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Several reports have shown that weak, extremely-low-frequency (ELF), pulsed magnetic fields (PMFs) can adversely affect the early embryonic development of the chick. In this study, freshly fertilized chicken eggs were exposed during the first 48 h of postlaying incubation to PMFs with 100 Hz repetition rate, 1.0 microT peak-to-peak amplitude, and 500 microseconds pulse duration. Two different pulse waveforms were used, having rise and fall times of 85 microseconds (PMF-A) or 2.1 microseconds (PMF-B). It has been reported that, with 2 day exposure, these fields significantly increase the proportion of developmental abnormalities. In the present study, following exposure, the eggs were allowed to incubate for an additional 9 days in the absence of the PMFs. The embryos were taken out of the eggs and studied blind. Each of the two PMF-exposed groups showed an excess in the percentage of developmental anomalies compared with the respective sham-exposed samples. This excess of anomalies was not significant for the PMF-A-treated embryos (P = 0.173), whereas it was significant for the PMF-B-exposed group (P = 0.007), which showed a particularly high rate of early embryonic death. These results reveal that PMFs can induce irreversible developmental alterations and confirm that the pulse waveform can be a determinant factor in the embryonic response to ELF magnetic fields. The data also validate previous work based on the study of PMFs' effects at day 2 of embryonic development under field exposure.

Breast cancer treatment during pregnancy involves a host of psychosocial, ethical, religious, and even legal considerations, as well as medical multidisciplinary decisions, since the effect of treatment on the fetus must be considered. For example, breast or chest wall radiotherapy should be avoided. The absorbed fetal dosage is at least 5 cGy early in pregnancy and increases to several hundred cGy late in pregnancy to the fetal part immediately below the diaphragm. In the second and third trimesters, chemotherapy is associated with intrauterine growth retardation and prematurity in about half of the babies; the risk of birth defects is a concern in the first several weeks. Typical anesthetic agents readily reach the fetus but are not known to be teratogenic. Although abortion will allow full and comprehensive treatment to the mother, it is not known whether the procedure itself is therapeutic. Early in pregnancy, abortion deserves strong consideration, since the effects of treatment on the fetus will not be a consideration. The poor prognosis of pregnancy-associated breast cancer in the past is probably attributable to a combination of initial delay of diagnosis and possibly to unfavorable biologic characteristics of the hormonal milieu of pregnancy. When pregnant patients are matched stage for stage with controls, survivals seem equivalent, although pregnant patients present with more advanced disease.

Previous studies have shown magnetic resonance imaging to be potentially teratogenic for eye development. An investigation was undertaken to ascertain the effects of 1.5 Tesla magnetic resonance imaging fields on crown-rump length and craniofacial perimeter, two less sensitive teratologic end points of the C57BL/6J mouse. A sham control and two experimental groups of dams (N = 12, 11, 12) placed in different magnet locations were exposed to magnetic resonance imaging fields under clinically realistic conditions. A T-2 weighted spin-echo technique of 36-minutes duration was used on each dam. Crown-rump length was chosen because it is a standard measure of embryotoxicity. Craniofacial perimeter was evaluated because of its relationship to the anterior neural plate, the same region in the developing embryo that gives rise to the eyes. Magnetic resonance imaging fields were found to produce crown-rump and craniofacial perimeter measures smaller than control animals (p < 0.05) when exposed at the isocenter (p = 0.038 and 0.008 respectively). Groups exposed to magnetic resonance imaging fields at the magnet entrance showed p values of 0.004 and 0.053 respectively. The results confirmed magnetic resonance imaging teratogenicity in the C57BL/6J mouse and demonstrates the need for further experimental investigation to ascertain the clinical safety of magnetic resonance imaging for humans.

This study was designed to investigate radiation-induced vertebral malformations in medaka embryos irradiated with beta particles from tritium. Embryos of two inbred strains (HO4 and HO5) of medaka, Oryzias latipes, were exposed either to different concentrations of tritiated water (9.25-37 MBq/ml) or to 137Cs gamma rays (dose rates of 0.44-1.89 Gy/day) continuously from morula to hatching. The newly hatched fry were removed from the radiation field and kept under usual conditions for 1 month. Young fish were fixed in 10% buffered formalin, cleared in 1% KOH, stained with alizarin red S, and kept in glycerine. There was almost no difference in the response to radiation between medaka strains. No marked reduction of hatching rate was observed after chronic irradiation with beta particles and gamma rays, but a considerable reduction in survival of fry was detected in irradiated groups within 1 month after hatching. From observation of whole-mounted skeleton specimens, the following vertebral malformations were found in irradiated groups: fusion of two or more vertebrae, incomplete formation of vertebrae, and lack of vertebral process. The incidence of vertebral malformations increased significantly in both groups irradiated with tritium beta particles and 137Cs gamma rays. A similarity in the incidences was also observed between beta-particle- and gamma-irradiated groups. The RBE of beta particles relative to gamma rays was estimated to be 1 based on the dose-response relationships observed.

On the basis of screening of 15939 newborns at the maternity homes of Kiev after the accident at the Chernobyl atomic station it was found that the number of children with congenital malformation of the locomotor apparatus in 1991-1992 increased by 28.7% as compared with the data of the first postaccident years (1986-1987). Congenital pathology of the hip joint (dysplasia in average 23.5 per 1000 births, hip dislocation 3.6:1000) and foot deformity (7.9:1000) had the highest incidence with a tendency to increase at the latest years.

This is an exploratory study on birth defects in municipalities through which overhead high voltage power lines (HVPL) pass. It was aimed to test the association between maternal residencial proximity to HVPL and congenital anomalies through a case-control study based on data from the Central-East France Registry of Congenital Malformations. Each of the 1688 malformed infants identified through the register was matched with two randomly selected controls in the same maternal age group of the general population. No excess of any specific type of malformation was observed in infants exposed to HVPL. An inverse association was even found between maternal residence in municipalities with potentially high exposure to electromagnetic fields from overhead power lines and congenital anomalies of all types. This was accounted for by low numbers of exposed infants with two types of malformations: skeletal defects and cardiac defects. Difficulties in interpretation of data are addressed and limitations of the study are discussed. If an inverse association were upheld in further work, a possible mechanism might be that exposure to electromagnetic fields may increase the risk of spontaneous abortion of fetuses with anomalies.

Purpose: To determine the genetically significant dose from therapeutic radiation exposure with Hodgkin's fields by estimating the doses to ovaries and testes., Materials and Methods: Phantom measurements were performed to verify estimated doses to ovaries and testes from Hodgkin's fields. Thermoluminescent LiF dosimeters (TLD-100) of 1 x 3 x 3 mm3 dimensions were embedded in phantoms and exposed to standard mantle and paraaortic fields using Co-60, 4 MV, 6 MV, and 10 MV photon beams., Results: Our results show that measured doses to ovaries and testes are about two to five times higher than the corresponding graphically estimated doses for Co-60 and 4 MVX photon beams as depicted in ICRP publication 44. In addition, the measured doses to ovaries and testes are about 30% to 65% lower for 10 MV photon beams than for their corresponding Co-60 photon beams., Conclusion: The genetically significant dose from Hodgkin's treatment (less than 0.01 mSv) adds about 4% to the genetically significant dose contribution to medical procedures and adds less than 1% to the genetically significant dose from all sources. Therefore, the consequence to society is considered to be very small. The consequences for the individual patient are, likewise, small.

The role of environmental radiation in the etiology of birth defects, stillbirths, and other adverse outcomes of pregnancy was evaluated for 13,329 Navajos born at the Public Health Service/Indian Health Service Hospital in the Shiprock, NM, uranium mining area (1964-1981). More than 320 kinds of defective congenital conditions were abstracted from hospital records. Using a nested case-control design, families of 266 pairs of index and control births were interviewed. The only statistically significant association between uranium operations and unfavorable birth outcome was identified with the mother living near tailings or mine dumps. Among the fathers who worked in the mines, those of the index cases had histories of more years of work exposure but not necessarily greater gonadal dosage of radiation. Also, birth defects increased significantly when either parent worked in the Shiprock electronics assembly plant. Overall, the associations between adverse pregnancy outcome and exposure to radiation were weak and must be interpreted with caution with respect to implying a biogenetic basis.

In Norway, external doses of radiation resulting from fallout from the Chernobyl nuclear accident were estimated from detailed measurements, including soil deposition patterns. Internal doses were estimated from measurements of radioactive cesium in meat and milk supplies. The doses were calculated as average monthly doses for each of 454 municipalities during 36 consecutive months after the accident in spring 1986. Prospectively collected data on all newborns listed in the Medical Birth Registry of Norway who were conceived in the period May 1983-April 1989 were used to assess possible dose-response relations between estimated external and food-based exposures and congenital malformations and some other conditions. A positive association was observed between total radiation dose (external plus food-based) and hydrocephaly, while a negative association was observed for Down's syndrome. However, an important conclusion of the study was that no associations were found for conditions previously reported to be associated with radiation, i.e., small head circumference, congenital cataracts, anencephaly, spina bifida, and low birth weight. Potential sources of bias, including exposure misclassification and incomplete ascertainment of cases, are discussed.

To assess the genetic effects of fission neutron, the induction of external malformations was studied in F1 fetuses after F0 male mice were irradiated. Male mice of the ICR:MCH strain were irradiated with 252Cf neutron at doses of 0.238, 0.475, 0.95 and 1.9 Gy. They were mated with non-irradiated female mice at 71-120 days after the irradiation. Pregnant females were autopsied on day 18 of gestation and their fetuses were examined for deaths and external abnormalities. No increases of pre- and post-implantation losses were noted at any dose. External abnormalities were observed at rates of 1.40% in the 0.238 Gy, 2.23% in the 0.475 Gy, 3.36% in the 0.95 Gy and 3.26% in the 1.9 Gy groups; the rate in the control group was 1.65%. The dose-response curve was linear up to 0.95 Gy, and then flattened out; the induction rate of external abnormalities was 2.7 x 10(-4)/gamete/cGy based on the linear regression. These results indicated that fission neutron effectively induces external abnormalities in F1 fetuses after spermatogonial irradiation.

Recent studies suggest that the lifetime cancer risks from exposure to low levels of ionizing radiation may be greater than previously estimated. This review first summarizes the findings of these studies as they pertain to dental radiology, then uses their concepts in combination with dosimetry from the dental literature to estimate the radiation risk from dental radiology. Estimation of risk from groups of exposed individuals requires use of mathematical models that fit the epidemiological data. The ICRP estimates that a single brief whole-body exposure of 1 Gy to 10,000 people results in about 500 additional cancer deaths over the lifetime of the exposed individuals, assuming a dose rate effectiveness factor of 2 for cancers other than leukaemia. Leukaemias are seen as a wave from 5 to 30 years following exposure. Cancers other than leukaemia typically start to appear about 10 years following exposure and remain in excess for as long as most exposed populations are followed, presumably for the lifetime of the exposed individuals. The gonadal dose is so small from dental radiography that the risk of heritable defects is negligible in comparison with the somatic risk. The dental literature contains several studies reporting sufficient dosimetric data for radiosensitive sites in the head and neck to allow estimation of the risk of fatal cancers from intra-oral and panoramic radiography. The highest estimated risks (using the ICRP data) are for leukaemia (bone marrow), thyroid and bone surface cancer. The total risk is estimated to be 2.5 fatal malignancies per 10(6) full-mouth examinations made with D-speed film and round collimation.(ABSTRACT TRUNCATED AT 250 WORDS)

Study of the environmental pollution (ambient air, drinking water, food and fodder) in southern Ukraine industrial region and study of congenital developmental defects were carried out. 78,678 newborns were examined. The most significant environmental factors responsible for congenital developmental defects, as authors proposed, were the ambient air pollution and environmental radioactivity.

The possibility of subtle hazards from weak nonionizing electromagnetic fields (EMFs) has been controversial for many years, shifting over a range of issues without resolution. The confusion arises partly from the weak evidence for hazard and partly from the inconsistent and speculative nature of some of the bioeffects literature. More attention is needed to define ways to resolve the issues.

Experimental results are presented which describe induction and pathogenesis of the hydro-micrencephaly in NMRI-mice after single X-irradiation with 0.9 Gy or 1.9 Gy on gestation day (gd) 12. The ultrastructural alterations in the ventricular walls are sequentially investigated up to gross developmental damage. The ventricular zone is the most sensitive region in the developing brain. Its constituting undifferentiated and proliferating cells lose their palisade like orientation and fail subsequently to differentiate into primitive neurons, glia cells, or ependymal cells. Structurally this results in the thinning of ventricular walls by more than 50% associated with periventricular oedema and a dilation of the brain ventricles by 20-60%. Damage is clearly more pronounced with the higher dose. Repair processes originate from regions with intact Zonulae adherents which give also rise to typical globular or cylindrical heterotopic structures; these are known as rosettes and made up from undifferentiated proliferating ventricular cells. Perinatally in these rosettes cell replication persists, at a time when cell production in the ventricular zone has ceased. Histological changes are most prominent in and around the telencephalic roof consisting in replacement of the ependymal lining by a felt of glial fibers, faulty myelinisation, and periventricular oedema; postnatally these structural alterations lead to hydro-micrencephaly. Results from this animal model can be translated to the human situation because the fundamental developmental processes in the brain of mammals are similar despite species related differences of the time scale.

This paper describes the mechanisms through which parental occupational radiation exposure could affect children's health. It then goes on to review briefly some of the early work on this issue, studies based not on occupational exposures but on the Japanese atomic bomb survivors and on intrauterine x-ray exposure. Most of the discussion focuses on recent studies that have examined risks of childhood cancers and congenital malformations in the offspring of exposed workers, particularly some of the controversy engendered by recent cancer studies.

A cluster initiated the present case-referent study to assess the relation between exposure to high-frequency electromagnetic radiation and congenital malformations. Through the linkage of a cohort formed from a union file of Danish physiotherapists with complete national registers of pregnancy outcome, cases (pregnancies terminated by the birth of a malformed child) and referents were identified. From responses in a blinded telephone interview without knowledge of case status, exposure to high-frequency electromagnetic radiation in the first month of pregnancy was assessed. Indices reflecting duration of exposure ("time") and maximum level of exposure ("peak") were composed. After a 7% dropout 54 cases and 247 referents were interviewed. No statistically significant associations between pregnancy outcome and high-frequency electromagnetic radiation were found (odds ratio 1.7, 95% confidence interval 0.6-4.3).

This article summarizes the basic facts about the measurement of ionizing radiation, usually referred to as radiation dosimetry. The article defines the common radiation quantities and units; gives typical levels of natural radiation and medical exposures; and describes the most important biological effects of radiation and the methods used to measure radiation. Finally, a proposal is made for a new radiation risk unit to make radiation risks more understandable to nonspecialists.

The annual and monthly distributions of congenital abnormalities and pregnancy outcomes as confounding factors were evaluated in Hungary in reflection of the accident at the Chernobyl reactor. The different congenital abnormality entities and the components of fetal radiation syndrome did not show a higher rate after the Chernobyl accident in the data-set of the Hungarian Congenital Abnormality Registry. Among confounding factors, the rate of induced abortions did not increase after the Chernobyl accident in Hungary. In the 9th month after the peak of public concern (May and June, 1986) the rate of livebirths decreased. Three indicator conditions: 15 sentinel anomalies as indicators of germinal dominant gene mutations, Down syndrome as an indicator of germinal numerical and structural chromosomal mutations, and unidentified multiple congenital abnormalities as indicators of germinal dominant gene and chromosomal mutations were selected from the material of the Hungarian Congenital Abnormality Registry. Diagnoses were checked, familial and sporadic cases were separated and only the sporadic cases were evaluated. The analysis of indicator conditions did not reveal any measurable germinal mutagenic effect of the Chernobyl accident in Hungary.

In one of the southern regions of the Ukraine, analysis was made over the recent three years of the genetic monitoring data on the incidence and structure of congenital developmental abnormalities in the newborn as related to the status of environmental pollution (the content of dust, carbon black, carbon and nitrogen oxides, nitrogen and sulfur dioxides, hydrogen sulfide, formaldehyde, phenol, fluorine compounds in the atmospheric air; the content of toxic chemicals and pesticides in foods, soil, water and feeds) as well as to the radiation situation. In the region under study, areas with varying degree of environmental pollution were distinguished. That was mainly done in terms of the characteristics of the atmospheric air and (to a less degree) varying annual dose of external radiation on conversion to one inhabitant. Analysis of the genetic monitoring has demonstrated the prevalence of congenital abnormalities, in the genesis of which the mutation component was of paramount importance, to be significantly higher in an ecologically unsafe area. The data obtained can be used in the regional programs aimed at the improvement of the environment, a reduction of the influence of exogenous risk factors implicated in the formation of congenital developmental abnormalities in children.

Various well-defined stages during completion of the second meiotic division and early organogenesis of mouse embryos were X-irradiated with doses of 1-4 Gy (100-400 rad). The major risk was prenatal mortality with radiation sensitivity changing markedly with dependence on the developmental stage irradiated; in the case of day 1 even within hours. The surviving fetuses did show a significantly enhanced frequency of malformations on day 19 of gestation (mostly gastroschisis and some exencephalies). This was true for all stages between days 1 and 8; only sensitivity again changed considerably. The radiation doses used in this study are markedly higher than doses that can be expected from radiation diagnostics, but exposure is in a range comparable to doses that can occur in radiation therapy (e.g., Morbus Hodgkin).

Human reproduction is a complex process and can be disturbed in many phases by both host and environmental factors. Therefore, it has been difficult to distinguish the occupational causes of spontaneous abortion and congenital malformations from other factors related to the parents' characteristics and their living environment. The extrapolation of results of animal studies to humans is often complicated because there are structural and functional differences between the species and the mechanisms of harmful effects are seldom known. There is also a lack of conclusive epidemiologic studies on the topic. At present knowledge on the potential reproductive toxicity of even rather common occupational exposures is limited and in many cases only suggestive. Paternal exposure to organic solvents before conception and maternal exposure during pregnancy may have adverse effects on the pregnancy and offspring. Heavy physical work during pregnancy may increase the risk of spontaneous abortion.

The diagnosis of carcinoma of the breast during pregnancy poses a challenging dilemma. Although once regarded as incurable, recent reports reveal similar long term survival rates for pregnant and nonpregnant patients who have carcinoma of the breast. When referred to a surgeon, a pregnant woman with a suspicious mammary mass deserves an expedient histologic diagnosis; delay may jeopardize the chances of survival. Once the diagnosis is established, pregnant patients should be treated in a manner similar to nonpregnant patients because there is no evidence that carcinoma of the breast in pregnant women is biologically different than carcinoma of the breast in other premenopausal women. Fears of fetal exposure to radiation should not deter a physician from ordering appropriate preoperative diagnostic tests to stage the patients. Operation may be performed safely when general anesthesia is administered and postoperative adjuvant therapy should be administered when necessary. The involvement of multiple subspecialties in the management of these patients is highly recommended.

This article summarizes recent epidemiologic studies of cancer risk among the children of atomic bomb survivors conducted at the Radiation Effects Research Foundation. These children include two groups: (1) the in utero-exposed children (ie, those born to mothers who had been pregnant at the time of the bombings of Hiroshima and Nagasaki) and (2) the F1 population, which was conceived after the atomic-bombings and born to parents of whom one or both were atomic bomb survivors. Although from 1950 to 1984 only 18 cancer cases were identified among the in utero sample, cancer risk did appear to significantly increase as maternal uterine dose increased. However, since the observed cases are too few in number to allow a site-specific review, the increased cancer risk cannot be definitively attributed to atomic bomb radiation, as yet. For those members of the F1 population who were less than 20 years old between 1946 and 1982, cancer risk did not appear to increase significantly as parental gonadal dose increased. Follow-up of this population will continue to determine if the patterns of adult-onset cancer are altered.

Studies of the survivors of the atomic bombing of Hiroshima and Nagasaki who were exposed to ionizing radiation in utero have demonstrated a significant increase in perinatal loss and the vulnerability of the developing fetal brain to injury. These studies have also helped to define the stages in the development of the human brain that are particularly susceptible to radiation-related damage. Exposure at critical junctures in development increases the risk of mental retardation, small head size, subsequent seizures, and poor performance on conventional tests of intelligence and in school. The most critical period, 8 through 15 weeks after fertilization, corresponds to that time in development when neuronal production increases and migration of immature neurons to their cortical sites of function occurs. The epidemiologic data are, however, too sparse to settle unequivocally the nature of the dose-response function and, in particular, whether there is or is not a threshold to damage. If a threshold does exist, it appears to be in the 0.10- to 0.20-Gy fetal-dose range in this vulnerable gestational period.

Current literature reports health hazards associated with using video display terminals (VDTs). This paper reviews a number of such hazards and recommends ergonomic changes to reduce or eliminate damage to the health of VDT operators.

Sequential panoramic radiographs were assessed for mandibular third molar development in 47 long-term survivors of childhood Hodgkin's disease after treatment with 37 Gy mantle field radiation. To make a comparison, panoramic radiographs of 149 healthy, nonirradiated children were reviewed for the presence of mandibular third molars. In children between the ages of 7 and 12 years, bilateral agenesis of mandibular third molars was more frequent in patients who had been treated with mantle radiation than in nonirradiated patients. Unilateral agenesis, crown hypoplasia, and root growth impairment of mandibular third molars were also found. Similar, apparent, radiation-induced developmental anomalies were noted in maxillary third molars of the irradiated patients.

The influence of medical drugs and X-rays upon early pregnancy causes problems of great responsibility for the physician. He is supposed to grant optimum consultation to the anxious women who finally have to decide to carry on their pregnancy or not. This topic is difficult to value as controlled prospective studies are not practicable for ethical reasons, and the results of animal experiments are rarely transferable to human medicine. In this paper the facts and data of our consulting activities are summarized from April 1985 to May 1986 in the sense of a prospective study. Over all 64 consultations were performed in these 14 months, up to now 30 women have been delivered of a newborn. The procedure and the principles of our consultations and the postnatal results are presented below.

This report presents a review of difficulties in the analysis of case-control studies in which multiple binary responses are observed for each individual and the number of controls per case varies. These statistical considerations are described in the context of a previously reported analysis of the influence of treatment of Hodgkin's disease on pregnancy outcomes.

A cohort study was made on 2,043 infants born to 2,018 females registered as physiotherapists at the time of pregnancy during 1973 to 1978. The incidence of perinatal death, serious malformation, short gestational duration, and low birth weight was slightly below the expected with consideration given to maternal age and parity distribution. Information on occupational exposure (use of shortwave, microwave, and ultrasonic equipment, X-ray exposure, use of electrostimulator or hexachlorophene-containing soaps) was obtained in a case-control study within the cohort from mail questionnaires with a 93% response rate. The only positive finding was a higher incidence of shortwave equipment use among the females with a dead or malformed infant than among controls. Various explanations for this finding are discussed.

The term radiation evokes emotional responses both from lay persons and from professionals. Many spokespersons are unfamiliar with radiation biology or the quantitative nature of the risks. Frequently, microwave, ultrasound, and ionizing radiation risks are confused. Although it is impossible to prove no risk for any environmental hazard, it appears that exposure to microwave radiation below the maximal permissible levels present no measurable risk to the embryo. Ultrasound exposure from diagnostic ultrasonographic imaging equipment also is quite innocuous. It is true that continued surveillance and research into potential risks of these low-level exposures should continue, but at present ultrasound not only improves obstetric care but also reduces the necessity of diagnostic x-ray procedures. In the field of ionizing radiation, we have as good a comprehension of the biologic effects and the quantitative maximum risks as of any other environmental hazard. Although the animal and human data support the conclusion that no increases in the incidence of gross congenital malformations, intrauterine growth retardation, or abortion will occur with exposures less than 5 rad, that does not mean that there are definitely no risks to the embryo exposed to lower doses of radiation. Whether there exists a linear or exponential dose-response relationship or a threshold exposure for genetic, carcinogenic, cell-depleting, and life-shortening effects has not been determined. In establishing maximum permissible levels for the embryo at low exposures, refer to Tables 4, 5, 6, 8, and 9. It is obvious that the risks of 1-rad or 5-rad acute exposure are far below the spontaneous risks of the developing embryo because 15 per cent of human embryos abort, 2.7 to 3.0 per cent of human embryos have major malformations, 4 per cent have intrauterine growth retardation, and 8 to 10 per cent have early- or late-onset genetic disease. The maximal risk attributed to a 1-rad exposure, approximately 0.003 per cent, is thousands of times smaller than the spontaneous risks of malformations, abortion, or genetic disease. Thus, the present maximal permissible occupational exposures of 0.5 rem for pregnant women (see Table 10) and 5 rem for medical exposure, are extremely conservative. Medically indicated diagnostic roentgenograms are appropriate for pregnant women, and there is no medical justification for terminating a pregnancy in women exposed to 5 rad or less because of a radiation exposure.(ABSTRACT TRUNCATED AT 400 WORDS)

The main and most valid evidence we have is that on direct follow-up of treated patients. This has been well done in thousands of patients in two countries with very good medical care and over long periods--10 to 15 years or more. On the other hand there is no doubt about radiation carcinogenesis, and thyroid cancer has been caused in children by low-dose x-ray therapy. The possibility of other cancer and of leukaemogenesis is also real. The evidence for this is reviewed and risk estimates given. Experimental work and radiation biology is reviewed and it is suggested that the risk of thyroid cancer from the usual radio-iodine doses given for treatment is low because of cell killing or sterilization, and animal evidence is discussed that supports this. The final position appears to be that no risk has yet been demonstrated in man and evidence in general suggests that if there is indeed a cancer risk it will be less than about 0.1%. It is suggested that this is not dissimilar to surgical risks, except that these are more immediate as compared with the long latent period for development of radiation-induced cancer. Genetic risks are also discussed and again have not been demonstrated in man from this treatment and should in any case be low. The risk to children is also considered; there is no direct evidence of risk but only small numbers have been treated--nevertheless the hypothetical risk may be counterbalanced by the benefits. Administration of radio-iodine therapy to pregnant or lactating women must be scrupulously avoided; both cause significant risks. Finally, if a more liberal policy be accepted it is worth while giving optimum treatment, and evidence is given suggesting low-dose treatment similar in effect to surgical thyroidectomy and followed temporarily if need be by anti-thyroid drug treatment.

The term radiation evokes emotional responses both from lay persons and from professionals. Many spokespersons are unfamiliar with radiation biology or the quantitative nature of the risks. Frequently, microwave, ultrasound, and ionizing radiation risks are confused. Although it is impossible to prove no risk for any environmental hazard, it appears that exposure to microwave radiation below the maximal permissible levels present no measurable risk to the embryo. Ultrasound exposure from diagnostic ultrasonographic-imaging equipment also is quite innocuous. It is true that continued surveillance and research into potential risks of these low-level exposures should continue; however, at present ultrasound not only improves obstetric care, but also reduces the necessity of diagnostic x-ray procedures. In the field of ionizing radiation, we have a better comprehension of the biologic effects and the quantitative maximum risks than for any other environmental hazard. Although the animal and human data support the conclusion that no increases in the incidence of gross congenital malformations, IUGR, or abortion will occur with exposures less than 5 rad, that does not mean that there are definitely no risks to the embryo exposed to lower doses of radiation. Whether there exists a linear or exponential dose-response relationship or a threshold exposure for genetic, carcinogenic, cell-depleting, and life-shortening effects has not been determined. In establishing maximum permissible levels for the embryo at low exposures, refer to Tables 4, 5, 6, 8, and 9. It is obvious that the risks of 1-rad (.10Gy) or 5-rad (.05Gy) acute exposure are far below the spontaneous risks of the developing embryo because 15% of human embryos abort, 2.7% to 3.0% of human embryos have major malformations, 4% have intrauterine growth retardation, and 8% to 10% have early- or late-stage onset genetic disease. The maximal risk attributed to a 1-rad exposure, approximately 0.003%, is thousands of times smaller than the spontaneous risks of malformations, abortion, or genetic disease. Thus, the present maximal permissible occupational exposures of 0.5 rem for pregnant women (see Table 10) and 5 rem for medical exposure, are extremely conservative. Medically indicated diagnostic roentgenograms are appropriate for pregnant women, and there is no medical justification for terminating a pregnancy in women exposed to 5 rad or less because of a radiation exposure.(ABSTRACT TRUNCATED AT 400 WORDS)