Radiation-induced Genetic Damage Research Articles

Studies on mutagen-sensitive strains of Drosophila melanogaster I. The enhanced X-ray sensitivity of a mutant strain ( ebony) which is UV-sensitive and also deficient in photorepair

Yegorova and colleagues (1978) showed that a mutant strain of Drosophila melanogaster (ebony) was more sensitive to UV-induced killing of embryos and also less proficient in photoreactivating (PR) ability than a wild-type ( Canton-S) strain and that the genes governing UV sensitivity and PR ability were different and presumably located on the autosomes. The experiments reported in the present paper were designed to compare the patterns of sensitivity of these 2 strains and their hybrids to X-irradiation. The sensitivity of the larvae to the killing effects of X-irradiation, and of male and female germ-cell stages to the X-ray induction of genetic damage was studied. It was found that the larvae of the ebony strain are more sensitive to X-ray-induced killing than those of the Canton-S strain. The frequencies of radiation-induced dominant lethals and sex-linked recessive lethals are higher in spermatozoa sampled from ebony males than in those of Canton-S males. In spermatozoa sampled from hybrid males, the yields of dominant lethals are no higher than in those sampled from Canton-S males and do not seem to depend on the origin of the X-chromosome. There are no statistically significant differences between the ebony and Canton-S strains in the sensitivity of their spermatozoa to the induction of autosomal translocations. Stage-7 oocytes sampled from ebony females are more sensitive to the X-ray induction of dominant lethality than are those from Canton-S females; oocytes sampled from hybrid females manifest a level of sensitivity that is significantly lower than that in either parental strain. The frequencies of X-chromosome losses induced in in this germ-cell stage are significantly lower in ebony than in Canton-S females at least at the exposure level of 3000 R at which 3 experiments were carried out. There are no measurable differences in the amount of dominant lethality induced in stage-14 oocytes of ebony, Canton-S and hybrid females. When X-irradiated Berlin-K males are mated to ebony or Canton-S females, the yields of dominant lethals are higher when ebony females are used, showing that there is a “maternal effect” for this kind of damage. Such a maternal effect is also found for sex-linked recessive lethals (irradiated Muller-5 males mated to ebony or Canton-S females). However, when irradiated ring-X-chromosome-carrying males are mated to ebony or Canton-S females, the frequencies of paternal sex-chromosome losses (scored as XO males) are lower when ebony females are used. These results have been interpreted on the assumption that the ebony strain is homozygous for recessive, autosomal genes that confer increased radiosensitivity and that the Canton-S strain carries the normal, wild-type alleles for these genes. The higher yields of dominant and recessive lethals in mature spermatozoa and of dominant lethals in stage-7 oocytes are a consequence of an enhanced sensitivity to the mutagenic (in particular, to the chromosome-breaking) effects of X-irradiation and/or of defective repair of radiation-induced genetic damage. The lower yield of XO males from irradiated stage-7 oocytes of ebony females is probably a consequence of a defect in the repair of chromosome-breakage effects, resulting in the conversion of potential X losses in females into dominant lethals. The “maternal effects” for dominant lethals, sex-linked recessive lethals and for the loss of ring-X chromosomes are assumed to have a common causal basis, namely, a defective repair of chromosome-breakage events in the females of the ebony strain.

Effect of hyperthermia on radiation-induced chromosome loss in female Drosophila melanogaster.

Three-day-old adult females of mutagen sensitive mutants: mus (1)101D1, mus(1)102D2, mus(1)103D1, mus(1)104D1, mus(1)105D1, mus(3)302D2; meiotic mutants: mei-9D2, mei-9D3, mei-218, and controls st, and w, were subjected to 38 degrees C for 1 hour and 1200R of gamma rays, brooded daily, and nondisjunction and the loss of X chromosomes determined. This was done in an attempt to gain more information on the hyperthermia sensitization of radiation-induced damage. In several strains the hyperthermia treatment sensitized immature class-1 oocytes--the most radiation-resistant stage--to radiation-induced chromosome loss. This class of oocytes is believed to have the greatest number of repair enzymes, and supports the hypothesis that hyperthermia increases radiation-induced genetic damage by interference with repair enzymes. The mature oocytes, which are believed to lack repair enzymes (stage 14), were the most sensitive to heat treatment and radiation. Hyperthermia failed to increase radiation-induced chromosome loss in the meiotic mutants. Hyperthermia may affect excision repair. There was no clear-cut correlation between other defective DNA pathways and influence of hyperthermia on radiation-induced chromosome loss in Drosophila females. The failure of hyperthermia to increase radiation-induced chromosome loss in meiotic mutants may indicate that radiation sensitization by hyperthermia also may be due to interference with chromosome segregation.

X-ray induced sex-chromosome loss, when ring-X chromosome males are irradiated and mated to females carrying mei-9, mei-41 or mei-218

Radiation damage induced in the sperm nucleus is repaired after this nucleus has enteredj the oocyte. The yield of induced genetic damage is known to be dependent on maternal genotype and can also be modified by treatment of the females with metabolic inhibitors. The experiments reported here were designed to find out whether a more specific analysis of the interaction between male gamate and oocyte cytoplasm can be carried out using mutants that are known to affect repair processes. Males carrying ring-X chromosomes were exposed to X-ray doses up to 1000 R and mated to females homozygous for a repair-deficient mutant. The mutants used were mei-9 9, mei-9 L1, mei-41 A10, and mei-41 D5. In addition a yellow ( y) X chromosome was used as a control and an attempt was made to obtain data using mei-218 15, a mutant at a locus not thought to affect repair. With mei-9 mutants there is an enhancement of the spontaneous and induced rates of paternal sex-chromosome loss. The mei-41 mutants did not affect the rates of paternal sex-chromosome loss. Mei-218 females were difficult to work with because they gave very few progeny. From these data it can be argued that repair-deficient mutants will indeed be useful for an analysis of the fixation of radiation-induced genetic damage.

The effect of dithiothreitol on radiation-induced genetic damage in Arabidopsis thaliana (L) heynh

A study was made on the effect of dithiothreitol (DTT; present during irradiation) on M 1 ovule sterility, M 2 embryonic lethals, M 2 chlorophyll mutants and M 2 viable mutants induced with fast neutrons or X-rays in Arabidopsis thaliana. DTT provides considerable protection against both fast-neutron and X-ray-induced genetic damage. However, a higher protection was observed against M 1 ovule sterility, than against embryonic lethals, chlorophylls and viable mutants. This implies a significant DTT-induced spectral shift (0.01< p<0.05), i.e. a shift in the relative frequencies of the different genetic parameters. This spectral shift is explained on the basis of a specific DTT protection against radiation-induced strand breaks, and by differences in the ratio strand breaks/base damage for the genetic parameters concerned, i.e. a higher ratio for ovule sterility than for the other parameters. The induction of the genetic damage by ionizing radiation, either with or without DTT, is described by a mathematical model, which includes both strand breaks and base damage. The model shows that the resolving power of a test for a “mutation” spectral shift depends on the relative values of the strand-break reduction factor of -SH compounds and on the ratio strand breaks/base damage of the genetic parameters. For each genetic parameter the DTT damage reduction factor (DRF) is calculated per irradiation dose, and in addition the average (over-all doses) ratio strand breaks/base damage.

Modification of radiation-induced genetic damage in Drosophila melanogaster male germ cells by butylated hydroxytoluene.

The effects of butylated hydroxytoluene (BHT) on genetic damage induced by ionizing radiation were studied in post-meiotic male cells of Drosophila melanogaster. Prior to submitting Samarkand males to 2 krad of X-rays, BHT was administered (a) with the food (0.2 per cent final concentration) from emergence of the imago for 7 days or (b) by intra-abdominal injection (0.05 per cent) to 7-day-old adults. Dominant lethality (embryonic and total), II-III translocations and sex-linked recessive lethals were recorded. The only effect of BHT observed was a decrease in the frequency of recessive lethals induced, detected in early spermatids. Since oxygen plays an important role in the high radiosensitivity of these cells, it is suggested that the sparing action of BHT was due to its antioxidative and radical scavenging properties.

The effects of gonadal irradiation in clinical radiation therapy: A review

Recent improvements in radiation therapy of some malignancies in lower abdominal sites are leading to a prolongation of life in persons of child-bearing age. These successes require an evaluation of the possible undersirable consequences of the unavoidable gonadal irradiation that occurs in these cases. A review of radiobiological data from experimental animal studies and retrospective clinical studies suggests that in most instances human gonadal exposures in both sexes are insufficient to cause permanent sterility, because the exposures are fractionated and the total gonadal dose is much less than 600 rads. As a consequence, return of fertility must be anticipated, and the worrison questions of radiation-induced genetic damage in subsequent pregnancies must be addressed. This review did not substantiate this fear, because no case reports could be found of malformed infants among the progeny of previously irradiated parents. Some experimental studies suggest that radiation-damaged spermatogonia are self-destructive, but any evidence for this phenomenon in the ovary is nonexistent. We suggest that the difference between fact and theory here may be the mathematical result of the interplay of low probability for occurrences and the few patients who until now have survived long enough for study.

Modification of radiation-induced genetic damage in Drosophila melanogaster male germ cells with nucleic acid precursors : III. Effects on the premeiotic cells

Using a 2-day brood pattern, the effect of 5-bromodeoxyuridine (BUdR) or 5-bromodeoxycytidine (BCdR) pre-treatment on the radiation-induced yield of sex-linked recessive lethals and translocations was studied in the spermatocytes and late gonial cells (p.i. DNA synthesis cells) of D. melanogaster. The p.i. DNA synthesis cells were irradiated ( I.2 kR γ-radiation) in the pre-meiotic or post-meiotic stage. Irradiation of p.i. DNA synthesis cells in the pre-meiotic stage resulted in enhanced lethal frequency with BUdR (3.0%) and BCdR (2.9%) over the other pre-treatment conditions: saline (S), thymidine (TdR) and deoxycitydine (CdR) in the spermatocytes but not in the late gonial cells. The radiosensitizing property was evident with BCdR even when the p.i. DNA synthesis cells were irradiated in the post-meiotic stage; but not with BUdR pre-treatment. Probable reasons for the contradicting results reported in the literature were discussed.

Modification of radiation-induced genetic damage in Drosophila melanogaster Male germ cells with nucleic acid precursors III. Effects on the premeiotic cells

Using a 2-day brood pattern, the effect of 5-bromodeoxyuridine (BUdR) or 5-bromodeoxycytidine (BCdR) pre-treatment on the radiation-induced yield of sex-linked recessive lethals and translocations was studied in the spermatocytes and late gonial cells (p.i. DNA synthesis cells) of D. melanogaster . The p.i. DNA synthesis cells were irradiated ( I .2 kR γ-radiation) in the pre-meiotic or post-meiotic stage. Irradiation of p.i. DNA synthesis cells in the pre-meiotic stage resulted in enhanced lethal frequency with BUdR (3.0%) and BCdR (2.9%) over the other pre-treatment conditions: saline (S), thymidine (TdR) and deoxycitydine (CdR) in the spermatocytes but not in the late gonial cells. The radiosensitizing property was evident with BCdR even when the p.i. DNA synthesis cells were irradiated in the post-meiotic stage; but not with BUdR pre-treatment. Probable reasons for the contradicting results reported in the literature were discussed.

Modification of radiation-induced genetic damage in Drosophila melanogaster male germ cells with nucleic acid precursors II. Effects on post-meiotic cells

Following the observation that the nucleoside pre-treatment reduced the radiation-induced dominant lethality in the post-meiotic germ cells, similar experiments were conducted using the same treatment conditions to study the influence of the nucleoside(s) pre-treatment on the radiation-induced (1.2 kR) incidence of sex-linked recessive lethals and translocation events in the post-meiotic male germ cells of 1-day-old D. melanogaster. The nucleoside pre-treatment reduced the translocation frequency (not statistically significant) and the lethal mutation frequency (statistically significant) in the post-meiotic cells (pre-injection DNA synthesis cells) especially in the mature sperms sampled in brood a (br a). The radio-protective effect of the nucleosides on the mature sperms was confirmed using 7-day-old virgin males and different radiation doses (2.4 kR and 3.6 kR). The frequency of lethal mutation was lowest when irradiation was preceded by the injection of an equimolar solution of thymidine (TdR), deoxyadenosine (AdR), deoxycytidine (CdR) and deoxyguanosine (GdR). However, when the nucleosides were injected after irradiation (within 10–30 min) there was no change in the yield of radiation-induced lethals. The possible mechanisms for the radioprotective action of the nucleosides in the post-meiotic germ cells such as ( a) “protection” by a radiochemical action of nucleosides competing for short-lived radicals that might otherwise cause damage to DNA and ( b) biochemical-physiological mechanisms such as metabolic events increasing the radioresistance of the cells, providing excess energy for repair or favoring and partaking in the DNA repair synthesis were discussed. Further studies were felt necessary to elucidate this phenomenon.

Modification of radiation-induced genetic damage in the male germ cells of Drosophila melanogaster with pyrimidine nucleosides and their halogenated analogues: effects on the F 1 generation

Modification of radiation-induced genetic damage in the male germ cells of Drosophila melanogaster with pyrimidine nucleosides and their halogenated analogues: effects on the F 1 generation

Persistence of Heritable Changes in an Irradiated Rat Population after Cessation of the Exposures

Studies to assess the importance of radiation-induced genetic damage, of kinds that persist following the cessation of repeated ancestral irradiations, imply that the obviously harmful expressions occur only prior to weaning and are not detected in young adults. Reductions in fertile matings and litter size, and an increase in postnatal mortality up to the time of weaning, were observed in a population of rats after 13 generations of parental irradiation and a 14th generation without irradiation. These findings indicate the persistence of induced genetic changes despite a substantial rate of elimination in each generation. Among young adult rats, however, the only observed effect was a small but significant decrease in the body weights of the males. This change is not believed to be indicative of any detriment to the adult animals because the opposite effect was found in adults of the preceding generation. It seems unlikely that both kinds of change, at least to this degree, would be harmful. It is conclu...

Effects of gamma irradiation on radiation sensitivity in the diploid potato species Solanum chacoense

The effect of ancestral exposure to radiation on the radiation sensitivity of progeny was tested the diploid potato species Solanum chacoense f. gibberulosum (Juz. and Buk.) Corr. Approximately 83 per cent of seedlings of a parental population that received 0 and 3 kR of gamma radiation survived and grew normally while only 26 per cent of those receiving 6 and 9 kR survived and appeared to grow normally. The survival and vigor of seedlings derived from plants that had survived these doses were compared following exposure to the same doses. The results indicated that radiation damage measured in terms of survival and vigor was increased following irradiation among most of those plants whose ancestors had received doses of 6 and 9 kR of radiation. This increase was attributed to the hereditary transmission of radiation-induced genetic damage in the form of recessive lethals and detrimentals. Certain lots failed to show increased radiation sensitivity as measured by decreased survival. This result was interpreted as resulting either from chance failure of mutation in the parental plants involved, or to somatic elimination of radiation damage induced in young seedlings.

Relative Biological Effectiveness of Different Types of Ionizing Radiations: Cytogenetic Effects in Maize

Seeds of a genetic stock of maize (Zea mays L.) heterozygous for the yellow-green locus, Yg2/yg2, were used in all experiments. The recessive gene, yg2, gives a yellowgreen color in the leaves when homozygous or hemizygous, and the presence of the dominant gene, Yg2, produces full green color, so that the heterozygote has normal green leaves. The Yg2 locus is located near the end of the short arm of chromosome 9. Loss of the Yg2 allele (deletion) or change in its function (mutation) in heterozygotes gives a yellowish green phenotype in leaf cells in which the phenomenon occurs and in cell lineages of the altered genotypes. The frequency of yellow-green streaks or sectors in leaves of seedlings grown from irradiated seeds was used as a measure of the frequency of radiation-induced genetic change or damage. This phenomenon was considered to be due mainly, if not exclusively, to breaks in chromosome 9 between the centromere and the Yg2 locus, with loss of the Yg2containing segment. Prior to exposure to radiation, the seeds were equilibrated over a saturated aqueous solution of CrO3 in an atmosphere of 35 % relative humidity. The water content of Yg2/yg2 embryos, excised from maize seeds so stored, was determined to be 6.7 % (1). The mutation rate per cell (or Yg2-carrying chromosome) was determined in 1 Research carried out at Brookhaven National Laboratory under the auspices of the U. S.

Energy Requirements and Relative Biological Effectiveness for Producing a Cytogenetic Phenomenon in Maize by Irradiating Seeds with X-Rays and Monoenergetic Neutrons

Seeds of a genetic stock of maize (Zea mays L.) heterozygous for the yellow-green locus, Yg2/yg2, were used in all experiments. The recessive yg2 gives a yellow-green color in the leaves, and the presence of the dominant Yg2 produces full green color, so that the heterozygote has normal green leaves. The Yg2 locus is located near the end of the short arm of chromosome 9. Loss of the Yg2 allele (deletion) or change in its function (mutation) in heterozygotes gives a yellowish-green phenotype in leaf cells and cell lineages of the altered genotypes. The frequency of yellow-green streaks or sectors in leaves of seedlings grown from irradiated seeds was used as a measure of the frequency of radiation-induced genetic change or damage. The phenomenon was considered to be due mainly, if not exclusively, to breaks in chromosome 9 between the centromere and the Yg2 locus, with loss of the Yg2-containing segment

Magnetic fields and ionizing radiation: effects and interactions during germination and early seedling development

Ionizing radiation is well known as a powerful modifier of plant growth, but the biological effectiveness of the magnetic field is less recognized. Experiments utilizing both agents, alone and in combination, were carried out for the purpose of comparing the effects of and ascertaining the interactions between acute 50,000 R X-irradiation of dormant barley grains and continuous application of a 3000 G steady homogeneous magnetic field during subsequent germination and early seedling development. X-irradiation by itself produced the familiar and significant retardation of germination and seedling growth during 5 days post hydration. The growth effects were of greater magnitude but in the same order of severity as those previously found with lower radiation levels: root length more affected than shoot height or coleoptile height; root number and rate of emergence least affected. Seedling size variability decreased; that for root number increased. Germination in the homogeneous magnetic field caused, by itself, only small, consistent, but statistically insignificant growth inhibition, accompanied by significant increases in variability. Effects on root number, emergence, and intra-embryonic size correlations, however, equalled or exceeded those produced by the radiation. When applied as a post radiation treatment, the magnetic field reduced the radiation effects on growth and root number. As with magnetic effects per se, the degree to which the magnetic field attenuated the radiation damage exhibited in any particular criterion was inversely correlated with the level of radiosensitivity possessed by that criterion. In addition, radiation-induced reductions in variability were lessened by the presence of the magnetic field, and alterations in intra-embryonic correlations, reversed. Synergistic interactions occurred between radiation and magnetic field with regard to the rate of emergence. The severity of growth inhibition produced by ionizing radiation has often been shown to be correlated with effects upon cell production and to reflect the amount of radiationinduced genetic damage, especially chromosomal aberrations. The homogeneous magnetic field, on the other hand, produced its largest effects and greatest attenuation of radiation damage (or the opposite, synergistic interactions) upon those aspects of seedling development which are least radiosensitive and most dependent upon cell enlargement for expression. This suggests that the biomagnetic effects observed must be mediated through physiological processes other than those of primary concern in producing radiation damage.

Reduction in life expectancy as a measure of radiation-induced genetic damage in mice.

SummaryLife span studies on first generation male and female breeders and on second generation virgin females from 20 generations of X-irradiated sires were done. The results of this and other studies strongly suggest that factual statements crediting reduction of life span as being a measure of a radiation-induced genetic decrement in viability are premature and inconsistent with experimental evidence at this date.

Relative Cytogenetic Efficiency of Muons and π - Mesons in Zea mays (L.) and Its Modification by Postirradiation Storage

Until recently, high-energy meson beams of sufficient intensity have not been available for biological research. The Alternating Gradient Synchrotron (AGS) at the Brookhaven National Laboratory now produces rmeson and muon (uparticle) beams suitable for use in biological experiments. The beam intensity is still low compared to that of other radiation sources. To achieve any measurable effect with most biological materials, long exposures are required. Dormant dry seeds, which have a low metabolic rate, seem especially well adapted for investigations at the present time. Special genetic stocks of Zea mays (L.), heterozygous for Yg2/yg2 alleles, have been used previously to study mutagenic effects of X-rays (1-3), deuterons (4), heavy cosmic particles (5), monoenergetic fast neutrons (6) and chemicals (2, 3). Seeds of these stocks were used in the experiments reported here. Presence of the dominant Yg2 allele produces a green color in the leaf, the recessive yg2 gives a yellowgreen color, and the heterozygote Yg2/yg2 has normal green leaves. Loss of the locus (deletion) or of function (mutation) for the dominant Yg2 allele gives a yellowishgreen phenotype in leaf cells and cell lineages of the altered genotypes. The frequency of yellow-green streaks or sectors in leaves was used as a measure of the frequency of radiation-induced genetic change or damage which was considered to be due mainly, if not exclusively, to breaks in the chromosome between the centromere and the Yg2 locus, with loss of the Yg2-containing segment. In the present

THE FAILURE OF SULPHHYDRYL COMPOUNDS, AET, MEA, AND GLUTATHIONE TO PROTECT AGAINST X-RAY INDUCED CHROMOSOME ABERRATIONS IN MALE DROSOPHILA.

SummaryPre-treatment with the mammalian radioprotective sulphhydryl compounds AET, MEA, and glutathione did not protect the Drosophila testis from radiation-induced genetic damage. Protection was not given to spermatozoa, spermatids, spermatocytes and spermatogonia. The responses measured were production of recessive sex-linked lethals, translocations, deletions, loss of X and Y chromosomes and ‘dominant lethals’. MEA increased the recessive lethals in the 3–6 day brood. Pre-treatment with glutathione increased the incidence of XO males in the 6–9 day brood and post-treatment in 0–3 day brood. MEA and glutathione increased the percentage of eggs that failed to develop in ‘dominant lethal’ tests.

The Effect of Ancestral Irradiation Exposure on Radioresistance in Their Descendants

Differences in radiosensitivity among strains of a species have been well documented (1-11). Strain differences in resistance to ionizing radiation exposure may be attributed to a number of genetic factors. However, Doolittle (1) has reported evidence which would suggest that even a single gene substitution can influence radiosensitivity. If ionizing radiations are capable of inducing harmful mutations which are cumulative, it may be possible to modify the genotype of a strain by exposing consecutive generations to ionizing radiation and to measure this genetic decrement quantitatively as a change in response to whole-body Xor y-ray exposure. Earlier studies (12-14) have suggested the inheritance of radiation-induced genetic damage detrimental to the propagation of a species and to survival under natural and accelerated stress environments. The following is a study on the comparative resistance of three groups of mice, each of which had ancestral backgrounds with different radiation histories, to chronic yand acute X-irradiation exposure.

Genetic effects in children and grandchildren, of women treated for infertility and sterility by roentgen therapy; report of a study of thirty-three years.

The deductions of the experimental geneticists are questioned by many because of the almost total absence of valid data concerning radiation-induced genetic damage to human offspring. In the present paper an analysis is made of the genetic changes observed in two successive generations of the offspring of 644 women who had received roentgen therapy for a tissue dose of approximately 65 r to the ovaries and 90 r to the pituitary, with a follow-up in over 50 per cent of the cases of five to thirty-two years. Material During the past thirty-three years there have been referred to the author 825 women for roentgen therapy for sterility; 800 have been treated. The statistical data are as follows: All of these women were referred by gynecologists, only after all other methods for the relief of sterility had been tried and had failed. The diagnosis of sterility was made by the referring physician, after performance of the usual diagnostic tests for sterility. In most instances the husbands had also been tested. The age of the women treated ranged from eighteen to forty-two years. In 277 of the series irregular menstruation was associated with sterility. In 64 patients menstruation was regular. The period of sterility prior to treatment ranged from one to nineteen years. Fifty-seven per cent of the patients were sterile from four to ten years and 43 per cent from eleven to nineteen years. In 5 patients there was a second marriage before irradiation treatments were instituted. In 60 cases the patient had previously conceived; 21 of this number had borne a child and 39 had miscarried and failed to conceive again until after irradiation. (The 21 children previously born to these women are not included in any statistical data of this presentation.) Methods High-voltage irradiation has been employed consistently over the past thirty-three years, with the following factors: 200 kv, 1 mm. Cu h.v.l., 50 cm. distance, 8 × 10-cm. portals for the pelvis and a round portal 5 cm. in diameter for the pituitary area. Treatments are given in three sessions at seven-day intervals with an overall time of fourteen days. At the first session, 50 r, measured in air, is administered to the right and left anterior pelvic areas, and 75 r, measured in air, to the central forehead, with the rays directed to the pituitary. Seven days later, 75 r, measured in air, is given to the right and left posterior pelvic areas, and 75 r, measured in air, to the central forehead. At the final session treatment similar to that of the first day is administered to the anterior pelvic areas and the forehead. With this procedure, the mean total tissue dose to each ovary is approximately 65 r, measured with back-scatter, in fourteen days. Because of the variation in the dimensions of the pelvis, the range was approximately 50 to 90 r. The mean total dose to the pituitary was about 90 r in the fourteen days. This procedure was fairly constant for most patients.