The r.b.e. of different-energy neutrons as determined by human bone-marrow cell-culture techniques.

The effect of X-rays and different-energy neutrons on human bone-marrow cells was studied using two different cell-culture techniques--diffusion chamber (DC) growth and colony formation in vitro (CFU-C). Based on the survival of proliferative granulocytes in DC on day 13, the D0 value was 80 rad with X-rays, and 117 rad as measured by the CFU-C assay. The D0 values for neutrons depended on the radiation source and the energy level. The r.b.e. values, which dropped with increasing energy levels of mono-energetic neutrons, were (i) 0.44 MeV; DC 3.7, CFU-C 4.1; (ii) 6 MeV; DC 1.8, CFU-C 2.0; (iii) 15 MeV; DC 1.6, CFU-C 1.6; (iv) fission neutrons; DC 2.6, CFU-C 2.4.     

The effects of ionizing radiations on the chromosomes ofTradescantia bracteata. A comparison between neutrons and X-rays

Journal of Genetics - 1. Neutrons produce qualitatively the same types of chromosome aberrations as X-rays, but more of all types of aberration are produced, per ionization, by neutrons. 2. The...     

Somatic aberration induction in Tradescantia occidentalis by neutrons, x- and gamma-radiations. II. Biological results, r.b.e. and o.e.r.

Biological results, including statistical features, are described for the irradiation of Tradescantia occidentalis with 250 kVp X-rays, cobalt-60 gamma-radiation and monoenergetic neutrons with energies between 0-08 and 15 MeV. The effect studied was that of the induction of pink sectors in the otherwise blue staminal hairs of the flowers at low doses of radiation. Statistical aspects of the results suggest that a fraction of the asynchronous cell population in the hairs is very sensitive to neutron radiation, but not necessarily to lower LET radiations. All the results were fitted by a least-squares method by polynomials of different degrees. Best fits to X- and gamma-ray data were provided by second-degree polynomials, and to the neutron data by either second- or third-degree polynomials. Limiting r.b.e. and o.e.r. values at low doses are derived. Some computed microdosimetric parameters are presented in comparison with the r.b.e. values. It is concluded that the effect studied is complex and may not provide a critical test of bio-physical theories of radiation effects.     

Quantitative characteristics of radiation injury of the spermatogenic epithelium and the rate of its recovery after exposure to fast neutrons and gamma-radiation

The paper submits the results of studies on the kinetics of spermatogenous epithelium cell number after exposure to fast neutrons (60-300 cGy) and gamma-radiation (200-600 cGy). It was shown that a relative decrease in the quantity of spermatocytes is determined by an exponential dose-response curve with D0 of 35 and 120 cGy for neutrons and gamma-radiation respectively. For spermatides and spermatozoa a single D0 value of 20 and 55 cGy was obtained for neutrons and gamma-radiation respectively. As the radiation dose increases the recovery process in the epithelium is substantially decelerated. The equation T1/2 = T1/2(0)e0.0009D well describes the dependence of the half-recovery period T1/2 upon the equivalent dose.     

Measurements of neutron energy using a recoil-proton telescope and a high-pressure ionization chamber

Two very different techniques for measuring the energy of neutrons in the energy range 0.1-10 MeV are presented and compared. A recoil-proton spectrometer is used to determine the energy spectra of neutrons produced by the d(4)-Be and p(4)-Be reactions down to the low-energy threshold of 0.7 MeV. The same radiation fields are also measured with a recently developed method using a high-pressure ionization chamber that can be used to determine the mean energy of the neutrons in a mixed neutron-gamma radiation field provided the gamma-ray absorbed dose fraction is determined independently. An intercomparison of the two methods shows that the high-pressure ionization chamber compares well and supplements the established recoil-proton spectrometer technique. The almost isotropic response of the chamber has enabled measurements to be made of the variation of mean neutron energy with depth in water for the two radiation fields.     

Neutrons and X-rays,comparative studies with Drosophila melanogaster: 1. the viability and fertility of induced autosomal translocations

Studies on the genetic effects of neutrons and X-rays have produced evidence that may be interpreted as indicating that neutrons induce clusters of closely linked genetic changes. According to this interpretation, it is to be expected that neutron-induced translocations will have a higher rate of associated recessive lethality, compared with translocations induced by low-LET radiation such as X-rays. The experiment reported here was designed to test whether this expectation is fulfilled. The dose-frequency response with neutrons for the induction of autosomal translocation was established by exposing males from the Oregon-K stock and then sampling treated mature sperm. From the data obtained, it was estimated that 10 Gy neutrons should induce about the same frequency of autosomal translocations as 27 Gy X-rays. These 2 doses were used to induce translocations in the spermatozoa of males carrying lethal-free autosomes, derived from the Oregon-K stock. Induced translocations were tested for homozygous viability and fertility. When these criteria were used, no qualitative difference was detected between the translocations induced by neutrons and X-rays.     

Inactivation and mutation of cultured mammalian cells by aluminium characteristic ultrasoft X-rays. II. Dose-responses of Chinese hamster and human diploid cells to aluminium X-rays and radiations of different LET.

The induction of inactivation and mutation to thioguanine-resistance of two types of cultured mammalian cells, V79 Chinese hamster and HF19 human diploid, was studied after irradiation with aluminium K characteristic ultrasoft X-rays, helium ion track intersections of different LET, 42 MeV d-Be neutrons, and hard X- or gamma-rays. The form of the dose-response curves was different for the two cell-types, and there was an overall difference in radiosensitivity, the human cells being the more sensitive to all radiations. However, for both inactivation and mutation-induction, the relative responses of both cell-types to these radiations was similar. Aluminium X-rays were considerably more effective than hard X- or gamma-rays and were at least as effective as helium ions of 20-28 keV micron-1, although aluminium X-rays produce tracks of very limited range (less than about 0.07 micron). Single track effects by aluminium X-rays cannot, therefore, extend beyond about 0.07 micron, and the subcellular sites involved in inactivation and mutation cannot be greater than this dimension or else the effectiveness of aluminium X-rays would be similar to that of low-LET radiations. This observation is in contradiction to models of radiation action which require relatively large sensitive sites; for example the 'theory of dual radiation action' requires a site diameter of about 0.4 micron to explain the shape of the dose-response curves for V79 hamster cells.     

Arterial wall damage by X-rays and fast neutrons.

Radiation-induced atheromatosis has been studied for 200 kVp X-rays and 15 MeV neutrons. From the results of two earlier experiments, a r.b.e. less than 1 was expected for neutrons. (1) Irradiation of blood-vessels causes depolymerization of the mucopolysaccharides in the vessel wall, resulting in atheromatosis, and (2) in two other mucopolysaccharide systems a r.b.e. less than 1 is observed for fast neutrons. Irradiation of the carotid arteries of a total number of 120 hypercholesterolaemic rabbits, divided over several groups, with 500 and 1000 rad of X-rays or neutrons results, however, in atheromatous plaques which are more pronounced for neutrons than for X-rays at the 500 rad dose-level; for a dose of 1000 rad the effect of neutrons is less extensive than the effect of X-rays. These results lead to the assumption that the origin of the atheromatosis seems not only to be the mucopolysaccharide depolymerization, but that radiation induced damage at the cellular level must be taken into account.     

Dose-response relationships and R.B.E. values of dominant lethals induced by X-rays and 1.5 MeV neutrons in prophase-1 oocytes and in mature sperm of the two-spotted spider mite Tetranychus urticae Koch (acari, tetranychidae)

Mature sperm and prophase-1 oocytes of Tetranychus urticae Koch were irradiated with 250-kVp X-rays or 1.5 MeV fast neutrons. The X-ray doses ranged from 0.5 to 24.0 krad, and those of the fast neutrons from 0.1 to 16.0 krad. The genetic endpoint measured was lethality, expressed in the stages from egg to adulthood in the F1 progeny. The frequency of recessive lethals in female germ cells was estimated by comparing survival of fertilized versus unfertilized F1 eggs, after irradiation with the same dosage. X-Rays induce dominant lethals in prophase-1 oocytes by the action of both single hits on single targets and multiple hits on multiple targets. 1.5-MeV neutrons induce these effects predominantly by the action of multiple tracks on multiple targets. Dominant lethals were induced in mature sperm by X-rays and by fast neutrons by the action of both single hits on single targets and multiple hits on multiple targets. Both for prophase-1 oocytes and for mature sperm the low R.B.E. value corresponded with the relatively large multiple-target component of induction of dominant lethals by fast neutrons. The nature of dominant lethality in relation to the kinetochore organization of the chromosome is discussed. A non-linear trend in the dose--effect relationship was observed for both X-rays and fast neutrons for the estimated frequency of recessive lethals induced in prophase-1 oocytes. X-Rays were more effective than neutrons in inducing recessive lethals in prophase-1 oocytes at doses lower than 3 krad.     

The response of mouse skin to hyperthermia combined with fast neutrons or X-rays

The effects of hyperthermia combined with fast neutrons (mean energy approximately 7.5 MeV) or X-rays (250 kVp) were studied in the skin of the mouse ear and foot. Hyperthermia was achieved by immersion in water at temperatures of 41.5-43.0 degrees C for 1 hour. The heat treatments used caused no observable tissue injury other than transient erythema but they enhanced the response to both neutrons and X-rays. The enhancement of neutron damage increased as the heating temperature was increased, as is well known for X-rays. When heat was given after irradiation the thermal enhancement ratio (t.e.r.) for neutrons was similar to that for X-rays. When heat was given before irradiation the neutron t.e.r. was less than that for X-rays. Consequently, the relative biological effectiveness of fast neutrons compared with X-rays was not altered by giving heat after irradiation but it was reduced by giving heat before irradiation.     

Free-radical disorders in the tissues of mice exposed to gamma irradiation and neutrons in vitro. The radiochemical yields

The ESR method was used to study free-radical disturbances in tissues of mouse liver and spleen exposed in vitro to gamma-radiation and fission neutrons. It was shown that both types of radiation induced damages to basic chemical components of the cell, namely, DNA, lipids, proteins, and water. The radiochemical yields of each radical registered were obtained and RBE of neutrons were evaluated with a reference to the formation in tissues of radicals of each type. Membrane lipids were shown to be markedly injured by neutrons.     

Aspects in practical neutron dosimetry with ionization chambers

Summary The calibration procedure to determine the absorbed dose within a phantom irradiated with fast neutrons is described for ionization chambers. A comparison between values of the neutron dose determined with paired ionization chambers and values of the neutron fluence measured with a fission chamber (²³⁸U) is given. The comparison indicates the energy variation of the fast neutrons within a phantom irradiated with 14 MeV neutrons.Dedicated to Prof. Dr. Dr. h. c. mult. B. Rajewsky on the occasion of his 80th birthday.     

The relationship between o.e.r., r.b.e. and number of fractions for X-ray- or neutron-induced skin damage.

The skin reactions in aerated and hypoxic mouse tails after single or fractionated doses of 250 kV X-rays or fast neutrons (6 MeV deuterons on beryllium) have been measured. The o.e.r. for one to sixteen fractions of X-rays remains constant, while that for one to ten fractions of neutrons decreases with increasing neutron fractionation and decreasing neutron dose/fraction. The o.e.r. for X-rays was 1.7, for single-neutron doses 1.4, and for ten fractions of neutrons 1.25. It was anticipated that the o.e.r. for neutron-induced damage would decrease further as neutron fractionation is increased because the contribution to damage from the highest LET components of dose, the alpha and heavy recoil particles, would increase relative to the lowe LET components. The r.b.e. values obtained for skin damage were higher at all neutron doses/fraction examined in this study on tails than all those previously obtained in studies on skin at other sites on four species. This may be due to the influence of hypoxia on the r.b.e. measurements in the mouse tail.     

Determination of the thermal and epithermal neutron sensitivities of an LBO chamber

An LBO (Li₂B₄O₇) walled ionization chamber was designed to monitor the epithermal neutron fluence in boron neutron capture therapy clinical irradiation. The thermal and epithermal neutron sensitivities of the device were evaluated using accelerator neutrons from the ⁹Be(d, n) reaction at a deuteron energy of 4 MeV (4 MeV d-Be neutrons). The response of the chamber in terms of the electric charge induced in the LBO chamber was compared with the thermal and epithermal neutron fluences measured using the gold-foil activation method. The thermal and epithermal neutron sensitivities obtained were expressed in units of pC cm², i.e., from the chamber response divided by neutron fluence (cm^?2). The measured LBO chamber sensitivities were 2.23 × 10^?7 ± 0.34 × 10^?7 (pC cm²) for thermal neutrons and 2.00 × 10^?5 ± 0.12 × 10^?5 (pC cm²) for epithermal neutrons. This shows that the LBO chamber is sufficiently sensitive to epithermal neutrons to be useful for epithermal neutron monitoring in BNCT irradiation.     

Radioresistance of mongolian gerbils. Fast neutrons.

Seventy-six 8 week old Mongolian gerbils were exposed to acute, whole-body fast neutrons produced by The University of Michigan 83-in. cyclotron. Groups of seven or eigth gerbils were given doses between 485 and 881 rad at 25 rad per minute. The LD 50/30 determined by probit analysis was 750 rad, with 95 per cent fiducial limits of 733 and 776. For the 50 per cent mortality level, an r.b.e. of fast neutrons compared with cobalt-60 of 1-45 was determined. For the same end-point, the r.b.e. for fast neutrons compared with X-rays is 1-33. Mortality data, body-weight and microhaematocrit changes are discussed.     

On the eptihermal neutron energy limit for Accelerator-Based Boron Neutron Capture Therapy (AB-BNCT): Study and impact of new energy limits

Background and purpose: Accelerator-Based Boron Neutron Capture Therapy is a radiotherapy based on compact accelerator neutron sources requiring an epithermal neutron field for tumour irradiations. Neutrons of 10 keV are considered as the maximum optimised energy to treat deep-seated tumours. We investigated, by means of Monte Carlo simulations, the epithermal range from 10 eV to 10 keV in order to optimise the maximum epithermal neutron energy as a function of the tumour depth.Methods: A Snyder head phantom was simulated and mono-energetic neutrons with 4 different incident energies were used: 10 eV, 100 eV, 1 keV and 10 keV. ¹⁰B capture rates and absorbed dose composition on every tissue were calculated to describe and compare the effects of lowering the maximum epithermal energy. The Therapeutic Gain (TG) was estimated considering the whole brain volume.Results: For tumours seated at 4 cm depth, 10 eV, 100 eV and 1 keV neutrons provided respectively 54%, 36% and 18% increase on the TG compared to 10 keV neutrons. Neutrons with energies between 10 eV and 1 keV provided higher TG than 10 keV neutrons for tumours seated up to 6.4 cm depth inside the head. The size of the tumour does not change these results.Conclusions: Using lower epithermal energy neutrons for AB-BNCT tumour irradiation could improve treatment efficacy, delivering more therapeutic dose while reducing the dose in healthy tissues. This could lead to new Beam Shape Assembly designs in order to optimise the BNCT irradiation.     

Reasons for the quantitative differences in the formation of chromatin breakdown products following exposure to neutrons and gamma radiation

Relative content of salt-soluble chromatin fragments in rat thymus increased after the effect of neutrons, as compared to gamma-radiation, while cell depletion of the organ was similar with both types of radiation. This was not associated with the rate and extent of chromatin degradation in thymocytes and was an indication of death of a larger number of thymocytes after the effect of neutrons.     

A source with a 1013 DT neutron yield on the basis of a spherical plasma focus chamber

Results from preliminary experimental research of neutron emission generated by a spherical plasma focus chamber filled with an equal-component deuterium-tritium mixture are presented. At a maximum current amplitude in the discharge chamber of ～1.5 MA, neutron pulses with a full width at half-maximum of 75–80 ns and an integral yield of ～1.3 × 10¹³ DT neutrons have been recorded.     

Mortality of monkeys after exposure to fission neutrons and the effect of autologous bone marrow transplantation.

In order to assess the risk of exposure to ionizing radiation in man, and to evaluate the results of therapeutic measures, the mortality of rhesus monkeys irradiated with X-rays and fission neutrons and the effect of autologous bone marrow transplantation have been investigated. The LD50/30d values for X- and neutron-irradiated monkeys amount to 525 and 260 rad respectively, resulting in an r.b.e. of approximately 2 for the occurrence of the bone marrow syndrome. Protection of the animals by autologous bone marrow transplantation was observed up to doses of 860 rad of X-rays and 440 rad of fission neutrons. After both fission-neutron irradiation and X-irradiation in the lowest range of lethal doses, the bone marrow syndrome was found to occur without the concurrent incidence of the intestinal syndrome. The studies indicate that, for humans accidentally exposed to what would otherwise be lethal doses of fast neutrons, bone marrow transplantation may be beneficial.     

'Repair' of fast-neutron and x-ray-induced damage to the permeabilities of red blood cells to sodium and potassium ions and its promotion by ghosts.

Damage to the permeability of red blood cells to Na+ and K+ caused by irradiation with fast neutrons or X-rays was investigated at different post-irradiation incubation temperatures. The extent of Na+ uptake and K+ loss by the cells after either radiation was higher at 4 degrees C than at 37 degrees C, but the extent of 'repair' of the damage caused by fast neutrons was lower than that caused by X-rays. The latter 'repair' was promoted by the addition of ghosts, but the former was not. On the other hand neither 'repair' process was influenced by haemolysates from which ghosts had been removed.