Effect Of Dose Fractionation Research Articles

Serial analysis of chromosomal aberrations and proliferation kinetics of mouse spermatogonia after single or fractionated X-ray exposures

Abstract Dose-fractionation studies on translocation induction in stem-cell spermatogonia of mice, as measured by spermatocyte analysis many cell generations after irradiation, revealed that a small conditioning dose of X-rays sensitizes the stem cells to the induction of translocations by a second dose 24 h later (Van Buul and Leonard, 1974, 1980). To find out whether such sensitization effects also occur at other spermatogonial stages, a comparison was made of the effects of single (50, 100 and 150 rad) and fractionated (100 + 50 rad, with 24 h in between) doses of X-rays on the induction of chromosomal aberrations in spermatogonia by analysing spermatogonial metaphases shortly after irradiation at multiple sampling times (0–48 h; every 4 h). In addition, the kinetics of spermatogonial proliferation was studied by using, in vivo, a BrdU chromosome-labelling procedure. The recorded frequencies of chromosomal aberrations did not indicate any sensitization effect of dose fractionation. It is concluded that the sensitization effects, as observed for chromosomal aberrations in male premeiotic germ cells, are characteristic for the stem-cell spermatogonia and do not occur in the more differentiated spermatogonia.

Dominant cataract mutations and specific-locus mutations in mice induced by radiation or ethylnitrosourea

In a combined experiment, dominant cataract mutations and specific-locus mutations were scored in the same offspring. In radiation experiments, a total of 15 dominant cataract and 38 specific-locus mutations was scored in 29396 offspring. In experiments with ethylnitrosourea (ENU), a total of 12 dominant cataracts and 54 specific-locus mutations was observed in 12712 offspring. The control frequency for dominant cataracts was 0 in 9954 offspring and for specific-locus mutations 11 in 169955 offspring. The ratio of radiation-induced recessive visible to dominant mutations was about 2.5:1. The difference was even more pronounced for ENU-induced mutations. The ratio of recessive visibles to dominant cataracts for chemically induced mutations in spermatogonia was about 5.4:1. The two characteristic features of radiation-induced specific-locus mutations--the augmenting effect of dose fractionation and the quantitative differences in the mutation rates between spermatogonial and post-spermatogonial stages--can also be demonstrated for the induction of dominant cataracts. The dominant cataract mutations recovered can be categorized into 7 phenotypic classes: total opacity, nuclear and zonular cataract, nuclear cataract, anterior pyramidal cataract, anterior polar cataract, anterior capsular cataract, and vacuolated lens. The largest class of mutations, a total of 11, affected the anterior polar region, while the number of total opacities in both experiments was 5. The only noteworthy difference observed between the radiation- and ENU-induced mutations recovered was that, of the 2 radiation-induced total lens opacities, both were associated with an iris anomaly and microphthalmia whereas the ENU-induced total opacities were not.

Dose-rate and fractionation studies with FBX dosimeter

The FBX dosimeter containing 0.20 mM ferrous ammonium sulphate, 5.0 mM benzoic acid and 0.20 mM xylenol orange has proved to be very useful for low dose measurements from ionizing radiations. This paper reports the studies on dose-rate and dose-fractionation effects in this dosimeter. The dose-rate varied from 40 to 1100 rad min −1 . The dose-fractionation studies included continuous irradiation to about 17 h interval between two fractions. The response of the dosimeter has been found to be independent of the dose-rate and dose-fractionation effects. It is important that irradiated solutions and blanks are measured simultaneously to avoid errors due to thermal oxidation in the dosimeter.

Experimental Radiation Carcinogenesis: What Have We Learned?

The data from a number of relatively large-scale animal experiments that were designed to examine the effects of dose rate, fractionation, and radiation quality are now accumulating. Apart from the answers obtained to the questions that the experiments were designed to elucidate there are a number of lessons to be learned about experimental design, the inadequacies of current models, and the areas of our ignorance and misconceptions. There is no single mechanism of radiation carcinogenesis. The induction of the initial events of tumorigenesis may be similar in most tumor types, whereas the factors influencing expression vary. In experimental animals radiation may (1) advance the time of appearance of a specific tumor type, (2) induce tumors by direct action on the target cells, or (3) induce tumors by a complex action on both the target and other tissues. The effect of dose rate will depend on the mechanism involved. It has become clear that dose-response curves for neutron irradiation bend over at low doses which makes the estimate of the initial slope difficult. The precise contribution of various factors influencing the shape of the curves is not clear. Because of the marked variation in the shape of dose-response curves for low-LET radiation, RBE values vary almost infinitely.

Effects of dose fractionation after irradiation with neutrons produced by 600 MeV protons

Biological effects produced by neutrons of various energies up to 15 MeV have been extensively studied through their use in therapeutic applications (Barendsen, 1968; Hall et al., 1973; Hornsey and Field, 1979). Possible further radiotherapeutic gains from neutrons of higher energies have been investigated recently (Harrison et al., 1976; Hall and Durand, 1980). Biological damage by neutrons with maximum energies of 400 and 600 MeV, produced by the CERN synchrocyclotron, have been investigated for several years. Un-expected effects were observed in the low-dose regions (Baarli et al., 1976; Di Paola et al., 1980; Diehl-Marshall and Bianchi, 1981).

Synergism between hyperthermia and cyclophosphamide in vivo: The effect of dose fractionation

The synergistic anti-tumor interaction between heat and cyclophosphamide (CP) was investigated. Synergism between local hyperthermia ( 42.5°C, 30 min ) and CP was observed in mice bearing the Lewis lung carcinoma tumor in their hind leg. Local hyperthermia reduced the CP dose needed for cure or a specific tumor growth delay. CP was less effective when given in fractions. A fractionated dose regimen was more effective than CP alone when combined with heat. The thermal enhancement ratio was larger when CP was administered in more than three fractions. It is concluded that combined heat and CP chemotherapy of cancer may be clinically feasible.

Explanation of Dose-Rate and Split-Dose Effects on Mouse Foot Reactions Using the Same Time Factor

The effect of dose rate on X-ray-induced skin reactions was determined for 1, 2, and 10 fractions using the mouse foot system. Data for 1.6, 0.15, and 0.06 Gy/min were obtained, and the time-course-dependent effects of these experiments were analyzed using an extension of the formulation by L. G. Lajtha and R. Oliver (Br. J. Radiol. 34, 252-257, 1961). r, the time for decay of the effective dose to 1/e of its initial value, was determined to be 114 + 28 min. On the basis of this analysis, predictions were made for split-dose and pulsed irradiations. These were consistent with experimentally measured results obtained using such irradiation protocols. Thus it has been shown that dose fractionation, low-dose-rate, split-dose, and pulsed irradiation effects can be handled conceptually as different particular examples of variable time-course irradiations. In addition, this analysis has been used to generate guidelines for minimum acceptable dose rates consistent with acute exposure and minimum fraction intervals consistent with complete repair, to assist in the design of future multifraction experiments using the mouse foot system.

Isoeffect curve for radiation myelopathy.

In a previous publication on the effect of X-ray dose fractionation on the total dose required to produce radiation myelopathy in rats, we showed that the slope of the Strandqvist-type isoeffect curve between one and 30 fractions to the cervical or lumbar cord was 0.4 (White and Hornsey, 1978). This was in good agreement with the observation of Van der Kogel (1977) on a different strain of rat, who obtained a value of 0.44 between one and 20 fractions. The slopes of these isoeffect curves are all steeper than that for skin damage which is 0.34, decreasing to 0.27 as fractionation is increased (Fowler, 1971). The slope of the curve for radiation myelopathy between four and 30 fractions for fractionation given in the same overall treatment time, which gives the exponent of N in the Ellis formula (total dose αNαTβ, Ellis 1969), was 0.35 (White and Hornsey, 1978). There was no indication of reducing slope with increasing number of fractions at least up to 30 fractions as is seen for both skin damage (Fowler, ...

The sparing effect of dose-fractionation in adult Drosophila.

The sparing effect of dose-fractionation was observed in adult male and female Drosophila melanogaster; 24-, 48-, 72-, and 96-h-old female flies, in general, show a higher recovery (increase in life-span) following dose-fractionation as compared to the males of the respective age. Recovery in 72-h-old females is maximal (31% increase in life-span) as against only 12% increase in the life span of the males.

Photodynamic inactivation of cancer cells in vitro. Effect of irradiation temperature and dose fractionation

Human cancer cells in vitro (NHIK 3025), derived from a carcinoma in situ are inactivated when exposed to visible light in the presence of hematoporphyrin. Irradiation at 4 degrees C results in much more efficient inactivation than irradiation at 37 degrees C. Furthermore, a given total light dose is more efficient when it is fractionated than when it is given in a single exposire. These findings may be taken advantage of in future photochemotherapy of cancer.

Effect of cell growth rate and dose fractionation on chemically-induced ouabain-resistant mutations in Chinese hamster V79 cells

Chinese hamster V79 cells were grown in medium containing either 10% or 2% FCS during the expression time following exposure to MNNG. The lower serum concentration was used to reduce the rate of cell replication, thereby allowing more time for DNA repair prior to "fixation" of the mutagenic lesion. In addition, fractionated and continuous exposures to MNNG and MAM, respectively, were carried out to determine their effect on the number of induced ouabain-resistant mutants. The results indicated that lowering the rate of cell growth effectively reduces the mutation frequency at low, but not at high doses of MNNG. Fractionated doses of MNNG result in a potentiation of their mutagenic effects compared to single doses. Also, continuous exposures to MAM result in an exponential increase in the mutation frequency. Collectively, these results suggest the importance of a repair process in Chinese hamster V79 cells which is dependent upon cell growth rate and the dose of the mutagen for its effectiveness.

Effect of single and fractionated doses of gamma radiation on pupariation of housefly.

Larvae of different ages from 40 hr to 72 hr were exposed to γ-rays ranging between 500R and 10000R ; all ages of the larvae showed dose-dependence pupariation delay up to 4000R. The shape of the puparia were not normal in the larvae irradiated with higher doses. Sparing effect of dose fractionation (SDF) was demonstrated for the pupariation delay. Sparing effect was quite marked at low dose-rate (15R/second) than at high dose-rate (80R/second) and maximum SDF was found with 2 hr interfraction interval as compared to 4.5 and 6.5 hr. The magnitude of SDF was comparatively less at 15°C than at 35°C indicating the occurrence of repair. Furthermore, the metabolic requirement of repair processes was evidenced by the abolition of SDF by inhibitors of energy metabolism, DNA binding agents and protein synthesis inhibitors.

Effect of dose fractionation on the enhancement by radiation or cyclophosphamide of artificial pulmonary metastases.

Thoracic irradiation or cyclophosphamide (CP) treatment of mice before an i.v. injection of tumour cells enhances the number of lung colonies produced by a factor of up to 100+. The effect of fractionation of the X-ray or CP dose on this phenomenon was investigated in several ways.The dose-response curve for the number of lung colonies as a function of the dose of thoracic irradiation was linear, and the degree of enhancement was independent of the number of tumour cells injected. Splitting a dose of 1,000 rad into 2 equal fractions separated by times varying from 1 to 24 h gave the same enhancement as that produced by a single dose of 1000 rad. Similarly, fractionation of 1000 rad into 5 × 200 rad, or 2000 rad into 5 × 400 rad (each interval between fractions being 3 h) had no effect on the radiation enhancement of colony formation.A single dose of 200 mg/kg of CP was compared with 3 doses of 66·7 mg/kg (each dose separated by 12 h) and with a continuous infusion of 200 mg/kg given over 24 h. In this case, fractionation and infusion produced a small reduction in the CP-induced increase, but the factor of colony enhancement compared to control mice remained >100.These data emphasize the potential hazard of prophylactic treatment of pulmonary metastases by X-rays or CP in clinical situations in which control of the primary tumour is not achieved.

X-ray dose fractionation and oncogenic transformations in cultured mouse embryo cells.

THE effect of dose fractionation on oncogenic transformation can be studied quantitatively by using recently developed cell lines in which transformation is scored by the loss of contact inhibition1,2. We report here that splitting the dose into two fractions enhances oncogenic transformation at low doses, whereas at high doses fractionation results in less effect than the same total dose in a single exposure. This observation is pertinent to the calculation of cancer risk estimates for multiple low-dose exposures, to which radiation workers or members of the general public are exposed, by means of a linear extrapolation from observed human data at high dose levels.

Influence of X-ray dose fractionation on the frequency of somatic mutations induced in tradescantia stamen hairs

Abstract X-rays were used to investigate the influence of dose fractionation on the induction of pink and colorless somatic mutations in stamen hair cells of Tradescantia clone 02. Inflorescences were exposed to a single acute dose of 60 rad, two acute doses of 30 rad, or three acute doses of 20 rad. The dose rate in all cases was 30 rad/min. Intervals between dose fractions were varied from 35 sec to 48 h and the mutation frequency was compared with that resulting after the single dose of 60 rad. The data show a reduction in mutation frequency for fractionation intervals longer than 15 and 6 min for pink and colorless mutations, respectively, but not for shorter intervals. One interpretation of the data predicts that pink mutation frequencies are reduced by 11% for fraction intervals of from 30 min to 6 h, and that colorless mutation frequencies are reduced by 24% for intervals of from 15 min to 6 h. The corresponding sparing effect of dose fractionation is equal to 6 rad for pink mutations and 9 rad at the colorless mutation endpoint. A calculation has been made which indicates that the percentages of the total repairable (presumably two-hit) damage that is repaired during fraction intervals up to 6 h, are 16 and 35% for pink and colorless mutations respectively.

The effect of dose fractionation on γ-radiation induced mutations in mammalian cells

The lethal and mutagenic effects of single and fractionated doses of gamma-radiation were studied in V79-4 Chinese hamster cells, as dose fractionation is of interest in radiation protection studies. The results show that the induction of 8-azaguanine resistant (Agr) mutants has a non-linear dose response curve following single doses of radiation. The lethal and mutagenic effects of fractionated doses were always less than if the radiation was given in a single dose. Any change in treatment which led to an increase in survival also led to a decrease in induced mutation frequency. There was a relationship between mutation and survival which was independent of the number of fractions in which the radiation was given. This could be of consequence in radiological protection.

Effect of dose fractionation on early and late skin responses to γ-rays and neutrons

Abstract Areas of pigs' skin were exposed to fractionated doses of γ-rays or E d = 50 MV ( B e ) neutrons and their responses measured in the acute phase in terms of desquammation and after several months as degree of contraction. The purpose of the experiments was 2-fold—to measure the biological effectiveness of these neutrons relative to γ-rays for acute and late effects and to determine the relative changes in acute and late responses when the dose fractionation pattern of a 6.5 week treatment was changed from five times to twice weekly. The relative biological effectiveness (RBEngamma) was 3.2–3.4 for late effects and less than that for acute desquammation. Dividing neutron doses of 200 rad or less into smaller fractions did not affect the dose-response relationship for late contraction. With γ-rays, however, there was a marked effect of dose fractionation on late contraction—when the 5 days per week fractionation pattern was changed to a twice weekly regimen, with an increase in fractional doses from 180–260 rad to 380–460 rad, there was a marked increase in the severity of late responses. This increase in late response was not predictable from acute responses which were the same or slightly reduced in the animals treated twice weekly. The two most important observations were, therefore, that increasing the size of dose fractions in conventional γ-ray therapy may be associated with severe late complications not predicted by increase in the acute response, and that the RBEngamma for late effects is higher than for acute effects in skin.

Split-dose and Liquid-holding Recovery after X-irradiation in Diploid YeastSaccharomyces Cerevisiae

Liquid-holding recovery (LHR) and the sparing effect of dose fractionation were investigated with 100 kVp-X-rays in diploid yeast from exponential and stationary phase. Exponential cells showed prompt and complete split-dose recovery. The ability to undergo LHR remained constant during 2-5 hours incubation after the first dose. Stationary-phase cells did not exhibit split-dose recovery (SDR) in a simple way: there was an increase in sensitivity after 3-5 hours followed by a gradual increases with time. It is suggested that stationary cells are starved of an essential co-factor which has to be synthesized de nova.

Action of a platinum complex [ cis-dichlorobis (cyclopentylamine)-platinum (II)] on chinese hamster ovary cells in vitro

cis-Dichlorobis(cyclopentylamine)platinum (II) (DBCP) treatment of Chinese hamster ovary (CHO) monolayer cell cultures was found to cause: (1) growth inhibition due to an impaired G1 leads to S transition and formation of a non-cycling compartment; (2) delayed cell death (with a maximum at 72 h after treatment); (3) decrease of [14C] TdR incorporation into DNA. Part of the surviving cell population was subject to non-lethal damage. The Do values of the dose--survival curves were 9.2 and 14 mug/ml in two kinds of media differing in Na+ and Cl- concentrations. There was no sparing effect of dose fractionation and no cell cycle phase specificity. In the dose range corresponding to the shoulder region of the dose-survival curve,the lethal effect of DBCP treatment was directly related to the decreased rate of DNA synthesis in DBCP-treated cells.

Acute Lethality after Fast-Neutron and X-Irradiation of Tribolium confusum

The acute lethal effects of fast neutrons and of X-rays on adults and larvae of T. confusum are compared. The time course of mortality of adults of the Oklahoma strain was the same after midlethal doses of neutrons and X-rays, although the neutrons were about twice as effective as X-rays in producing lethality, based on ${\rm LD}_{50(35)}$. The neutron RBE for adults of the Ebony mutant strain was also about 2, but that for Oklahoma larvae was about 3.85. Larvae surviving midlethal doses of neutrons showed a tendency toward wing abnormalities and delayed pupation. Dose-fractionation recovery with neutron doses in the midlethal range was not detectable in the adults or in the larvae. A considerable sparing effect of dose fractionation was found in X-irradiated adults. Also presented are techniques for using a beam port of a Triga research reactor for fast-neutron irradiation and a method of neutron and gamma dosimetry.