kVp X-rays Research Articles

Continuous irradiation of P388F lymphoma in vitro sensitization by 5-iodo-2'-deoxyuridine.

SummaryP388F lymphoma cells in vitro were exposed to non-cytotoxic concentrations of IUdR (5-iodo-2′-deoxyuridine), either as a 30 min pulse, or continuously for 20 days. Both treatments caused an increase in sensitivity (increase in doubling time) to continuous irradiation.Sensitization, reduction in extrapolation number, to acute doses of 300 kvp x-rays was demonstrated after 16 days growth in low IUdR concentrations (up to 0·28 µM).Populations given 30 min treatments (5·6 µM IUdR) and subsequently grown in normal medium were also more sensitive to acute doses of x-rays. There was again a decrease in extrapolation number with no change in the D0 value. This increased sensitivity was still demonstrable in two of the treated populations after 20 days' growth and in a third after 30 days' growth in normal medium.Sensitization, after 30 min treatments, was not due to a change in the relative proportions of the stages of the cell-cycle as shown by the rate of increase of labelled cells and labelled mitoses.

Intranuclear 3H thymidine: dosimetric, radiobiological and radiation protection aspects.

It appears from a study of available data that the degree of early somatic biological effect from intranuclear 3H is that anticipated on the basis of calculated average absorbed dose to the cell nucleus, at least down to doses of 5 rad or less. This result indicates: (a) the absorbed dose concept holds down to the order of 10−11 g or less, and somatic effects can be predicted on this basis; (b) the distribution of 3H atoms incorporated into DNA as 3HTdR (and ion pairs from the beta particles) are randomly distributed as far as dose calculations for the purpose of predicting somatic effects are concerned; (c) every part of the cell nucleus lies within one 3H beta range of some part of a chromatid, and the nucleus contains no sizeable contiguous “insensitive” volume of a radius exceeding the effective range of 3H beta rays (1–2 μ); (d) the origin of 3H beta tracks in, or their close juxtaposition to the DNA molecule does not appear to enhance the degree of somatic effect. “Transmutation” effects of the disintegrating 3H nuclide in DNA appear to have been demonstrated to produce genetic mutations in microorganisms, and data suggestive of this mechanism in Drosophila are available. The degree to which this factor in addition to absorbed dose must be taken into account in estimating possible genetic effects in the mammal cannot be assessed adequately at this time, but appears to be small. From available data, it appears that the degree of genetic effect in mammalian cells can be approximated closely from the average absorbed dose to the nucleus. The “intrinsic” RBE of 3H beta particles appears to be 1.0 (compared to 250 kVp X-rays), rather than the value of 1.7 currently used for radiation protection.

Proliferation characteristics of cultured mammalian cells after irradiation with sparsely and densely ionizing radiations.

SummaryClone size distributions of mammalian cells cultured by Puck's technique have been determined after irradiation with various single doses of 250 kvp x-rays and 3.2 mev α-radiation. The distributions broadened progressively with increasing doses of either of the two types of radiations. No qualitative differences were observed between the actions of the two radiations.In addition proliferation kinetics were studied of microclones, which 15 days after irradiation with x- or α-radiation, corresponding to 14 doubling times of clones developed from unirradiated cells, contained less than 50 cells. Some of these microclones decreased with respect to their number of cells and finally disappeared. However, other microclones slowly increased in cell number and had retained the capacity for unlimited proliferation. Nevertheless, these macroclones which had developed from microclones show many unsuccessful mitoses even after a large number of divisions. No differences were observed in the characteristics of t...

Protective effect of 5-hydroxytryptophan against lethal doses of x-radiation in mice.

Many investigators have shown that 5-hydroxytryptamine (5-HT), one of the biogenic amines of pharmacodynamic action, has an excellent radiation protective ability (Gray, Tew and Jensen 1952, Bacq 1954, Langendorff and Koch 1957, Langendorff, Melching and Ladner 1959). Its metabolic precursor, 5-hydroxytryptophan (5-HTP), on the other hand, has been reported to have only a weak or insignificant protective effect and so far has not received attention as a radioprotective agent (Langendorff and Melching 1959, Thomson 1962, Van den Brenk and Haas 1961). In the course of study on the role of biogenic 5-HT in the development of radiation injury, however, we found that 5-HTP could be as good as, or even better than, 5-HT in protecting mice against lethal dose of ionizing radiation. In this paper we examine the optimum time of 5-HTP administration prior to irradiation and the relationship of 5-HTP dose and protective effect at this optimum time. Animals used were male mice of ddN strain, 8 weeks of age at irradiation time, weighing 23 to 30 g. They were housed individually, given laboratory chow and tap water ad libitum. The radiation factors were: 200 kvp x-ray; 20 mA ; 05 mm Cu plus 05 mm Al filters; h.v.l., 115 mm Cu; dose-rate, 96 R/min as measured in air with Victoreen dosimeter (Type 575). Ten mice were irradiated simultaneously at a single whole-body exposure in individually separated lucite chambers. 5-HTP was obtained from Sigma Chemical Co. (Lot No. H102B-205) or Nutritional Biochemicals Co. (Control No. 5754), U.S.A., was dissolved by twice glass distilled water into solution of 10 mg per ml. concentration immediately before use. No contamination by 5-HT was found in the 5-HTP samples from both sources, as is shown by thin-layer chromatography (figure 1).

Radiosensitivity of melle-pasture type perennial ryegrass seeds ( Lolium perenne) at different moisture levels in relation to wavelength and with or without a pre-germination storage period

Melle-pasture type perennial ryegrass seeds ( Lolium perenne: a crossfertilizer) were subjected, after equilibration to 4 different moisture levels, to acute X-rays (90 kVp–4 mA: 2000 rad/min) and semi-chronic Co 60 γ-rays (25 rad/min) with the same total energy dissipation in the tissues. For each moisture level a survival dose curve was constructed. The percentage survival of the seedlings after 4-weeks growth in a Knop's nutrient solution was used as a criterion of radiation damage. A definitely higher potency of the semi-chronic γ-ray treatment of dry seeds (watercontents respectively: 4·60 and 6·65%) could be observed by germinating them immediately after irradiation as well as with a 3-week storage period prior to germination. However with moist seeds (water-contents respectively: 14·24 and 16·93%) the same total amount of damage for both radiation sources could be observed, by germinating them immediately as well as with a 3-week storage period. Thus the differential effect immediate as well as after storage with dry seeds really represents a difference in the potency of the two sources. As with dry seeds the indirect action of both radiations is at work, the cause of this differential action should be sought in a possible quenching effect of excited molecules either because of the higher dose rate of acute X-rays, or simply because of the higher LET-value of 90 kVp X-rays (100 ionpairs/μ) over Co 60 γ-gays (8 ionpairs/μ). The differential LET-value seems to play no role in the direct action with moist seeds.

The effect of 2000 r of x-rays on the acid and alkaline phosphatase of mouse tibiae.

SummaryThe effect of 2000 r of 200 kvp x-rays on the acid and alkaline-phosphatase content of mouse tibiae up to 80 weeks after irradiation is described. The enzymes were demonstrated histochemically using the coupling azo dye method. The alkaline phosphatase content was diminished within 24 hours after irradiation, due mainly to the loss of mesenchymal cells from the metaphysis and the disorganization of the epiphyseal plate. The amount of enzyme present further diminished with time compared with controls, except where nests of apparently normal cartilage cells appeared in the epiphyseal plate. These eventually gave rise to a new epiphyseal plate which was relatively normal in structure and enzyme content. The articular cartilage cells contained apparently normal amounts of alkaline phosphatase throughout the period of observation and the periosteum and endosteum made good recovery.The acid phosphatase content was not so markedly affected by irradiation. After an initial transient increase there was a reduction in the acid phosphatase content compared with the control except in tibiae where a new epiphyseal plate was being formed or in areas of necrotic bone where there were increased amounts of enzyme.

The effect of oxygen on impairment of the proliferative capacity of human cells in culture by ionizing radiations of different LET.

SummaryOxygen-enhancement ratios (OER) have been determined for the inhibition of clone-formation by cultured cells of human origin irradiated with α-particles and deuterons of different energies, fast neutrons and 250 kvp x-rays. The results of experiments with mono-energetic charged particles, whereby narrow distributions of linear energy transfer (LET) are obtained, show that the OER decreases with increasing LET from about 2·6 at a LET∞ of 5·6 kev/μ of unit density tissue to a value of 2·05 at 61 kev/μ, followed by a more rapid decrease to 1·0 at 165 kev/μ. With fast neutrons, produced by bombarding Be with 16 mev deuterons, an OER of 1·6 was obtained and with 250 kvp x-rays the OER was 2·7.The relation between the relative biological effectiveness (RBE), the OER and the LET is discussed.

Biological Effects of Ionizing Radiation on Milk Synthesis. II. Milk Production and Composition

A study was made of the milk produced by X- and gamma-irradiated cow and goat mammary glands. Exposures of 34 to 78 r were made with a 250-kvp 30-ma X-ray machine; higher levels (150-2,500 r) were administered with a specially designed Co60 irradiator. Milk samples were taken at frequent intervals before and after irradiation for determination of chemical composition.Dose levels of less than 1,000 r had no demonstrable effect on milk production or per cent composition of fat, solids-not-fat, total solids, lactose, citrate, total nitrogen, nonprotein nitrogen, total phosphorus, inorganic phosphorus, chloride, ash, sodium, potassium, calcium, or magnesium. Exposure to 1,000 r or more of gamma irradiation, however, always inhibited milk production.

Chemical Protection against 440-Mev Protons in Mice Pretreated with Mercaptoethylamine (MEA) or p-Aminopropiophenone (PAPP)

We report in this paper studies on protection against lethality in mice totalbody-irradiated by 440-Mev protons after preirradiation treatment with mercaptoethylamine (MEA) or with p-aminopropiophenone (PAPP), and a comparison with similar effects in mice irradiated by 250-kvp X-rays. MEA and PAPP are known to protect a variety of biological systems against medium-energy and high-energy photon radiation, but their effectiveness against high-energy charged particle radiation has been little studied. For the specific situation of chemical protection of mammals from whole-body high-energy proton radiation, the only work known to the present authors is that of Yarmonenko and associates (1). These workers reported an increased survival in mice irradiated with 660-Mev protons by pretreatment with various mercapto and other coimpounds. Since the time-average spatial distribution of secondary particles resulting from the interaction of high-energy protons with matter is not identical with that resulting from high-energy photon interactions (although the space-average linear energy transfer is about the same), it appeared worth while to compare radioprotection between protectors for a given radiation, and between radiations for a given protector. The two protectors were selected chiefly on the basis of familiarity, and secondarily on the hypothesis (2) that they confer protection by two different but complementary phenomenological mechanisms: MEA by increasing the concentration of active sulfhydryl hydrogen in the cells, PAPP by decreasing the concentration of molecular oxygen in the cells.

EFFECTS OF BRAIN LESIONS ON ELECTROENCEPHALOGRAPHIC ACTIVATION 35 KVP AND 100 KVP X-RAYS.

SummaryBrief head exposures to 35 kvp and 100 kvp x-rays were given to three groups of rats. Electroencephalographic recordings were made on sleeping rats before, during and after exposure. Exposure to 100 kvp x-rays produced, electroencephalographic activation in rats without brain lesions or with lesions of the cerebral cortex, but 35 kvp x-rays were much less effective. These results indicate that peripheral sensory stimulation is not essential to the reaction. Lesions of the olfactory bulbs almost abolished the resopnse to x-rays, indicating a critical role for this brain region in radiation-induced neural activation.

Histological Changes in the Larger Blood Vessels of the Hind Limb of the Mouse after X-irradiation

SummaryThe effects of 2000 r of 200 kvp x-rays on the structure of the larger blood vessels of male albino mice are described. Irradiation was delivered to one hind limb of mice either 3 or 12 weeks old. Histological studies show that at 9 weeks after irradiation and thereafter there is an increased incidence of intimal proliferation, fragmentation of the elastic lamina, over-production of elastic tissue, necrosis, hyaline thickening, thrombosis and production of collagen, in the larger vessels. The implied reduction in efficiency was found to correlate with information obtained by arteriograms (Sams 1963). It is suggested that the direct effect of radiation on the components of the vessel wall and the effect of radiation-induced fibrosis of the surrounding tissues on the vessels were both instrumental in bringing about these changes.

X-Ray and Ultraviolet Sensitivity of Synchronized Chinese Hamster Cells at Various Stages of the Cell Cycle

Populations of Chinese hamster cells, synchronized by selecting for cells at or close to division, were exposed to 250 kvp x-rays and to ultraviolet light at different stages of the cell cycle and colony-forming ability examined thereafter. These cells were found to be most resistant to x-rays during the latter part of the DNA synthetic period (S) and to be about equally sensitive before (G(1)) and after (G(2)) this period. Multitarget type curves of the same slope (D(o) approximately 200 rad) only approximately fitted the survival data at different stages in the cycle. The changes in response were primarily due to variations in the shoulders (or extrapolation numbers) of the curves however. The response to ultraviolet light differed from that to x-rays. Resistance was greatest in G(2) and changes in both shoulder and slope of the survival curves occurred throughout the cell cycle. The x-ray and ultraviolet responses for component stages of the cell cycle were respectively compounded into expected survival data for a log phase asynchronous population of hamster cells and found to agree well with direct experiment.

INACTIVATION OF BACTERIOPHAGE T6 IN AN AQUEOUS SYSTEM BY HIGH ENERGY PROTONS.

SummaryT6 bacteriophages were irradiated in water by a 218 mev proton beam, LET of which covers a range from 4·3 to 30 mev/g cm−2 as the beam traverses a stack of samples and absorbers. The total phage inactivation including both immediate and delayed effects was dose-dependent and independent of LET. A separate measurement of the delayed inactivation showed that 240 mev protons have the same after-effect coefficient as that of 250 kvp x-rays. For the direct phage inactivation in a broth suspension, 240 mev protons also showed the same efficiency as 250 kvp x-rays.

THE FREQUENCY OF DICENTRICS IN HUMAN LEUKOCYTES IRRADIATED IN VIVO AND IN VITRO.

The authors present a comparison of the frequency of dicentrics in human leukocytes irradiated in whole blood in vitro and in vivo. The results indicate that the frequency induced in vivo can be a factor of two higher or lower than the frequency in vitro for the same radiation dose. Whole blood was heparinized and irradiated in plastic bottles at 37° C. immediately after drawing. The oxygen tension in the blood during irradiation was essentially that of normal venous blood. Irradiations were carried out with the x-ray beam from a 6 Mev Linac (effective photon energy about 1.9 Mev) at dose rates of 200 rad/min. and 10 rad/min. The leukocytes were separated from the whole blood and incubated for seventy-two or ninety hours; chromosome preparations were then made in standard fashion. Every metaphase figure was scanned for chromosome aberrations, but tetraploid cells were excluded from the scoring. Data are presented herein for the class of aberrations known as dicentrics only, because these can be readily detected and can be scored unambiguously. Figure 1 illustrates, as an example, a dicentric in a leukocyte from a radiation worker. At the bottom of the figure is the cell as it appears under the microscope. At the top, the chromosomes are arranged in pairs, revealing that the dicentric was formed from the fusion of chromosomes numbered one and eleven. Figure 2 shows the results obtained in vitro. Data procured at the two dose rates and the two incubation times were not significantly different and therefore are not separately indicated on the graph. Also included are two points obtained with 100-kvp x-ray and one point obtained with 250-kvp x-ray. None of the three points is significantly different from the results obtained with the Linac, but effects of x-ray energy of as much as 20 per cent are not excluded. The figure clearly reveals that from a dose of 25 rads to one of 1,200 rads the yield of dicentrics is directly proportional to the square of the dose. The proportionality constant is 2.7 ± 0.14 × 10−6 dicentrics per cell per rad-squared. This figure is almost exactly half that reported by Bender and Gooch (1); we assume that one roentgen in their work corresponds to 0.93 rads. The reasons for the difference in results are not known, but do not appear to be a matter of x-ray energy, dose rate, or oxygen tension. They may be due to an accumulation of small errors; a discrepancy in absorbed dose of 10 per cent, for example, leads to a discrepancy of 20 per cent in dicentric frequency. Or they may be due to differences in the incubation conditions during the short-term culture of the leukocytes. At the highest dose, 1,200 rads, the yield is 4.2 dicentrics per cell. The failure of the yield to depart from a dose-squared dependence at this dose shows that the number of sites per cell at which chromosome exchanges can occur (2) must be large, probably in excess of ten sites per cell.

The Relative Biological Efficiency of 20-Mev Electrons and 250-Kvp X-Rays in Saccharomyces cerevisiae Inactivation

The experiments reported here are concerned with the determination and existence of an RBE for haploid and diploid Saccharomyces cerevisiae when irradiated with 20-Mev electrons or 250-kvp X-rays. The RBE values obtained are based on survival curves for macrocolonies and are expressed as the ratio of the mean lethal dose (37 % survival) for X-rays to that for the electrons. Part of the purpose of these experiments was to clarify, if possible, the nature of the differences in results reported by various investigators (1-3). Evidence was obtained that the RBE obtained is not a constant feature but varies from one cell population to another.

LD 50(24 hours) Observations in the Chick Embryo after Exposure to X-Rays

The chick embryo is recognized as an excellent tool for the study of radiation effects on embryonic tissues. The separation of the chick embryo from many maternal contributions permits evaluation of responses attributed solely to the effects of ionizing radiation on the embryo. The strict environmental controls that can be maintained during chick embryogenesis reduce to the minimum the variables that may alter the radiation response. As indicated previously by Boland (1) and by Goff (2), comparative evaluation of reported lethality studies on the chick embryo is difficult. Parameters have been varied by the investigators and include 112-kvp (3), 150to 180-kvp (4-8), 250-kvp (1, 2, 9, 10), and 1000-kvp X-rays (10), as well as Co60 (1, 11, 12) and radium y-rays (13) and fission neutrons (12). The dose rates in these studies varied from 5.3 r/min (13) through 220 r/min (7). Physical factors such as half-value layer were frequently varied, and the methods of dosage determinations were frequently unexplained, or the doses were not obtained at the embryo site. The postexposure study period varied from shortly after exposure (3) to LD5o0 (22 days), the lethality at the time of hatching (6). Some workers used nearly all ages (1 to 16 days) of embryos (2, 4, 6), whereas others used 20-hour (2), 33-hour and 60-hour (7), 50-hour (3), 4-day (8, 10, 12), or several ages (13, 14). As a result of the considerable variation in lethality studies reported by others, the estimation of LD50(24 hours) was undertaken to establish a reference point for a study of pathologic effects of ionizing radiation on embryonic tissues.

The Relative Biological Effectiveness of High-Energy Photons and Electrons

In the past decade or more, few radiobiological quantities have received as much attention as the biological effectiveness (or RBE) of high-energy photons and electrons relative to conventional 200 to 300 kvp x-rays. Many of these studies have had a clinical rather than a radiobiological objective, namely the specification of the RBE for clinical therapy. No doubt it has often been felt that the effectiveness of a radiation measured, say, in the growth of broad bean roots or even in the survival of mice might have little bearing on its effectiveness as a therapeutic agent. In radiotherapy, the location and type of the lesion to be treated, the volume irradiated, the integral dose, the distribution of dose, the sparing of particular normal tissues, the dose fractionation technic, and many other factors in addition to RBE, must be involved in the choice of one type of radiation in preference to another. Nevertheless, the RBE is an important factor in guiding the thinking of the radiotherapist and in determining the dose protocol. It could be much more important if studies were to show a different RBE in tumor cells compared to normal cells. No such effect has been clearly established, and it must be emphasized that RBE per se does not imply any change in differential effect between the response of tumor and normal tissue. In radiobiology, these high-energy radiations are of limited interest in evaluating radiation mechanisms based on the variation of effectiveness with quality, because of the small range of RBE and LET (linear energy transfer) they encompass. Nevertheless, a number of features are of interest in RBE studies in this energy region, where dosimetry is now comparatively precise, which will be pointed out below. It will be our objective to review briefly some of the physical and biological considerations that enter into an RBE measurement in the high-energy region, to discuss many of the recently reported RBE studies, and to indicate some of the more interesting features. Concept of RBE The concept of RBE and the design of RBE determinations have been discussed elsewhere in detail (1, 2), and in the report of the RBE Subcommittee to the International Commissions on Radiological Protection and on Radiation Units (3). According to the ICRP definition, the RBE of a “test” radiation compared to a “standard” radiation is equal to Ds∕Dt, where Ds and Dt are the absorbed doses of the standard and test radiations, respectively, that produce the same effect in a particular biological system.

A HIGH RELATIVE BIOLOGICAL EFFICIENCY OF 650-KEV NEUTRONS AND 250-KVP X-RAYS IN SOMATIC MUTATION INDUCTION.

THE mean linear energy transfers of 650-keV neutrons and of 250-kVp X-rays are so markedly different that it is not usually possible to establish a unique value for their relative biological efficiency. For example, it is well known that the densely ionizing neutrons induce linear dose-response relationships for chromosome aberrations, whereas the dose-response curves for X-rays are often non-linear. Moreover, the former radiation but not the latter is almost independent of environmental factors such as oxygen tension during irradiation. Under certain conditions, and with certain biological test systems, however, some of these difficulties are minimized. For example, Neary et al.1 compared the relative biological efficiency, in terms of chromosome aberration induction, of 0.7- and 3.0-MeV neutrons with cobalt-60 γ-rays administered at low dose rates. There the dose-response relationships were almost linear, and relative biological efficiency values of 35 were obtained; they also derived ultimate maximum relative biological efficiency values from a comparison of the one-hit components of the neutron and γ-dose-response curves and found that these could be as high as 100. Similarly, Smith et al.2, using a test system (somatic mutation induction in dry seed) in which the dose-response relationship for X-rays was linear, obtained an average relative biological efficiency value of about 75 for mono-energetic neutrons of 0.43–1.80 MeV.

The angular distribution of radiation scattered from a phantom exposed to 100-300 kVp x-rays.

Measurements of the angular distribution of radiation scattered from a phantom exposed to 100–300 kVp X-ray beams are presented and discussed.

The Relative Potency of Fast Neutrons and 250-Kvp X-Rays in the Guinea Pig

The 30-day lethality response in Hartley strain guinea pigs was determined for fast neutrons and 250 kvp x rays. The LD 50/30 for animals exposed to neutrons was 155 rads, while for animals exposed to x rays it was 273 rads. Most deaths occurred 9-16 days after irradiation, and no deaths occurred before day 7 post-irradiation with either neutrons or x rays. Morphological examination indicated no marked gastrointestinal damage in the guinea pig following either neutron or x-ray exposure in the lethal range. The niost frequent finding at autopsy was hemorrhage. Only minimal gastrointestinal damage was seen following supi alethal exposures of neutrons or x rays. Body weight, food consumption, and water consumption were also determined for 30 days following irradiation. The relative potency of neutrons with respect to x rays was greater than unity for depressions in the three measurements. Food and water consumption values of survivors returned to control values by 30-days post- irradiation. Body weight, however, remained less than controls for at least 30 days in a dose dependent fashion. The gastrointestinal syndrome was essentially absent in the guinea pig followlng irradiation. lt is suggested that the greater potency of neutrons for lethality in the guinea pigmore » may be explicable on the basis of radiation damage to the hematopoietic system. (auth)« less