High-energy Fast Neutrons Research Articles

Enhancement of thermal neutron shielding of cement mortar by using borosilicate glass powder

Concrete has been used as a traditional biological shielding material. High hydrogen content in concrete also effectively attenuates high-energy fast neutrons. However, concrete does not have strong protection against thermal neutrons because of the lack of boron compound. In this research, boron was added in the form of borosilicate glass powder to increase the neutron shielding property of cement mortar. Borosilicate glass powder was chosen in order to have beneficial pozzolanic activity and to avoid deleterious expansion caused by an alkali–silica reaction. According to the experimental results, borosilicate glass powder with an average particle size of 13µm showed pozzolanic activity. The replacement of borosilicate glass powder with cement caused a slight increase in the 28-day compressive strength. However, the incorporation of borosilicate glass powder resulted in higher thermal neutron shielding capability. Thus, borosilicate glass powder can be used as a good mineral additive for various radiation shielding purposes.

Design study of neutron flux intensity monitor between ten and several hundred keV for BNCT

Based on the activation method using 71Ga(n,γ)72Ga reaction, two spherical monitors with gallium nitride (GaN) wafers as activation material were designed by Monte Carlo simulations to precisely measure the absolute integral neutron flux intensity between ten and several hundred keV. The two monitors are almost the same in shape and have an absorber/moderator/absorber/GaN arrangement from outside to inside. The differences between the two monitors are the kind of materials, the thicknesses of the absorbers and the diameter of the moderator. By making difference of the sensitivities between these two monitors, the contributions of thermal, epithermal and very high energy fast neutrons were removed completely, and constant monitor sensitivity to neutrons between ten and several hundred keV was extracted. The simulation results and related analysis indicated that the absolute integral neutron flux intensity between ten and several hundred keV could be precisely measured by the presently designed two monitors.

Radioisotopic neutron transmission spectrometry: Quantitative analysis by using partial least-squares method

Neutron spectrometry, based on the scattering of high energy fast neutrons from a radioisotope and slowing-down by the light hydrogen atoms, is a useful technique for non-destructive, quantitative measurement of hydrogen content because it has a large measuring volume, and is not affected by temperature, pressure, pH value and color. The most common choice for radioisotope neutron source is 252Cf or 241Am–Be. In this study, 252Cf with a neutron flux of 6.3×10 6 n/s has been used as an attractive neutron source because of its high flux neutron and weak radioactivity. Pulse-height neutron spectra have been obtained by using in-house built radioisotopic neutron spectrometric system equipped with 3He detector and multi-channel analyzer, including a neutron shield. As a preliminary study, polyethylene block (density of ∼0.947 g/cc and area of 40 cm×25 cm) was used for the determination of hydrogen content by using multivariate calibration models, depending on the thickness of the block. Compared with the results obtained from a simple linear calibration model, partial least-squares regression (PLSR) method offered a better performance in a quantitative data analysis. It also revealed that the PLSR method in a neutron spectrometric system can be promising in the real-time, online monitoring of the powder process to determine the content of any type of molecules containing hydrogen nuclei.

Simple Bayesian analysis in clinical trials: A tutorial

In this tutorial paper we give a simple Bayesian analysis of data that arise in clinical trials. We consider the case when there are two treatment groups and the response in each group can be assumed to be binomially distributed. We also assume that prior beliefs about the rate parameter in each group can be adequately expressed by a Beta distribution. Using such a model approximate posterior inferences can then be made about the odds ratio between the two groups. We illustrate this methodology by analyzing a randomized trial to assess the benefits of treating patients with carcinoma of the pelvic region (rectum, bladder, colon, cervix) using high-energy fast neutrons as opposed to conventional megavoltage x-rays (photons). In this trial there was prior information about the relative efficacy of neutron therapy based on the beliefs of 10 clinicians. Some of the deficiencies of this simple approach are highlighted and other approaches to analysis indicated. The paper facilitates practical consideration of a Bayesian approach without the complexities that a fuller analysis necessitates.

Photon versus fast neutron external beam radiotherapy in the treatment of locally advanced prostate cancer: Results of a randomized prospective trial

Purpose : To evaluate the effectiveness of fast neutron radiation therapy in treatment of locally advanced carcinomas of the prostate. Methods and Materials : From April 1986 to October 1990, 178 patients were entered on a prospective, multi-institutional randomized study of the NCI-sponsored Neutron Therapy Collaborative Working Group. This trial compared external beam photon irradiation (7000–7020 cGy) with external beam neutron irradiation (2040 ncGy) for patients with high-grade T 2 or T 3–4, N 0−1, M 0 adenocarcinomas of the prostate. Eighty-nine patients were randomized to each treatment. Six patients were subsequently judged to be ineligible, leaving 85 photon and 87 neutron randomized patients eligible for analysis. Results : With a follow-up time ranging from 40 to 86 months (68 months median follow-up) the 5-year actuarial clinical local-regional failure rate for patients treated with neutrons was 11%, vs. 32% for photons ( p < 0.01). Incorporating the results of routine posttreatment prostate biopsies, the resulting “histological” local-regional tumor failure rates were 13% for neutrons vs. 32% for photons ( p = 0.01). To date, actuarial survival and causes-pecific survival rates are statistically indistinguishable for the two patient cohorts, with 32% of the neutron-treated patient deaths and 41% of the photon-treated patient deaths caused by prostate cancer ( p = n.s.). Prostate specific antigen (PSA) values were elevated in 17% of neutron-treated patients and 45% of photon-treated patients at 5 years ( p < 0.001). Severe late complications of treatment were higher for the neutron-treated patients (11% vs. 3%), and were inversely correlated with the degree of neutron beam shaping available at the participating institutions. Neutron treatment delivery utilizing a fully rotational gantry and multileaf collimator did not result in an increase in severe late effects when compared to photon treatment. Conclusion : High energy fast neutron radiotherapy is safe and effective when adequate beam delivery systems and collimation are available, and it is significantly superior to external beam photon radiotherapy in the local-regional treatment of large prostate tumors.

High energy neutron treatment for pelvic cancers: study stopped because of increased mortality.

To compare high energy fast neutron treatment with conventional megavoltage x ray treatment in the management of locally advanced pelvic carcinomas (of the cervix, bladder, prostate, and rectum). Randomised study from February 1986; randomisation to neutron treatment or photon treatment was unstratified and in the ratio of 3 to 1 until January 1988, when randomisation was in the ratio 1 to 1 and stratified by site of tumour. Mersey regional radiotherapy centre at Clatterbridge Hospital, Wirral. 151 patients with locally advanced, non-metastatic pelvic cancer (27 cervical, 69 of the bladder, seven prostatic, and 48 of the rectum). Randomisation to neutron treatment was stopped in February 1990. Patient survival and causes of death in relation to the development of metastatic disease and treatment related morbidity. In the first phase of the trial 42 patients were randomised to neutron treatment and 14 to photon treatment, and in the second phase 48 to neutron treatment and 47 to photon treatment. The relative risk of mortality for photons compared with neutrons was 0.66 (95% confidence interval 0.40 to 1.10) after adjustment for site of tumour and other important prognostic factors. Short term and long term complications were similar in both groups. The trial was stopped because of the increased mortality in patients with cancer of the cervix, bladder, or rectum treated with neutrons.

Neutron therapy for nonresectable radioresistant tumors.

Locally advanced, nonresectable, radioresistant tumors can often be ablated by external irradiation using high-energy fast neutron beams. Long-term local control has been achieved in a wide range of malignant tumors, notably sarcomas of bone and soft tissue and adenocarcinomas in various sites. Complete response and long-term remission, with local control rates between 50% and 70%, have been reported in a number of very large osteogenic sarcomas, soft-tissue sarcomas (particularly neurogenic tumors), melanomas, and adenocarcinomas of the alimentary tract. Malignant salivary gland tumors and carcinoma of the prostate appear to be the most responsive to neutrons, with a high frequency (70% to 90%) of successful remission and significantly improved survival even in advanced stages of disease. The biological mechanisms underlying radioresistance of tumor cells and the rationale for using heavily ionizing particles are described. Neutrons are shown to be a valuable adjunct in managing nonresectable malignant tumors that resist conventional therapy.

The Use of Neutron Beam Therapy In the Management of Locally Advanced Nonresectable Radioresistant Tumors

Locally advanced nonresectable radioresistant tumors can often be ablated by external irradiation using high-energy fast neutrons. Long-term remission, with local control rates of 50 to 70 percent, have been reported in a number of very large osteogenic sarcomas, soft tissue sarcomas, melanomas, and adenocarcinomas of the alimentary tract. Malignant salivary gland tumors and prostate carcinomas respond well to neutron therapy, with high remission rates and significantly increased survival, even in locally advanced stages of the disease. Neutron beam therapy is a valuable adjunct in the management of nonresectable cancers that are resistant to conventional therapy.

The results of high energy fast neutron dose optimization studies in the head and neck, thorax, and pelvis

The results of high energy fast neutron dose optimization studies in the head and neck, thorax, and pelvis

High energy fast neutrons from the Harwell variable energy cyclotron. II. Biologic studies in mammalian systems

A high energy fast neutron beam potentially suitable for radiotherapy has been described in a companion paper. Its biologic effects have been studied in the following experimental systems: clonal survival and mutation induction after irradiation in vitro in Chinese hamster cells and human diploid fibroblasts; survival of reproductive capacity in vivo of murine hemopoietic colony-forming cells and murine intestinal crypts after irradiation in vivo; survival of reproductive capacity in vivo after irradiation in vitro or in vivo of murine lymphocytic leukemia cells; acute intestinal death following total body irradiation of mice and guinea pigs; and hemopoietic death following total body irradiation of mice and guinea pigs. The relative biologic effectiveness of these high energy neutrons varied among the different biologic systems, and in several cases varied with the size of the radiation dose. The oxygen enhancement ratio was studied in murine lymphocytic leukemia cells irradiated under aerobic or hypoxic conditions in vitro and assayed for survival of reproductive capacity in vivo. Compared with x-rays, the potential therapeutic gain factor for these neutrons was about 1.5. This work represents a ''radiobiologic calibration'' program which it is suggested should be undertaken before new and unknown fast neutron spectra are used for experimentalmore » radiotherapy. The results are compared with biologic studies carried out at high energy fast neutron generators in the United States.« less

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.

Biological effects of high LET radiation (January 21, 1977)

Biological effects of high LET radiation (January 21, 1977)Published Online:28 Jan 2014https://doi.org/10.1259/0007-1285-50-595-535SectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail AboutAbstractA high energy fast neutron beam potentially suitable for radiotherapy has been built at the Harwell variable energy cyclotron. Using 42 MeV deuterons on a “thin” (2 mm) beryllium target at 20/μA beam current the surface dose rate 150 cm from the target was about 60 rad/minute, and 130 rad/minute with a “thick” (4 mm) target. For the former the dose-rate decreased to 50% at depths of 11.3–15.4 cm in the phantom depending on field size. The use of mainly hydrogenous materials for shielding and collimation provided beam edge definition similar to that of 60Co teletherapy units, and off-axis radiation levels of about 1% which compares favourably with 14 MeV D-T generators. Previous article Next article FiguresReferencesRelatedDetails Volume 50, Issue 595July 1977Pages: 459-538 © The British Institute of Radiology History Published onlineJanuary 28,2014 Metrics Download PDF

Local Energy Density in Irradiated Tissues: I. Radiobiological Significance

When tissues of limited extent are irradiated with penetrating ionizing radiation, the absorbed dose, i.e., the energy absorbed in a volume divided by the mass of that volume, is sensibly constant throughout the medium, provided the ratio is taken over a sufficiently large volume. Thus if a mouse has received 100 rads of hard X-rays or high-energy fast neutrons, each gram of the animal absorbs very nearly 10,000 ergs. The energy density in masses that are not very much smaller is also 104 ergs/gm. However, when one considers masses of tissue that are of a size comparable to the one of cell nuclei or subnuclear structures, the energy absorbed per unit mass may differ from this value because of the random nature of energy deposition. Whereas masses of the order of 1 gm are traversed by a vast number of charged particles, subcellular structures are traversed by but a few, and, when the volume under consideration becomes very small, these variations become exceedingly large. In fact, ultimately the ratio of E/m may frequently be zero, since it may be found that no charged particle traverses a volume having dimensions of the order of a fraction of a micron. Thus material that has been subjected to uniform irradiation and has received a well-defined absorbed dose exhibits strong variations of energy density on a microscopic scale. A knowledge of these local variations is essential for an understanding of the biological action of radiation, since it must be assumed that the energy instrumental in the inactivation of the cell originates in a volume that is certainly no larger and probably a good deal smaller than the cell. The fact that the same absorbed dose delivered by radiations of different LET can give rise to different degrees of biological effect is perhaps the most convincing evidence that the efficacy of an absorbed dose must depend on the manner in which the energy is delivered on a microscopic scale.