Fertility Impairment and Graph Showing Percentage of Effects

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Another non-lethal effect of radiation exposure occurs i n the gonads, which are among the more radiosensitive organs o f the , -6ecause o f the much greater facility with which male spermatogenesis can be studied, experimental hyman data pertaining to the male i s available. Two recent studies in particular provide contemporary information o n the effects of radiation on human spermatogenesis. In one of these 6 4 male volunteers received a single mid-organ dose io both of. their testes ranging from 7.5 t o 400 R. and for mitosis halting i t was 27 R. was 501 days w i t h eventual recovery observed i n each individual where the followup was complete. (Thor s lund, T.W.. and Paulsen,'C.A., Effects of, X-Irradiation o n Human Spermatogenesis,. Proceedings National Syrnposiuin on Natural and Han-Made Radiation in Space, E.A. Warinan; -Editor; NASA For cell killing the ED50 !/as 75 The maxiinun observed sterile period 2 The second study involved exposures t o the testes of .-- sterility was produced-in the period from-46 t o 67 diys postexposure..-..; produced markedly reduced .sperm,.counts while : l o w e r doses .including-.20 rads::.ii:

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Ionizing Radiation o n the Human Testis, Radiation Research, 59:665, 7974.) To sum a rize,in the human male, radiation doses beginning above 10 rads and extending t o 600 produce a decrease o r absence i n sperm beginning atleast6to7 weeks after exposure and continuing for a few months t o several years with subsequent recovery ensuing within this dose range.' The de-pth of fall and the rate of return are related t o the magnitude o f the exposure. Itis noteworthy however, that even the dose a t the high end o f the range, which would be in the potentially lethal area i f administered t o the whole body, is not sufficient to It is also to be noted that the biological mechanisms for expressing libido and potency are not affected in this dose range, a1 though psychologic factors may affect sexual performance. o f importance because the relative radioresistance of spermatozoa allows - a period of about 46 days before the deficiency o f the more rad-iosensitive precursor cells results in a fall in sperm count. The directly irradiated spematozoa therefore can be involved i n conception within th2first six weeks postexposure unless measures are taken for its prevention.FEventua1 recovery of spermatogenesis i s due tothe = comparative radioresistance o f the primitive sptymatosoniurn (Type A) which has an LDSO -of ab'out 600 rads. spermatogsniurn are much more .radiosensitive; .being affected by as low 1. cells into type 6 and these into spermatocytes-occurs even though-: In man, unlike-some other species, maturation of type A . replenishment by mitosis of the full complement of type A cells has - not been completed. .--This makes - f o r the very .slow return t o normal sperm levels following exposure. It also accounts for the fact observed by

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Heller and Rowley (Rowley, M.J. Personal conmunication, 79751, t h a t 11 fractional doses of5 rads t o the human testes produce a nore rapid fall csur-c.i n the spermAand a longer recovery time requirement than single exposures t o the same total dose of 55 rads. would, o f .coursk, produce different results. Different patterns o f fractionation -The data on dose-response relationships for azoospermia production from these two studies, presented i n Figure 3, show reasonably Radiation effects on the human ovary differ from those i n the testes because unlike the testes, the ovaries contain their en tir2 supply of germ cells or oocytes early in life and lack stem cells capable o f replacing any which are lost thereafter. relatively radiosensitive, loss of such cells due t o radiation damage irreversibly reduces the reproductive potential of the woman exposed. The age of the ova and their stage of development have an effect on their Since the oocytes are Although human experimental data is lacking, there i s information from studies of the effects :of localized radiation therapy:: as well as followup studies of the-Japanese atomic bomb survivors:and Radiation therapy data have been reviewed in detail - .

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Cytokinetic and Histopathologic Considerztions of Irradiated Male and Female Gonadal Tissues ,in Frontiers of Radiation Therapy and Oncology, 4that emerge are that single doses o f 125 to produce prolonged, o r permanent amenorrhea in about 50% of women while about 600 " tissue roentgens" or rads are required t o produce permanent . ? amenorrhea in virtually all women so exposed. One t o two thousand rads may be needed t o reach this endpoint if the exposure i s fractionated over about two weeks and the subjects are young women, who are more radioresistant,..-If the exposure i s delivered over six weeks a t 100 rads daily five-days a week, kshbaugh has estimated that the 50% probability level for permanent sterility would be about 2000 rad s in young women.