Threshold X-Irradiation Sterilization of the Ovary

Size: px

Start display at page:

Download "Threshold X-Irradiation Sterilization of the Ovary"

Ashlynn Jordan
5 years ago
Views:

1 Threshold X-Irradiation Sterilization of the Ovary Roberts Rugh, Ph.D., and Joan Wolff, B.A. X-IRRADIATION of the ovary may result in its sterilization,18. 1D although this gonad was once thought to be rather radioresistant. 2 In clinical practice irradiation sterilization of the ovary is prescribed in certain cases of fibroids and of breast cancers.1 The former practice of using it to control premenopausal bleeding has been abandoned. The range of dose delivered to each ovary for temporary or for permanent sterilization varies considerably. This may be due to (1) the normal variations in biological response of ovaries of different individuals, (2) the difficulty of coning the radiations to the ovaries when its position may vary considerably, (3) variations in size or obesity of patients so that the delivered dose will vary, and (4) the margin of insurance desired by the various clinicians. The doses to each ovary recommended by d'fferent radiologists of the same department are as follows: Temporary Sterilization* Single G r H r M.... Fractionated days 1200/10 days 2000/at 200/wk. in 10 wks. 400 r/wk.a 400 r/wk. Permanent Sterilization Single 400 Fractionated days 900/wk. 800 r/10 days 1800 r 15 days From the Radiological Research Laboratory, Columbia University, New York, N. Y. Based on work performed under contract AT-30-1-GEN-70 for the Atomic Energy Commission. Received for publication February 15, 1957.,. In young females this temporary sterilization may last from 3-5 months only, and in older females it may last for a year. It must be remembered that there is a latent period for sterilization, that it should not be expected for 2-3 months after treatment. 428

2 Vol. 8, No.5, 1957 THRESHOLD X-IRRADIATION STERILIZATION 429 Radium is also being used. To cause complete sterilization the exposure consists of mg.-hr. of radium (given in 32 hours), accomplished by placing 50 mg. of radium in the fundus of the uterus. This dose is increased for younger females. In this way both ovaries are irradiated simultaneously. On the basis of practice within one department, the range of exposure of x-rays (delivered to each ovary) is r for temporary sterilization and r for permanent sterilization, depending upon whether the exposures are fractionated. Human data are collected very slowly. There are data on the dose received by the ovary during diagnostic procedures. 2l 23 It may well be that the above doses will all be revised downward after a few decades when more data are available. In the meantime, it seemed appropriate that we collect statistical data from the fast-breeding, prolific, and short-lived mouse in order to determine the minimum whole-body exposure of x-rays which will render all exposed mice permanently sterile. Such data cannot be extrapolated to the human, but the findings may well be suggestive. MATERIALS AND METHOD A total of 253 sexually mature, 2-month-old, virgin female efl mice were used in this experiment. There were 38 unirradiated controls and 15 experimentals in each of 15 different dose levels or categories of x-irradiation. These included one group exposed to each level of 20, 40, 60, 80, and 100 r in single whole-body exposures, followed by immediate mating with tested males. A second group was exposed to similar levels of single whole-body irradiation but was not provided with mature males for mating until 30 days after exposure. A third group was exposed to the same levels of total body x-irradiation fractionated at 5 days per week over 20 days in a period of 4 weeks. This latter group was not provided with males until the total exposure had been accumulated. Those with fractionated exposures received from 1 r to 5 r per day until they had accumulated from 20 r to 100 r respectively. At 4 months the males were exchanged for younger and more virile males, and toward the termination of the study such exchanges were made when there was a suspicion of female sterility in order to insure male adequacy. In this way vigorous and fertile males were provided constantly. The mice were examined at weekly intervals; all litters were counted, and the number recorded. The newborn mice were then discarded so that lacta-

3 430 RUGH & WOLFF Fertility & Sterility tion would cease and the females had maximum opportunity for production. The x-irradiation facilities consisted of a Quadrocondex constant potential x-ray therapy machine run at 210 KVP and 15 MA, with 0.27 eu and 0.50 mm. AI filters, and at a target distance of 1 meter to the level of the ovaries. The output in air at this distance was 24 r/minute. EXPERIMENTAL DATA Since there were a few deaths among this large group of mice, and a few animals were lost during the year of feeding, watering, and recording of data, the exact total is expressed in terms of mouse weeks. This simply means that the records represent only the actual number of weeks of observation of each particular mouse. In this way the total number of mouse weeks for the various categories of x-irradiation varied slightly. It allowed for the elimination of those mice that were lost or had died during the progress of the experiment. On this basis it will be noted that the data for all x-irradiated mice are comparable. The value for the controls was some what greater because there were more than twice as many animals, but the base line of comparison is the same for all, namely mouse weeks. The total number of litters produced following different levels of x-irradiation was reduced as the dose of x-rays was increased. However, the effeot was more obvious when there was a lapse of 4 weeks between x-irradiation and mating. In other words, there is a latent period for the effect on the ovary. This latent period may be due to differences in radiosensitivity of the mature vs. the immature ova. The least effect of x-irradiation as a means of sterilization of the ovary occurred when the exposure was fractionated. For instance, a single exposure of 40 r has essentially the same sterilizing effect as 100 r given at 5 r/ day over 20 days (4 weeks). Thus, the effect of x-irradiation on sterilization is cumulative but not completely so. It is of interest to note that those females mated immediately after exposure gave results which were intermediate between those with delayed mating and those with fractionated exposures. When we divide the total number of litters produced by a mouse by the total number of weeks of observation, we obtain the weekly average of litters for that mouse. This may be regarded as the index of fertility. These data are particularly significant for the various categories. The control value is 0.12 which means that under optimum conditions for breeding, any single mouse will produce litters at this weekly rate. This value was found to

4 Vol. 8, No.5, 1957 THRESHOLD X IRRADIATION STERILIZATION 431 obtain for females exposed to a single dose of 20 r or up to 60 r fractionated over 4 weeks, so that we may consider these irradiation conditions as substerilizing. However, a single exposure of 40 r reduced the fertility index to (to 42 per cent) which was comparable to that produced by 100 r if it was fractionated at 5 rl day over 4 weeks (index 0.051). By providing fertile males immediately after x-irradiation it is possible to determine the minimum exposure to x-rays whch will cause immediate sterilization of the female. Some mice were sterilized immediately by 60 r wholebody x-irradiation. If, however, there was a delay of 4 weeks before providing males, some mice were found to be sterile after a single 40 r exposure. Thus, 4 weeks' delay was equivalent to 20 r additional exposure. These facts support the proposition that there is either a latent period in x-irradiation effect (which is seen in most tissues) or that mature ova are less radiosensitive than are the immature ova. In the latter instance the «less damaged" mature ova are ovulated during the 4 weeks when the female is without benefit of a male. These data also substantiate the contention that while the effects of x-irradiation are not exactly additive, they are cumulative. For genetic sequelae they appear to be both cumulative and additive. The average size of litters produced was in no way altered by any level of irradiation used, whether or not it was fractionated. If an x-irradiated female mouse produced offspring at all, it produced essentially the normal number. Further, even though complete sterilization eventually followed 40 r for all mice, the final litter produced was always within the normal range with respect to number. This was also true of higher levels of exposure. However, there was no consistent evidence of x-ray stimulation of ova production, as some have contended. These facts suggest that the ova productivity of the mouse is an. all-or-none phenomenon. If it produced any ova, it produced essentially the normal number at any single maturation stage. As the level of x-irradiation increased, not only was the number of litters produced by any mouse reduced, but the onset of sterility occurred at an earlier date. Fractionation was similar to dose reduction. A whole-body exposure of 100 r sterilized all female mice within 8 weeks, but it required 24 weeks to sterilize all mice exposed to 100 r when this dose was fractionated at 5 rl day over 20 days (4 weeks). Thus, the irradiation effect of sterilization was extended 3 times by fractionation. During the 53 weeks of observation there was not one single instance of recovery of a female mouse from x-irradiation sterilization, no matter what

5 432 RUGH & WOLFF Fertility & Sterility level of exposure was considered. Certainly none of these exposure conditions could be considered as providing "temporary sterilization," a term used by clinicians to describe temporary amenorrhea following x-irradiation of the ovaries, with probable correlated cessation of ovulation. DISCUSSION The process of x-irradiating a mouse involves but a few minutes, initiating the destructive effects on the radiosensitive ovary. At high levels of exposure, much higher than used in these experiments, these destructive effects may be evident histologically within a few hours. 4, 8 At low levels of exposure the latent period between exposure and the his to- or cytological changes may be extended to weeks or even months.a. 17 In a recent study20 at levels of 50 r to 300 r, which was made to determine the onset and the duration of sterility in the female mouse, the levels of exposure were somewhat higher than those used in this present study and the duration of the experiment was only 6 months. It was decided, therefore, to explore the effects of still lower levels of exposure, namely 20 r to 100 r in single and in fractionated doses, and also with delayed mating. In the study by Rugh and Wolff20 a drop in litter production was seen after a weekly exposure of as little as 4 roentgens over the 38-week period of the study. The earliest sterility following this 4 r/week level of exposure occurred at 8 weeks, or after 32 r accumulated dose. It was found that 100 r sterilized all female mice by 8 weeks and this finding was confirmed in the present study (Table 1). This present study also showed that 60 r in a single exposure sterilized some females immediately, as did 40 r plus 30 days' delay in mating, or 60 r fractionated over 20 days. Thus, sterilization of some female mice will occur at very low levels of exposure, and immediately. Complete sterilization of all exposed females occurred earlier with the higher doses, so that there was an inverse relationship between dose and sterilization time. However, this relationship was more drastic with single than with fractionated exposures, so that the highest exposure used, namely 100 r, caused complete sterilization of all females in only 8 weeks when given in a single exposure, or in 24 weeks when fractionated as 5 r/day over 4 weeks. Nevertheless, all exposed females were eventually sterilized at every dose used, even 20 r/day fractionated as 1 r/day for 20 days. There has appeared in the literature from time to time suggestions that

6 "'" TABLE 1. Threshold Sterility: 52 weeks X -ray plus 0 time X-ray plus 30 days Daily exposure: 1 month Control 20r 40r 60r 80r 100r 20 r 40r 60r 80 r loor 20r 40r 60r 80r loor Total no. mice Total mouse wks Total no. litters Average litter per mouse per week Average litter per mouse Average no. per litter... Range: litters per mouse Range: no. per litter Final litter size Earliest sterility weeks... Latest Oa oa Oa O' 0- O' sterility weeks ] a Sterilization immediate.

7 434 RUGH & WOLFF Fertility & Sterility low exposures to x-rays might be stimulating Kaplanu - 15 has utilized this to justify his direct x-irradiation of human ovaries in attempts to overcome sterility. He claims some 35 per cent success. If one examines the above data, it might appear that 60 r single exposure prolongs fertility over 40 r exposure, and 60 r fractionated over 20 r fractionated. In other words, there is some evidence of longer fertility following the higher than the lower exposure to x-rays. A prejudicial interpretation of this might favor the idea of stimulation. However, the difference is not statistically significant and all females exposed to any level of x-irradiation used became sterile eventually as a result. The idea of x-irradiation stimulation of ovulation remains unproven. That the ovary undergoes histologic and other changes following x-irradiation of either the ovary or of the whole body has been known for some time Ovarian tumors appeared 1 year after 200 r exposure of female mice. 7 Furth 5 and Furth and Kahn 6 found various types of mouse tumors in 17 m~nths after exposure to as little as 87 r. The growths were transplantable and metastasizing. Speert,22 in a review of the literature and many histories, concluded that therapeutic irradiation had no etiologic significance for human ovarian neoplasms. In an average of 6.7 years following irradiation of 948 patients for radiotherapeutic menopause, only 4 tumors appeared. This may indicate the failure of irradiation at the levels used to disrupt the endocrine cycle of the human, although it may be effective in the mouse. It might also indicate that 6.7 years was far too short a time for ovarian tumors to develop. This period in the human life span (i.e., 6.7 years) is equivalent to about 2 months in the life of the mouse, and no mouse tumor has ever developed in so short a time following irradiation. The latent period for radiogenetic tumors in mice is equivalent to about 27 years of the human life span. It may well be that the tumorigenic hazard of irradiation in the human is relatively unimportant when the latent period may be 27 years, more or less. However, it may be unwise to assume that ovarian irradiation at any level in the human is without the tumor hazard until the longer time span has been considered. There are no such data available as yet. Degeneration of the germinal epithelium in young white mice takes place rapidly after x-irradiation,4 but the mice treated with gonadotropic hormone show remarkable regeneration even to the extent of producing ova and

8 Vol. 8, No.5, 1957 THRESHOLD X-IRRADIATION STERILIZATION 435 follicles. None of the follicles produce m ature ova, however, and no young result from matings with normal males. "Recovery" by the sterilized human ovary of its ability to produce fertilizable ova has been reported by Jacox. 10 This has never been demonstrated in mice where the usual procedure has been whole-body x-irradiation where there is no possibility that the ovary can escape exposure. There is temporary sterilization of the human ovary by low-level irradiation, and this is followed after some months by "recovery" in the sense that viable ova are again ovulated. Certainly none of the mature ova damaged by irradiation could "recover" in the sense of becoming fertilizable. There is known to be a differential in radiosensitivity among the various maturation stages in both oogenesis and spermatogenesis. The earlier stages in maturation, which are somewhat less radiosensitive, eventually become mature. The "recovery" is due to a lapse of time which allows the less radiosensitive immature ova to become mature, and ovulation then produces viable ova. There is every presumption that, even though ova are viable and fertilizable, x-irradiation at levels used for temporary sterilization ( r) alters them genetically. Viability is no criterion of genetic constitution. SUMMARY AND CONCLUSIONS 1. In the mouse there appears to be no level of x-irradiation which will render the female only temporarily sterile. An exposure of as little as 20 r, whether given at one time or fractionated to daily exposures of 1 rover 20 days, will reduce the fertile life span of every female mouse. 2. Some female mice are rendered sterile immediately following an exposure of as little as 40 r while others, similarly exposed, may produce litters for 26 weeks. If the dose is fractionated they may produce litters for 43 weeks before sterilization is complete. The over-all fertility of female mice exposed to 40 r whole-body x-rays was reduced to 31 per cent. The controls would continue to produce litters for almost a year beyond the time of complete sterilization of the irradiated mice. 3. A single exposure of 100 r sterilized every female mouse by 8 weeks but when this dose was fractionated over 30 days complete sterilization was achieved in 24 weeks. Thus the effect of fractionating this dose was a threefold extension of fertility. The exposures were additive but not entirely cumulative, as they are believed to be for genetic sequelae. 4. There is no evidence from litter size that the ovary is stimulated by

9 436 RUGH & WOLFF Fertility & Sterility x-irradiation to produce more ova. This applies to every exposure used, whether single or fractionated. 5. While there is a considerable range in the response of ovaries of different female mice, the minimum levels for the sterilization of any and all mice have been established. 6. A latent period in irradiation sterilization exists, as shown by the fact that 40 r followed by a delay of 30 days in mating rendered some mice immediately sterile. Even 20 r rendered all mice sterile when enough time was allowed. The latent period is shortened by increasing the levels of exposure and lengthened by fractionation. REFERENCES 1. Am..BORN, H. Castration by roentgen rays, as an auxiliary treatment in the radiotherapy of cancer mammae at Radiumhemmet, Stockholm. Acta radiol. 11 :614, BLASS, G. Marked resistance of ovary to roentgen rays. Strahlentherapie 86:370, BRAMBELL, F. W. R., and PARKES, A. S. Changes in the ovary of the mouse following exposure to x-rays. Proc. Roy. Soc., London, s.b. 101 :316, ESSENBERG, J. M. Response of germ cells to gonadotropic hormone in x-ray injured ovaries of young white mice. West.]. Surg. 57:61, FURTH, J. Factors in induction of ovarian tumors by x-rays: Types, character, histogenesis of these growths. Acta Unio Internat. contra cancrum 6:785, FURTH, J., and KAHN, J. B. Experimental radiation induced ovarian tumors: Adenocarcinoma with hyperolemia. Acta Unio Internat. contra cancrum 7:827, GEIST, S. H., GAINES, J. A., and ESCHER, G. C. Vaginal estrus in irradiated mice. Endocrinology 29:59, HALBERSTAEDTER, L., and ICKOWICZ, M. The early effects of x-rays on the ovaries of the rat. Radiology 48:369, HAMAN, J. O. X-ray irradiation to promote ovulation. West. J. Surg. 55:107, JACOX, H. W. Recovery following ovarian radiation. Radiology 82:538, KAPLAN, I. I. Irradiation for stimulating or suppressing menstrual function. New York State J. Med. 88:626, KAPLAN, I. I. The use of high voltage roentgen therapy in the treatment of amenorrhea and sterility in women. Am. J. Roentgenol. 59:370, KAPLAN, I. I. A study of the effects of x-rays on the grandchildren of women who have been irradiated for the treatment of female sterility. J. Obst. & Gynaec. Brit. Emp. 60:872, KAPLAN, I. I. Third generation follow up of women treated by x-ray for menstrual dysfunction and sterility twenty-eight years ago, with detailed histories of the grandchildren born to these women. Am. J. Obst. & Gynec. 67:484, KAPLAN, I. I. Therapeutic abortion followed by x-ray sterilization and resumption of normal menstruation, after three years with birth of two normal children. New York State J. Med. 55:3630,1955.

10 Vol. 8, No.5, 1957 THRESHOLD X-IRRADIATION STERILIZATION LICK, L., KIRSCHBAUM, A., and MIXER, H. Mechanism of induction of ovarian tumors by x-rays. Cancer Res. 9:532, MURRAY, J. M. A study of histological structure of mouse ovaries following exposure to roentgen irradiation. Am. J. Roentgenol. 25:1, PECK, W. S., et al. Castration of the female by irradiation. Radiology 34:176, ROCK, J., et al. The effect of subcastrative roentgen therapy on ovarian physiology. Surg. Gynec. & Obstet. 70:903, RUGH, R., and WOLFF, J. X-irradiation sterilization of the female mouse. Fertil. & Steril. 7:546, SONNENBLICK, B. P. Considerations concerning x-ray dose received by the human ovary during diagnostic procedures. Genetics 40:597, SPEERT, H. The role of ionizing radiations in the causation of ovarian tumors. Cancer 5:478, STANFORD, R. W., and VANCE, J. The quantity of radiation received by the reproductive organs of patients during routine diagnostic x-ray examinations. Brit.]. Radiol. 28:266, Grants-in-Aid The Ortho and Carl G. Hartman grants-in-aid of the American Society for the Study of Sterility, each of $500.00, are available for Applications for these two grants-in-aid should be sent to the Chairman of the Research Correlating Committee of the American Society for the Study of Sterility, DR. S. LEON ISRAEL, 2116 Spruce St., Philadelphia 3, Pa., by November 30, No application will be considered by the Committee unless it is accompanied by 3 copies of a brief outline of the research project for which the grant-in-aid of $ is being sought.

Hormonal Changes Following Low-Dosage Irradiation of Pituitary and Ovaries in Anovulatory Women

Hormonal Changes Following Low-Dosage Irradiation of Pituitary and Ovaries in Anovulatory Women Further Studies A. E. Rakoff, M.D. Tms PRESENTATION is a second progress report in a long-term study of the