Protection of the maternal and fetal thyroid from radioactive contamination by the administration of stable iodide during pregnancy. An experimental evaluation in chimpanzees

The safety and efficacy of the administration of stable iodide to protect the fetal thyroid from exposure to radioactive iodide were investigated in chimpanzees in weeks 19 to 21 of pregnancy. The mean 24-h uptake of iodide in the fetal thyroid, determined with 123I-, was 1.8%. Administration of stable potassium iodide (KI), 0.65, 1.95 or 6.5 mg per kg body weight, 1 h before tracer injection reduced the fetal uptake satisfactorily. Only the higher doses were effective after 20 h. Excess iodide may impair a child's thyroid status. However, adverse effects were not found during the 11 days the animals ingested these doses. Tracer concentrations in the amniotic fluid were 30- to 130-fold lower than in the urine. The dose to the fetus from radioactivity in the maternal bladder was estimated by computer simulation. The potential increment of the risk from this dose during the ingestion of stable iodide is smaller than the reduction of risk achieved by inhibiting the uptake of radioactive iodide by the fetal thyroid. The conclusion of the experiments is that stable iodide can be used safely and effectively to protect the fetal thyroid against contamination with radioactive iodine.

Protection of the infant thyroid from radioactive contamination by the administration of stable iodide. An experimental evaluation in chimpanzees

Protection of the thyroid from radioactive contamination by the administration of stable iodide was investigated in chimpanzees aged 2 to 98 weeks. The uptake of iodide in the thyroid was measured with 123I-. The animals were subjected to a control measurement first, and subsequently the thyroid uptake of 123I- was determined twice; once at the start and once at the end of 11 days of ingestion of 0.5, 1.5 or 5.0 mg of stable iodide per kg body weight per day. The three doses of iodide reduced the control thyroid iodide uptake of 10 to 30% to lower than 1% when ingested 1 h before exposure to the tracer and to 2-4% when ingested 20 h before exposure. In the latter experiments 0.5 mg iodide/kg was less effective than doses of 1.5 mg/kg or higher. The physiological state of the thyroid of control infant chimpanzees does not differ from that of human infants. Incidentally, an increased level of TSH was found during the ingestion of iodide, but with unaltered thyroxine levels. Therefore, it is concluded that a daily dose of 1.5 mg stable iodide/kg body weight and higher offers optimal protection of the thyroid against exposure to radioactive iodine in infants and that, when used during 10 days, it leaves the thyroid unaffected.

Survey of CT techniques and absorbed dose in various Dutch hospitals

The purpose of this study was to make an inventory of the radiation dose from CT in the Netherlands and to relate the dose to the way the examination was performed. Details were obtained from approximately 3000 CT examinations carried out in 18 hospitals (22 CT scanners). Effective dose was calculated for each examination using CTDI-to-effective dose conversion factors. For most scanners, the conversion factors were available from the literature, for some they had to be derived with a computer model using a Monte Carlo algorithm. The data on effective dose, examination parameters and patient population are presented on a per hospital basis. Mean effective doses from brain CT were 0.8-5 mSv, from lumbar spine CT 2-12 mSv, from chest CT 6-18 mSv and from abdominal CT 6-24 mSv. The general indications for the various CT examinations were as follows: for the brain ischaemia and malignancy, for the lumbar spine disc herniation and for the chest and abdomen a known malignancy. This explains the relatively advanced age of the patients. In many hospitals intravenous contrast is used less than is recommended in current literature.

Probable risk of tumour induction after retro-orbital irradiation for Graves' ophthalmopathy

Retrobulbar irradiation for Graves' ophthalmopathy is considered as a safe treatment and has recently been recommended as the initial treatment for patients with moderately severe eye problems. However, calculations using risk factors presently known reveal a theoretical risk of radiation-induced cancer of 1.2%. Therefore, the authors suggest that this treatment should be reserved for the elderly patient, for example above the age of 40-50 years.

[Radiation risks in dental and medical radiography]

Biological effects of exposure to ionizing radiation in diagnostic dental and medical radiology are stochastic effects such as carcinogenesis and genetical effects. Today, radiation exposure due to an x-ray or nuclear medicine examination varies from less then 0.001 mSv to more then 10 mSv effective dose. The background level of natural radiation in the Netherlands is about 2 mSv. Assuming that an appropriate indication for the examination exists, it can be stated that generally the diagnostic information obtained outweighs by far the risks involved in the exposure to radiation.

Long-term consequences of high-dose total-body irradiation on hepatic and renal function in primates

Radiation effects in non-human primates were studied in order to define the long-term risk of total-body irradiation (TBI) for bone marrow transplantation patients. The long-term effects of TBI could be investigated by keeping 84 monkeys of different ages, from an experiment on acute effects, under continuous observation for a period up to 25 years. The control group consisted of non-irradiated monkeys with a comparable age distribution and identical housing conditions. Since radiation was the common toxic agent, the different age groups provided the possibility to investigate the occurrence of deterministic effects after TBI. In the present study emphasis was placed on the assessment of hepatic and renal function and the associated histopathology. The values of the liver function parameters, such as alkaline phosphatase and gamma glutamyl transferase in the irradiated group were significantly increased after TBI (p < 0.05). Also the parameters of kidney dysfunction, e.g. haematocrit and blood urea nitrogen showed a significant change in the irradiated old-aged (post-irradiated interval > 15 years) cohort (p < 0.005). The impairment of the liver and renal functions, did not lead to clinical symptoms and were only associated with mild morphologic changes in the irradiated group of monkeys. In the population of bone marrow transplant patients treated with TBI, alterations in hepatic and renal function parameters after a post-irradiated interval of > 10 years can be anticipated. This could have consequences for the tolerance and toxicity of a broad range of drugs to be administered as additional medications.

General ion recombination for ionization chambers used under irradiation conditions relevant for diagnostic radiology

General ion recombination has been studied under irradiation conditions relevant for diagnostic radiology and with four different ionization chambers. When the exposure time is appreciably shorter than the ion transit time, the exposure can be designated as pulsed irradiation. On the contrary, for relatively long irradiation times, the term continuous irradiation can be applied. Recombination was estimated by measuring the collected charge at various collecting potentials of the ionization chamber. This is a well-known method in radiotherapy, but unfortunately it cannot be used in diagnostic radiology with typical exposure meters, since they do not offer the option of varying the collecting potential. For exposures with diagnostic x-ray units, an alternative approach is to vary the exposure or exposure rate over a wide range at a constant collecting potential. Experimental and theoretical estimates of ion recombination did not yield similar values. This might be due to several causes, such as differences between the actual and the nominal dimensions and volumes of the ionization chambers, due to errors and uncertainties in the physical parameters used in the theoretical models or due to deviations of the shape of the ionization chambers from the perfect cylindrical or parallel plate geometry. For better accuracy, corrections for recombination losses should therefore be based on experimental verification rather than on theoretical models.

Radiation exposure in standard and high-resolution chest CT scans

It has been suggested that radiation doses due to high-resolution computed tomography (HRCT) of the chest are considerably higher than those from conventional CT. We compared the effective dose (E, mSv) in conventional chest CT (10-mm contiguous slices) and HRCT (1.5-mm slices, gap 10 mm). In our study, the effective dose from a HRCT (0.98 mSv) is about 6.5 times less than the effective dose from a standard CT scan (6.5 mSv), and only a factor 12 higher than from a conventional chest examination (0.085 mSv).

Carcinogenic risk in diagnostic nuclear medicine: biological and epidemiological considerations

During the last decade new data have become available on the mechanism of carcinogenesis and on cancer induction by ionizing radiation. This review concentrates on these two items in relation to the use of radiopharmaceuticals in diagnostic nuclear medicine. On the basis of reports of expert committees, the concept of radiation risk is elucidated for high and low doses. Mortality risk factors due to ionizing radiation are put in perspective to other risks. The extra risk for patients who undergo a scintigraphic examination for fatal cancer is very small and is of the order of 1.4 x 10(-4). It is most unlikely that this figure can even be verified by actual measurement since the majority of nuclear medicine patients will die of other causes before the radiogenic cancer manifests itself.

Neoplastic transformation of C3H 10T1/2 cells: a study with fractionated doses of monoenergetic neutrons

As most occupational and environmental exposures to ionizing radiation are at low dose rates or in small dose fractions, risk estimation requires that the effects of the temporal distribution of dose are taken into account. Previous in vitro studies of oncogenic transformation, as well as in vivo studies of carcinogenesis induced by high-LET radiation, yielded controversial results concerning the presence of an inverse dose-rate effect. The present study tested the influence of one scheme of dose fractionation of monoenergetic neutrons on neoplastic transformation of C3H 10T1/2 cells. Neutrons of 0.5, 1.0 and 6.0 MeV were used. Cells were exposed to doses of 0.25 and 0.5 Gy, given acutely or in five fractions at 2-h intervals. The acute and fractionated irradiations with each energy were done on the same day. No significant difference between the two irradiation modes was found for both cell inactivation and neoplastic transformation at all energies. These results are in agreement with our data for fractionated fission-spectrum neutrons from the RSV-TAPIRO reactor.

Comparison of two methods for assessing patient dose from computed tomography

Radiation exposure of the patient during routine computed tomography (CT) examinations is known to be relatively high. In this study organ doses were determined using two methods and these served as a basis to calculate the effective dose. Thermoluminescence dosemeters (TLDs) were used to measure organ doses in an anthropomorphic Rando Alderson phantom. In addition organ doses were obtained from measurement of the computed tomography dose index (CTDI) and the application of published organ dose conversion factors. Effective dose values obtained with the Rando phantom for CT head examinations are about 1-2 mSv. For CT examinations of thorax and abdomen the estimation of effective doses with the Rando phantom yielded values of 18 and 24 mSv respectively. Effective doses determined from CTDI values were similar for CT head examinations (1-2 mSv) but were smaller for the CT thorax scan (11-15 mSv) and the CT abdomen scan (15-20 mSv). In this study effective dose values are relatively high compared with the results of other investigators who indicate effective doses and effective dose equivalents of 7-9 mSv for CT of the thorax and of 4-16 mSv for CT of the abdomen. Discrepancies between our results and those from other studies could be attributed to differences in the selected CT protocols and to differences in the phantoms employed. Measurements in an anthropomorphic phantom were laborious and time-consuming. Assessment of organ doses from CTDI values and organ dose conversion factors will therefore be the preferable method for future dose intercomparisons at different locations in The Netherlands. It should be realized, however, that this method tends to yield up to 40% lower effective dose values compared with the assessment of effective dose with a Rando phantom.

PCDOSE: an interactive software system to calculate internal radiation dose on a personal computer

An interactive, menu directed, software system to calculate committed dose equivalents for individuals with different physiques after inhalation, ingestion or injection of radionuclides has been developed. The calculations are based on ICRP 26/30 methods. The programs are written in PASCAL and can be implemented on a personal computer with a MS-DOS operating system and a hard disk with a storage capacity of at least 20 Mb. This paper describes the development and features of the system.

AMBER and conventional chest radiography: comparison of radiation dose and image quality

The authors compared the radiation dose to the patient and the image quality in advanced multiple-beam equalization radiography (AMBER) with those in conventional chest radiography. Organ doses were estimated for an anthropomorphic phantom from measurements with thermoluminescence dosimeters. These measurements were supplemented with area-air kerma products obtained during chest examinations of 223 patients. Image quality was determined by means of a contrast-detail image evaluation test. An improvement in image quality in regions of high absorption and an increased dose to the patient were found for the AMBER technique compared with the conventional technique. However, for both techniques, the radiation exposure was relatively low compared with other reported values of patient dose during chest radiography. The estimated effective dose for an average-size patient during chest radiography with posteroanterior and lateral projections is 0.085 mSv for the conventional and 0.14 mSv for the AMBER technique.

Dosimetry of ruthenium-106 eye applicators

In view of the importance of clinical applications of ruthenium-106 beta-ray sources for the treatment of choroidal melanoma, experimental, and theoretical approaches are presented for the dosimetry of such sources. The absolute dose and percentage depth dose of ruthenium applicators have been measured with an extrapolation ionization chamber. For a special flat applicator the absolute dose could be measured with an accuracy of +/- 5%, which is determined by the collection efficiency of the extrapolation chamber. The percentage depth dose of concave applicators, employed in the clinical situation, could only be measured at a distance larger than 5 mm due to their geometry and the outer dimensions of the extrapolation chamber. A computer simulation was therefore developed for the absorption and scattering of electrons, taking into account the geometry and materials of the applicator, to predict the percentage depth dose at distances smaller than 5 mm. The calculated and experimentally determined depth doses are in good agreement. With the aid of the computer simulation a depth dose determination for concave applicators can be made for clinically relevant distances less than 10 mm from the source surface with an absolute accuracy of +/- 10%.

Relative biological effectiveness for neutron carcinogenesis in monkeys and rats

The risks of total-body irradiation with large doses of X rays (average dose 6.7 Gy) and fission neutrons (average dose 3.4 Gy) were investigated by keeping a group of long-term surviving monkeys from an experiment on acute effects under continuous observation. On the basis of the number of animals developing tumors in each group as a function of the total observation period and the average absorbed dose, relative biological effectiveness (RBE) values between 4 and 5 have been derived at these high dose levels. In experiments on mammary carcinogenesis in rats the highest RBE values are observed for neutrons with energies of 0.43 to 1 MeV as produced by the p + T reaction or by the fission process. Based upon linear dose-response curves for neutrons and X rays, a maximum RBE value of 15 was observed for induction of adenocarcinomas in WAG/Rij rats. Appreciably higher RBE values would be obtained if the results of the gamma-ray exposure, indicating a nearly quadratic dose-response relationship, were used as a baseline. For radiation protection applications it should be realized, however, that such an increase will be caused by the lower efficiency of low-linear-energy-transfer radiation rather than by an increase in efficiency of the neutron irradiation at low doses.

Flow cytometric DNA measurement and cytomorphometric analysis of formalin fixed rat mammary tumours

Archival paraffin embedded material was used to examine whether additional quantitative criteria would be helpful to discriminate between histologically benign and malignant rat mammary tumours. To this end nuclear DNA content expressed as DNA ploidy index (DI) was measured using flow cytometry (FCM). A total of 63 benign and malignant mammary tumours were investigated. Thirteen out of 38 (34%) mammary carcinomas were DNA aneuploid against 0 out of 25 benign mammary tumours. Aneuploidy was not significantly increased in tumours showing histological signs of greater malignancy such as cribriform-comedo type or invasive growth. In addition to DI other quantitative criteria indicative for malignancy, such as mitotic count and nuclear morphometric characteristics, were estimated in 24 benign and malignant tubulopapillary tumours, a category where the histological classification may be difficult. It appeared that five out of nine noninvasive tubulopapillary carcinomas and six out of seven invasive carcinomas had abnormal values for either DI, mitotic count or nuclear area or for a combination of these parameters. Each single parameter however was abnormal only in a minority of the malignant tumours. In this respect our data are in accordance with the fact that rat mammary carcinomas are clinically and histologically less malignant than their human counterparts.

Monoclonal gammapathies in long-term surviving rhesus monkeys after lethal irradiation and bone marrow transplantation

Late effects of total body irradiation and subsequent autologous bone marrow transplantation on the development of age-related monoclonal gammapathies (MG) were studied in 14 long-term surviving Rhesus monkeys. Together with 27 untreated control monkeys, they have been followed up for more than 20 years. In contrast with the control group, the experimental monkeys developed MG with aging in higher frequencies, earlier and mainly of the benign MG category. One experimental monkey developed a multiple myeloma, the first observed in the nonhuman primates so far. These results indicate an accelerated senescence of the immune system in the experimental monkeys as a late consequence of tissue or cell damage during irradiation.

Dosimetric aspects of exposure of the population to ionizing radiation

Radiation carcinogenesis is generally considered to be the most important detrimental effect of exposure to ionizing radiation. The collective effective dose-equivalent values due to medical procedures amount to values between 10 and 20 per cent of the doses received from natural radiation. Risk factors have been derived up to the present from three large epidemiological studies, notably atomic bomb survivors, spondylitis patients and female patients treated for cancer of the cervix. The assessment of the absorbed doses received by the inhabitants of Hiroshima and Nagasaki has received continuous attention and the latest estimates are summarized. On the basis of original radiotherapy records the absorbed doses in organs adjacent to the primary treatment field can be derived from computerized dosimetry and this source of information should be further exploited. European co-operation has been established to investigate dosimetric problems for medical applications and radiation protection. The risk factors obtained up to the present are derived at relatively high dose levels (in excess of 0.3 Gy). The uncertainties in the extrapolation of these values to the area of low doses administered at low dose rates are discussed.

Dosimetry for radiation accidents: present status and prospects for biological dosemeters

The induction of chromosome aberrations in human peripheral blood lymphocytes is still the most useful dosimetry system for accidental whole-body irradiation; however, in the case of a very large number of casualties the micronuclei technique might provide advantages. For partial-body irradiations, determination of hair diameter and chromosome aberrations in skin fibroblasts and hair might be advantageous, since better information on dose distribution might be obtained. The latter cytological techniques are complex and require considerable culture time. Flow cytometry for determination of chromosome aberrations, a staining technique for hair follicles and an immunochemical method for quantitative detection of persistent DNA damage in mammalian cells might be applicable in the future.