual energy images were reconstructed with a) linear mixed blending of 90 and Sn150 kVp data, b) virtual monoenergetic algorithm from 40 to 150 keV (at 10- keV intervals), and c) noise-optimized virtual monoenergetic algorithm from 40 to 150 keV. Image noise, iodine signal-to-noise-ratio (SNR), and contrast-to-noise ratio (CNR) for calcified and non-calcified plaque were measured. Qualitative readings of image quality were performed. Semi-automated software (QAngioCT, Medis) was used to quantify coronary plaque. Linear mixed-models that account for within-subject correlation of plaques were used to compare the results.Results100–150 keV noise-optimized virtual monoenergetic images had lower image noise than linear mixed images (all P < 0.05). The highest iodine SNR was achieved in 40 keV noise-optimized virtual monoenergetic images (33.3 ± 0.6 vs 23.3 ± 0.7 for linear mixed images, P < 0.001). 40–70 keV noise-optimized virtual monoenergetic images and 70 keV virtual monoenergetic images had superior coronary plaque CNR versus linear mixed images (all P < 0.01) with a maximum improvement of 20.1% and 22.7% for calcified plaque and non-calcified plaque (38.8 ± 2.2 vs 32.3 ± 2.3 and 17.3 ± 1.3 vs 14.1 ± 1.4, respectively). Using 90/Sn150 kVp linear mixed images as a reference, the plaque quantity was similar for 70 keV noise-optimized virtual monoenergetic images whereas low keV images (e.g. 40 keV) yielded significantly higher coronary plaque volumes (all P < 0.001).ConclusionSpectral coronary CTA with low energy (40–70 keV) post-processing can improve the CNR of coronary plaque components. However, low energies (such as 40 keV) resulted in different absolute volumes of coronary plaque compared to “conventional” mixed 90/Sn150 kVp images.     

BINP accelerator based epithermal neutron source

Innovative facility for neutron capture therapy has been built at BINP. This facility is based on compact vacuum insulation tandem accelerator designed to produce proton current up to 10 mA. Epithermal neutrons are proposed to be generated by 1.915–2.5 MeV protons bombarding a lithium target using ⁷Li(p,n)⁷Be threshold reaction. In the article, diagnostic techniques for proton beam and neutrons developed are described, results of experiments on proton beam transport and neutron generation are shown, discussed, and plans are presented.     

Chromosome aberrations induced in vitro in human lymphocytes by monoenergetic 2.5 MeV neutrons and 60Co gamma rays

The aim of the present experiments was to evaluate the relative biological effectiveness (RBE) of monoenergetic 2.5 MeV neutrons, in view of the scarcity of data on the RBE of neutrons in this energy range. Human peripheral blood lymphocytes from two donors were exposed to doses of neutrons ranging from 0.005 Gy to 0.5 Gy. Gamma rays produced by a telecobalt therapy unit were used as reference radiation. RBE values were of the same order of magnitude, whatever was the model of the dose-response curve chosen for the neutrons (linear or linear-quadratic). As expected, RBE increased markedly with decreasing doses and went beyond 30 at a dose level of 0.2 Gy. The present results, compared with RBE values obtained with neutrons of higher energy (6.5, 14 and 21 MeV), confirm that low energy neutrons are more effective in producing genetic effects, especially at low doses.